Gas Chromatography - Analytical Chemistry (ACS Publications)

Review of Fundamental Developments in Analysis

Gas Chromatography Stephen Dal Nogare

E. 1. du Pont de Nemours and Co., Wilmington, Del. Richard S. Juvet, Jr. University o f Illinois, Urbana, 111.

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published in 1959, and S i 5 papers which appeared in 1960 in the third volume. A comprehensive subject and author index is provided. New books dealing wholly m-ith GC and its applications include a revised English translation of Bayer’s 1959 German book on applications (22) and several German texts, one by Schay (389), emphasizing a theoretical treatment of gas chromatography, and one by Kaiser (243), which like Bayer’s text contains extensive tables of relative retentions and selectivity coefficients. Kaiser has also published two volumes, Part I on General GC and Part I1 on Capillary Column GC, as part of the College Handbook series of the Bibliographische Institut, West Germany (242). An English text by Ambrose and Anibrose (5) has recently appeared REVIEWS AND BOOKS and a comprehensive text by Dal The 1961 AKBLYTIC LL CHEMISTRY Nogare and Juvet (83)and a monograph by Purnell (369) are scheduled for a1)plied reviews cover applications of publication in early 1962. A text on G C to air pollution studies (293), chromatography and electrochromatogclinical chemistry (25Q), food analysis raphy (202) contains several chapters ( b y ) , gaspons fuels (362) and petroleum on GC. Papers presented at internaproducts (284),essential oils (178), and tional symposia held a t Edinburg, pharmaceuticals (359). ComprehenScotland (398), in 1960 and a t Michigan sive reviews dealing with many aspects State University (349) in 1959 have of GC include those of 3lcTVilliam been collected in book form. (316), Keller, Sten art, and Giddings (25l), and Dal Sogare and Safranski (85)in English, Pimon (412) in German, PACKED COLUMNS and Chovin (66) in French. Other Efficiency, Resolution, and Speed. excellent re1 ieii s COT ering biochemical Golay (168) characterized the difference applications (221, 288) and detector between packed and capillary columns systems (294, 406) also have appeared. as arising from their closeness and Extensive bibliographies giving full openness, respectively, and noted t h a t titles of papers have been compiled the theoretical limit of his performance by Litlinovs et al., covering the period index is much more closely approached 1052-5S (290), and by Ettre, covering with the latter columns. He also rethe period 19% through June 1960 ported that a more ideal column can be (119). prepared by coating the inner walls of a Complete abstracts of all papers on capillary with colloidal clay, which GC are available through a commercial serves to maintain a uniformly thin source (300). These valuable abstracts liquid film. An extended equation for appear on 5 X 8 Unisort cards and packed columns has been written by generally are inade available nithin a Jones (239) which takes into account matter of weeks follon ing publication of the original article. The first three velocity distribution, resistance to mass transfer in the gas phase, and a term volumes of an annual series, Gas Chromatography Abstracts (R63), have corresponding to the interaction between these two gas terms. The Jones equaappeared, covering in the first volume 1468 papers published to the end of tion is formally related to the Golay 1958, in the second yolume 717 papers equation for capillary columns. Several HIS R E T I L : ~surveys

developments in gas chroniatography since the publication of the last review in this series (89)and covers the years 1960-61. Gas chromatography (GC) is one of the most rapidly growing areas in analytical chemistry. More than 1170 articles and major addresses covering applications, theory, and apparatus IT ere publishid in 1960 and this number exceeded 1600 in 1961. The rate of increase in published n-ork has been between 40 and 507; per ycar over this period. Considerable selection therefore was necessary in the preparation of this rev i m . As in the preiious review, technique-centered aspects are mainly considered, and most publications to about Soveniber 1961 are included.

rate equation terms have been derived by Khan (268) to account for all possible column processes, including longitudinal diffusion in the liquid and interfacial resistance to mass transfer. Several mathematical column models have been described (148, 390) and the theoretical plate theory has been formulated for the case where adsorption isotherms (GSC) are nonlinear (878). Giddings has continued his theoretical examination of band spreading in chromatography by the nonequilibrium method (157,158) and has examined the contributions of lateral diffusion to plate height (160, 161). Liquid diffusion in narrow pores, gas diffusion in support particles, and the contribution to HETP of adsorption and desorption processes in GLC n-ere derived (156). Similar processes occurring in GSC also were investigated (163). The velocity-dependent “eddy” diffusion term derived by Giddings has been criticized (262) and defended (162). Jones (239) identified his velocity distribution term 1% ith Giddings’ velocitydependent term. An early version of the Jones HETP equation mas experimentally studied by Kieselbach (254, 256), who establishpd the need for additional gas terms in packed columns. Seven different column equations were compared by Giddings and his associates (166) by evaluating equation terms for full, half, and quarter-length columns. Their results suggest that an entirely adequate equation is still Ranting. However, the validity of the molecular diffusion term was established (38, 165) and, in fact, this term provides the most convenient approach to determining gas diffusion cocfficients. The effect of column length and inlet pressure on efficiency was reported by de Wet and Pretorius (103) and a wide range of other column Yariables \vas also studied (292). Duffield and Rogers determined the influence of the distribution ratio, liquid phase, and diffusivity on the van Deemter mass transfer term (107) and methods for obtaining and reproducing optimum column conditions have been given by several workers (199, 406). Of particular interest in VOL. 34, NO. 5, APRIL 1962

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connection with column pressure effects

is the paper by Haruki (198), who showed that efficiency is decreased and retention remains unchanged under reduced pressure conditions for a constant pressure drop in the column. An interesting observation on the peak sharpening effect of expanded column sections has been made by Sicilio et al. (408).

Resolution and efficiency, their interrelationship, and the distinction between capillary and packed column performance were thoroughly examined by Purnell (371, 372) and Giddings (166). The required efficiency parameters and separation factors for analytical separations also have been noted (184, 473). Considerable attention has been paid recently to high speed chromatography with its obvious implications to routine analysis and process and process control applications. The optimization of the resolution-time ratio was derived by Loyd, Ayers, and Karasek ( S o l ) , who showed that small-diameter packed columns using low liquid phase loading and low density carrier gases resulted in a ninefold increase in this ratio. A more extensive treatment with DeFord was recently reported (10, 93). The theoretical aspects of speed and resolution were also treated by other prominent workers in GC (166, 264, 373). Liquid Phases. A number of new liquid phases have been described since the last review. General Electric's methyl silicone polymer, SE-30, .\vas used in the analysis of steroids a t 220' with liquid coatings of 2 to 3% (4.49)and for the separation of lipides (346) and alkaloids (291). Xeopentyl glycol succinate and silicone polymer QF-1 have also proved useful in the separation of steroids (181, 447) and sugars (48). Craig (78) evaluated o-phthalic-ethylene glycol polyester as a liquid phase for analysis of fatty acid esters. Metcalfe (331) separated longchain unesterified fatty acids directly by use of a phosphoric acid-diethylene glycol adipate polyester phase. Sand and Schlenk (386) recommend the use of the acetates and propionates of CYand P-cyclodextrin and their mixtures for fatty acid methyl ester analysis, since the thermal stability of these materials greatly exceeds that of butandiol succinate. Sucrose diacetate hesaisobutyrate has similar advantages over polyester phases (416). Thirteen liquid phases were evaluated (203) for application to the separation of hydrocarbons boiling in the range 295' to 310' C., and the most selective liquid found for paraffin-naphthene mixtures was Carbowax 20,000 for use a t 225' C. Carbowax 400 has also been recommended for extreme selectivity for aromatic compounds (108). The application of THEED (tetrahydroxyethylethylenediamine) as a selective polar liquid phase

