Gas chromatography - Analytical Chemistry (ACS Publications)

Gas Chromatography Stuart P. Cram, Department of Chemistry, University of Florida, Gainesville, Fla. 3260 I Richard S. luvef, lr., Department of Chemistry, Arizona State University, Tempe, Ariz. 8528 I

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HIS REVIEW SURVEYS developments in the field of gas chromatography since publication of the last review in this series (496) and covers the years 1970-71. Gas chromatography continues to be one of the most active areas in analytical chemistry. A recent report by the American Chemical Society (791) is based on the employment specialty choices of 84,925 chemists and chemical engineers who reported to the 1970 National Register of Scientific and Technical Personnel, an activity of the National Science Foundation. Those listing analytical chemistry as their major field of interest exceeded in numbers both those listing physical chemistry and those listing inorganic chemistry and were greater than half the number listed under the classically defined field of organic chemistry. This report shows that 20.9% of analytical chemists list chromatographic analysis as their first specialty choice, an increase from the 16.0% reported in the 1968 National Register of Scientific and Technical Personnel, and a number greater than any other area of analytical chemistry. This is consistent with results reported in the 1971 Directory of Membership of the ACS Division of Analytical Chemistry in which 19.6% of the membership listed gas chromatography as one of their top specialties (416). Thirty-three companies are currently marketing gas chromatographs in the United States and 112 models are listed in the Industrial Research 1971 Instruments Specifier issue along with comparative data on each (473). We estimate that 2600-2700 articles and major addresses directly involved with the theory, apparatus, and novel applications of gas chromatography were published during each year in the 197071 biennium. This estimate may be compared with a more accurate count of 2790 in 1969 and 2590 in 1968. Because of this vast literature, considerable selection was necessary in preparing this review. Technique-centered aspects are mainly considered and most such publications through November 1971 are noted.

BOOKS AND REVIEWS

Books on gas chromatography publised during this biennium include the second edition of Littlewoods’ comprehensive text, “Gas Chromatography: Principles, Techniques and Applications” (595); a Spanish text, “Teoria y

Practica de la Chromatografia en Fase Gaseosa,” by Gasco-Sanchez (938); a book entitled “An Introduction to GasLiquid Chromatography” by Jones (494), providing a basic introduction to the theory and practice of GC for the organic chemist; “Selected Readings in Chromatography,” which includes the original papers by Tswett, James and Martin, Kirchiner, and others in the several areas of chromatography (618); an excellent monograph by Guiochon and Pommier (409) entitled “La Chromatographie en Phase Gazeuse en Chimie Inorganique,” which reviews the rapidly growing field of inorganic GC and includes chapters on separation of the permanent gases, metal halides, metal hydrides, organometallic compounds, metal chelates, and isotopes; “Preparative Gas Chromatography,” a monograph edited by Zlatkis and Pretorius (1019) covering this topics in depth; “Recent Advances in Gas Chromatography,” which includes several lectures offered since 1962 a t short courses on GC presented by the Chicago Gas Chromatography Discussion Group (260) ; a monograph entitled, “Identification Techniques in Gas Chromatography” by Leathard and Shurlock (683),which surveys the literature for methods of peak identification through October 1969; a monograph by Helfferich and Klein entitled “Multicomponent Chromatography: Theory of Interference (445); an English translation of Kiselev and Yashin’s 1967 monograph on “Gas-Adsorption Chromatography” (540); Vol. I11 of “Progress in Separation and Purification” (743); “A Guide to the Analysis of Fatty Acids and their Esters by Gas Chromatography,” which includes instructions and hints for esterification, physical properties, and a selected bibliography listing 684 references to fatty acid analysis (769); and a monograph on thermal conductivity covering both theoretical and practical aspects of measurement (939). The proceedings of the 16th annual instrumental symposium of the Instrument Society of America (116) also includes chapters on gas chromatographic separations, as does a text entitled, “Separation Methods in Organic Chemistry and Biochemistry” by Wolf (1003). Volume 9 of “Advances in Chromatography” edited by Giddings and Keller was published during this biennium (364)and contains a number of chapters on GC including the determination of

optimum conditions for separation, lightly loaded glass bead columns, radiochemical separations, and the analysis of volatile flavors by GC. Several useful reference books were published, including the second edition of Supplement 1 of the ASTM “Gas Chromatographic Data Compilation” edited by Schupp and Lewis (826), the ACS supplement to “Reagent Chemicals” (34), the second edition of the comprehensive EastcGerman reference book, “Handbuch der Gas-Chromatographie” edited by Leibnitz and Struppe (584); a compilation of literature retention data relevant to hydrocarbon analyses (766), a technical dictionary of chromatordaphy with the German, French, Russian, and English equivalents to some 3000 specialist terms (SO), the second edition of “A Guide to the Analysis of Pesticides by Gas Chromatography” which includes an extensive compilation of retention data on pesticides (767), and a publication tabulating literature abstracts of 900 papers on the gas chromatography of pesticides, a number estimated to be 90% of all papers published in this area up to 1970 (286). The proceedings of several symposia on GC have also appeared including the 6th and 7th International Symposia on Advances in Chromatography held in Miami Beach, Fla., in June 1970 (1026) and Las Vegas, Nev., in November 1971 (1026), respectively; a Ciba Foundation symposium entitled “Gas Chromatography in Biology and Medicine” (760) ; and the 5th International Symposium on Separation Methods held in Lausanne, Switzerland, in October 1966 (558). Published short reports of these and other symposia include the Lausanne Symposium (181), the Eighth International Symposium on Gas Chromatography held in Dublin (267), the second Conference on the Use of Gas Chromatography and Related Analytical Methods in the Petroleum and Petrochemical Industries held in December 1969, in Bratislava, Czechoslovakia (909), as well as the sixth meeting of the GC/MS Discussion Group in Miihlheim, Germany (35’7) and informal symposia of the British Gas Chromatography Discussion Group (166,266).

The 1971 applied review issue of

ANALYTICALCHEMISTRYcites several hundred references to applications of gas chromatography published during 1969 and 1970 in the fields of air pollu-

ANALYTICAL CHEMISTRY, VOL. 44, NO. 5, APRIL 1972

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tion (667), clinical chemistry (63f?), 1971/72 International Chromatography coatings (887), essential oils and related which are specialised Guides (gf?), products (396), food analyses (%‘I), directories of manufacturers of instrupesticide residues (913), petroleum ments, accessories, supplies, and services (6.29), pharmaceutkals and related used in the various chromatographic drugs (886), analysis of high polymers techniques, have been compiled on the (663), rubber (976), solid and gaseous basis of replies from over 450 companies fuels (456), and water analysis (317). worldwide. An International ChroIndependent reviews have also appeared matography Book Directory ( @ I ) and a on the determination of micro amounts table of GC symbols and nomenclature of organic substances in aqueous soluas adapted by ASTM (969) have also tions (889), volatile flavor components been published. of foods (476), fatty acids (384),steroids PACKED COLUMNS (1W4), new GC methods for pesticide residues (693), and herbicides and plant Column Theory. A critical review growth regulators (1016). Fundamental of the theory of separations as applied developments in radiochemical separat o chromatographic column. perfortions and analyses were reviewed by mance was written by Chiehkov (177) Cram (207) while Gough and Walker who also described the use of the separa(368) cited 287 references in comparing tion of isotopes of heavy elements using the performance characteristics of the a gravitational field. Guiochon (408) various GC detectors. Other reviews described the theoretical methods for provide a literature survey of thermal evaluating the performance of existing conductivity detectors (783), the charcolumn types, and their principal characteristics of a great variety of detectors acteristics. The relationship between (451), integrators (674), pressure (flow) chromatographic variables was deprogramming (896),GC in space research scribed in terms of set theory (807). (138) including some Russian space Various dynamic GC methods for deprobes, on-line digital computers (868), termining distribution isotherms in gassolid and gas-liquid systems were comand column switching (178). The present status of molecular adsorption chrcpared by Huber and Gerritse (465),and matography (657) and the construction the influence of the column length, of laboratory-built GC instruments sui& carrier gas velocity, and the nature of able for teaching (650) are the subjects the carrier gas was discussed. Methods of two other reviews. for simultaneously measuring absorption The Preston-Technical Abstract Co. and adsorption a t gas/liquid interfaces (770) continues its invaluable service were based on the equilibrium theory to workers in the field of gas chromatogof GC (88). Static and dynamic methraphy by issuing abstracts of all papers ods were compared for the measurement and major addresses within a short of the partition coefficient in order to period foIlowing publication. The abdetermine the separation mechanism on stracts are available in bound booklet porous glass beads (587). Guiochon form, issued monthly, and carefully and Jacob (408) used an isotopic frontal referenced to aid in literature searches. analysis to prove the theory of finite Each monthly issue contains approxiconcentration GC. mately 200 abstracts plus an index An important contribution by Q7eiss which classifies all abstracts in that (991) extends the stochastic theory to include diffusion effects end the n-site issue. An annual index issue a t the end adsorption problem. Using high temof each year breaks down the large categories in considerably greater depth peratures and large solid supports, it indexing by carbon number and by type was found that it was necessary to of product analyzed. Both 16 mm and consider the diffusion in the gas phase 35 mm microfilms of these abstracts are in the solid support when calculating also available for use with a microfilm HETP (1010). From literature data, reader. A computerized information the coefficient for radial convective retrieval system of the gas chromatogdispersion and the composite coefficient raphy literature allowing searches of for longitudinal dispersion by eddy over 22,700 abstracts is the most recent diffusion and the macroscopic velocity item made available through this group. profile are estimated as a function of hfagnetic tapes updated annually are the ratio of the diameters of the column available (770) and are designed for use and of the packing (843). A mathematical model was developed by Wicar on a Type 360 IBbl/DOS system with a 16,000 byte record size and a density of and Novak (993) which postulates that either 800 or 1,600 b.p.i. for a 7- or the liquid and gas phase mass transfer 9-track operation. terms are dependent on each other. The 1969 volume of “Gas ChromaA theoretical evaluation of the relatography Abstracts” edited by K n a p tionship of the columri length to the man and containing 1100 abstracts was HETP illustrates the effect of varying published by the Gas Chromatography the column length a t a constant outlet Discussion Group of the British Instipressure and variable inlet pressure, or tute of Petroleum during this biennium vice versa (697). The experimental results of Novak and Bocek (698) (569). The 1970/71 (480) and the 214R

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showed that columns operated a t a constant outlet pressure shifted the van Deemter curves toward lower values of the KETP and flow velocity. The coefficients of resistance to mass transfer appear to be influenced by column pressure and carrier gas velocity in both the gas and liquid phase (706). The applicablility of the equivalent Gaussian inlet profile for the prediction of bandwidths was evaluated by comparison of the elution profiles with those resulting from a plug inlet (836). The high precision methods of Glenn and Cram (368) for determining the instrumental contributions to HETP used an analysis of moments. A purity index based on the specific entropy was derived as a general separation criterion (a%’), and a new column characteristic, G , which is related to the first moment, was defined by Funk and Rony (384) and developed to describe all of the dynamic column characteristics. The relationship of the retention time to the first moment, peak shape, and peak area may be characterized by a single parameter, 6, which is a measure of the rate of the diffusional mass transfer into the stationary phase relative to the mobile phase convective mass transfer in the axial direction (798). Partial normal statistical moments must be used with experimental data due to the presence of noise and base-line drift and the limitation of the upper limit of integration (797). Grubner (588) has shown how the first four moments can be calculated once the inflection points of an asymmetric elution curve have been determined. A moment analysis can be used to sense the presence of two overlapping Gaussian peaks from the skew and excess of the peak profile (395). The resolution of a binary mixture was established on the basis of the theory of finite concentrations (407). The concept of the extent of separation has been extended and compared for 12 separation methods (796). The maximum number of solutes which can be resolved between the air peak and the last component is the peak capacity and Grushka (390) showed the influence of the experimental conditions on this efficiency factor. The separation efficiency of a column has been expressed by the separation rate (798) and the number of peaks attainable per unit time (783). The former was defined by Rohrschneider to be the square root of the ratio of the number of plates to the air peak retention time and should be independent of the distribution ratio. Smuts and Pretorius (868) derived some very useful equations to relate the separation time to operational parameters which can be measured in the laboratory. The factors affecting the speed of a GC

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separation were exemplified by Ettre (295) for packed, wall-coated open tubular, and supporecoated open tubular columns. Guiochon (404) derived a theoretical approach to the optimization of isothermal, isorheic separations of complex mixtures and discussed the dependence of the relative retention time on the phase ratio. An experimental method of optimization for minimizing analysis time developed by Scott (831) is a generally applicable approach. Other experimental studies have included column systems where the retention of the solute is independent of the temperature (636), and the effect of column coiling on the dispersion of solutes (918). Time normalization GC has been extensively treated by Grushka by treatint the variable of length and temperature (391, 392), the amount of stationary phase and temperature, and the amount of stationary phase and carrier gas velocity (394). This is a powerful technique in experimental maximization of the resolution without a loss in the analysis time, as pointed out by Rony (795) who applied the concept of extent of separation to time normalization. I n studying the structure and flow dynamics of packed columns, Hawkes and Steed (437) showed that neither the column efficiency nor permeability were affected by the packing technique. They have also proposed that the differences in the static and dynamic measurements of the obstruction factor can be explained by sample adsorption and by coupling of obstruction with mass transfer. The effect of pressure drop on column performance was analyzed by statistical moments in order to derive exact expressions for the standard deviation and skew of a breakthrough curve (944). “Aerogel” or high porosity columns were patented which offer higher efficiencies than conventional packed solumns. The columns use 20 to 500 A spherical particles linked together in branched chains to form an irregular three-dimensional network and can be packed so that they occupy only 2.5% of the column volume (422). il general expression for the plate height in packed columns was derived which describes the variation of the plate height in laminar and turbulent flow regions. I t accounts €or the role of turbulence in band broadening and indicates that in the turbulent region the plate height is a function of the mass transfer coefficient (867). Doue and Guiochon (264) found the retention time to be independent of the inlet pressure and the flow rate under turbulent flow condibions. By comparing plate heights on GC and LC columns over a range of lo7 in the outlet velocity, it mas concluded that turbulence does not have a major effect until Reynold’s numbers

reach about 100 and that GC plate height maxima are induced by turbulence while LC maxima are controlled by coupling (508). The effect of the mean absolute column pressure was investigated as it affected the fall-cff in H E T P a t given carrier gas velocities (699). The difficulties in standardizing the performance of chromatographic columns has been treated by Scott (832) and a method of producing columns of differing lengths with known and reproducible resolution and optimum operating conditions for each column length is given. Burke and Ackerman (150) measured surface areas and adsorption isotherms by frontal analysis with a computer control and data acquisition system. The continuous flow method of surface area measurement was improved by stabilizing the carrier gas flow such that surface areas of 0.1 m2/g or less could be determined (303). A theoretical treatment of continuous countercurrent GC related the column temperature and flow rates for the stationary and mobile phases required for the separation of two component mixtures (38). The influence of the major component on the GC characteristics of trace components was illustrated by the dependence of the peaks width on retention times as well as by H E T P values as influenced by the carrier gas velocity (88). The fundamentals of reversion chromatography were reviewed by Kaiser (506) who pointed out the applicability of the method for microtrace analysis. A statistical experiment was designed for evaluating the influence of the column temperature, column length, per cent stationary phase, and flow rate on the resolution coefficients and the time of analysis (1007). The results were evaluated by a polynomial of the second degree and applied to the optimization of the experimental conditions for the separation of CHzC12 and CzHdC12 (380). A number of papers have described the calculation of the dead time in GC on the basis of relationships between retention times and the carbon number for homologous series (364, 671, 725, 924). It has also been pointed out that the log net retention time us. retention index scale for 7talkanes is not perfectly linear (504) and that deviations caused by partitioning (especially Ha) must be taken into consideration (924). A review of GC techniques for separating isotopically substituted stable molecules and the theory of their separation by Van Hook (951) indicates that the literature data agrees with the predictions of the statistical theory of isotope effects in condensed phases. Physical interaction between the sample and stationary phase during GC separations may result in severe isotopic frac-

tionation of the effluent, as evidenced by the data of Gunter and Gleason (412). Harrison et al. (429, 430) used the plate theory to compute the behavior of a system in which a reversible bimolecular reaction of the type A C = 2B occurs during the passage of a mixture of A, B, and C through the column, and an apparent equilibrium constant may be calculated. A generalized retention effect was defibed and the integral retention effect is shown to be directly related to the partial partition coefficient a t a given temperature because it is characteristic of the solute-solvent interaction (692). Jaworski (489) theoretically explained the relationship between the chemical structure of the solute and the retention index. However, the prediction of various retention parameters has been extensively treated on the basis of structurally similar types of compounds (196, 297), the molecular structure (55, 477, 826, 735, R08), the relationship between a compound’s vapor pressure, molecular weight, and density (256), and specific ?r electron interactions or steric effects (332). The influence of the sample size (586), column temperature (21, 632, 894), and the number af carbon atoms, position of halogen substitution, and the number and position of branchings (166) on the retention time or retention index were reported. Kovats retention index has taken on greater significance with studies outlined above and through the development of functional relationships such as the effect of molecular configuration (described by the quadratic mean of the radius and the density) on the temperature dependence of the retention indices (21). A method was developed for interconversion of retention indices of solutes in a given partitioning liquid a t any two temperatures or for determining the retention index of a compound in any stationary phase from another (654). Liquid Phase. A symposium on the possibility of standardization of liquid phases led to the conclusions t h a t they should be reproducible, a minimum number should be accepted, and that they have well defined properties and be characterized by their Rohrschneider constants (658, 768). The use of the Rohrschneider constants to characterize stationary phases was described by Supina and Rose (884). McReynolds (639) characterized over 200 liquid phases by determining the AI value of the liquid phases with respect to squalane for 10 different compounds. Lists of GC liquid phases produced in the USSR (860) and the US (883) which have been characterized by their chemical and physical properties, Rohrschneider constants, and maximum column temperatures have been published.