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ANALYTICAL CHEMISTRY

solutions of organic compounds. A has been reviewed (187). Desty and measure of polarity based on the ratio Swanton (99) found excellent separation of the relative retention of two succesof m- and p-xylenes using 7,8-benzosive normal paraffins in the homologous quinoline and several other condensed series was proposed (66). ring compounds. Patents on the use of safrol (l-ally1-3,4-methylenediosyben- A simple mechanical device for packing one or two GC columns simultanzene) (276) and propylene tetramer eously has been described and illus(286) as liquid phases have been issued. trated (452). Smith (418) proposed Olefins, aromatics, naphthenes, alcothe preparation of a column packing in hols, esters, and ethers are well retained a manner identical to that of frontal by 1,2,3- tris(2- cyanoc thoxy) -propane analysis by percolating a solution of the (314). The silica flour present in Dow liquid phase through the dry solid supCorning high vacuum grease greatly port placed in a column. =In apparatus influences retention behavior of solutes for preconditioning columns of lengths (419). Complex mistures of C2 to C6 up to 2.5 meters a t temperatures in hydrocarbons are resolved on dimethyl sulfoxide and sulfolane a t 30' (450). excess of 400' nas described (73) and a preconditioning method for polyester Temperature limits and the stability of columns given (163). various liquid phases as well as the Solid Supports. I n the past t n o effect of conditioning certain liquid phases have been reported (76,166,336). years, the emphasis has been on the evaluation of the catalytic and adsorpAn exhaustive list of liquid phases usetive capacity of the "inert" solid ful for the separation of the yarious support, their effect on retention and compound types has been compiled by resolution, and means of eliminating McWilliam (315). these undesirable properties. SevMetal chelate compounds have been eral new supports and the use of used as liquid phases and retard specifitypical adsorbents as supports also cally those molecules which can act a,s have been reported. ligands (65). Fused inorganic salts Adsorption isotherms m-ere obtained and inorganic eutectic mixtures, first for firebrick (37) and for Chromosorb-P reported by Juvet and Wachi (a.41) for (394). Bens (68) compared different the separation of volatile inorganic supports, including glass beads, treated metal halides, have been applied to the in different ways by means of twodirect GC analysis of a cadmium-zinc column GSC plots. In all cases, retenalloy (91) and to the separation of tions were small and reproducible only polynuclear organic compounds (194). nith very small samples, indicating the The application of fused salt liquid low adsorption capacity of these matephases for the ultrapurification of semirials. Adsorption is evident, even in the conductor materials has been suggested presence of liquid phase as shown by a (86). Keulemans (262) reports that plot of log V , us. sample size (394). the volatile chloride of almost any metal Adsorption increases with decreasing may be made by heating a compound of liquid phase, decreasing polarity of the the element with carbon in a stream of liquid phase, and increasing solute chlorine a t 1000" C., and he has chropolarity as shown by several systematic matographed such chlorides a t temperastudies (79, 147, 437). tures up to 350" on columns of anhyMethods for reducing adsorption drous aluminum chloride, or aluminum activity have been reviewed ($04, 366). chloride-zinc chloride eutectic, susNone of the acid or base treatments pended on active charcoal. The lower were helpful in improving the symmetry boiling transition metal halides may of water peaks (356). Nitric acid also be eluted, with some apparent washing of firebrick was effective for decomposition, from hydrocarbon liquid the separation of acidic gases on polyphases (249, 260). The acetylacetoglycols, while base treatment of Teflon nates of beryllium, aluminum, and (polytetrafluoroethylene resin) in some chromium were separated (33) on an cases improved its performance in Apiezon L-glass bead column. ammonia analyses (454). Peak tailing Progress has been made on the of pyridine bases was eliminated by HCl prediction of retention data based on washing, followed by soaking in 5% solution theory and the physical propersodium carbonate and drying (171). ties of the solute and solvent (313, 321). Polyglycol liquid phases are stable on Martire (321) applied the van Laarsuch base-treated supports but decomScatchard-Hildebrand treatment of regpose on HC1-containing supports (454). ular solutions to the estimation of Silanizing Chromosorb and Celite with activity coefficients and the prediction dimethyldichlorosilane gave reproducof retention times. The use of mixed ible results in fatty acid methyl ester polar and nonpolar liquid phases for analyses @io), and Bohemen et al. (37) improving resolution and predicting reessentially eliminated adsorption OR tention times has been studied by several firebrick by intensive reaction with workers (64, 317, 418). Murata and hexamethyldisilazane. Takenishi (341) employed a mixed The catalytic effect of various supglycerol-silicone grease liquid phase for ports has been noted, particularly in the the direct analysis of dilute aqueous

isomerization of terpenes (455). As expected, the effect was most pronounced with nonpolar liquid phases and acidic-type supports. Decomposition, isomerization, and adsorption were observed with a viide range of solute types on a number of supports (526). A theoretical treatment of the changes in the chromatogram occurring when a first-order reaction occurs on the packing has been reported by Kallen and Heilbronner (244). Klinkenberg (261a) studied slow reversible chemical reactions of chromatographed substances. Surface area measurements of the common GC supports were reported by Ettre ( l a g ) , who concluded that efficiency and resolution were not significantly different in supports with specific areas greater than 1 sq. meter per gram, although adsorption (and reactivity) increased with specific area. The effect of particle size and liquid film thickness on efficiency in packed columns was treated by de Wet, Haarhoff, and Pretorius (100) with the conclusion, among others, that H E T P is proportional to particle diameter. An enipirical equation relating gas permeability of packed columns to bulk density of the packing, density and amount of liquid phase, particle size, and column diameter mas developed by Reisch, Robison, and W-heelock (S75). Among the new or novel supports are an inert fluorocarbon resin (1S8) n hich effectively eliminates tailing with amines. water, HC1, etc., and unglazed tile (303) ~ i t hno reported reactivity toward terpenes. Crushed quartz (nitric acid-washed) also was found to exhibit negligible adsorption and reactivity toward labile compounds (326). A new solid support derived from the porous inorganic material in a commercial detergent gave symmetrical peaks and superior resolution for a series of pyridine bases (92). Halasz and Wegner (192) reported on the use of alumina as a solid support. The activity of the adsorbent may be controlled by suitable pretreatment and by varying the amount and nature of the liquid phase to suit the desired separation. Molecular Sieve 5-4 has been similarly treated (89). Adsorbents. GSC continues to prove useful for the determination of adsorption isotherms as demonstrated by Cremer for moderate temperatures (80) and in the region 300' to 550' C. (81). Isotherms for CO1 on charcoal by GSC gave results in agreement with static measurements, while the high temperature studies on various catalysts also provided heats of adsorption from adsorption isotherms. Isotherms were also measured for COz on silica gel and charcoal (444),and for benzene and n-hexane on Molecular Sieve 13X, silica gel, alumina, and platinum-alumina (111). Stock (431)

showed how an isotherm may be simply obtained from a single adsorptiondesorption curve. Carberry (58) pointed out that curved isotherms can give heats of adsorption from GSC retention data only when concentrations fall in the linear portion of the isotherm -e.g., low coverage. However, Beebe and Emmett (26) reported excellent agreement between adsorption heats calculated for pure nitrogen and 1% nitrogen in helium samples by GSC and between these values and static calorimetric results. The adsorption activity of firebricktype, glass bead, and extracted detergent supports has been measured and the effectof contamination from irreversibly adsorbed materials noted (29). Adsorption phenomena (pressure surges and displacement), their effects, as well as means of minimizing these were also discussed (461). The influence of silica gel structure on the separation of hydrocarbons and the polymerization of olefins, and methods of modifying this adsorbent were noted (456). Addition of dimethylformamide to y-alumina made possible the separation of 13 components in a C1 to Cb mixture a t room temperature in 30 minutes (195). The subtractive technique with Molecular Sieve 5A a t about 200' C. was successfully used by Eggertsen and Groennings (112) for the separation of normal from nonnormal hydrocarbons. Brenner et a2. (45) had extended their subtraction studies to include 4-1,5A, and 13X Molecular Sieves. High molecular weight hydrocarbons (n-Cls to C2J were separated at temperatures around 250" C. with alumina specially deactivated with sodium hydroxide (396). By careful removal of water from both sample and carrier stream, Nomur8 and Nukada (360) extended the life of a 13X Molecular Sieve column in a process chromatograph to over 10,000 analyses. The literature on the separation of hydrogen isotopes and isomers by GSC was reviewed in a paper in ahich the separation of these materials on Molecular Sieve 13X was reported (276). Activated alumina and ferric oxide (149) and alumina-chromia (216) a t low temperatures were used, tvith the former providing the ortho-para-hydrogen split. On alumina alone, the HD/ o-Hz split proved difficult (S38). Another class of important gases, the nitrogen oxides, continue to receive attention with regard to the quantitative measurement of small amounts (0.25 to lye) of X O in N2 (386) and KO, in 32 (416). The latter procedure involves reducing NOz to NO in the column. Retention data for the various oxides and associated common gases on speciaIly prepared silica gel also were reported (322). The speed of a procedure for the analysis of krypton and

xenon isotopes in helium on charcoal was enhanced by stepwise temperature programming (266). Blood gases extracted by the Van Slyke method may be analyzed for oxygen, nitrogen, and C 0 2 on silica gel and/or hlolecular Sieve 13X columns with a total analysis time of 10 minutes per sample (S42). Carrier Gases. Gases commonly used in G C have received only little attention i n the recent literature. A G C study of impurities in helium showed neon, oxygen, argon, nitrogen, krypton, and methane as predominant contaminants (327). Ultrapure (a few parts per billion of impurities) hydrogen for use in flame ionization devices can be conveniently generated by the Serfass apparatus, which is commercially available (407). The permeability of plastics, particularly tubing, to gases of interest in GC was covered in a British report (18), which showed nylon to have the lowest permeability index. Details of construction were given for an interesting horizontal soap bubble floa meter which overcomes the problem of maintaining a soap bubble for low flow measurements (417).

Sample Introduction and Trapping. A study of the effect of sample size and other factors on column performance showed the expected decrease in efficiency with increasing sample size and a trend to larger optimum flow rates with larger sample size (SO). The novel method of enclosing a weighed liquid or solid sample in a fusible metal capillary provides a means of quantitatively introducing samples (105). I n the case of liquid samples, a new microliter syringe has been patented recently (499). Other means of introducing samples include a device for inserting and crushing small ampoules containing reaction mixtures in the chromatograph (62), a small trap for conveniently introducing concentrated trace components (344),rotating Teflon seated valve suited to vacuum or pressure sampling (67), and an all-metal sliding valve which was recently patented (319). I n the case of sample introduction into capillary columns, the question of sample splitter linearity n as investigated by Ettre (123),a new commercial linear splitter was announced ( I C ) , and Halasz (190) reported on quantitative results obtained with a new splitter design. Several rotating valves of minimum dead volume design for sampling gaseous mixtures were described for manual operation (205, SS9, S66) and one suited to automatic sample sequencing (358). Two valves suitable for vacuum sampling also have been described (144, 361), the latter being particularly simple to construct. A combination sampler and VOL 34, NO. 5, APRIL 1962

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fraction collector which is also useful for mass spectrometry was described (25). The efficient collection of GC fractions was reported in traps which were fitted with detachable collection tubes (335), with cutoff collection tips (170), and with removable capillary collectors (270). An enrichment trap consisting of a length of cooled nylon capillary coated with the liquid phase (404) can also be used to transfer isolated fractions to capillary columns. Fogging of high boiling components in cooled traps has been eliminated and collection efficiency increased to 90% by the use of the Cottrell precipitator principle (269). Automatic fraction collectors have been designed 11hich are actuated by the detector signal (409)and automatically change the collector (424). I n one case, the collectors have been fitted with infrared cells (468). Combined cold trap-infrared cells also were designed n hich require no manual transfer of the trapped coniponent (58, 468). I n connection with the infrared examination of GC fractions, the simple KBr powder trap of Leggon (281) is of interest. CAPILLARY COLUMNS

Interest in capillary columns has increased rapidly during the last two years. A patent (169) covering the invention of capillary columns, first announced by M. J. E. Golay in 1958, has been issued. A laboratory apparatus for the construction of long coiled glass capillary columns was described by Desty, Haresnape, and Whyman (98) and by Kregenbuhl (271). A commercial source is now available for stainless steel capillary tubing in coiled sections up to 3000 feet in length and with internal diameters of 0.010 to 0 020 inch (Superior Tube Co., Norrist o m , Pa.). Both nylon (480)and glass (97)columns m-ith efficiencies exceeding 1,000,000 theoretical plates have been prepared. Purnell (371) warned that caution must be used in comparing reported efficiencies measured on capillary columns with those reported for packed ,4 separation factor was columns. proposed (371) as a more exact means of comparing the relative merits of capillary and packed columns and of explaining the observation that under unfavorable conditions a capillary column of 500,000 theoretical plates gave approximately the same resolution as a n efficient packed column of only 5000 plates (370). The separation factor is given by S

=

16 (Ti&’y)2

where ‘VR; is the adjusted retention volume of the second component measured from the calculated or measured

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0


position of the air peak. This equation eliminates the effect of the relatively large gas holdup in capillary columns which greatly increases the apparent efficiency, especially for early peaks. Scott and Hazeldean (402) and the Barber-Coleman Co. ( I S ) recommended methods for coating capillary columns. Capillaries coated \vith 7,s-benzoquinoline and phenoxythiin, high melting liquid phases, were observed to undergo a severe decrease in efficiency when allowed to cool to a temperature beloiT the melting point (380). This decrease in efficiency was attributed to either decomposition during storage or globule formation upon remelting of the crystallized stationary phase. Several stream splitters which deliver only a small fraction of a normal syringe injection to the capillary, while allowing most of the sample to vent to the atmosphere, have been dcsigned (97, 109, 123, 190). The problem of fractionation appears to have been solved in several commercial capillary chromatographs (14, 123). Ettre and Arerill (123) reriewed three criteria for judging the linearity and absence of fractionation of a sample splitter. The effects of sample size, carrier and scavenger flow rates, column efficiency, column coating, component concentration, molecular type of component, and other parameters affecting quantitative results using a flame ionization detector have been thoroughly studied (109, 188, 379). Durrett, Simmons, and Dvoretzky (109) conclude that the flame detector is preferable to the argon detector for quantitative capillary column analyses because of a wider and more convenient dynamic range. Haarhoff and Pretorius (182) presented a mathematically rigorous theory of linear nonideal GLC for coated capillary columns. ,4 term, H B A R , is proposed to express the height equivalent to a theoretical plate based on apparent retention. I n a second paper ( 1 8 9 , these authors used the expression R study the effects derived for H B ~to of the distribution coefficient, the diffusivity of the solute in the liquid and gaseous phases, and the thickness of the liquid l a p on column efficiency, and demonstrated the existence of a n optimum thickness of liquid layer. The effect on H E T P of changing various parameters such as column diameter and length, carrier gas density, film thickness, and the molecular weight of the solute has been discussed and the results presented graphically (96, 3.99, 402). Scott (399) found that any column has an optimum operating temperature to give maximum resolution between any two substances. The minimum time of analysis for a pair of substances requires a column having optimum film thickness operated a t optimum temperature. The