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The characterization of stationary phases has become a study in itself. The application of the Hammett Equation to GC behaviov correlated the retention data of isomeric phenols on different liquid phases with specific s o l u t e solvent interactions such as intermolecular hydrogen bonding (190). Thermodynamic characteristics of nonvolatile stationary phases have been measured by use of a piezoquartz microbalance and the diffusion method (400). Sheehan and Langer (842) determined the liquidliquid distribution coefficients by GC and found the method useful for screening potential solvents for solvent extraction or pairs of solvents for liquidliquid chromatography. The ability of a polar solute to induce a dipole into a nonpolar solvent has been estimated from the energy of attraction (649). A calculation of the dispersion forces in solutions of polar substances in nonpolar stationary phases and a comparison of heats of solution have been used to describe the interaction of such systems (666). Russian workers established the d e pendence of the partition coefficient and retention volume on the molar refraction of the stationary phase for a homologous series so that chromatographic behavior can be predicted for similar phases (844). The retention of compounds containing ether groups was examined by correlation of the retention data obtained on polar and nonpolar polymeric sorbents (811). The adsorption of hydrocarbons on very polar liquids (e.g. water) was investigated under conditions approaching aero surface pressure by Karger et al. (617). The formation of charge transfer complexes between the solute and stationary phase has been shown and the theory of the GC method developed by Eon, Pommier, and Guiochon (991). The dependence of chromatographic retention on the dielectric permeability of the stationary phases, e, has been shown. The function (e - 1)/(2e 1) is proposed as a measure of the stationary phase polarity and there is a linear relationship of this function with the resolution coefficient (373). GC liquid phases have also been characterized by I R and NMR (696) and imbrication patterns (420). Annino and McCrea (33) described a new class of liquid phases whose selectivity can be varied over a wide range by changing the column temperature. The phases are mixtures of stearic acid and 1,Q-nonanedioic acid and undergo reversible temperature dependent compositional changes. The influence of temperature on the polarity was characterized by Petsev (744) through the temperature coefficient. Jaglan and Gunther (484) confirmed that when nonpolar solutes are analyzed on nonpolar phases, the liquid loading

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has no effect on the relative retention. The influence of the structure of the stationary phase on the activity coefficients was studied using 25 esters of benzenedicarboxylic acids, their isomers, and other similar compounds (746). The influence of molecular structure (661) and stationary phwe polarity (18) on the retention has been explained in terms of steric hindrance ( 4 3 , 611) and chain length (746). Altenburg (2.9) developed an expression for the retention index of isomeric alkanes in terms of the number of carbon atoms, mean square radius, and experimentally derived constants. Experimental results of Deans (936) show that overloading the column with sample enables the sample to act as the stationary phase. The effect is that some of a trace component accumulates on the back edge of the major component to produce a visible peak, but an appreciable amount spreads unsymmetrically forward under the major component. Exponentially loaded columns were treated mathematically by Bunting and Meloan (147) and demonstrated superior resolution for solutes with low or intermediate partition coefficients. When polymer beads were coated with a liquid phase, the effective surface area decreased, retention times were usually lowered, and a minimum HETP value was found with a 2% liquid load (488). The elution behavior of various classes of polar and nonpolar solutes on GC packings with chemically bonded phases was investigated in terms of the chain length of the bonded phase (694). These “Durapaks” were shown to obviate the necessity of long periods of column conditioning and to be satisfactory for the separation of the methyl esters of C I fatty ~ acids (680). Organic phases were chemically bonded to controlled surface porosity supports with a variety of functional groups, resulting in column materials with widely diverse selectivity and show low vapor pressures a t high temperatures, excellent column life, minimum bleed, homogeneous distribution on the support, and good column efficiencies for GC and LC (656). Locke, Schmermund, and Banner (698) bonded alkyl and aryl substituents to the surface of siliceous materials via a Grignard reaction. Bonding of various silicones to diatomaceous earth, silica gel, silica and glass beads by polymerization, and their thermal stability for GC separations, was investigated (43, 435, 43.6). Scanning electron microscopy showed that most of the liquid phase covered the periphery rather than the interior of the support and implies that the area covered is much less than the BET surface and that this layer is about ten times thicker than would be assumed from an isotopic distribution (44).


The stability and regularity of coated liquid phase columns was improved by a vacuum mating method and the addition of an insoluble modifying agent to eliminate adsorption at the gas-liquid interface (1021). However, about 50% of the diethylene glycol succinate on a column reported previously (&0) evaporated a t 200 OC and most of the remaining liquid phase was heataenatured and underwent heterogeneous redistribution. A method for estimating the upper temperature limit of a stationary phase used direct measure ment of the weight concentration of the liquid phase in the carrier gas stream and Luskina and Turkeltaub (613) considered the upper limit to be lo-* g/l. Chlorosihnes were shown to be stable up to 350 OC and capable of separating a wide range of organic compounds (90). Thermal aecomposition of cross-linked polystyrenes was sufficient to interfere with the separation efficiency of Porapak P a t 200 OC and Porapak Q at 300 OC (23.9). Silicone SE-52 air oxidized on Gas Chrom Q possesses high temperature capability (to 350 “C), good baseline stability, is easy to prepare, and is of general utility (868). An improved method of preparing thermally stable stationary phases for temperature programming to 400 “C uses cross-linked stationary phases on a flux-free calcined diatomaceous earth support (834). These high temperature columns may be sealed with asbestos gaskets impregnated with Dexsil300 (93). Several new polyamide type polymers were prepared and evaluated as liquid phases. They have good thermal stability, good solubility for hydrocarbons and polar compounds, can be coated in thin films on siliceous supports or metal capillary tubing, and have separated amino acids, fatty acids, steroids, and sugars (630). Polyimides were used to 325 OC to separate hydroearbons and steroids and should prove useful for high boiling polar molecules (6.99). The retention indices indicate that two new hydrocarbon formaldehyde resins are of moderate polarity (449) while interlamellar organic complexes prepared from clay minerals show high selectivity for aromatic hydrocarbons (906). Studies were reported which investigated liquid phases for the separation of nonpolar components and included several Apiezons (969), AgNOsglycol solutions (666),cable insulating oil, polyphenylether, and phenoxybenzenes (670) and high molecular weight fatty acid esters in aromatic alcohols (16). Enhanced selectivity for polar solute separations was reported with ethylene glycols and polyethyleneimine (866), ethylene glycol succinate and butanediol succinate (.978), and a phosphoric acid ion exchanger (468). The separation of the enantiomers of various esters of N-TFA-amino acids

on open tubular columns coated with

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N TFA - L - valyl- L - valine cyclohexyl ester was investigated on columns up to 500 ft in length (680, 681). Feibush and Gil-Av (309) discussed structural considerations leading to the interaction between asymmetric solutes and solvents. Separations of TFA-amino acid isopropyl esters were reported on the nonpolar stationary phase SF-96, and on the newly synthesiaed optically active N-TFA-L-phenylalanyl-cleucine cyclohexyl ester with high efficiency (649) and with the N-TFA-cvalyl-c leucine cyclohexyl ester (731). Racemic amino acids can be resolved as the pentafluoropropionyl isopropyl esters in less t h m half the time of previous separations without a significant loss in resolution so that i t is now possible to resolve 17 pairs of protein amino acids (732). The racemization of some aamino acids was studied as a function of temperature by GC (688). The structural effects of systematically substituted peptide stationary phases on the GC separation of amino acid enantiomers indicated that the major part of the separation occurred a t the amide end of the dipeptide (199). I n a search for new complex forming reagents suitable for GC, a series of Rh(C0)Z P-diketonates in squalane solution were formed to interact rapidly and reversibly with olefins (555). A wide range of cornpounds were ana!yzed on a column of potassium tetrathiocyanotocobaltate on Chromosorb P and it was found that polar compounds, especially water, were strongly retained (164). Aqueous solutions of silver and mercuric salts were selected as stationary phases to illustrate how solute selectivity for hydrocarbons may be obtained because of the large surface and complexing effects of this system (986). Gump (411) separated polycyclic aromatic hydrocarbons on diatomaceous earths supports modified with inorganic salts. In separating aromatic, terpene isomers, and derivatives on liquid crystal substrates, a correlation was noted between the geometric shape of given isomer pairs and the liquid crystal structure (769). Reversible changes in peak shape and the retention time were produced by applying an electric field across a capillary column that employed a liquid crystal as a stationary phase. In general, the applied potential caused peaks to be retained longer and to be more symmetrical in shape (907). Young (1013) treated the kinetics and thermodynamics of mixed liquid phases and concluded that any correlations of solvent selectivity founded on the assumption thEt heterogeneous homogeneous columns are equivalent must be regarded as a rough but useful approximation. Equations for the relative retention of various compounds on

binary mixtures of polar, semipolar, and nonpolar substrates were developed and the nonadditivity of polar properties for mixed polar phases was discussed (781). Retention of model mixtures on mixed colloid solutions of polystyrene (706) and 42 pesticides on QF-l/OV-17 (997) have shown the utility of mixed solvents for the analysis of complex mixtures. Solid Supports. A thermodynamic study of solid supports established that adsorption a t the solid support surface is significant and insignificant at the gas-liquid interface (83). Sorption experiments with HzS added to the carrier gas have been carried out to investigate the influence of uncoated area in solid supports on the retention data, and a criterion was proposed for the degree of support coating by the stationary phase (84). Kirkland (634) patented a superficially porous refractory solid support which employs colloidal particles such as silica and silica coated TiOz on the surface of an impermeable bead to give it surface porosity. The same supports were used in large diameter columns but the capacity of the stationary phase limits the amount of sample than can be used (248). Surface activity of glass bead supports has been reduced by substituting the Na+ with H + on the surface and deactivating by silanization (419). The efficiency was increased when the glass contained 5-50 mole per cent of an alkali metal oxide and was leached with ammonium bifluoride (316). Another improvement was the development of a solid support comprised of cellular glass modules which are glass pellets coated with A120s+H20and fired. They may then be coated with a large variety of stationary phases (168). Three novel column packing configurations were patented by Reynolds and Petersen (779). These include a brush in which the fine wires or fibers are supported on a central member, packing fine wires or fibers are supported on a central member, packing fine wires or fibers in the form of a coiled screen, and packing a plurality of screen disks. Inorganic supports such as the nickel form of a cation exchange resin (716) and metallic powders with 1% liquid phase (1009) have been shown to have plate heights as small as 1 mm. Schwartz and coworkers (828) found dendritic sodium chloride supports gave low pressure drops, no tailing or losses by adsorption, and no reaction with polar compounds. A comparison of the results of Hg-porosimetry, electron microscopy, and GC studies of six supports proved Chromosorb W to have the best physical properties (142). A new kind of diatomite solid support has been characterized after various hydrothermic, heating, and chemical treatments (143). Various washing, heat

treatment, and silanization methods have reduced the adsorptive and catalytic properties of the diatomaceous supports (961, 967, 998). Elderberry cellulose, Juncus glaucus cellulose, and pink and white diatomites were evaluated as column packings and then chemically modified by methylation, nitration, trifluoroacetylation, and cycanoethylation to study the polarity effects (739). A polyurethane support was formed in situ by Ross and Jefferson (801) which is porous and may be used as formed or coated with a liquid phase (up to 70%). It appears to be particularly useful for preparative columns because the support is bonded to the walls of the column, thus preventing channeling a t the wall surface, and the density, porosity, and surface characteristics can be controlled. Polyethylene foam, columns and prefoamed materials (latex and natural rubber) demonstrated good efficiency although there are upper temperature limitations (820). Van Wijk (954, 965) reported that polymeric columns packed with poly(2,6diphenyl-para-phenyl oxide) were stable to 400-450°C and that the separations were comparable with those on the cross-linked polystyrene porous polymers. “Synachrom,” a new sorbent based on a styrene-divinylbenzene bead copolymer, was shown to behave as both an adsorbent and as a nonpolar stationary phase (277). The porous polymers Chromosorb-101 and -102 appear to be satisfactory for the separation of fluorinated compounds because they act as weak specific adsorbents (418). The active surface sites of Chromosorb-102 were found to be unreacted vinyl groups and were removed by the addition of HF to the double bond of the vinyl group (44’7). The variation in performance of different batches and types of porous polymer bead columns indicated that Porapak Q-S was the most satisfactory for mixtures of polar compounds (366). Zado and Fabecic (1015) derived characteristic functional group incremental energies for Porapak Q (nonpolar) and T (polar) in order to explain the retention behavior of organic adsorbates. Porapak T exhibited a strong interaction with alcohols, ethers, and ketones, and both materials showed a strong interaction with the hydroxyl hydrogen. The adsorption isotherms for Porapak Q were found to be of the Langmuir I I I type and the isosteric heats of adsorption decreased with increased sample size (341). Temperatures as low as 76’K were used to separate He3, Ne, and H2 in He4 on a 4.9-m Porapak Q column (989). The active sites on Porapak Q will actually undergo exchange with a-hydrogens of ketones (58) and NOz reacts with this support to give NO, water, and nitration of the aromatic rings of the polymers (928).


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Although Teflon has been reported from the dependence of statistical moto be an excellent column material ments of the elution curves on the linear for nanogram amounts of tetraethyl flow velocity of the carrier gas. The pyrophosphate (217) and for the eluresults obtained give evidence that the tion of sharp, symmetrical peaks of orover-all transport rate of the sorbate ganophosphorous pesticides (413), Conmolecules from the surface of the granule der (191) has shown that it is not as to the adsorption site is limited by actiinert as originally thought as 14y0of the vated diffusion within zeolite crystalretention of n-hexane may be attributed lites (1093s). Values of the coefficient to adsorption on Teflon. New Teflon of mass transfer for packed capillary supports were formed by treatment with GSC columns were measured from the tetrafluoroethylene/vinylidene fluoride dependence of HETP on flow rate and copolymer to improve the mechanical used to explain the low values of zone properties and gave plate heights of 1-2 diffusion (883). mm for polar and/or corrosive subThe principles and applications of instances (134,809). ert solid supports with macropores A method for testing the residual surpacked with finely dispersed active adface activity of GC solid supports was sorbents were compared with macropordeveloped (868) while the effects of ous Chromosorb partitioning supports silanization on the separation efficiency (691). A system of equations has been were measured for HMDS and DMCS developed by Grubner and Underhill (978) and DMCS and TMCS (chloro(389) for the calculation of the adsorptrimetbylsilane) (448). Biernachi (102) tion bed capacity by the theory of statisdeactivated Chromosorb P and W with tical moments. The heterogeneity of the sodium salt of 3-aminobenzene-1the energy surface on a support was used sulfonate for the separation of aliphatic to establish the adsorption properties of amines. The adsorptive and catalytic supports and adsorbents and explain properties of several Czechoslovak supsteps on the adsorption isotherms (977). ports were studied and compared with An electrical simulator for chromatothe Chromosorb P and W supports graphic behavior on GSC columns was (967). The efficiencies of various supproposed to simulate adsorption kinetports for GC and LC were compared by ics, mass balance in the column, and to the reduced plate height and reduced calculate the statist,ical m0ment.s (647, mobile phase velocity in order to ob648). serve the change in the column capacity Calculation of the differences in the ratio with the particle size (646). Surisoteric heats and differential entropies face structures of the diatomaceous of adsorption on graphetized carbon earth supports (439), glass beads ($4~5)~ black was reported. These calculaand porous polymer sorbents and Teflon tions take into account the differences (810) have been correlated with their in the potential functions of the interGC performance after scanning with the action between isotopic molecules and electron microscope. In one of the the adsorbent surfac,e and the differstudies, scanograms were taken to deterences in the quantum effects for the mine the pore depth (810). vibrations of the isotopic molecules Adsorption Columns. An excellent mass centers normal to the surface (761). review of molecular adsorption chroThe retention volumes for a series of matography by Kiselev (687) presents hydrocarbons adsorbed on the basal some statistical approaches to the use of face of graphite a t zero surface coverage various constants, e.g., virial coefficients, were calculated by a semi-empirical some analytical applications using new molecular-statistical method. Calcuadsorbents, and a cornparison of GC lations of the retention volume for unand liquid adsorption chromatography. saturated and aromatic hydrocarbon Adsorption in gas-liquid chromatogmolecules made it possible to estimate raphy was treated by the equilibrium the difference between the potential theory (82) and the effect of inducing functions of interaction of the carbon nonequilibrium with a 60-HZ pulsed gas atoms of saturated, unsaturated, and flow was a decreased HETP a t high aromatic molecules with graphite (768). flow rates (1011). Band spreading Szlaur (890) measured the adsorption in molecular sieve columns followed a kinetics of polar compounds on molecutheory based on the additivity of the lar sieves in order to determine the efmechanisms of axial dispersion and slow fective diffusion coefficient into the mass transfer (764). Moreland and granules. Chromatographic techniques Rogers (660, 661) described the effects were employed to measure chemisorpof slow mass transfer when using microtion rates of Hz on Co (4) and the rate porous adsorbents in gas-solid chroof adsorption of Hz on Zn as a function matography (GSC). When diffusiviof pressure (6). Henry's constants and ties were large enough to allow total heats of adsorption were measured on access to the pore, the molecular size and carbon black to determine the influence degree of adsorption of the adsorbate of molecular structure and compared had significant effects on the HETP with results of theoretically evaluated values. The radial coefficients of inpotential energies of adsorption (539). ternal diffusion have been determined High resolution NMR line widths and 218R


chemical shifts showed hydrogen bonding on silica and the effect of silanization (761). The thermodynamics of adsorption as a function of the molar refraction, dipole moments, and specific interactions have been determined by Okamura and Sawyer (716). Their data allow prediction of retention volumes for other compounds as well as the molecular confirmation of adsorbed polar molecules. Others have used the polarizability and thermodynamics to explain the effect of molecular structure on retention in GSC (557). Kiselev et al. (558) studied GC on monolayers by preparing densely adsorbed layers of polyethylene glycols on carbon black and polyarylate on macroporous silica gel. They found that monolayers of polyethylene glycols possess the property of specific molecular interactions and that the contribution of the energy of specific interaction to the total heat of adsorption increases with decreasing molecular weight of the glycol. Thin films on treated carbon black reduced the retention time and the amount of tailing of polar compounds (268). The adsorption of He, Ar, and Conon Porapak S was found to be governed by a single pseudo adsorption isotherm and that because of the uncertainty of t,he carrier gas adsorption isotherms, GSC would not be a suitable method for the determination of the viral coefficients (224). Optimum carrier gas velocities for maximum column efficiency in GSC preparative columns were found to be less flow rate dependent than normally expected (1019). High pressure adsorption of CHI on silica was measured from 5 to 120 atm. for -92 to 31 "C (459). An improved method for the measurement of adsorption isotherms from elution chromatography (259) and the feasibility of determining surface properties of support materials from the adsorption isotherms determined by frontal GC were developed (979). il comparative study of adsorption isot,herms and physical properties of etched glass is of particular interest for isotope separations a t low t,emperatures (9). Isotherms were measured by the pulse and frontal chromatographic methods and the st,atic (volumetric) method in the investigation of propylene chemisorption (343). The impulsion-displacement method has also been used to measure adsorption (28). Hydrogen/deuterium exchange can be catalyzed by palladium on silica gel (562), and molecular rearrangement of olefins was shown to involve proton donation by the surface active sites yielding carbonium ions which undergo rearrangement or cyclization before elimination to form olefin mixtures (298). Adsorption separations of the isotopes of hydrogen were effect'ed on 0.35-m columns of crushed glass (342,

763), alumina columns covered with Fe(OH)a (548), and the separation of some polar isotopic pairs (CHaOHCD30H, CzH&OH-C2D60H, and CHaCN-CD&N) was obtained on GSC columns employing a modified carbon black (256). High efficiency packed adsorption columns (HETP 1 mm) were built for the semi-preparative separation of isotopic mixtures (861). These same columns were investigated for the separation of 14N2-16N2(141) and deuterated methanes (255). Metal betadiketonates were separated on porous fluoropoiymers (662) and the adsorption and displacement effects in metal chelate separations were shown by Uden and Jenkins (940). Carbon molecular sieves were prepared by thermal decomposition of organic polymers. The surface is very nonpolar as evidenced by the elution of water before methane (501). Separations of trace amounts of air pollutants were reported on short packed capillary columns in less than 10 seconds by Zlatkis, Kaufman, and Durbin (1027). Porous polyacrylonitrile adsorbents were evaluated by running a series of compounds of widely differing polarities (67). Studies on the standard adsorbents have included the determination of the effects of water presorption on the separation of fixed gases on zeolites (737)and the modification of the surface reactivity of graphite fibers by water (138). From COU chromatograms on NaX zeolite crystals and on NaX bound zeolite, the isotherms showed the dependence of the isosteric heats of COz adsorption on the extent of absorption a t low occupation of zeolite surface areas (78). Type X zeolites containing alkali cations may exhibit some selectivity to olefins and change the order of elution of hydrocarbon gases (29). Molecular sieve studies on columns as short as 0.5 nm have separated oxides of carbon and nitrogen (633) and longer columns were reported successful for ppb analyses of NzO (673) and the separation of CZOto c32 paraffin waxes (17 5 ) . The specific interaction of aerosilica gel (Silochrom C) consists of the reversible formation of hydrogen bonds according to Bebris and coworkers (66). The structural characteristics were determined from the adsorption isotherms for Kr end CBHE. The surface area can be varied from 30 to 300 m2/g and the pore diameters from 300 to 1500 -4(65, 56). Clxomosorb W' and G were treated with a suspension of Aerosil but the surface must be further treated with 0.1% Xpiezon L to rectify the peak asymmetry (85). A number of modified silica gels were prepared by Rowan and Sorrel1 (804) and their GC behavior correlated with high energy adsorption site distributions. X systeniatic study of the separation mechanism of Sphero-

sil (microbeads of silica) measured the activation temperature, specific surface area, and the porosity as they affected chromatographic parameters (402). The selectivity and analysis time on Spherosil was dependent on two fundamental parameters: the thickness of the stationary phase and the surface area. Because of the spherical shape, columns up to 1400 plates per meter were reproducibly obtained for column diameters of 1-4 mm and a bead diameter to column diameter ratio of 0.03-0.18 (401). Graphitized carbon black was used to separate reactive gases (HF, HCl, Clz, and BF3) (255) and low boiling polar compounds after modification with liquid stationary phases (254). Jequier and Robin (492) sought to make an inert adsorbent and compared the retention data, heats of adsorption, and isotherms to show that the common adsorbents are not truly inert. Sawyer and coworkers (159, 160, 637) modified silicas, aluminas, magnesium si!icates, and Graphon with various salts. The dependence of the thermodynamics on the thermal and chemical pretreatment gave an insight into the nature of the active sites a t the adsorbent surface and the adsorption process. The Na2S04 modified aluminas were superior adsorbents for separations of isomeric mixtures of olefins and Lac13 modification should form complexes of varying strengths with electron donor molecules. The behavior of aromatic hydrocarbons on NaCl impregnated, NaOH modified aluminas was reported by Vernon (968). Graphitized carbon black has been modified with various phthalocyanines and their affinity toward different organic functional groups (960). A new adsorbent was prepared by impregnating Chromosorb G and hydrolyzing a beta (3,4-epoxy cyalohexyl) ethyl substituted silane. It was especially suited to the separation of complex gas mixtures and can be used a t temperatures to 400 "C (121). A large number of new studies and materials were reported for inorganic adsorbents. These have included Xi (747) and Ag complexes (197), alkali metal fluorides for the separation of mixtures of oxyfluoxidcs (454), and finely divided diamonds on CaF2 for separations requiring high surface areas (623). Grob et al. (384) observed the influence of varying ?r electron densities and heats of sorption on the separation of alkanes, alkenes, and alkynes on VCl2, ;1/InC12, and CoC12. The halide salts of Ba and Sr were shown to generally elute alcohols, carbcxylic acids, and isomeric compounds in the order of their boiling points (383). From thermodynamic studies of some cyclic olefins and aromatic hydrocarbons on BaS04, the isosteric heats of adsorption and iso-

therms were derived (79). Oxide adsorbents studied have shown chemisorption on ZnO (gar), multilayer adsorption of alcohols on MgO (908), 02-NZ separation and reversible H2 adsorption on CrnOa (846,949), COSand SO2 on alkaline earth metal oxides (721), and thorium oxide (685). The mineral, attapulgite, may be found in Georgia (USA)and in India and was examined as an adsorbent and found to have a large external surface area, high porosity, and zeolitic properties (622). Clay minerals were modified by epitaxial modification with quaternary ammonium ioas to produce stable adsorbents (904). OPEN TUBULAR COLUMNS

Novotny, Blomberg, and Bartle (709) described some of the factors affecting the coating of open tubular columns and comparative tests indicated that the static coating method offered few advantages over the plug procedure. A simple and versatile method of coating glass capillary columns was developed which is equally suited for polar and nonpolar phases and treated or untreated surfaces (4rO). An equation has been derived (709) relating liquid phase film thickness to the column radius, the velocity of the coating plug, the concentration of the liquid phase in the solvent, and the viscosity and surface tension of the coating liquid. Guiochon (405) extended this work to predict the average film thickness for any solution. A relationship which allows the accurate calculation of the retention time for the air peak in capillary column research was developed and requires only the pyecise measurement of the retention times of the 2,4-hexadienes (571). Behrendt (71) theorized that extremely high resolution can be obtained in correspondingly long capillary columns by propelling the carrier gas with a driving force other than the inlet pressure. The performance characteristics of "sandwiched columns,'' consisting of carbon threads inserted in a glass capillary and coated with a liquid phase, were evaluated by Liberti and coworkers (530). Short capillary columns (e.g., 10 m) were found to be versatile and applicable to a wide variety of separations as they were able to elute petroleum fractions with end points above 530 "C (372). High t>emperature separations on glass capillary columns with carborane stationary phases were used to 350 "C with good efficiency (710) and polyphenylether capillary columns separated aromatics, phenols, and aliphatics in the 350400 "C boiling fraction of tars (760). The preparation of stable columns with a uniform coating of liquid phase on the walls has received considerable attention during the past biennium.

ANALYTICAL CHEMISTRY, VOL. 44, NO. 5 , APRIL 1972

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Use of the quaternary phosphonium halide, benzyltriphenyl-phosphonium chloride is reported to aid in the coating of open tubular columns with liquid phase, causing them to adhere more firmly (681) and permitting use of the column with some substrates at temperatures of 250 “C and above. Novotny and Bartle (707) investigated the effect of chemically modifying the surface of glass capillaries with a number of silylating agents including dimethyldichlorosilane, trimethylchlorosilane, allytrichlorosilane, phenyltrichlorosilane, and a mixture of hexamethyldisilazane plus trimethylchlorosilane prior to coating with a liquid phase, and they report that best results were obtained using allytrichlorosilanized glass capillaries after subsequent treatment with oxygen at high temperatures. Pretreatment of glass capillaries with aqueous hydrofluoric acid followed by alkali treatment prior to coating open tubular columns was also recommended (469). A patent has been issued to Mine Safety Appliances Co. (182) for the preparation of stable, glass opentubular columns. This patent involves etching the bore, rinsing, drying, coating with a hydrolyzable organosilane, and finally hydrolyzing by flushing with warm air satruated with water vapor. A metal-to-glass seal was described (337) allowing direct connection of a special alloy called “Dilver P” to borosilicate glass capillary tubing so that leakproof connections to instrumentation may be made with the usual metallic fittings. The burrs often formed while fabricating stainless steel capillary tubing and which partially or completely obstruct the tube opening may be removed by a chemical treatment involving aqua regia (64). The preparation of porous layer open tubular (PLOT) columns using either powdered borosilicate glass and acid- and basewashed Celite 545 together with a tungsten wire over which the glass-Celite mixture is drawn on a Desty-type glass capillary drawing machine ($14, or cobalt phthalocyanine on graphitized carbon black (326) has been described. Liberti and Zoccolillo (691) recommend roughing capillary walls to decrease the contact angle between the liquid and the glass by applying a layer of carbon or a polymerized material such as polybutadiene or polytrifluorochloroethylene. These authors found that both polar and nonpolar high resolution columns could be prepared in this way. Surface active agents may be added to the liquid phase to improve coating of the walls in open tubular columns, but peak-order reversal with variations in sample size were reported in some instances (826). The advantages of using a short l/s-inch packed column followed by a support-coated open tubular column in series were enu220R

merated by Walker and Wolf (980) for the separation of a mixture with a wide boiling point range. Several papers appeared during the past two years involving the interfacing of open-tubular columns with a mass spectrometer. Eyam (899) recommended use of an added stream of helium to the capillary column effluent when a Becker-Ryhage molecular separator is used, claiming that the additional helium behind the column resulted in higher sample recovery since both the column and the molecular separator were then working under optimal conditions. A device for coupling glass capillary columns to a mass spectrometer consisting of a joint, a constricted stainless steel capillary, and a splitter junction were described (696). Sellier and Guiochon (838) confirmed that capillary columns may be readily coupled directly to the inlet of the ionization source of a mass spectrometer, and they investigated the column efficiency, the optimum flow rate and the column diameter from a theoretical standpoint when the column works under reduced outlet pressure. Open tubular columns have been applied to the separation of steroids (711, 718) ; aliphatic amines using glass capillary columns (663) ; methylphenols (462) and the lower free fatty acids (461) by adding orthophosphoric acid to the liquid phase to reduce peak tailing; the nuclear spin isomers of hydrogen and deuterium below 60 OK (771); dieldrin in butter, cognac aroma in head space gases, and automobile exhaust using appropriate injection techniques (381); the gas phase of tobacco smoke (69); and the rapid analysis of hydrocarbons in gasoline (789). INSTRUMENTATION