concept of optimum practical gas velocity (OPGV) for fast analyses was introduced (402). The length of the column and the time necessary to effect rapid separation of substances may be calculated from the OPGV and fundamental physical data of the solute, solvent, and column. Similar equations have been derived by Purnell and Quinn (373) in an approach to higher speed GLC. The speed of analysis has also been studied by Knos (2641, who shov-ed that there should be no significant difference in ultimate analysis speeds attainable mith capillary and packed columns; by Ayers, Loyd, and DeFord ( I O ) , n h o studied high-speed GC in packed columns; and by Desty, Goldup, and Smanton ( N ) , mho carried out the partial separation of 25 components of reformed methylcyclohexane in only 7 seconds using a capillary 200 em. X 68.6 microns in i d . , and the separation of 15 C5 to C? hydrocarbons in less than 2 seconds on a capillary colunin 120 cm. x 34.5 microns in i.d. Scott and Cuniming (400) showed that cathode-ray presentation of chromatograms is useful for high-speed analyses. DETECTION

Detection methods have been covered in a review which encompasses developments to 1959 (405) and in several reviews extending to more recent work (305, 475). Ionization detectors were broadly discussed by Lovelock and Stirling and Ho (294, 429). Detectors. The response of thermal conductivity (TC) detectors derived from thermal conductivity and electrical factors was comprehensively developed (392). Grob and associates (175) have continued their study of thermal conductivity response factors noting that, for alcohols, corrected relative peak areas are a function of weight per cent. I n the case of H*-HD mixtures, peak height response n as strictly linear with mole per cent (9). Relative response data also have been obtained for a variety of organic compounds including substituted esters (22i?, Z24), higher fatty acid esters (268, 212), aiid aroniatic compounds (223). The problem of T ariable detector response !vas eliminated by combustion of the solutes to COZ (273). Details of T C cell construction were published for a glass and a metal hotwire cell (272) and for a unique microcell of 3-pl. volume n ith reported sensitivity of mole per cc. (388). A new, commercial tungsten filament detector was shown to improve chromatograph performance (309). T C cells were modified to reduce sensitiyity to flow by venting the cell to a constant pressure head (397) and by a patented niultiple path design providing a short

diffusion path (391). Kieselbach (266) reported a screened thermistor cell of low flow and shock sensitivity, in conjunction M ith a n improved electrical circuit. X compensated Rheatstone bridge (289), a stable a x . circuit for T C cells (368), and a multiple cell circuit for four-column operation (40) also were reported. A method of mounting hot-n ire elements for easy interchange and freedom from gas leaks and abnormal noise was described by Faley and Long (132). Performance data for three argon detectors s h o ~the Lismall” and triode modification by Lovelock to be superior in sensitivity and linearity (295), while the merits of integral and differential forms of this type of device were compared by Matousek (323,324). Experimental performance of the triode argon detector n ith capillary columns (60) and a SrgO-equipped“large” cell (446) gave excellent results for trace analyses and fatty acid methyl ester studies, rmpectivcly. A versatile argon detector has been dcsigned for use with both large and small columns (440), and modifications necessary for operation around 300’ C. have been noted (177). Several different p-radiation sources have been examined; a 100-mc. titanium tritide source was found by Johnson to give good sensitivity for normally undetectable gases (234), and Pml47 was found 8 satisfactory 0 source for this detector (357). Haahti, Kikkari, and Kulonen (180) made the interesting observation that an ionization detector functioned satisfactorily without a p source. Because of the high energy of metastable helium, detection of permanent gases other than neon should be possible with this carrier. Hydrogen, argon, nitrogen, methane, carbon monoxide, and carbon dioxide were detected with purified (31, 115) and commercial (278) helium, and the results obtained n i t h helium and argon as carrier gases have been compared (474). B y using argon-nitrogen mixtures ranging from 0 to 100% nitrogen, larger concentrations of solute can be tolerated by the argon detector (462). Useful detector response also was obtained with hydrogen carrier, which does not involve energy transfer through metastable atoms (476). Kormally undetected gases are made detectable by introducing a small, constant amount of organic material with the argon (285). Presumably, the signal results from a reduction in the standing current. Ionization by ultraviolet radiation offers the possibility of eliminating both the radioactil e source and standing current in this type of detector (139, 297). The electron-capture detector described by Lovelock (174, 296, 298) offers extraordinary sensitivity for halogenated compounds and polynuclear aromatics. Clark (68) has utilized this

detector for halogenated pesticide trace analysis. Calibration of the argon detector response to loner fatty acids (4.2) and volatile solvents (4031, as ne11 as its application to food volatiles (3081,has been made. Of special interest is the comparative evaluation of the argon and flame ionization devices by Condon, Scholly, and Averill (72) and RIcSair (312). An equation has been proposed for locating the carrier gas front (“air” peak time) with ionization dptectors which normally do not respond to air or inert gases (562). The flame ionization detector ( F I D ) has been investigated with respect to the mechanism of ion formation (426) and its response to different functional types (581). The former study lends support to the chemi-ionization theory of ion formation, and the latter suggcsts different pyrolysis mechanisms are responsible for the response obtained from hydrocarbons, amines, and alcohols. Operating and response characteristics of the F I D detector also were studied by several other n orkers (125, 201, 354). Sensitivity, linear range, and detectability were specifically evaluated by Condon, Claudy, and Scholly ( ” I ) , and nonlinearity, peak inversion, and the critical positioning of the lower electrode were specifically noted (351). The FID \\as calibrated by Desty et ul. by means of a diffusion dilution apparatus which provides known low concentrations of vapors (96). ,4patent covering the F I D was issued recently to Harley (197). Details of a commercial unit (150), a capillary-FID apparatus (189), and an alternatingcurrent modulated detector (335) have appeared. The circuitry and precautions required in a simple d.c. amplifier suitable for high impedance current measurements were published (114 ) . The substitution of CO for H2 as fuel was found to overcome problems associated with the detection of halogenated compounds (11). Recent developments in thermionic emission detectors were revien ed by Guild and Lloyd (179). Characteristics of a detector based on emission were reported (??IS),while a modification incorporating a radiofrequency mje analyzer gives both qualitative and quantitative information about eluted components (451). Glow discharge detectors nere described in which the signal was obtained by current measurements in the transformer primary (37’6) and by optical or d.c. probe methods (427). Karmen and Bowman (246) haye continued their research in the area of glow discharge detectors with the development of a d.c. discharge apparatus having high sensitivity with argon carrier. The principle and construction of a n acoustical gas composition detector

were reported by Soble (347) and in a patent (377). ‘l’csterman and hIacLeod utilized the fiequency of a ahistle to serve as a uscful GC detector signal (442).