Carrier Gas. The purity of carrier gases is rapidly becoming a more significant limitation to the accuracy and precision of GC. A procedure which reduces impurities in He to less than 1 ppb uses cryogenic adsorption on charcoal (837). Larrat (680) reported the generation of high purity gases by ionization of He, H P , or Nz in a high frequency discharge and separation on Molecular Sieve 5A (with 2.5% HPO) and Porapak Q columns. Oxygen was removed from NP with a copper catalyst for use with an electron capture detector (969). King (630) adapted a “heatless dryer” to prepare hydrocarbon-free air for use with the FID. The permeability of polytetrafluoroethylene (PTFE) tubing introduces Nt and 0 2 into the carrier gas by diffusion and results in a base-line change (799). Bader and Bryselbout (61) pointed out the advantages of using Ne as a carrier gas. When NH3 was used as a carrier gas, normal paraffins were separated twice as fast as with Nz, the sensitivity


of the FID was enhanced, and the tailing of amine peaks was decreased (471). The effect of CClr, CsHs, and CzHsOH as carrier gases on the partition coefficients, retention data, mean column pressure, virial coefficients, and dif€usion coefficienta was measured (933). Wagaman and Smith (976) indicated that low molecular weight hydrocarbon carrier gases may be as efficient as Nz. Gas chromatography with mixed carrier gases was evaluated as an on-line derivative analytical technique for process control (38). New techniques, such as chromatography without a carrier gas, were described (1020). Myers and Giddings (673) have shown that high pressure methods of GC (up to 30,000 psi) give increased efficiency and speed and can be used to separate large, nonvolatile compounds. A new precision pressure regulator has been reported to have an accuracy of better than 1% (644). The need for effective pressure control in GC was elucidated by Catz (169), and the influence of pressure on retention indices was shown to be a function of the structure of the compound (964). A differential thermal sensor for flow measurements has the advantages of being able to be used on-line for real-time measurements, it is sensitive, and has a rapid response (916). Czubryt and Gesser (882, 223) studied the effect of carrier gas nonideality and adsorption on the net retention volume and found a second flow mechanism for He in adsorption columns. Sampling. The importance of sampling has been emphasized by some fundamental studies which rely on the precision of the sampling step, and by the development of an increasing number of new, novel, and automated sampling systems. Macnaughton and Rogers (617) reported that quantitative GC analyses were obtained by overlapping two or more chromatograms on the column by rapid repetative sample injection. I n this manner, treatment of a system that involves severe tailing is simplified because the overlapping samples will deactivate the most energetic adsorption sites. Other potential uses include the summation of the peaks of strongly retained components and deconvolution of overlapped peaks. Pseudo-random sampling and integration of the delayed output signal has been used to enhance the signal-to-noise ratio of small signals by cross-correlation (861). The technique is of particular importance in trace analysis and requires a stable chromatographic system and high precision time base. The relationship between peak shape and symmetry, retention time, sample volume, and column type were measured in order to study the effects of overloading the

column (61). The precision and significance of this work is directly dependent upon the type and mode of sampling

used. The preparation of TFA derivatives of amino acids on a platinum support was incorporated in the inlet of a GC for direct sampling (910). Another sample reactor-inlet system forms volatile metal fluorides from solids by reaction with CLFS in a radiofrequency induction heater ( 2 6 ) . An instrument was reported by Stockwell and Sawyer (878) which mixes internal standards with the analytical samples and then automatically samples and controls the experiment. Other sampling techques for quantitative analysis include the development of an improved exponential dilution flask (601), a stream splitter which compensates for the mass fractionation of sample components (421), and a disk type splitter for capillary columns which has a split ratio of up to 10*:1 and is reproducible to 1% (276). A solution to the problem of delivering stable flows of volatile compounds a t low concentrations over a long period of time has been reported by Chizhov et al. (179). Their diffusion controlled method has a concentration range of IO4, a lower concentration limit of 10-8M, and an error of less than 1%. Methods of sampling for preparative GC were studied in an effort to minimize the loss, in sampling efficiency during the injection step (472). Storage columns have been used as a sampling inlet system. This method has found application in trapping organic vapors from the atmosphere ( 4 6 ) , quantitative analysis of fragrant components by collection on an adsorption microcolumn (4469, analysis by GC or mass spectrometry (697), and as a means of eliminating solvent peaks (229). Methods of sampling from closed, pressurized systems (rod), and vacuum systems have been found to be of importance in studying gas phase reactions (366). Encapsulated samples using a fusible metal (628) or indium tubing (280) have been an asset in sampling light hydrocarbons. These devices can be readily automated and will withstand pressures of 300 psig. Sampling of gaseous hydrocarbons in soils was automated by combining an automated syringe and valve inlet assembly (866). Specialized liquid sampling systems have been designed which will eliminate any air contamination of the sample (274), for sampling liquids under high pressure (314 , and automatically inject thermally labile materials such as herbicides and insecticides (284). A digitally controlled automatic microliter syringe sampler has been patented and is now commercially available (692). The influence of septum construction on the performance of a high temperature,

high sensitivity chromatograph has shown that interior facings such as polytetrduoroethylene or fiberglass give minimum bleed rates and minimize the problem of ghost peaks (161). The latter problem has been attributed to the use of glass wool plugs and to the formation of charred deposits in the injection area, from biological fluids (94.4). Sheppard (849) has suggested a septumless inlet which still allows syringe injection. Sampling valves appear to be a developing peripheral device as they can be readily automated, have the potential of high precision, and have a great deal of versatility. Valves for concentrating components from process streams (814), sampling corrosive gases a t temperatures above 220 "C ( 1 9 ) , and high pressure sampling valves (91 0) have been patented. Pollock and coworkers (766) described a valve for sampling dilute solutions for either packed or open tubular columns. It may be used for pyrolitic studies, evaporation, or flash heating. A diaphragmsealed valve was found to be particularly useful in utilizing a high pressure carrier or sample fluid against a low pressure fluid flow (136). Quantitative aspects of valve sampling were treated by Myers and Rosman (6'72) with respect to sample adsorption and by Dodd (268) for trace gas analysis with a helium ionization detector. A novel method of automatically reintroducing a selected portion of the column effluent into the system upstream from the column through a semipermeable membrane type diffusion cell was published by Green and Littlejohn (976). I n another embodiment, permeable membrane type diffusion cells were utilized in the serial combination of detectors. Pyrolysis. The principles, techniques, and applications of pyrolysis GC were discussed by Wolf, Levy, and Walker (1002) in a general survey of the subject. A comparative study was also made (981) of three different thermal degradation techniques: a capacitive discharge filament heater; the Curiepoint induction heating approach; and the vapor-phase, flow-through tubular reactor. Fragmentation patterns in pyrolysis GC and in mass spectrometry were compared in another publication (621). A progress report was made (206) on a collaborative study of the pyrolysis GC subgroup of the British Institute of Petroleum's GC Discussion Group on attempts to standardize procedures and working conditions to improve interlaboratory reproducibility. Levy and coworkers (688) enumberated the factors affecting the interlaboratory reproducibility of filament and Curiepoint pyrolyzers and confirmed the importance of temperature rise time of the sample.

Juvet and coworkers (498) criticized methods based on thermal degradation because of the difficulties found in achieving interlaboratory reproducibility due to fundamental experimental uncertainties associated with these procedures. They showed that photolytic degradation yields considerably more simple and reproducible decomposition patterns owing to greater control of input energy and the more predictable manner in which compounds decompose photolytically, and they demonstrated (498) that polymer identification as well as both quantitative and qualitative determinations of trace polymer additives-antioxidants, plasticizers, etc.-could be rapidly made by this simple procedure. Tanner (903) has studied the elucidation of organic structures by photolysis GC. Detailed analytical studies of ethyl iodide were reported by Barker and Purnell (66) following photolysis with 253.7 nm radiation, and the photochemistry of bioactive compounds such as heptachlor was reported (638). Numerous workers have investigated laser methods in an attempt to obtain reproducible thermal degradation. Extremely rapid heating of polymer samples may be obtained using either a neodymium-doped glass laser (414) or a ruby laser (319). In both of these studies, carbon was mixed with the sample for rapid absorption of the laser thermal energy, and the fragmentation chromatograms were greatly influenced by the diameter of the impinging beam and the amount of added carbon. Use of a special cobalt glass holder has also been studied as a means of coupling the energy from a pulsed ruby laser to transparent organic materials (908), and the effects of total laser energy and sample thickness were reported. A laser degradation inlet system, used with a pulsed ruby laser and made of quartz or Vycor tubing to prevent fractures observed with borosilicate glass has also been described (786) and used with polystyrene samples. An on-line laser pyrolysis cell featuring a ruby crystal optically pumped by a helical flash lamp to produce outputs of 5-10 joules and utilizing a quartz roof prism and a sapphire etalon to complete the optical cavity was also described by Biscar (104). Laser pyrolysis has been applied to the examination of polymer samples (SIQ), amino acids and salts of fatty acids (662),aliphatic and aromatic solid hydrocarbons (786), and oil shales (106). The latter analysis is very rapid and can be done in less than one minute compared to several hours required by the Fischer assay method or organic carbon test technique. Further research on the use of Curiepoint pyrolysis units has been reported by Buhler and Simon (144), and a Curie-point pyrolyzer was used for the


221 R

analysis of soluble and insoluble rubbers, including insoluble tire compounds (Sod), and in the pyrolysis of the copolymer, polystyrene-polyisoprene, and the polymer-like compound, bis-m(m phenoxy phenoxy)phenyl ether (483). A U.S.patent developed by Keulemans (634) and assigned to Perkin-Elmer, L a . , of Buckinghamshire, England, has been issued for a pyrolysis apparatus for use with previously vaporized samples and consists of a long narrow tube of a t least 5o:l length to width ratio lined with gold, silver, or copper and heated in the temperature range 200800 "C. A high-speed, closed-loop pyrolyzer which enables the sample to be submitted to thermal degradation a t successive increments of temperature was designed by French workers (713). Application of a step voltage to the pyrolysis filament has been used by other workers as well (687). A single pulse shock tube was used in a study of pyrolysis products of cyclopropane (129). A compact concentric pyrolytic unit designed for quantitative measurements of the total organic content of aqueous solutions (686) and municipal wastes in waterways (614) was also developed 2s was a Russian pyroiytic device ( I S ) for polymer analyjsis. The advantages of combining pyrolysis with hydrogenation have been outlined by Gough and coworkers (369), and this method was applied to a series of alkylbenzenes (367). Deur-Siftar (249) developed a trapping procedure for the low-temperature pyrolysis of polymers which eliminates problems of GC analysis of a pyrolyzate formed over extended periods of time, and she appiied the procedure to the deterninat,ion of the microstructure of polypropylene. A trapping procedure may also be applied when analyzing trace amounts of volatile materials in polymers (800). Functional groups in a parent molecule may be identified by use of controlled thermolytic dissociation and characterization of the lower molecular weight compounds formed, such as CO, COz, H20, HzS. and the C1-G hydrocarbons (586). A somewhat similar approach was reported by Merritt and coworkers

('4'J 646)'

Pyrolysis techniques have been used for determining organic matter present in an organic matrix (590) such as that found in the Pueblito de Xlleiide meteorite (589), in 3 X 109 year old preCambrian Onverwacht sedimentary rocks (833), and in lunar samples (675, 676). Pyrolysis has also been used in the characterization of human hair (240), nucleotides and nuc!eosides (93'3, ribonucleosides, ribonucleotides, and dinucleotides (938), acetylcholine in perfusates of the stimulated vagus nerve (377) and in nanogram amounts 222 R

in the effluents from rat phrenic nervediaphragm preparation (819), antimycin A components (818), four fungi of the Aspergillus jbw group (966),antifungal antibiotics (163), peptides and sequence determination in actinomycins (631), ,%hydroxy amino acids (630), the microorganisms, micrococcus lutew and Bacillus subtilis var. niger, to provide data that might be useful during a Mars landing planned for 1975 (866), lyophilized samples of 10 strains of Clostridium botulinum, types A, B, and E (196), fatty acids by in situ methylation by pyrolysis of their tetramethyl ammonium salts (886), fatty acid salts by analysis of the alkyl methyl ketones formed by the thermal decarboxylation reaction of long-chain fatty acid salts and acetates (678), arylsulfonic acids and salts (863),alkyl anilinium salts and cationic surfactants (947), p,p'-DDT in tobacco smoke (180), and naturally occurring materials-proteins, carbohydrates, and amino acids-typical of those that might be present in tobacco leaf (451). Other applications to the polymer field include evaluations of the thermal degradation of epoxy resins (106); oxyethyl and oxypropyl groups in ethyleneoxide (668); the thermal degradation of some polyolefins (146); copolymers of vinylaromatic hydrocarbons and aliphatic dienes (14); the degree of formalization of polyvinylformal (925); the composition of ethylene-vinyl acetate copolymers (718); the pyrolysis products of poly(viny1 chloride) (720); the composition of divinylstyrene copolymers (1024), styrene-methylmethacrylate copolymers (936), and styrene-acrylonitrile copolymers (974); the determination of polybutadiene in high impact polystyrene (40) and the composition of styrene-butadiene copolymers (717); the structure of chlorinated 1,4-polybutadienes (476); the quantitative analysis of 6-66 Xylon copolymers by measurement of the relative yields of cyclopentanone and j-caprolactam produced a t 620 "C; the vapor phase pyrolysis of methyl esters (246); and the identification of alkanes (139). Reaction GC. Interest remains high in reaction gas chromatography, which involves the use of on-column reactors in the chromatographic system to bring about chemical transformations of components being analyzed, allowing for example, enhanced detection of a specific coniponent. Beroza (92) pointed out that the combination of chemical reactions with chromatography has allowed some classical methods to be scaled down one-thousand fold to microgram levels and enumerated examples of this such as ozonolysis, hydrogenation, carbonskeleton determinations, argentation, and subtractive processes. Catalytic reactions have been studied directly


using column materials which function both as catalysts and as stationary phases and the stopped-flow technique. Phillips et al. (677, 748) discussed the kinetic heterogeneity of adsorption surfaces, the consequences of hydrocracking, isomerization, hydrogen transfer, and polymerization of hydrocarbons, and the way in which the dehydration of alcohols can yield information about surface sites and provide a possible method for ultratrace analysis. A study of the kinetics of thermolytic reactions in GC microreactors showed that a correction for nonideal kinetic behavior can be applied in order to obtain reliable kinetic data (919). Selective reactivities of the metal hydrides, NaBH4, NaBH(OCH&, LiBH4, and LiAl& toward alcohols, aldehydes, ketones, esters, and epoxides in a GC flow reactor were reported (776). Similariy, tJhe hydrogenation of cyclopropane on rhenium powder was shown to be quantitative and pseudo first order (982). Recirculation gases from ethylene polymerization were analyzed by Russian workers (564) using the following specific reactor subtraction reagents: alcohols (CaH2), aldehydes [0.1N ?THzOH.HC1in 0 5 N N(CH2CH20H)3 on Chromosorb], acids or esters (5% solution of NaOH on Chromosorb), olefins [&SO4(d = 1.83) on silica gel], unsaturated compoHgS04 on Chrornonents (HzS04 sorb) , acetylene '(5% solution of AgN03 on Chromosorb), n-olefins and paraffins (Molecular Sieve 5%). Hydrogenation of double bonds using a platinum catalyst (reduced by alkali formaldehyde) and selective hydrogenation of coiijugated double bonds using platinum catalyst on CaC03 modified by 5% NaOE was also supplied for reaction GC identification (12). Volatile derivatives of amino acids were prepared by forming the li-tfa-amino acid methyl esters on a platinum support (910). Langer and coworkers (578) recommended a reaction GC column as a source of unstabie reagents and demonstrated this use by conversion of trioxanetetrahydrofuran to formaaldehyde and dicyclopentadiene to cyclopentadiene. Picioram and other herbicides containing carboxylic acid and esf,er groups may be determined by on-column decarboxylation over Vycor chips a t 385 "C and measurement of the decarboxylated product (423). ReactionQC on Ca(OH)., was used for the separation and identification of carbamate and urea herbicides (874). The pesticide, N-methylarbamate a t levels as low as 10-9 gram was determined (6'63) by reaction GC both by on-column thermal degradation to methyl isocyanate and by on-column transesterification with methanol and sodium hydroxide, quantitatively yielding methyl N-methglcarbamaie. Residues of czr-

+

bofuran and its major metabolite, 3-hydroxylcarbofuran, in lettuce were also evaluated by this procedure (952). The hydroxyl group content of epoxy resins was estimated (694) as active hydrogen using LiAlH4, t,he sample reacting with the reagent in a cell attached to the gas chromatograph. The composition of binary mixtures of hydrazine and methyl substituted hydrazine,- was determined in aqueous solutions of ammonia, amides, and amines by react.ion on a CEO catalyst and separation of the decomposition products on a 5A Moiecular Sieve column (876). The polysorbate esters in food products were saponified in a reaction GC determination using soda-lime beads (612). The lactic acid in molasses and process juices was oxidized with periodic acid in the injection port of a gas chromatograph, and the acetaldehyde formed was a quantitat'ive measure of the lactic acid contents and covered the range 0 to 10 Fg (719). Hygroscopic water in clay minerals ]nay be measured by placing the sample in a GC pyrolyzer unit (450). Radioactively labeled compounds of pharmacological interest were converted (441) to 14C- or Ti-iabeled COz, CHI, or NH3 as they were eluted from the column by oxidative combustion or hydrogenative craking for counting a t room temperature in a propcrtional counter. -4 U.8. patent was issued (749) for a reaction GC method useful for the analysis of high molecular weight organic materials such as crude oil in which the eluted components are convert'ed to COP prior to reaching the detector to avoid the need for response factors. Another patent (48) described a reaction GC method for hydrogenatable mat'erials in which the amount is indicated by the difference in temperature of the gas stream measured before, during, or after hydrogenation on a catalyst. A number of authors have used reaction GC for det'ermining the elemental composition of eluting components. Berezkin and Tatarinski (87) showed that the C : H : N : O ratios may be immediately evaluated as components are eluted. by using an outlet splitter which sends a portion of the effluent to a 800 " C quartz reactor containing CuO and reduced Cu, thus converting t,he sample to 602, HzO, and N P Jand t'he reinaining portion is sent, to a quart.z reactor containing platinum and anth;.acene carbon black operated at, 900 "C which produces N2 and CO. Nickel and manganese oxides as well as silver peroxide have been evaluated as possible alternatives for the cupric oxide solid oxidant (184). The ebrlier work of Uelcher et al. ( 7 3 ) ,in which accuracies of 0.31y0for C, 0.28% for B, and O . i l % for N were report,ed using Co304 or the decomposition product of AgMnO4 in the combustion taube is worthy of mention. The decomposi-

tion products of silver permanganate plus reduced copper were also recommended by R e d (780). Moore et al. (659) determined the carbon and nitrogen abundances in lunar samples by means of a combustion-GC technique, all nitrogen compounds being reduced to N2when heated to 2400 "C in a graphite crucible. Organic samples may be burned in an atmosphere of fluorine (@), and the CF,, HF, and Clz obtained are a measure of the elemental composition. Reaction GC was used in the determination of NO and NO2 by reduction to Nz a t 300-500 "C on a suitable catalyst (e.g., Pt, Pd, or Cu/Cr) in a reducing atmosphere of CO (878). Organic nitrogen compounds may also be catalytically reduced to ammonia and measured in a Coulson conductivity cell using nickel with hydrogen as carrier gas, and this procedure was developed (164) for pesticide residues such as the carbamates. Rhoades and Johnson (782) used a similar procedure €or examinabion of cigarette tar for the possible presence of N-nitrosamines. Kojima et al. (550) passed organic oxygen containing compounds through a column packed with a carbon-platinum mixture a t 900 "C using nitrogen with 1y0 hydrogen as carrier gas, oxidizing the CO produced to COZover anhydrous iodic acid, and absorbing the COz in demineralized water, the conductivity of which is measured. Low concentrations of oxygen in mineral oils and tars have been measured by a series of reaction GC columns (548) wherein the sample is first pyrolyzed over activated carbon black converting the oxygen to CO, the CO is catalytically reacted with hydrogen carrier gas using nickel on Chromosorb W to give CH4 and K20, the consumpt'ion of hydrogen, as measured with a thermal conductivity detector, being taken as the measure of oxygen in the sample. Sulfur in organic compounds has also been determined by oxidizing the sample in a pure oxygen atmosphere with a high voltage discharge from a, Tesla coil (824) Sulfur trioxide may be determined in thy presence of sulfur dioxide and air by passing the mixture through a reactor containing sodium formate on punice a t 120 "C, thus converting the EOa to CO, whkh is separated from the other gases present chromatographically (685). Phosphorus in microgrsm quantities in organic compounds may be determined by injecting the sample directly into a stream of H z in a quartz combustion tube maintained a t 9001000 "C, separating the PHa thus produced or1 a two-stage column, and detecting the phosphine with s sodium thermionic detector (486). Inorganic halides in aqueous solution were determined (616) by exchanging the cations for tetraalkylammonium ions us-

ing a cation exchange column, injecting an aliquot into the heated injection port of a gas chromatograph where thermal decomposition to the trialkylamine and the alkyl halide takes place, these products being a measure of the inorganic halide present in the original sample. The indirect gas chromatographic determination of aluminum and aluminum carbide is based on reactions with HC1 giving stoichiometric amounts of Hz and CHI (689). Trace amounts of water in gases were determined (17) by concentration on a CaClZ precolumn, desorption of the water by heating to 450 "C, conversion of the released water to CO on a platinum carbon black mixture, and, optionally, further conversion to CH, for detection with a flame ionization detector. Carbon monoxide in ambient air has been determined a t the 0.1 ppm CO level by catalytically converting the CO to CH4 using a nickel catalyst at 285 "C and the carrier gas mixed with H2 ( 7 ) . Temperature and Flow Programming. Takemura (896, 897) has

studied the relationship between relative retention times for isothermal and program temperature GC and correlated the experimental data wit,h the theoretically predicted retention temperature. The effect of the polarity of the solute on the linearity of the retention time relat,ionships was shown to be less well behaved for polar solutes (898). Erdey, Takscs, and Szalanczy (29.@,294) derived an expression for the temperature dependence of the retention index that is an exact expression which does not require data from normal hydrocarbons. The application of an equivalent isothermal retention index was proposed as a better means of identifica.tion in linear temperature programmed GC (363). Robinson and Ode11 (788) developed the concept of an average temperature of elution to show that a correlation may be made between retention indices determined under nonlinear temperature programmed conditions and those found from plots of retention index os. column temperature. The elution time and temperature were found to be independent of the type of gradient used in a gradient loaded column. For the optimum operating conditions, the resolution was best on evenly loaded columns and it was suggested that columns with a negative liquid load gradient could be especially useful in preparative temperature programmed GC (183). The relative errors of the factors that affect the reproducibility of GC retention values in temperature programmed separations were reviewed and estimated (285). The effect, of isothermal and programmed temperature operation on the lower limit of det.ection and quantitative analyses was discussed by Ivarson (478). The design of the injection port was


223 R

modified to prevent septa bleeding and subsequent elution of ghost peaks during temperature programmed operation (935). A new variant in chromathermography has been reported which is based on the use of a positive longitudinal temperature gradient (203) and a negative temperature gradient combined with programmed changes in temperature in the oven (89, 201), which has been shown to give decreased retention times and peak widths (306). The theory of the method was developed mathematically (202, 208, 306) and a graphical method of integration was used to calculate retention times when their isothermal retention data are known (304, 306, 308). An equation for determining the retention time was derived which was based on the thermodynamics of the solute-solvent interaction (307). By introducing four parameters (value of the temperature gradient, rate of temperature change, column length, and inlet temperature a t the time of injection), the method provides more versatility and decreased analysis times when compared to other methods (396). Step programmed temperature GC has been used with electrically heated capillary columns, but is applicable only when the column temperature increases during a time interval which is short compared to the analysis time (276). Goforth and Harris (360) developed the technique of high-rate (up to 400 "C/ min) linear temperature programming and report a neglible temperature variation along the column. Heats of adsorption have been measured under conditions of nonlinear temperature programming (968). The application of temperature programming to pyrolysisGC separations was reviewed (428),and the problems unique to using temperatures between 500 and 1000 OC were considered for the analysis of metal alloys (869). The analytical advantages of pressure (flow) programming were reviewed (296), and the dependence of the peak area on the flow rate was examined for samples over a wide range of boiling points (891). Theoretical models to predict retention time, peak width, and resolution under exponential and linear flow programmed GC were used for optimization of the experiment by Tredrea (926). The validity of several local plate height equations was studied using programmed pressure GC (114). A system for maintaining a constant carrier gas flow rate through the detector was patented by varying the current to two hydrogen generators (186). Jentoft and Gouw (491) pressure programmed supercritical fluid chromatographic separations of a wide range of molecular weights. Novotny, Bertsch, and Zlatkis (708) described the manner 224R

*

in which the selectivity of separation in supercritical fluid chromatography can be controlled by pressure and inverse temperature programming. Preparative Scale. A review citing twenty-four references t o industrial applications of preparative GC has appeared in the Hungarian literature (889). Condor and Purnell (193) presented some theoretical considerations related to chromatographic throughput and showed that this may be increased by introducing the feed band with a much greater width than is usual in analytical work (194). An expression for the production rate in preparative elution chromatography was derived and used to illustrate the roles played by the relevant variables (838). The specific productivity of a column was evaluated by investigating the effects of carrier gas linear velocity, column temperature, amount of stationary phase, and diameter of the solid support. The results clearly indicated the optimum conditions for highest productivity (665). Other authors (267, 812) have presented complementary studies of the factors influencing the optimization of a preparative column. The effects of various operating parameters on the resolution obtained with a 4-inch column were evaluated ( a l l ) , and it was observed that throughput is inversely related to resolution. Thus, for a selected value of resolution there is a corresponding maximum throughput and injection size. Hupe (466) formulated the equation, P = (l/n)[(g".u. E.F)/(h.k)],where P = product weight per unit time, n = number of theoretical plates, g" = specific load capacity, u = carrier gas velocity, 5 = porosity factor, F = column cross section, h = theoretical plate height, and IC = the partition coefficient. Other authors (970, 1019) investigated the influence of several parameters on column performance and a critical analysis of radial velocity profile on band broadening in preparative scale GC has appeared (684). A number of papers have appeared on improved instrumentation for preparative scale work. Optimum designs for open, packed, and screened cone inlet distributors were thoroughly studied by Musser and Sparks (671). A U S . patent describing a closed cycle chromatograph (239) has been assigned to Phillips Petroleum. A circulating preparative gas chromatograph was also described by Russian workers (971) who listed among the advantages of circulating preparative GC the low pressure operation and the compactness and economy of the sorbent. The design, construction, operation, and performance of a newly developed East German automated preparativescale unit designed primarily for separation of industrial hydrocarbon mix-


tures was described by Struppe and coworkers (349). An instrument using 5 different columns in parallel with one detector was shown to be versatile and suitable for preparative separations (676). The Russian CHT5 preparative unit which features a semi-backflush system for the carrier gas and traps to remove impurities in the carrier gas was also described in detail (230). A temperature programmed 3-inch diameter preparative unit containing heating elements with which it is possible to maintain a temperature gradient along the column was developed by Weinreich (990). Astudy of different packing techniques and the resulting flow profiles by Albrecht and Verzele (10) shows that the "shake, turn and pressure" technique is best for packing large bore columns. These authors found the shaking amplitude must be adapted to the density and mesh size of the packing material, and using the best sample introduction technique devised to date, they attained a plate height of 1.15 mm for a 0.5-ml sample and 1.30 mm for a 2 m l sample of ether in 8-cm diameter columns (10). A Russian patent was issued (664) on a preparative-scale column consisting of several sections with stepwise decreasing per c m t liquid phase loading, the section adjacent to the column inlet being higher load than optimum in order to increase the column capacity. Preparative GC columns of variable diameter are said to be much more efficient than those of cocstant diameter (764), and a simple and inexpensive device to change trapping positions on an equal time basis was suggested (730). The I R and NMR spectra of 17 polyesters, polyethers, and silicones commonly used as GC liquid phases were measured (596) to facilitate their detection in fractions obtained by preparative GC. A few novel applications of preparative-scale gas chromatography include the separation of 14N2and lSN2 (141) and CH4-CH3D mixtures (251, 696), the resolution of the optical isomers of 3,3-dimethyl-2-butanol as the N-trifluoroacetyl-1-alanyl esters (49) and the diastereoisomers of Zalkanol esters of L(+) mandelic acid (216),the separation of milligram amounts of Sa-steranes and triterpanes isolated from Green River oil shale (346), and as a clean-up procedure in toxicology (634). Trapping. Efficient collection of GC eluents from preparative columns have been designed which utilize large volumes (957), disposable pipets (%'a)), microliter syringes (467), glass capillary tubes (565), and condensors (931). Van Dyke (950) described a trap for collecting air and moisture sensitive compounds. Trapping systems designed specifically for mass spectrometry have in-

cluded syringe or coiled hypodermic needles (669, 876), porous layer open tubular glass (916, 614) and cigarette filters, which can be washed with CSZ (389). Trapping efficiencies for IR analysis were measured by using a 14C labelling technique (198). Cooled glass tubes with solid support (198) or open silver tubes (163) followed with a wash of CClr or CS2 continue to be effective for I R identification of microgram GC fractions. Greaseless glass traps are generally required for trapping volatile radioactive compounds (947). DETECTORS

General detector characteristics, their physical principles of operation, operating characteristics, and limitations of the most common detectors were reviewed by Hartmann (431) and Hill (462). Data were also tabulated for a large number of ionization and selective detectors. King and Dupre (631) pointed out some of the basic limitations of the current techniques used for determining the linear performance of flame ionization detector systems. A continuous, steady state flow system was developed for dynamic detector calibration. A theoretical analysis of the effects of the background detector response on the quantitative performance of detectors treated the change in relative response factors caused by column bleed and the systematic errors incidental to the use of a volatile stationary phase in program temperature GC (700). Thermal Conductivity. The response characteristics of the thermal conductivity detector (TCD) have been reviewed in some detail by the GC Committee of ASTM (783). Fundamental developments include the absolute calibration of the T C detector from an accurate value of the temperature dependence of the relative thermal conductivity of a component in a given mobile phase. I n this manner, concentrations may be calculated directly from the peak height (1018). Novak and Janak (701) studied the factors affecting the relative molar response of the detector and derived expressions for calculating the response. The range of linearity over which such relationships are quantitative will depend on the temperature and the design of the detector cell. Relative molar response factors were calculated from the p r o p erties of the chromatographic solute and the carrier gas by Barry and Rosie (67). Their calculations were found to be valid for both polar and nonpolar compounds and the decrease in response with increasing molecular symmetry for isomeric compounds was accurately predicted. The TCD geometry was modified to position the filament axially a t

the very center of the chamber, such that velocity around the sensing element is zero and the noise is decreased because of the absence of any turbulent flow (963). The base-line stability was found to be improved when the filaments were treated with a chlorohydrocarbon (830). Hohmann (468) reported a switching circuit to shut off the current to the detector bridge which prevents filament burn-up in the event of a sample overload or the onset of an abnormal flow rate. Another instrumental modification incorporated a palladium transmodulator with a TCD which resulted in a gain in sensitivity of los (606). A new thermistor bead detector has been developed by Model1 (667). The sensing element is packed in a bed of thermally insulating beads so that the response is independent of flow or turbulence in the gas stream and exhibits a high signal-to-noise ratio. Chowdhury and Karasek (182) used a single thermistor bead detector which gave a detection limit of 60 ppb of hydrocarbon. A life detection system using a thermistor detector was reported for determining the microbial respiratory gases a t levels aslow as 6.8 X 10+ pmole of 02 (162).