An ionization chamber GC apparatus (70) and a proportional counter (46‘7)

have been modified to increase their operating efficiency. 1he latter report contains the suggestion that pure methane be used as both carrier and counting gas. X combination of ionization detector and gas counter also n a s utilized in a chromatographic apparatus (478)*

The potential of a far ultraLio1et detector was explored by Ilsye (247), and visible light from a hydrogen flame provided the signal for a n emissi! ity detector (141). Winefordner, Steinbacher, and Lear (4%) have described the theory and performance of a dielectric constant detector. Automatic coulometric, titration of chloride ion obtained by combustion is the basis of a detector for the GC analysis of chloride-containing pesticides ( 7 7 ) . The Martin gas density balance in conjunction with a chromatograph and pressure-volume apparatus was usc’d to determine the molecular weights of vapors with excellent results (364), and a modification of the balance has been described (232). Identification of solutes was achieved with a conventional mass spectrometer as detector (287). Radioactive Tagging. Tritium labeling continues t o look attractive as a means of preparing tracer compounds for t h e study of complex mixtures b y GC. Olefins have been prepared by several routes (466), nhile fatty acids (237) and a number of organics (51) have been labeled by the simple Kilzbach gas exposure technique and by exchange with tritiated water ( 2 ) . An interesting heterogeneous exchange reaction mith a metal tritide (CaT2 prepared in situ in a precolumn) TT as shon n by Stocklin el ul. (432) to yield labeled hydrocarbons. Readout. T h e magnitude of response speed, dead zone, etc., in commercial recorders and their contribution t o accuracy i n GC v-ere discussed by Daneman and Talbot (86). Also of interest to gas chromatographers is the infinite resolution straingage voltage-to-position transducer which supplants the conventional slidewire in recorders (471). Long-persistence cathode ray tube presentation of chromatograms which requires only seconds to complete n as described by Scott (400). This presentation method is particularly useful in process analyzers. Integrators, their use, and an evaluation of tR o commercial units were published by Schm-enk et al. (396). The VOL. 34, NO. 5, APRIL 1962

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evaluation of errors arising from the use of such devices and a method for compensating these errors have appeared (366). Several new integrators for reading standard strip chart chromatograms have been developed (151, 2 7 4 , and Blyholder (35) has simplified the problem of integrating radioactive solute peaks by efficiently condensing the solute a t the counter window. Various electromechanical integrators employing d.c. integrating motors (106, 377), a velocity-servo output (227), and ball and disk displacement (219, 434) were reported. The ball and disk drives photographic paper past a noncritical illuminated slit, so that the distances between black lines are a direct measure of the peak integral (434). Electronic amplification with output proportional to the time integral of the input permits automatic or manual presentation of the integral as a spike or square wave on the same chart (90, 367). Alternatively an automatic two-recorder system may be used with multiregister pulse counters to espand the useful concentration range which can be integrated (220). An electronic counting device also was used in analog integrators in which the light pulse (191) and electrical pulse (39) rate are proportional to recorder pen displacement. Potentiometric attenuation of detector signals was accomplished automatically by means of microswitches which activate a stepping switch (87). I n another instance, a manual attenuator, which applies precise bias voltages to the recorder input (193), was used; this principle was also applied to increase the accuracy of analyses for major concentrations of hydrogen (260). Equipment for the automation of analytical GC described by Johnson et al. (233) and by Karasek, Burk, and Ayers (245) include automatic attenuation, base-line reset, integration, digital readout, and transfer to IBM cards. Storage of GC data, including literature references on punched I B M cards, was shown to facilitate the duplication and selection of conditions for the analysis of a wide range of compounds (286). Qualitative and Quantitative Measurements. Merritt and Walsh (330) developed a dual column apparatus useful for qualitative analysis by measurement of the retention volume ratio on two columns packed with appropriately different liquid phases. Brown (47) proposed a three-column method for the identification of organic compounds from retention data measured with three types of liquid phases: electron-donor (Reoplex 400), electronacceptor (lJ3,5-trinitrobenzene), and nonpolar (Apiezon L). I n this method an “affinity fraction” for a solute on each column is calculated and identification made from a plot of these data on

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triangular graph paper. A method for distinguishing between unsaturated and branched fatty acid isomers based on the change in separation factor as a function of temperature was given by Landowne and Lipsky (277). An electron affinity detector showing promise as a tool for the identification of functional groups has been developed (299).

The relation between the size of the permanent dipole moment and relative elution volumes was studied for aromatic amines and nitro compounds (142). Kovats (266, 267) has continued the study of the use of the “retention index” as a means of identifying the structure of organic compounds. In this work useful rules were formulated for prediction of retention indexes of those compounds for which experimental data are not available or, conversely, for the determination of the structure of unknowns from retention data on polar and nonpolar columns. Applications of Kovats’ method have been reported by Huguet (216) and by Ferrand (135). The R,, method of Smith (422) was extended (129) by use of an equation related to Kovats’ to give a method of predicting retention data from a knowledge of molecular weight and structure. An interpolation method (128) for calculating retention times of unsymmetrical molecules from those of symmetrical homologs has also proved useful. Measurement of the chromatographic “spectra” of products produced by pyrolysis of organic substances holds promise in the qualitative identification of relatively nonvolatile materials. -Janak (226) and others (16,236,286,420, 431) determined the chromatographic pyrolytic spectrum of a number of materials and found that the characteristic chromatographic spectra obtained are due not only to primary decomposition products but also to rearranged fragments formed in the pyrolysis process. ‘Nalsh and Merritt (458)employed chemical functional group classification tests as vel1 as retention data for the identification of substances. Quantitative functional group analysis techniques in conjunction with GC have been applied to a micro-Kjeldahl determination of nitrogen and the determination of hydroxyl groups (469). The differences in chromatogram profiles before and after application of class reagents chosen t o remove certain functional groups are useful in the identification of n- and isoparaffins, n- and iso-olefins, aromatics and naphthenes (383), and carbonyl compounds and organic sulfides (19). The peak shift resulting from conversion of volatile compounds to volatile derivatives was suggested by Langer and Pantages (679) as a means of qualitative analysis. I n this procedure alcohols in a hydrocarbon mixture were identified by selective

conversion to their trimethylsilyl derivatives by reaction with hexamethyldisilazane and observation of the shift in retention time. The determination of blood alcohol was performed using “reaction gas chromatography” which consisted of conversion of the alcohol to olefin by injection of the aqueous solution into a column of Sterchamolphosphoric acid previously heated to 300” and conversion of matcr to hydrogen on a Sterchamol-calcium hydride column just preceding the chromatographic column (104). Potential analytical applications of the methylene insertion reaction, the random insertion of methylene (generated by the photolysis of diazomethane) into the carbonhydrogen bonds of a hydrocarbon, have been reviewed (411). Cacace, Cipollini, and Perez (50) calculated the C:H ratio of each compound eluted from a column from the peak areas of COz and Hz produced when the organic compounds were decomposed as they were eluted by passage through a coiled silica tube maintained a t 725” and packed with one section of cupric oxide and another section of reduced iron on an inert support. Methods for the direct collection of chromatographic effluents in infrared absorption cells were reported (68, 468). Jamieson (622) has tabulated T C relative responses of a number of functional group classes of compounds. Relative response mas observed to increase with molecular weight for each homologous series. Relative molar response values for a series of alcohols using thermal conductivity cells have also been measured by Grcb et al. (176), and the conclusion was drawn that peak areas are a measure of weight per cent of individual components rather than mole per cent. A theoretical treatment by Hoffman (208) based on the kinetic theory of gases explains why the detector signal is nearly proportional to the weight fraction of components in some cases, but in other cases is more nearly proportional to mole fraction. A study of the direct proportionality between peak area and carbon number with the flame ionization detector nas reported and found to be not strictly quantitative (44, 120). Application of a “reduced peak area” for the quantitative determination of hydrocarbons mas suggested (44). VBradi (451) described a new type of ionization detector employing both a radiofrequency m/e analyzer and a thermionic detector for simultaneous quantitative and qualitative analysis. Conditions required for quantitative analysis using the hydrogen flame or argon ionization detector have been studied by several workers (109, 120, 190, 381, 410). Janak (226) has made a statistical evaluation of seven geometrical methods and three types of integrators (mechanical, elec-