The operating principles and the factors affecting the operation of the gas density balance were discussed by Adam, Fock, and Harangozo (2). Its analytical utility, stable base line, low noise, and application to the analysis of toxic materials in air and water were emphasized. The theory of the gas density detector was developed by a Russian group who suggest that hydrodynamic pressure drops in the detector channels can be interpreted by nonlinear functions of the gas velocities and that the mass transfer resistance of the channels is proportional to the viscosity of the gases. This interpretation was used to calculate an optimum geometry for the detector (231). Recent applications of the detector have included the determination of the 15N content in a nitrogen sample (992), and the analysis of some organosilicon compounds (1006). An indirect GC detection system was reported which measured the gas density by means of a diaphragm and a TCD. The advantage of this detector is the isolation of the TCD corrosive components in the sample (669). A discussion of detector types claimed that the gas density balance was the most satisfactory for quantitative analysis, the TCD was unsuitable for quantitative work with Nz carrier gas, and that the Brunel mass detector was the only type that gave quantitative information without calibration and qualitative data (368). By using a mass detector and gas density balance in series, a technique for the determination

of molecular weights of sample com, ponents was reported (99). Ionization. Micro methods of GC were developed for screening serum and urine samples which utilired combinations of the flame ionization detector (FID), alkali flame ionization (AFID), and the electron capture detector (ECD) (666). These detectors, the microcoulometric (MCD), and the flame photometric (FPD) detectors were compared for minimum detectability, accuracy, reproducibility, and measurement rapidity in the measure ment of part per billion levels of PHa in food-stuffs, air, and water (81). These papers exemplify the interest in the sensitivity, selectivity, and interchangeability of the ionization detectors. Gaspar (339) has suggested that the sensitivity of the F I D may be expressed in terms of the ionization efficiency. The problem of defining the lower limit of detection of the detector was studied by measuring the effect of trace impurities in the H Z and air gases, and temperature and flow rate changes (609). McWilliam (640) points out that the linearity of response of the F I D at high concentration levels is depndent on the hydrogen flow rate and that marked nonlinearity may be observed a t high HZ/Nz flow ratios. The response of the detector in the overloaded nonlinear region was found to be linearly related to the logarithm of the sample size (802). One study of the anomalous behavior of the F I D to CSZ indicated that the detector response rises sharply with the hydrogen flow rates (268), while a second shows that ion formation is linearly dependent on the CS2 concentration in the carrier gas (107). The effect of barometric pressure on the performance of the F I D has been shown to cause changes in the ion producing reaction, to influence the pattern of the flame, and to give rise to variations in the ionization efficiency (112). The authors extended the pressure range to 25 atm where it was found that at pressures above 10 atm the ionization efficiency becomes practically independent of pressure (113). Two independent studies of the quantitative effects of instrument control on the analytical precision of the F I D have been reported (380, 372). The results of these studies enable estimates to be made on the precision of instrument control necessary to achieve set precision levels in analysis. A modified detector was devised which used the burner jet as the collector electrode and gives an enhanced sensitivity of a factor of about 3 and an increase in the signalto-noise ratio of up to 100: 1 (765). On the other hand, the dependence of the F I D relative response factors on the configuration of the electrodes indicates that detectors with the burner jet used as a polarizing electrode is the preferred

ANALYTICAL CHEMISTRY, YOL. 44,

NO. 5, APRIL 1972

0

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mode of operation (708). The use of an alternating current field in the detector and measurement of the resultant change in the phase angle was found to be satisfactory when using a threeelectrode system, but no unique analytical advantages were reported (315). I n order to extend the applicability of the FID, the various indices proposed for the characterization of the detector sensitivity have been reviewed (840). The response of the F I D has been reported for compounds which range from CO and COz (817) to inorganic sulfur compounds (816), to sugars ($251, and wide boiling range materials (763). Dead volume measurements of a GC with a F I D have been measured directly when the detector is operated at about 60% of the optimum hydrogen and air flow rates (208). A chemi-ionization detector has been developed to detect phosphorous compounds by using a gas phase ionization reaction between CsBr vapor a.nd phosphorous-containing compounds. The detector is insensitive to hydrocarbons because of the absence of a flame. Scolnick (829) also discusses some of the existing theories of operation for alkali flame ionization detectors. The mechanism (133) and response of the alkali flame ionization detector (AFID) have contributed to the further understanding of this detector. The effect of background current and structure of the halogenated sample on the detector response was reported with molar response data for chloro, bromo, and iodo compounds (270). The general behavior of the detector toward halogens, nitrogen, phosphorus, and carbon containing compounds was discussed in a detailed study of the analytical characteristics of a Rb2S04 AFID detector (360). A study of the spectral response of the detector by Aue and Moseman (45) has shown that the alkali emission decreased when GC effluents entered the flame and that the response for Chlorinated hydrocarbons is proportional to the number of chlorine atoms entering the flame. Various anode configurations and positions were tested for the RbzSO4 AFID in order to study the phosphorous response in various regions of the flame. The selection of optimum conditions and configurations was discussed and shown to be dependent on the gas composition and flow rates ( 2 4 ) . The AFID was made selective for nitrogen and phosphorous compounds by using a 1: 1 mixture of RbzS04and KBr (120). A report of the optimum operating conditions for the detection of nitrogen compounds studied alkali metal sulfates, carbonates, and halides and found CsBr to be the salt of choice (206). The AFID has been shown to respond to N, P, S, As, and halogen compounds and a recent study has extended the applica226R

bility of the detector to include Si, Sn, and Pb compounds (271). Karmen and Kelley (519) devised a fluorine analysis by combusting the organofluorine column effluent to HF, followed by reaction with CaC12, and detection of the resultant HC1 with the AFID. Other applications have included the determination of chlorinated hydrocarbons using the negative AFID response (574), P=O and P=S in pesticide residues from plant and animal tissues (915), and phosphine in air (979). Nitrogen determinations have included drugs in urine (862), TMS derivatives of urinary acids (467), and APC tablets (8). The optimum operating conditions of the electron capture detector (ECD) has been extensively studied by Devaux and Guiochon (860) and Landoune (576). Both studies indicate that the optimum current is approximately 85% of the saturation current. Analog conversion of the detector signal to a linear function of the sample concentration and the use of pulse intervals from 100 to 2000 psec. has extended the linear dynamic range of the detector to 1 X lo6 (311). The sensitivity of the detector has been further studied by measuring the effect of the detector temperature (1028) and the standing current (166). A tritium source on a rare earth matrix has been used at temperatures as high as 400 OC (318) and a 14'Pm source on a gold foil gave sensitivities of 0.1 ppb for pesticide analyses a t 400 "C (607), A treatment of the health physics hazards and control problems of radioactive foils points out that exposure to radioactivity during cleaning of the foils is a major problem (460). The ECD has also been operated with the detector current held constant while varying the freqoency of the applied pulses. The response was estimated to be linear over a range of 5 X lo4 with a detection limit of 4 X lo-" gram/ml of Dieldrin (619). The sensitivity of the conventional detector has enabled detection of 2 X lo-'* gram for amines (983), and subnanogram quantities of amino acids in urine (1031) and pesticides in blood and brain tissue ('7%). Part per million analyses have been reported with the ECD for volatile sulfur compounds (62'?),nitrogen oxides (582), and impurities in breathing oxygen (165). A new universal, high temperature, radio-ionization detector can be used as a cross-section, argon ionization, or electron capture detector by changing the electrode configuration, the carrier gas, and voltage supply (581). Part per million analyses of inert gases and inorganic compounds and the response factors, linearity, and dynamic range for various organic and inorganic compounds with the helium ionization de-


tector were reported (966). The argon ionization detector linearity for high boiling solutes (648) and the limits of detection for inorganic sulfur gases (1018) have shown a minimum number of difficulties in operating the detector. The effect of water vapor and changes in flow conditions on the detector response were studied by a smoke visualization technique. Negative signals arose from adsorption on the source (984). Silas (854) has patented an analytical method employing the ionization potential of metastable krypton atoms for detecting unsaturated compounds. A francium detector and a surface ionization detector were postulated to be extremely sensitive detectors for GC (70). A catalytic ionization detector oxidizes organic compounds on the surface of a heated platinum filament in the presence of oxygen. The ion current is of the same magnitude as a FID, but is determined by the molecular structure of the oxidized compound (943) Freeman and Wentworth (318) reported a helium photoionization detector which shows great promise. It gives a universal response and has a lower limit of detection of 1.3 x gram/ml. The current, noise level, and response me independent of the temperature. The W-value detector, based on the energy from an ionizing particle traversing the gas during the production of an ion pair, measured concentrations of oxygen and anaesthetic vapors in air in -the range 0.02 to 100%. The detector is insensitive to large changes in temperature, pressure, and gas flow rates and thus very stable (985). Miscellaneous. A number of different methods for peak identification have appeared during the last two years, but clearly the emphasis has been on mass spectrometry. It is no longer possible to characterize detection techniques and instrumenta! methods only as on-line or off-line methods because all of the detectors described here have now been used on-line by one or more groups. A comprehensive review of the development, instrumentation, and applications of the various spectroscopic and chromatographic methods of petroleum hydrocarbon analysis was written by Kagler (499). The flame photometric detector (FPD) measures the chemiluniinescenc emission above a hydrogen rich flame. Grice, Yates, and David (378) have characterized t,he detector and found minimum detectable quantities of sulfur and phosphorous of 200 pg and 40 pg, respectively. Data were also presented for determining the mutual interference of the two bands to the response when both are present in the sample. The FID to FPD response ratio for hydrocarbons was found to be greater than 108,depending on the compound and the a

concentration. Mizany (666) found the optimum sulfur emission to be at a On/Hz flow ratio of 0.44.5. The rate of total gas flow through the flame jet and the oxidation state of the sulfur atom also affected the response. A lower limit of detection of 7.1 X gram for was measured at 546 nm when the F P D was optimized for its response to boron (873). Instrumental innovations have included a venting system to avoid extinguishing the flame when the solvent peak elutes (988) and a rapid reignition system for flame blow outs (1O00). A GC detector based on the 589 nm flame emission of a Tu'a&h AFID was found to be highly selective and linear in its response to halogenated compounds with the exception of fluorine (128). Earlier, Bowman and Beroza (125) and Gutsche and Herrmann (416, 417) reported an indium-sensitized F D P which was also selective for halogens a t 360 nm when burned in an oxyhydrogen flame over a stainless steel screen coated with indium. The detector has been reported to be able to detect nanogram quantities and to be linear over three decades (724). The popularity of the F D P may be attributed directly to its applicability as a very sensitive, selective detector for sulfur gas in air a t the part per billion level (877), detection of a large number of sulfur compounds in cigarette smoke (385) and beer (273j, and phosphorous and sulfur containing pesticides and pesticide residues at levels as low as 2 ppb (124, 125, 127, 300, 841, 1014). Juvet, Shaw, and Khan (497) measured inorganic complex stability constants in fused salt systems with the FPD, and elemental phosphorous leveis as low as gram were detected ( 3 ) . Optical emission detectors for GC have primarily used discharge sources. A spark discharge detector permits the detection of 10-8 gram of hydrocarbon when argon is used as a carrier gas (822). A dielectric constant response radiofrequency detector is sensitive, compact, srnd is nonselective for organic compounds (635). Beche and Lisk (50) detected organic mercury salts with a microwave helium plasma. The analysis of organosuifur and phosphorous compounds with the microwave discharge detector has been extended in a series of papers ( 1 1 , 226, 227). h i p pold and Beauchamp (610) used a similar source to determine the presence and extent of deuterium labaling in hydrocarbons by measuring the increase in ionic emissions and decrease in atomic emission intensities. Vacuum UV atomic emission detection was shown to be a very sensitive and selective method for qualitative and quantitative elemental analysis of C, N, and S compounds. A low pressure microwave helium discharge, with added trace

amounts of molecular oxygen, produced complete fragmentation of all compounds tested (131). A gas phase fluorescence detector has been developed for the analysis of polynuclear arenes. Scattering in the gas phase is less but in order to compensate for the loss in fluorescence intensity, an ellipsoidal condensing mirror and carrier gas separator were used with the cell. Measurement is more sensitive and specific than with the ECD (148). A review of procedures in handling small GC! samples for I R analysis treats batch sampling, tandem combination of GC and IR, interrupted elution GC, rapid scan IR, the internal reflection technique, and GC-Raman spectrometry (329). Ten different techniques for preparing 0.5-15 bg of drug samples for identification by IR are compared by Brannon (130). Watson (987) has pointed out that the technical difficulties of interfacing the GC and mass spectrometer (MS) have been eliminated or minimized, and now the MS appears to be the most powerful peak identification technique available. Four modes of GC/MS operation were described by Kienitz (526) and the requirements for their application are explained. Details of GC/MS developments are discussed in the peak identification section of this paper. However, it is of interest to point out the types of problems presently being solved with this combination of techniques. Perkins and Argoudelis (?'go) determined the double bond position in polyunsaturated fatty acids, and others elucidated the structure of various isomers by their differences in relative cross section ionization (757)). Other applications have ranged from lunar analyses (353,722), to complex hydrocarbon mixtures (566), food and flavor research (474), drugs (23), and steroids (30, 52,778), A microreactor a t 1000 OC was placed between the GC column and a coulometric detector to detect quantities as small as 10*yo of sulfur containing compounds (533). Lovelock, Maggs, and Adlard (604) developed a gas phase coulometer which uses thermal electron attachment for ionization and is an accurate and absolute method of analysis. Coulometric detection of 0.1 ppm H:S (37) and 20 ppb of chlorinated pesticides (479) include the applicability of the detector to sulfur and chlorine analyses. 4 novel method was developed for selective detection of oxygen-containing compounds with an electrolytic conductivity detector. The selectivity factor was lo3 and 10-10 mole of oxygenated compounds was detected (550). The priilcipal application has been for nitrogen compounds where the selectivity is 10' and the detection limit has been extended down to 0.1 ng or 0.02 ppm of pesticides in crops (733).

Other electrochemical detectors studied have included the polarographic detector (818), a solid electrolyte detector for the determination of trace amounts of oxygen in the presence of other gases (187), and an ion selective membrane electrode (661). The latter measures HzS and HCl absorbed in an alkaline solution. A semiconductor detector of indium sesquioxide is made sensitive to hydrogen by adsorbing atomic hydrogen on the sensor film and then measuring the change in resistivity of the film (600). Films of ZnO to sense surface reactions with adsorbed 02 have also been reported (399)*

A wide diversity of specialized detectors may be found in the literature. Chemical spot tests should not be overlooked for simplicity (233). The piezoelectric detector has a reported sensitivity in the ppm range and its response increases as a function of molecular weight (513). The micro adsorption detector has found application in supercritical fluid chromatography (163). The mass detector also operates on the basis of adsorption. A series of papers by Bevan, Gough, and Thorburn have compared the mass detector to the gas density detector ( N ) , described the calibration of other detectors with the mass detector ( 9 8 ) ,applied it to quantitative analyses ( 9 6 ) , and evaluated the analytical characteristics ( 9 5 ) . A diaphragm detector has the advantage of a short time constant and can be operated a t temperatures up to 1350 OC (870). The ultrasonic detector was primarily designed for trace gas analysis. Development of the detector was described (922) and patented (149, 579). An efficient counting system for continuous scanning of soft beta ray emitters mixes a liquid scintillator with the column effluent and nebulizes the emulsion into the counting chamber (847). The application of interrupted elution to combustion-radio-GC was justified on the basis of reducing statistical errors (157), and a perinanent gas analysis and identification method was developed by using isotope exchange (282). Readout. The sophistication of handling and interpreting GC data has undergone significant changes during the 1970-72 bienpium and should continue as digital computers become a more common peripheral device. Signal conditioning must be a first consideration and was treated by Knapp and Keller (543). They show that the peak height and peak shape are undistorted if the time constant of the transducer system is less than 10% of the peak half-width. A current amplifier having a bandwidth of 5 Hz and capable of resolving currents of 10-15 A was specifically designed for the F I D by Meigh (643). Studies of the distortion of peaks by a linear-log

ANALYTICAL CHEMISTRY, VOL. 44,NO. 5, APRIL 1972

0

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filter (831) and a n RC filter (989) showed their effect on the peak height and peak position, and the dependence on slewing rate. Approaches to overcoming noise levels and peak sensing were treated with an analog computer (436). R i g s (784) developed a circuit which provides an auto-zero function and correction of base-line drift during isothermal or program temperature GC. Kaiser (600) presented an extensive discussion on the location of the base line and the effect of changing the temperature on the base line. Information theory and the problems of data reduction, noise, drift, and overlapping peaks in chromatography are outlined by Huber and Smit (464). Chesler and Cram (176) examined the effect of peak sensing and random noise on the precision and accuracy of measuring statistical momenta of both G a w sian and nonsymmetrical peaks. Their data show how the digitization error in any peak parameter can be determined, and how to choose the optimum data acquisition rate. Kishimoto and Musha (641) calculated peak areas from Simpson’s rule and determined the retention time and peak height from the quadratic equation. Digital GC data have been logged by systems ranging from integrators with programmable calculators (999) to magnetic tapes (688), to the extensive digital logic system of Glenn and Cram (368). On-line digital computers have been surveyed (741) and reviewed (748) by Perone. The latter paper is an excellent introduction to the fundamentals and basic concepts of digital computers. Five different system d e signs and concepts are described by Gill (366) and a comparison of the advantages and limitations of each is included. Software considerations were discussed by Anderson (97) in the ACS Symposium on “Computer Automation of Analytical Gas Chromatography” which was published in the December 1969 and January 1970 issues of J . Chromatogr. Sci. Off-line data systems and time-share computer services were characterized and evaluated by Oberholtzer (714). Commercial digital integratortimeshare data reduction packages have been described (881,861). Different laboratory configurations have been used for quantitative analysis (784) and molecular weight distribution determinations (991). Both packed and capillary column separations and analysis were successfully used with an on-line time-shared computer (774), These systems have tied in 16 or more GC’s for both routine and research applications and allow the operator to selectively edit peaks, use detector response factors, identify peaks, choose a calculation method, save his data, and plot the digital chromatographic data (920). 228R

Baumann, Brown, and Mitchell (68) have emphasised the need for accuracy and flexibility of on-line system for nonroutine applications. The hardware and software capabilities of a small multichannel on-line system have been ex&ded to include programmed feedback actuation of valves and auto-injectors (818, 1001). Wilson and Price (996) have reported successfullongrange tramission of analog signals, the elimination of ground loops in the detector signal circuits, and elimination of inductor AC interference in the signal circuits. Small laboratory computers have been developed for online analyses and identification (619)and peak area integration followed by sophisticated routines run in large central processors (4.43). Other types of complex computer calculations have solved the problem of optimization of operating conditions to achieve maximum resolution coefficients in a required time of analysis (1008), and the detailed peak parameter and noise analysis of Kelley and Harris (699, 693). I n a review of methods of digital data analysis, Marson (686) and Metzger (647) treated a few methods of fused peak deconvolution and peak area reallocation. Computer resolution of unresolved peaks was shown to be enhanced by fast Fourier transform analysis of Gaussian (636) and asymmetrical peaks (641), the numerical method described by Goldberg (361), an iterative nonlinear regression analysis with a skewed Gaussian (94, 86), an algebraic analysis of overlapping peaks (186),and the four parameter, skewed Gaussian method (486). Other workers have investigated more classical methods such as the perpendicular drop (703), and the derivative peak height ratio method (610). An on-line, interactive approach offers a number of distinct advantages which were pointed out by Frazer et al. (397). Computer based GC systems have been developed for teaching the theory of chromatography (830), calibrating columns for quantification of biological compounds (899), leaat squares analysis (787), and selection and integration of a peak which is independent of changes in temperature, flow rate, and column load (31). With the computer in a closed loop configuration, new, state-ofthe-art experiments are beginning to appear and these include ensemble averaging by GC (609),the high precision, real-time experiments of Swingle and Rogers (888), and the real-time computer control reported by Burke and Thurman (161, 917). The computer control experiments were designed to vary the carrier gas flow rate and the column oven temperature by automating a van Deemter experiment.