tromechanical, and analog) for measuring the area under a chromatographic curve. Recorder-integrator errors and accuracy in quantitative determinations have received considerable attention (86,285,355,395). Chino, Kasamatsu, and Suzuki (63) concluded that the major error in GC results from error in area measurements, particularly when quantitative measurements are attempted on unresolved peaks. Methods for measurements of areas of partially resolved peaks have been proposed by Grant and Vaughan (173) and by Bartlet and Smith (17). Standard Data. Hively (207) has reported relative retention d a t a for 93 C1 t o C7 hydrocarbons (methylal = 1) a t one or more temperatures on columns of diniethylsulfolane, tricresyl phosphate, di-n-decyl phthalate, mineral oil, and @,@'-oxydipropionitrile. IllcNair (311) measured the retention volumes of 50 compounds a t 5 5 O , looo, and 153' C. on 14 liquid phases. A catalog of the relative retentions (carbon tetrachloride = 1) of nearly 200 probable air pollutants has been prepared for tri-m-cresyl phosphate and fl,P'-oxydipropionitrile columns a t two widely different temperatures (463). The retention behavior of a wide range of chemical types has been tabulated for 10 commercially available columns (n-pentane = 1) and graphically presented by Scholly and Brenner (393). Extensive tables of retention volumes and selectivity coefficients have appeared in monographs by Bayer (22) and Kaiser ($48). Smith (429) discussed the advantages of using a single theoretical standard for reporting relative retention data. The standard proposed corresponds to the retention of n-nonane as extrapolated from the best straight line through a graph of log retention time Y S . C number for the n-paraffins. SPECIALIZED OPERATIONS

Mulcistage. -4four-stage apparatus has becn designed by Bloch (34) for the routine determination of about 70 C1 through C7hydrocarbons and inorganic permanent gases in a single run. Three detectors and recorders are used in this design. A portable tlvo-stage GC unit has been described (520) t h a t permits separation of the complex reaction products formed in flash pyrolysis by a combination of an adsorption column for the fixed gases and a liquid column for the heavier solutes. Programmed Temperature. Theoretical treatments of the behavior of solutes under programmed temperature conditions (PTGC) have been derived by a number of workers (84,159, 186,382,384,477). I n some cases, solution of the retention equations requires

computer calculation, and in others reduced parameters are employed to permit graphical evaluation. The relation between observed plate height and local heights in PTGC has been treated by Stewart (428) and, similarly, by Habgood and Harris (187). The latter also have discussed various aspects of resolution (146), and a significant retention temperature has been proposed by Giddings (164) to relate resolution in isothermal GC to PTGC. The general problem of optimizing the temperature program for specific separations and practical apparatus problems was examined by Burnell and Said (48). Chromathermography, both theory and practice, was explored by Ohline (355), who showed that the advantages and disadvantages of the technique are very similar to those of PTGC. A novel modification of chromathermography in vihich a changing temperature gradient is repeatedly passed over the column was described by Serheim (346). Several chromathermographs n ere described, along with different modes of operation, by Russian viorkers (88). A system in which a column has different adjustable temperature zones was demonstrated to yield excellent results with wide boiling range mixtures (134). Borfitz (41)showed that in a conventional isothermal apparatus one could simply shut off the carrier flow, adjust the column temperature, and continue elution of solutes after temperature equilibrium in cases where severe tailing was a problem. Conventional temperature programming of capillary columns without flow control also was noted (4411.

Apparatus for PTGC has been discussed (8), one commercial design unit described (59), and another evaluated (235). Two commercial instruments for operation to 500' and 1000° C. were also reported (87, 126). -4double-column apparatus to compensate base-line drift a t high programmed temperatures and its application to polyphenols R ere reportfd by Emery and Koerner (117). Isothermal and PTGC for the separation of C1to Ca nitroparaffins Ivere compared on theoretical and practical grounds (32). Eggertsen, Groennings, and Holst (113) obtained boiling point data for hydrocarbons using PTGC nhich compared favorably Kith precision distillation but required less time. The technique was successfully applied to the analysis of wide boiling range solvents and thinners (118) and to alkanol and alkane systems (280). Trace Analysis. Concentration techniques are generally employed in trace determinations prior to analysis. In certain cases, compounds may be removed from a gas stream by selective chemical reaction (20, 168). Trace components in an

essential oil were determined (20) after all polar matrix compounds had been removed by liquid-solid chromatography on silica gel. Ion exchange resins have been used to isolate small amounts of fatty acids from fish (214) and fats (209), followed by GC analysis of the matrix-free concentrate. Mackay (307) and Nawar and Fagerson (343) reported the use of a cyclic trapping procedure for the isolation of food volatiles, which seems generally applicable in any case where the sample matrix is relatively nonvolatile. A quantitative technique for the determination of trace amounts of moisture in butane was based on the retention of the water by a polyethylene glycolfirebrick trap (53). Helium impurities (340) have been concentrated in cooled traps packed with activated charcoal. An enrichment trap for use with capillary columns also was described (404). Precolumns which selectively retain either the matrix or the desired materials are often useful. Brenner et al. (45, 124) referred to this technique as subtraction and investigated the selectivity of Molecular Sieves for this purpose. Certain effects altering the apparent selectivity were attributed to chemical reaction on the basic Molecular Sieves (124). Precolumns have also been used for separating dissolved gases from petroleum liquids (211). Kirkland (261) applied a precolumn in conjunction with a traveling furnace to concentrate and displace the trace components as a plug onto the chromatographic column. After initial isolation of a trace material from a large sample by means of a preparative scale unit, as little as 10 p.p.b. of impurities in vinyl chloride mas measured by Mikkelsen (334). A discussion of trace analysis by GC as applied to hydrocarbon concentrates was given by Jones (238). Andreath and Feinland (7) described the design and construction of an inexpensive, portable analyzer with flame ionization detector useful for the continuous determination of trace amounts of hydrocarbons in the part per billion range. The minimum determinable amount of aromatic materials in air has been reported (438) for several detectors and concentration methods. Aromatic hydrocarbons a t concentrations in the part per hundred million range have been determined directly in atmospheric samples using a flame ionization detector (4). Other publications on air pollution (121) and incinerator effluents (445) have appeared. The purification and GC determination of helium hare been reported (318). The insensitivity of the hydrogen flame detector to water is the basis of a method for the determination of low concentrations of the lower fatty acids in water (116). Potential applications VOL 34, NO. 5, APRIL 1962

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in cancer research and the correlation of trace contaminants in saliva with tooth decay may be possible (61) following part per billion determinations of trace constituents in human body fluids by GC, using a sampling technique developed by the Southwest Research Institute. Hexane extracts of various crops have been analyzed successfully for 0.05 p.p.m. of aldrin and 0.1 p.p.m. of dieldrin without prior cleanup, using a n argon detector as an electron-capture detector (172). Coulson et al. (77) applied coulometry to the quantitative determination of a number of chlorinated pesticide residues a t concentrations of a few parts per million on food products. High Temperature. An all-glass high temperature unit with carefully designed injection port has been developed by Ferrero (236) and is suitable for temperatures up to 400" C. An instrument fitted with leak-proof metal connections and special high temperature glass insulators for electrical leads and detector filaments was reported by Alexander and Marsh (1). The upper temperature limit of this instrument is 500" C. Two programmed temperature chromatographs, useful also for isothermal operation, have been announced (131) which have upper temperature limits of 500" and 1000" C. The latter unit has proved useful (127) in the separation of inorganic halides using inorganic fused salt liquid phases as proposed earlier (36, 241). Several heterocyclic amines and substituted aromatics, polyphenyls, terpenes, and various ethers were successfully separated on a sodium nitrate-potassium nitrate-lithium nitrate mixture by Hanneman, Spencer, and Johnson (194) over the temperature range 250' to 400" C. Smith and Gudzinowicz (423) separated isomeric polyphenyl ethers with boiling points between 285" and 650" C., using SE-30 as liquid phase and temperature programming. The use of molten metal stearates (64) appears promising for the separation of polar solutes capable of forming complexes with the metal. Dubsky and Janak (105) have introduced liquid and solid samples into a high temperature unit by weighing the samples into a 50- to 100-mg. capillary tube made of TVood's metal. It was shown that the period required for melting the capillary and vaporization of the sample was acceptable for GC determinations a t temperatures above 150". An interesting modification of detection was made by Franc and Wurst (143, who placed a small combustion chamber a t the outlet of a high temperature column, converted the water formed to hydrogen gas measurable by thermal conductivity at ambient temperatures, and thus avoided many

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problems associated with high cell temperatures. An alternative to high temperature operation for obtaining short retention times is to reduce the amount of liquid phase on the column. Hishta et al. (206) used glass beads rather than firebrick or Celite supports to reduce adsorption effects. Hishta and eoworkers chromatographed chrysene (b.p., 448") a t only 190" on a 0.05% silicone oil-glass bead column. A 2 to 3% liquid loading of SE-30 silicone gum rubber has been used on Chromosorb W a t 220' for the resolution of a number of natural products without decomposition or structural changes (291,449). Preparative Scale. Several methods are available for increasing column capacity, such as enlarged crosssectional area, automatic column operation, and parallel columns. Contributions to t h e theory of large diameter column technology have been made by Golay (167);by Huyten, van Beersum, and Rijnders (217), who studied the effects of velocity profiles and gas diffusivities on the efficiency when the diameter was increased to 3 inches; and by de Wet and Pretorius (101, 102), who studied the effect of column diameter and length on efficiency. The effect of temperature, gas flow rate, and sample size on the efficiency of a preparative column has been studied (56) and a systematic investigation of several problems involved in preparative scale work reported (69). Huyten et al. (217) studied the effect of efficiency of various packings and methods of filling large diameter columns. Golay (167) suggested that the efficiency of large diameter columns should be improved if the inner wall of the column is roughened. Frisone (145) reduced the loss in efficiency from the wall effect by spacing a series of filter paper rings of varying aperature and saturated with liquid phase a t intervals along the column. Evidence was presented that the velocity-independent term, -4,of the van Deemter equation is largely due to mixing a t the column head and a method for reducing this effect has been proposed by Kieselbach (267). Bayer, Hupe, and Witsch (23) separated 50- to 200-gram amounts of mixtures of volatile substances in ideal cases in from 10 to 60 minutes on a 10.1-cm.-diameter column. Golay (168) suggested that in designing columns for greatest throughput per unit time per unit aeight of packing, the columns should be made longer than analytical columns, should be operated a t appreciably more than optimum flow rate for analytical columns, and should provide for the bare separation of the components of interest. Restrictions of small diameter tubing along the length of a large diameter preparative scale column was found to

improve resolution, but could lead t o anomalous bumps in the resulting chromatogram due to pressure surges (6) a t each restriction. The design and construction details of a number of large diameter instruments have been given (302,528,425). An automatic cycling instrument which can separate liters per day of pure components unattended has been developed by Felton (I%?), and an instrument of this design is now commercially available (366). A somewhat similar instrument developed by Catalette et al. (55)\vas used in the separation of cyclohexane from benzene in a purity of 99.94 to 99.96%. The boiling points of these materials differ by only 0.6' C. Johns and coworkers (49, 228, 229) have described an instrument, now commercially available (hlegachrom, Beckman Instruments, Inc., Fullerton, Calif.), t h a t employs eight parallel 6foot columns of 5/8-inch internal diameter for an effective cross-sectional area of 2.6 sq. inches. One of the most important considerations in obtaining efficient separations is the rapid vaporization of the large samples used. -4 ne\v sample injection system capable of volatilizing up to 10 grams of sample almost instantaneously has been described (414). A one-way valve was recommended (101) to prevent the vaporizing sample from being forced back into the preheater, where mixing could occur. Although a high vaporizer temperature is desirable for efficient separations (101), too high a temperature may lead to decomposition. A thermostatically controlled vaporizer n hich employs a low thermal mass, high-wattage heater that "supplies heat on demand" has proved useful (229). Haarhoff, Van Berge, and Pretorius (185) studied the role of the sample inlet volume in preparative chromatography and presented a mathematical treatment in mhich the recovery of a solute of given purity from t n o overlapping bands is considered by dividing the eluent into three fractions. Factors to be considered in the selection of a stationary phase for preparative scale work have been pointed out (23). Ethylene glycol-bis(propi0nitrile) ether and glycerol-tri (propionitrile) ether are recommended (21, 24) for the selective separation of aromatic and alicyclic compounds in large amounts, since overload of the column is possible n-ithout peak overlap and these materials are useful in preparative work to 140" and 170" C., respectively. -4 trap designed to overcome mist and snow formation, often encountered in condensing high-boiling compounds, has been developed (460). Continuous Separation. Thompson (443) has developed a bench scale continuous chromatographic unit for both

GSC and GLC systems and described its application for the separation of several binary mixtures of light hydrocarbons. Barker and Critcher (15) also give a complete description of a continuous preparative scale process for the separation of binary mixtures. This system involves a n inert solid containing a n adsorbed solvent moving countercurrent to an inert gas stream while the sample is continuously injected into the mid-point of the column. Benzene (b.p., 80.1’) and cyclohexane (b.p., 80.7’) were separated with a purity of 98.9 to 99.9yo a t a n injection rate of 30 ml. per hour. Continual Analysis. Various aspects of process control by GC mere discussed in detail by Wherry (465) and by Scott (401). Process analyzers are used to monitor hydrorarbon streams (306, 479), moisture in a polymerization batch (363), sulfurcontaining compounds (dOO), and part per million concentrations of methyl chloride in plant streams of a n LPG plant (46). The “in-line” separation and determination of reactive halogen and inorganic interhalogen gases were described by Iveson, Hamlin, and Phillips (218). The design, construction, and application of several U.S. commercial process gas chromatographs have been discussed in detail and the functions of the components outlined (46, 1.40, 316, 348, 479). A Japanesemade process analyzer has also been described (200). The advantages of multiple column techniques for process control units have been noted (12, $04). New liquid-sampling valves have been described by Penther and Hickling (360), Keidel and Lewis (245), and Stirling and Ho (430). I n the latter, special reference is made t o the case in n hich the process stream contains materials which may later deposit in the system, and a sampling system for gas streams containing solids and steam is shown schematically. One of the major disadvantages of GC for process control-namely, the cyclic nature of analyses-is largely overcome by employing high-speed units which perform analyses so fast that operation is essentially continuous. A definite trend ton-ard high-speed process control units is indicated. Scott (401) has pointed out the advantages derived from capillary columns run a t a carrier gas flow rate greater than t h a t for maximum efficiency. High-speed equipment with analytical cycles of 1 minute or less for components through the Cs range has been used in closed-loop control of chemical processes (140). The total analysis digital system developed by Phillips Petroleum and handled commercially by Perkin-Elmer makes i t possible to program the sequence of operation of several chromatographic