IDCNllACAllON AND ANALYW

Qualitative Analysis and Andllary Techniques. Reviews dealing with qualitative analysie of components using classical retention measurements have appeared in the G e m n (793), Hungarian (893), and R w i a n (666) literature. Considerable interest in the use of retention indices waa expressed during the past two years. Tests by the Groupement pour 1’Avancement des Methodes Spectrographiques with the cooperation of several French laboratories which were o r g a n i d to study the precision and reproducibility of r e tention indices concluded the principal factors contributing to variation in determination of retention indices are lack of precision in retention time measurement and column temperature control (699). Kaiser (603) and Takacs (893) both considered errors in the d e termination of retention indices and confirmed the conclusions of the French group. Cramers et al. (909)with carefully controlled conditions obtained reproducibility of 0.03 I-unite. The theory of Flory-Huggins or Miller-Guggenheim was applied to calculation of retention indices (9.48), and correlations were made with solute molecular structure (768, 896). The temperature coefficient of I was evaluated as a new parameter in the identification of GC peaks (806) and the we of “zero point indices” (retention index extrapolated to 0 OK) was recommended (1, 899). Several authors (397,638, 788) considered the variation of I with temperature. Retention indices in programmed temperature GC was determined and compared with values measured isothermally (99%). A proposal was made (313) to base retention indices on a series of polyacenes-bensene, naphthalene, anthracene, tetracene, etc.-for condensed aromatic and hetero-aromatic compounds with high boiling points, such a system being influenced by temperature to a smaller extent than Kovats indices. The effects of sample size, nature of the liquid phase, and the existence of mixed separation mechanisms upon Kovats indices have been examined and the use of pure, discrete polymeric entities as stationary liquids has been proposed as a better means of specifying stationary liquids (603). The shifts of peak maxima brought about by the nonideality of the column processes were found to be an exclusive function of the Peclet number. I n the region of a predominent influence of the interphase mass transfer rate, the relative deviations can be correlated with the dimensionless ratio of the van Deemter C-terms and the dead time (994) * The adherence of the logarithm of adjusted retention time to the additivity rules, as the regularity in appearance of the peaks of substances in the same

homologous series, is the basis for the correlations between retention and structure. A general rule was described that permita predictions to be made for any C,,.+Z isomer if data are available for all Cn+land C. isomers of a particular class (670). Polish (@O), French Finnish (618), and Japanese (946)groups have studied the correlation of retention data with structural identification. The classical method of qualitative GC analysis, of course, involves comparison of retention between unknown and authentic samples, and measurement of retention is therefore basic to qualitative analysis. The highly precise measurement of specific retention volumes (996) and sources of errors in the evaluation of retention times (369) were considered in some detail. Reproducibility in retention times of a few parts per ten thousand is possible under favorable conditions (369). Kaiser (602) discussed the accuracy and precision of measuring retention data and retention indices, and experimental data on Porapak columns showed large differences from batch to batch and varied with the method of conditioning (972). A linear relationship has been found between the standard deviation of corrected absolute retention data and their magnitudes, the numerical expression of which can be looked upon as characteristic for the solute, the stationary phase used, and the experimental conditions employed. Thus it is possible to estimate the standard deviation of relative retention data and retention indices from the variance of the experimental absolute retention data (941). A computer program was published for calculating retention indices under all experimental conditions (167). Peak shifts caused by changes in the experimental conditions were corrected by normalization techniques (499). The possibility of using the many branched hydrocarbons which are formed by radiolysis of an alkane as an internal standard time base was suggested (39). Studies of reproducibility of retention in temperature programmed separation (286) have shown that *0.23’% is a typical reproducibility when considerable effort is taken. A method is described for correcting the observed retention times of peaks with leading edges obtained with an overloaded column (738). Retention relationships with flow programming were studied by Nagy et al. (677), and Rohrschneider (794) investigated the relationship between absolute and relative retention data with the aim of developing a method for calculating specific retention volumes from retention ratios. A relative retention ruler was devised for rapid qualitative identification of chlorinated hydrocarbon pesticides

(w),

(190). Several papers were published

on the relation between chromatographic retention data and solute structure (668, 679, 808, 94.5). Retention times were correlated with molecular topology using the DARC topological system (686), and a 7-parameter equation was developed for prediction of retention data. The combination of gas chromatography with other instrumental methods, such as infrared and Raman spectrometry, 1lllt98 spectrometry, and thinlayer chromatography, has now become routine with almost 600 papers published on applications of combined instrumentation during the past two years. Some of the more techniquecentered papers on the infrared spectrometry-GC combination include papers on trapping the effluent prior to I R investigation (198, 241, 628, 930, 932) and one on a rapid-scan I R spectrometer which can cover the spectral range between 3700 and 650 cm-l a t a scan rate as great as 5 sec using samples of 20 pg or larger (140). Unknown samples pyrolized in a thermogravimetric analyzer were separated by GC and analyzed by vapor phase I R to demonstrate the utility of a combination of analytical techniques (219). Rochkind (790) identified column effluents by using the matrix isolation technique to prepare samples for I R identification. This technique is sensitive and is highly selective for identifying organic compounds in a nonscattering, polycrystalline film. Behrendt (72) points out that various types of optical spectra could be obtained from capillary column effluents with a helium recoil I R microspectrometer. Technique-centered papers on GC/ MS combination include several describing interface units employing a modified glass frit interface (62.4, porout stainless steel (661) and porous nickel enrichers (173), a silver membrane separator (374, 609), a two-stage separator containing in the first stage a thin membrane or dimethylsilicone polymer and a silver frit in the second stage (376), and a palladium or palladium-silver alloy Hz separator which removes as much as 99.9999% of the carrier gas in one separation stage (606, 608, 867). Rees (776) reviewed the several interfacial systems now in common use in some detail. A direct introduction probe for the mass spectrometer with sample temperature control over the range -150 to 200 “C (486) was developed and a U.S. patent was issued to Varian Associates (80) for a GC/MS system with automatic interface which detects the output of the gas chromatograph and selects from each GC peak a predetermined quantity of sample for transfer to the MS. A U.S. patent was also issued to two Russian citizens (900) for a device comprising a GC column, a n

&usion cell for determining the molecular weight of components, and a MS. Karasek (189, 611) has described the “Plasma Chromatograph,” an ion-molecular reactor with an ion drift spectrometer operating a t atmospheric pressure, and has outlined its applications. The advantages of field ionization (998) and chemical ionization (36, 41, 893) as GC/MS systems were also investigated. By using CHI as a carrier gas, it also serves as a reactant gas for the chemi-ionization source and thus eliminates the separator. Other authors dealt with data processing and computer matching of GC/MS data (90, 91, 466, 646). Novel applications of GC/MS include the analysis of organic compounds in meteorites (346) and planetary atmospheres (866) and the development of a tandem thermogravimetric analyzer-GC-high resolution MS system (179). Qualitative identification of GC effluents have also employed Raman (146) and UV spectrometry ( 8 3 4 , NMR (1017), and thin-layer chromatography (466). Spots separated on a TLC plate may be introduced into a gas chromatograph for further separation and identification (242). Quantitative Analyses. Anderson, Gibb, and Littlewood (26,26)described a mathematical procedure for the analysis of non-Gaussian chromatographic peaks involving the construction of a synthetic chromatogram which is fitted to the experimental chromatogram by iterative nonlinear regression analysis, and these authors applied the procedure to the analysis of unresolved non-Gaussian peaks (24). Guiochon and Goedert (406) studied the sources of error in quantitative analysis in detail and showed precision could be greatly improved when all contributions to errors are limited to acceptable values, while others (261) treated the errors in retention data in terms of the stability of the column. The reliability of peak area measurements was re-investigated (370) using planimetry, triangulation, peak height method, peak height-width method, ball and disk, digital integrators and a new method of internal programmed integration with the conclusion that no single method is satisfactory for all types of peaks. The product of the peak height and the deflection time for the recorder to go from the base line to the peak height was found to be linear function of the peak area, and peak shapes were discussed and interpreted (901). A method for determining peak areas based on straightening the Gaussian curve was studied (806). Kaiser and Klier (607) outlined several rules for allocating peak areas by a separating line between unresolved peaks. Application of the statistical method of linear regression for interpretation of


229R

calibration data waa considered in depth (If 0 ) aa well aa a statistical comparison of low concentration regreasion equations to evaluate the validity of incorporating internal standards (496). Sanchez ( 8 f S ) derived a working equation for the internal standard method for the case where each sample contains the same concentration. Then the calculation of the unknown concentration does not depend on the volume of the sample or the absolute value of the concentration of the internal standard. Another method was described which enables one to calculate the detector response factors without the use of pure components (486, 487). Kaiser (606) pointed out that reversion GC does not entail any sampling and dosing errors and does not require Calibration of the measured values at trace concentrations (5 X ppb to 0.5 ppm). A ceramic gas dilution device was developed for preparing known gas concentrations in the 10 to 1000 ppm range (47). Calculation of the relative correlation coefficients for binary s y 5 tems was described (663)and used in the internal normalization method (667). An objective statistical comparison of the quantitative GC techniques was made. The standard d d i tion method proved to be less precise than the other methods studied (111). Multivariate statistics have been successfully developed for identifying and determining the origins of complex mixtures such as essential oils and petroleum products (289, 9 2 ) . Class separation of GC data was used to correlate aroma analysis with organoleptical qualities (973). Trace amounts of components may be analyzed in the presence of large concentrations of interfering components by using mixed carrier gases (%), but the peak area and height depends on the composition of the carrier gas as well as that of the sample. Determiuation of concentretion directly from peak height using thermal conductivity cells without the use of calibration mixtures, but only the temperature dependence of the relative thermal conductivity of a component in the carrier gas, is claimed to be practical (1018). Novak and Janak (701) ccnfirmed that hydrogen or helium should be used as carrier gas with katharometer det,ectors but not nitrogen, and they studied the various factors affecting relative molar response, such as molecular weight and structure of the solute, temperature, concentraticn of the substance chromatographed, and carrier gas flow rate, Isotope dilution GC minimized the errors associated with the internal standard technique and was illustrated with microdeterminations of cholesterol (123) and simulated air pollution studies (929). High precision quantitative GC has made possible the determination of the kinet230R

ics of copolymerisation (361). In the quantitative determination of trace additives in polymer samples by a new technique, photolysis-GC, Juvet and coworkers (498) showed that if the amount of W radiation of the polymer film h maintained constant, linear Calibration curves are found for antioxidants and plasticizers. MISCELLANEOUS

Metallic Compounds. Considerable research on the chromatographic separation of metallic compounds as metal chelates, organometallics, and metal halides continues and justifies a separate section once again in this review. The recent comprehensive monograph by Pommier and Guiochon on “La Chromatographie en Phase Gazeuse en Chimie Inorganique” (409) reviews each of these areas in some detail. Chromium at physiological levels has been determined in biological tissues (116) and in serum and urine (816j as the trifluoroacetylacetonate and in blood and plasma chelated with l,l,ltrifluoro-2,4-pentanedione (427). Ultratrace analyses for Be in biological specimens (906), terrestrial, meteoritic, and lunar samples (287), and human and rat urine (3B) have been reported. Adsorption and displacement effects in the elution of aluminum, chromium and iron chelates of l,l,l-trifluoropentane2,4dione and 2,2,6,6-tetramethylheptane-3,5-dione were reported by Uden and Jenkins (940). Pivaroyltrifluoroacetonates of Be, Ai, Fe, In, Cu, Co, Th (902) and the rare earths (848) were eluted a t temperatures ranging up to 270 “C, and 1,1,1,2,2,3,3heptafluoro - 7,7 -dimethyl-4,6 - octanedione complexes of thorium and uranium were found to be volati!e enough to be analyzed by GC (322). The acetylacetonates of 39 different elements were eluted a t 115OC using CC12F2 as the mobile phase and pressures of ca. 800 psi (616, 616). Aluminum and chromium may be determined in uranium a t ievels of 0.1 ppm as volatile chelates (347), Al, Cr, and Fe separated in preparative quantitives as pdiketonates, especially when coordinated with l,l,l-trifluoro5,&dimethylhexane-3,bdione (74). Mixed-ligand complexes of uranyl and Th(1V) with hexafluoroacetylacetone and di-+butylsulfoxide (862),and of Yt and all the rare earths with hexafluoroacetyiacetone and tri-wbutylphosphate (166) were separated and deternined. Other metal chelates eluted include ruthenium complexes of 4(hexachlorobicycloheptene - 2 methylene)-thiosemicerbizide (68),the Ni(II), Pd(II), and Pt(1I) chelates of bisacetylacetone-ethylenediimine (76) and bis monothiotrifluoroacetylacetonates (76), selenium complexes of 4-nitro-0phenylenediamine (860), the Be, Al,

-

-


Cr, Ni, Fe, Lu, and Er chelates of diisobutyrlmethane (849), a tris(2,2,6,6 tetramethylheptane3,kiione) Eu(II1) complex (879), 13 arene-tricarbonylchromium derivatives (836), and the Cu, Zn, Fe, Ni, Pt, Pd, Cd, and P b hexafluoromonothioacetylacetone complexes (63). Schwarberg et al. (8.97), found Mg, Ca, Ba, and Sr chelates of 2,2,6,6tetramethyl-3,5-heptanedione were sufficiently volatile to be eluted from a 5-inch column packed with 0.5% Apiezon L on silanized glass beads a t 250 “C, and Eisentraut and Sievers were granted a U.S. patent (288) for the GC separation of rare earth elements as their volatile p-diketone chelates. The etiporphrin I1 chelates of fourteen elements were eluted using high pressure GC in the range 1000-1700 psi with dichlorodifluoromethane as the solvent gas (616). The determination of water associated with metal chelates is an important measurement and was done with GC by Gaede and Meloan (336). The gas chromatographic separation of organometallic compounds has also been very active during the past two years. A number of papers were devoted to the GC separation of organic mercury compounds and include the determination of methylmercury and other mercury compounds in fish using both the electron capture detector (690) and emission spectrometry in a microwave-powered inert gas plasma (60) and the determination of methylmercury compounds in samples containing sulfide (333). The methyl-, ethyl-, and phenyl-organomerccric compounds of the RHgX type were also determined by GC using subtractive techniques (693). Organotin (117, 220, S o l ) , -aluminum (119, 438), and -gallium (119), n-butylboronic acid derivatives of 1,2- and 1,3diols (137), organohalogermanes (687, 1032) and compounds of the type (C~H&N-M’-(CZH&where NI and M‘ are Si, Ge, or Sn and form heteroelement-heteroelement bonds (118, 120) were also successfully eluted. Papers dealing with the separation of organosilicone compounds are numerous (136,S31,966,1006). The metal carbonyls of Fe, Cr, Mo, and W may be eluted from squalane and Apiezon columns (768). Benzene tricnrbonylchromium and the three isomeric xylene tricarbonylchromium complexes may be eluted from a GC column (948) but the 2,3-dimethylnaphthalene tricarbonylchromium complex is thermally unstable even a t 145 “C. Butts and Ilainey (166) preprtred volatile trimethylsilyl derivatives of the ammonium salts of borate, carbonate, oxalate, phosphite, sulfate, arsenite, phosphate, vanadate, and arsenate using bis(trimethylsily1)-trifluoroacetamide, and the trimethylsilyl derivatives of the silicate anions Si%-’, SizO,”, Si3010-’, and Si4012-8 were