units and transmit the results in any desired sequence (563). MISCELLANEOUS

Wilson, Oyama, and Vango (470) have revealed design features of a GC unit which is a n integral part of the Surveyor moon probe being developed for launching in 1963. The GC unit occupies only 675 cubic inches and weighs 11.5 pounds. A 4-ml. sample obtained by drilling several feet into the moon’s surface will be heated in a furnace to volatilize or pyrolyze materials present, and a telemeter will relay analytical information after passage of the gases through the column. The application of gas chromatography to carbon-hydrogen analysis of organic samples was simultaneously reported by Duswalt and Brandt (110) and Sundberg and hfaresh (436) and later b y Vogel and Quattrone (456). Continuous carbon-hydrogen analyses have been performed as materials are eluted from the column (50). A method for the direct microdetermination of oxygen has been proposed (435) based on the quantitative reduction of the oxygen to carbon monoxide, followed by determination of the carbon monoxide on a RIolecular Sieve column. -4 number of publications have appeared on surface area measurements by GC (94, 122, 176, 431, 459). A precision of 0.003 sq. meter per gram of sample mas reported (94) and samples below 1 sq. meter per gram may be determined. The separation of ortho- and para-hydrogen, hydrogen deuteride, and ortho- and para-deuterium (43, 149, 216, 275, 4.21) continues to be actively investigated. hfore than 200 papers and addresses appeared in 1961 alone on the determination of fatty acids in biologically important materials and foodstuffs. Although free fatty acids may be determined directly on a phosphoric acidLAC-2R-446 column (%I), they are most frequently determined as the methyl esters. Ester formation using the ketal, 2,2-dimethoxypropane ( 3 7 4 , anhydrous methanol-hydrogen chloride (4SS), and methanol-boron trifluoride (332) have been recommended. A new G C method which permits the separation of 36 amino acids, including 19 protein amino acids, was developed by Johnson, Scott, and hleister (230, 231) and deserves special note. These authors describe techniques for the preparation of the volatile K-acetylamino acid n-amyl esters, or the corresponding isoamyl, isobutyl, or n-butyl esters, which are separable on a 1-foot, 0.5% Carbowax-Chromosorb-W column at temperatures between 125” and 150” C. Other volatile derivatives of amino acids proposed for analytical applications include the a-chloromethyl esters

(329) and the N-trifluoroacetylmethyl esters (587,457,464). Numerous papers were published on the application of GC to solution kinetic and thermodynamic studies (3, 74, 75, 196, 24O), and the collection of other physical data, such as the heats of adsorption (26, 81) and vaporization (310),adsorption isotherms (81), vapor pressures (154), activity coefficients (130), molecular weights (364), and gaseous diffusion coefficients (165), are a n indication of the great versatility of this fast expanding technique. LITERATURE CITED

(1) Alexander, D., Marsh, R. F., “Gas Chromatography,” H. J. Xoebels et al.,

eds., p. 163, Academic Press, Xew York, 1961. (2) Aliprandi, B., Cacace, F., -4nn. chim. 50, 931 (1960). (3) Allen, R. H., Yats, L. D., Crley, D. S., J . Am. Chenz. SOC.82, 4853 (1960). (4) Altshuller, A. P., Clemons, C. A.,

140th Meeting ACS, Chicago, Ill., Sept. 3, 1961, Abstracts, p. 12W; Chem. Eng. A-ews, 39 (38), 82 (19611. (5) Ambrose, D., Ambrose, B. A,, “Gas Chromatography,” George Newnes, London, 1961. (6) Amy, J. R., Brand, L., Baitinger, lv., 12th Pittsburgh Conf. on Anal. Chem. and ilppl. Spectroscopy, Feb. 27, 1961. (7) Andreath, A. J., Feinland, R., 12th Pittsburgh Conf. on Anal. Chem. and Appl. Spectroscopy, Feb. 27, 1961. (8) hraki, S., Kishimoto, K., Yasumori, Y., Japan Analyst 8, 699 (1959). (9) Arnett, E. M., Strem, M., Hepfinger, N., Lipowitz, J., McGuire, D., Sczence 131, 1680 (1960). (10) Ayers, B. O., Loyd, R. J., DeFord, D. D.. ANAL.CHEJI.33.986 (1961). (11) ’Baddiel, C. B., Cullis; C. F., Chem. and Ind. (London) 1960, 1154. (12) Baker, W,J., Zinn, T. I,., Control Eng. 8 , 77 (1961). (13) Barber-Coleman Co., Rockford, Ill., Chromatography Bull. WCE 8-1 (1960). (14) Barber-Coleman Co., Rockford,, Ill., literature on linear sample splitter, 1960. (15) Barker, P. E., Critcher, D., Chem. Eng. Sci. 13,82 (1960). (16) Barlow. A , . Lehrle, R. S.. Robb, J. C., Polymer 2; 27 (1961).’ (17) Bartlet, J. C., Smith, D. M., Can. J . Chem. 28,2057 (1960 . (18) Barton, R. S., British Information Service, S e w York, A.E.R.-M599. (19) Bassette, R., Whitnah, C. H., A 4 ~ ~ ~ . CHERI.32, 1098 (1960). (20) Baxter, R. hl., Dandiya, P. C., Kandel, 8. I., Okany, A., JTalker, G. C., Xature 185,466 (1960). (21) BaS er, E., “Gas Chromatographie 1961,” 3rd Symposium on Gas Chromatography, Schkopau, East Germany, May 16, 1961, Preprints, p. 3. (22) Bayer, E., “Gas Chomatography,” Elsevier, Amsterdam, 1961. (23) Bayer, E., Hupe, K. P., Kitsch, H. G., Angaa. Chem. 73,525 (1961). (24) Bayer, E., Wahl, G., Witsch, H. G., 2. anal. Chem. 181, 384 (1961). (25) Bazinet, M. L., Walsh, J. T., Beu. Sci. Instr. 21, 346 (1960). (26) Beebe, R. A,, Emmett, P. H., J. ~

Phys. Chem. 65, 184 (1961). (27) Bennett, C. E., Martin, A: J., hlartinez, F. W., 137th Meeting, ACS Cleveland, Ohio, April 5, 1960, Program, p. 5B. (28) Bens, E. M., ANAL. CHEM.33, 178

(1961).

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ism

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\ - - - - ,

\ - - - - ,

I

~

,

(443) Thompson, D. W., 1960 C.I.C. Ottawa Conference, June 13, 1960; Chem. in Canada 12 (4), 59 (1960) .

Acad. Sca. Hunl

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‘ 48(1961). ’ (472) Winefordner, J. D., Steinbacher, D., Lear, W. E., ANAL.CHEM. 33, 515 11961). ,---, (473) Wiseman, W. A,, iYature 185, 841 (1960). (474) Ibid., 190, 1187 (1961). (475) Wurst, AT., Chem. Zisty 54, 1042

( 1 !xn) \ - - - - I .

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Gas Chromatography - Analytical Chemistry (ACS Publications)

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