separated by GC (864, 1006). These separations have been shown to be functional by the analysis of organic impurities in diborane, silane, and germane after GC separation of the latter as hydrides (1030). Indian authors investigated seven complexes of the dithiocyanatotetrakis (1-alkylarzlamine) nickel (11) type, substituted in a number of ways about the aromatic ring and alkyi chain, and six complexes of the general type iVB4(CNS)2 (101). Rotzsche (803) has reviewed some of the special instrumental considerations required in the GC separation of corrosive and labile substances such as the halogens, metal halides, hydrides, and organometallic compounds. The design of a reactor injection assembly for the formation of volatile metal fluorides using chlorine trifluoride was described (225), and another worker separated Fz, UFe, SFe, MoF6, and SbFb making use of sodium fluoride, lithium fluoride, and aluminum trioxide column packings (756). Volatile xenon fluorides were separated by Zado and Fabecic (1016), and the isotope pairs of 12CF4-WF4and a2SF@4SFswere separated by Bayer, Nicholson. and Sievers (64). A number of papers on metal chloride separations have appeared. VOCla and Tic14 were separated by gas chromatography (6). The chlorides of Sn, Ge, Si, I?, As, and Ti were eluted using DC-550 silicone oil 9s liquid phase (727) and conditions were given by Parissakis et al. (798), for the separation of the pairs SiCl4-GeCl4, SiC14-PC13, SiC14-SnCi4, SiClr-AsC13, GeC14-.4sCla, PC13-AsC13, and SnC14-AsC13. In another publication (729), these authors discussed in detail the reactivity of metal chlorides with the several organic stationary liquids used in their studies. Stumpp (881) reported the separation of A1C13GaCls, NbClb-ZrCl4, TaClb-NbClb, KbCl~-NbOCl3,HfCld-ZrC14, and AlC13HfCl4 using as column packing a high purity synthetic reactor-grade graphite preheated in a stream of C12 a t 8001000 "C and cooled in vacuo. A detection limit of 4 pg of Sn was obtained in the separation of SnC14in a chlorinated Zircaloy sample (68). Zvarova and Zvara (1033) reported that the rare earth chlorides formed volatile complexes with AlCL, and they were able to separate rare earths on uncoated glass capillaries a t temperatures less than 250 O C when AlCl3 vapors were made a component of the carrier gas. Separation of transuranium elements, as well as Pr and U, by the addition of A1C14- to the carrier gas to form the chloride derivatives was reported (1034). The elution characteristics of the chlorides of Ti, C, Si, Ge, Sn, P, and As on six organic liquid phases were studied to measure the solute-solvent interactions (972). Sokolov and coworkers (869, 871) describe an apparatus which has been

used up to 1000 OC for separation of some high boiling inorganic halides as well as Cd and Zn metals on various adsorbents. Cremer and Deutscher (913) attempted unsuccessfully to separate metallic Na and K or Li a t temperatures ranging from 600 to 1000 OC with a column packed with various sorbents. Of the packing materials investigated, only pumice and steel beads allowed the elution of these materials, but elution occurred without separation.

Physical-Analytical Measurements. Greatest, emphasis during the past two years in the application of GC to physical-analytical measurements has been in the evaluation of the-,modynamic constants, activity coefficient#§,adsorption isotherms, reaction kinetics, and the second virial coefficients of non-ideal gases. These research areas plus a few others with novel developments, which would properly be classified in this section, will be reviewed below. High precision gas chromatography was used by Rogers and coworkers (221) to obtain relative retention, enthalpy, and free energy values with a precision of *0.2% and heats of adsorption measurements with a precision of &0.6%. Kiselev and coworkers (94) reported heat of adsorption measurements wilh a relative error not greater than 3% and heat capacity measurements a t a somewhat lesser degree of accuracy. A thermodynamic treatment of partition experiments gave rise to an equation for the relationship between the distribution coefficient and solute parameters such as the partial molal volume and the molecular area (466). The effects of the experimental variables in thermodynamic measurements at finite concentrations by frontal analysis were reported by Chen and Parcher (174). They also found that the viscosity and flow rate of the carrier gas do not influence the activity coefficient measurements. Thermodynamic functions may be estimated for solutes from a knowledge of molecular dimensions, carbon number, location of functionai groups in the molecule, etc., and compared with experimentally measured values in the qualitative identification of components (654). The standard partial molar free energies, enthalpies and entropies of vaporization in Apiezon M for a number of hydrocarbons and pyridine derivatives were measured (424) and used to examine the validity of Butler's additivity rule for the enthalpy of vaporization. Using the variation of the retention index with temperature, it was possible to determine the enthalpy and entropy of vaporization, assuming ideal solutions (398),and GC method for the determination of heat of solution from retention indices has been devised (362). Berezkin

et al. (86), measured the heat of adsorption by GC methods, while other authors (108, 109, 410) measured molar and differential heats of dissolution. Taking into account the non-ideality of the gas phase and using carefully designed instrumentation, the differential heat of adsorption can be measured with an accuracy of 1% over very small temperature ranges (108, 109). The heats and entropies of adsorption of ortho- and para-hydrogen on alumina (726) were evaluated, as were the heats of adsorption of CO on bone mineral and thorium oxide (683); the latter research indicating that the pulse method gives results somewhat in error in cases where the isotherms fail to conform to Henry's law. The thermodynamic behavior of primary, secondary, and tertiary C1-Cb alcohols on Carbowax 400 was interpreted in terms of the activity ccefficients, thermodynamic excess function, and the Flory-Huggins theory (103). Sawyer and coworkers determined thermodynamic quantities for substituted hydrocarbons on salt-modified alumina and silicates (159,637) and on salt-modified silica gel and graphitized carbon (160). A comparison of activity coefficients at infinite dilution measured both by GC and a static method was made (174, 840). The deviation of the activity coefficients of alcohols on a nonpolar liquid phase was employed (773) for the calculation of the association equilibria of the alcohols, the equilibrium vapor pressures of the monomeric and dimeric components, the mean entropy changes of the dimerization reaction, and the heat of vaporization of the monomeric and dimeric components. Several other studies involving the gas chromatographic measurement of activity coefficients were also made (16, 290, 336, 911,912).

Aewell and Stock (840) compared activity coefficients measured by static and dynamic methods. A theoretical interpretation of activity coefficients was based on measurements of 23 hydrocarbon solutes in 3 normal alkane solvents (911). A study of solute adsorption of two electron donor amines a t the gas-liquid interface containing a n electron acceptor has shown that relationships between activity coefficients and the complexation strength do not arise as a result of adsorption (218). The GC method of determining the virial coefficient of interaction was compared to other methods and a generalized expression which considers different magnitudes of pressure is presented (886). Thermodynamic data from high pressure GC methods were.found to be in agreement with second cross virial coefficients obtained from solubility measurements a t high pressures (188). Adsorption isotherms are conveniently measured by gas chromatography


231 R

(869,341,979).The water vapor s o r p tion isotherm and the diffusion c+ efficient of water on textile fibers (polyamide-6-6, polyethyleneglycol terephthalate, and polypropylene) were evaluated by French workers (170, 171) while the heat of adsorption of vapors on the surface of carbon fibers was determined by others (77) using gas chromatography. Reaction kinetics is another area of physical-analytical chemistry readily studied by GC. Van Swaay (963) derived mathematical expressions enabling kinetic studies from the distortion of chromatographic elution peaks. Mathematical models were developed from nonlinear elution chromatography and it was shown that reaction rates from 20 sec-l can be studied. Modification of the injection port of a commercial gas chromatograph enabled it to be used as a microreactor suitable for catalyst studies a t temperatures as high as 400 “C (666). Other kinetic studies include the direct determination of the kinetics of gas phase thermolysis reactions (669), measurement of the rate of reversible adsorption of hydrogen on a nickel catalyst (846), study of solvent effects on the activation volume of the Diels-Alder reaction of isoprene and maleic anhydride at pressures up to 1400 atmospheres (379), and evaluation of the rate constant and activation energy for decomposition of IBR in the Brz-IBr-12 system (429). Second virial coefficients at both medium and high pressures (188, 926, 963), the specific surface area of carbon black (627), the ~ K ofB weak organic bases (100), and the formation constants for alkyl benzene r-complexes with 2,4,7-trinitro-9-fluorenone a t infinite dilution (646) are among the varied physical-analytical measurements conducted by GC. Formation constants of complexes formed between dibutyl tetrachlorophthalate and ethyl-2-thiophene, an electron acceptor and an electrondonor, respectively, confirmed the value of GC for determimition of equilibrium constants (891). A piezoquartz microbalance has been applied to the measurement of saturation vapor pressure, heat of vaporization, and the activity of hydrocarbons (400). Purnell and coworkers (192) considered all sources leading to retention in GC including liquid surface adsorp tion and used a newly devised data treatment procedure to circumvent the problems of liquid and solid support interfacial adsorption (168). The effect of other molecular species on the permeation of organic molecules through a dimethyl polysiloxane membrane is the subject of another interesting report (679). Sheehrtn and Langer (842) used a new reaction kinetics approach to the detection of void zones in column packings permitting the estimation of void 232R

zone volumes as small as 0.5 cc (736). Stability constants were measured by GC for the r-complexing of aromatic solvents and monomers with a nitroxide radical in squalene on a 50-m capillary column (60). The determination of boiling points was done on a glass column for some alkyl astatides (368). Methods of determining specific surface areas have used the dynamic desorption method for measuring small surface areas in large volumes of gases (660), the decomposition of NzO on copper (983), and the thermal desorption of Ar from coke (869). Finally, a few interesting and novel applications including the detection of marihuana and the three major cannabinol components (668) in human urine (880) and in the mouth and the fingers of smokers (69), the analysis of blood and other body fluids for toxic substances (644), the determination of total body water by DzO dilution using saliva sampling (914), the isothermal separation of COZ, COS, HzS, CSZ, and SO2 using a Deactigel column operated a t 122 “C (688), the determination of mixtures of NO and NOz in air (949), the separation of 02 and NZ on CrzOa gel (777), the determination of vitamins DZ and Da (934), the GC detection of irradiated horse meat (468),the identification of alkaloids in the venom of the fire ant, Sobnop& saeviesima (616), and the study of the metabolism of Planavin herbicide in a lactating cow are strong reminders of the great versatility of gas chromatography. LITERATURE CITED

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(860) Sladkov, A. Z., Zavod. Lcrb., 36, 1017 (1970). (861) SGt, 8. C., Chromotographia, 3, 515 (1970). (862) Smith, D. E., J. Ass. O j k . Anal. Chem., 52, 206 (1969). (863) Smith, E. D., Oathout, J. M., Cook, G. T., J. Chromatogr. Sei., 8, 291 (1970). (864) Smith, I. B., Msason, C. R., Can. J . Chem., 49, 683 (1971). (865) Smith, J. R., Waddington, D. J., J. Chromato r., 42, 183j1969). (866) Smith, A., Harris, W., ibid., 53, 358 (1970). (867) Smuts, T. W., Jordaan, J. T., Pretorius, V., Separ. Sei.,6 , 653 (1971). (868) Smuts, T. W., Pretonus, V., ibid., p 583. (869) Sokolov, D. N., J . Chromatogr., 47, 320 (1970). (870) Sokolov, D. N., Vakin, N. A., Z d . Lab., 36, 1314 (1970). (871) Sokolov, D. N., Valun, N. A., Halmykov, Yu. B., ibid., 35,150 (1969). (872) Sokolovskii, D. V., Mekeyev, Ye. Ye., Alekseyeva, G. K., Vestn. A W . Nauk Kaz. SSR, 25 (lo), 62 (1969). (873) Sowinski, E. J., Suffet, I. H., J . Chromatogr. Sei.,9, 632 (1971). (874) Spengler, D., Hamroll, B., J . Chromatogr., 49, 205 (1970). (875) Spigarelli, J. L., Meloan, C. E., J . Chromatogr. Sci.,. 8 , 420 (1970). (876) Snyder, R. E., abid., 9, 638 (1971). (877) Stevens, R. K., Muhk, J. D., O’Keeffe, A. E., Krost, K. J., ANAL. CHEM.,43, 827 (1971). (878) Stockwell, P. B., Sawyer, R., ibid., 42, 1136 (1970). (879) Stolzenberg, G. E., Zaylskie, R. G., Olson, P. A., ibid., 43, 908 (1971). (880) Stone, H. M., Stevens, H. M., Formsic Sci. SOC.J . , 9 (1-2), 31 (1969). (881) Stumpp, E., 2. Anal. Chem., 242, 225 (1968). (882) Sukhorukov, 0. A., Vatulya, N. M., Zavod. Lab., 35, 146 (1969). (883) Supelco, Inc., Bellefonte, Pa.: Product Catalog., 1971, p 3. (884) Supina, W. R., Rose, L. P., J. Chromatogr. Sci., 8,214 (1970). (885) Sutherland, J. W., Williamson, D. E., Theivagt, J. G., ANAL.CHEM.,43, 206R (1971). (886) Suzuki, M., Hirano, J., Yukagaku, 19, 468 (1970). (887) Swann, M. H., Adams, M. L., Esposito, G. G., ANAL.CHEM.,43, 41R (1971). ,--.-,. (888) _ _Swingle, R. S., Rogers, L. B., ibid., p 810. (889) Srepeey, L., Magy. Kem. Lapja, 25, 376 (1970). (890) Srlaur, J., Ropa Uhlie, 11, 37 (,-1969 - - - ,).. (891) Srynagel, P., Zymon, S., Jedrychowska, M., Chem. Anal. (Warsaw), 15, 81 (1970). (892) Takacs, J., Erdey, L., “Column Chromatography,” E. sz. Kovats, Ed., SwiaS Chemists’ h o c . , 1970, p 177-8. (893) Takacs, J., Kralik, D., Chromatogr., 50, 379 (1970). (894) Taka?, J., Rockenbauer, M., Olacsi, I., zbid., 42, 19 (1969). (895) Takacs, J., Szita, C., Tarjan, G., ibid.. 56. 1 (1971). (896) Takemura, I., Bunseki Kagaku, 19, 39 (1970). (897) Zbid.. v 1174. (898j Ibid.; io, 531 (1971). (899) Talbot, P., Pellizzari, E. D., Brown, J. H., Farmer, R. W., Fabre, L. F., Jr., J . Chromatogr. Sci., 9, 24 (1971). (900) Talroze, V. L., Grishin, V. D., US. Patent 3,566.674 (March 2, 1971). (901) Tamura, ‘H., Hozumi, K., B&eki Kagaku, 20, 149 (1971).

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Infrared Spectrometry Robert S. McDonald, General Electric Corporate Research and Development Center, Schenectady, N. Y . I2301

T

covers the same twoyear period as Chemical Abstracts (CA) volumes 72-75 (1970-71). Selection of References. For the most part, the initial selection of referencea was based on a computer search of HIS REVIEW

Chemical Abstracts Crmdensates (CAC). Concurrently with the preparation of this review, the author has been developing an interactive computer program called LISE (LIterature Search and Edit). LISE is designed to assist an author in compiling and editing references. The basic objective in the design of LISE has been to maintain the bibliography in computer readable form while a user organizes his references. The ultimate aim is to have the computer type out the bibliography in a form acceptable to a journal,

As is often the case with a new computer program, LISE has interfered with preparation of this review as much as it has helped. LISE, itself, has benefited greatly by direct involvement with the practical problems of the review. The bibliography was actually typed by computer directly from the CAC data base with only minor corrections. The latter were carried out with an interactive text editor. I n addition to getting LISE to work, i t has been necessary to develop procedures for its use. Only now is a n effective procedure beginning to evolve, too late for its impact to be felt in this review. The logical unit of CAC is a condensate. Each condensate corresponds to a n abstract in CA, and contains the C A

reference, title, authors’ names, location, journal reference, and a set of keyword phrases designed for computer searching. The keyword phrases together with the title amount to a highly abbreviated abstract. Computer listings of the condensates have played a large part in the selection of articles for this review. The edition of CAC on 7 track magnetic tape was used. This data base makes use of a limited set of about 50 graphic characters (upper case letters only). It was necessary for LISE to translate back to capitals and lower case for the journal. A search consists of a character-bycharacter comparison of both title and keyword phrases to a set of term which make up a projile. A term is a phrase,


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Gas chromatography - Analytical Chemistry (ACS Publications)

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