(641) S’erheydeii, J., Colt>, B., Clin. Chzm. ,lctn, 18, 32,; (1B67). (642) Yestergaard, P., Abqtracts, Eastern Aiialytical Symposium, S e w York, Xovrmber 1967.1) 18. (643) Voigt, J., St;.ger, II., . ~ r c h . Tierernaehr., 17, 289 (196i). (644) Viirek, C;. G., Pegram, 8. E., dnnl. U i O C h P t i l . , i6, 409 (1966). (64.5) IVagiier, 1:. B., Ed., “Journal of Virology,“ YO^. 1, No. 1, American .Irbor, Society for lIicrobiology, -11111 X c h . , February 1967. (646) IVaitier) A , , J . Chrojnafog., 2 6 , 4S (1967). (647) \Vnlsh, J. AI., J . Chetn. Edue., 44, 29.2 (1967). (648) JVniig, I),, ~Iaticiiii, I)., Contrib. Hoycc Thompson Insi., 23, 93 (1063). (Gi!)) Ward, 1). X.> Coffey, J. A , Ray, 1). B., Lamkilt, Ij-.l I . , .lnal. Biocheiii., 14, 243 (1966). (6.50) \\-aid, 11. L., NAS.1 Acce.5ioii To. N65-25023. l t e u t . XU.TID-3512, SiilJpl.
~I
B., Ibid., 15, 296 (I!KG). (6.53) JVeiiiateiii, B., “Methods of Biochemical A\~i:ilysisj” 11. (;lick, Ed., T’ol. 14, Ititerscietice, Sew York, 1966, p 203.
(636) Werner, ll.,J . Chromatog., 28, 59 (1967). (6.57) West, C. E., Ronbotham, T. R., Ibid., 30,62 (1967). (658) \Vied, G. L., Ed., “Iiitrodiictioii to
Qiiantitative Cytochemi-try, ’’ Academic Pres>,Kew k’ork, 1966. (639) IVielaiid, T., l)etermaiiii, IT., J . Chivnmtog., 28, 2 (1967). (660) \Vietier, S.,, Schade, J . P., Eds., “Progress i i i Biocyberiietics,” Yol. 3, Elsevier, Amsterdam, 1966. (661) Williaiii~, C. A,, Chase, 11. LT., Eds., “Methods in Imniiuiology atid Immtitio-Chemistry,” Academic Press, Kew York, 1967. (662) \Villiamsj P. P., :tppl. .lIicmbioZ., 15,6S1 (1967). 1663) \Villiani*. lt. J.. Laiisford. F. _\I.. Jr., Eds., “kiicyclipedia of Biochem: istq-,” I:eiiihold, Sew York, 1967.
(666) ITiiizor, I ). J., Biochim R i o p h y s . .lcta, 133, 171 (1967). (667) \Vhite, F. A,, Formaii, L., Rev. Scl’.Instr., 38, 3.5.5 (1967). (668) \Vhite, J. JV., Kushnir, I., d n a l . Uiochem., 16, 302 (1966). (669) \Vhittick, J . S., IIoraca, 11. F., Cavaiiayh, 1,. A , ShS.1 ltept. S o .
SP-5083 (1967).
(6i,O) Wolfrom, 11. L., Tipsoii, R. S., hds.. “hdvances in Carbohvdrate Chemiztry,” T’ol. 21, Academic Press, New
York, 1967.
(671) \Voof, J. B., Pierce, J. S.,J . Chrom a t o g , 28,9.2 (1967). (622) n’otiL. If. H.. Claik. S. J.. Eds.. “Gaq Chrornatogrnphy ii; the knalysis of Steroid IIormoiies,” Pleiiiim PLtblishitig Corp., l-ew York, 1966. ( 6 7 3 ) 1-amagiichi, )I., rIoward, F. D., Pratt, 11. K., dnal. Biochem., 16, 338 (1966). (6i4)Yiinosov, S.Yii., Ed., “Chemistry of Satiiritl Compoiuids,” Yol. 1, Y o . 1, The Faraday Press, S e w York, 10fi.i. - _
(67.5) Zasepa, IV., I)obry-lliiclaus, A., J . Chinz. Phys., 63, 675 (1966). (676) Zeit/, L.. Lee. lt., .-trial. Biochem.. 14. 101 (1966). ( 6 i 7 j Zerfing, It. C., S’eeriing, H., ANAL.
CHEW,38, 1312 (1066).
(678) Zimmer, C., Ileiiiert,, II., :lnal. Bz‘ochein., 14, 1 (1966). (679) Ziporiii, Z. Z., Ilaiiion, 11. W., Ibid., p 78. iGS0) Zlat,ki*. h..Ed.. “,ldvaiices iii Gas
Chromatography l!j67,” Pre;itoti Techiiical iibstract.;, Evaiistoii, Ill., 1967. (681) Zwaau, J., dnal. Biochem., 15, : (682) Ibid., 21, 1.53 (1967). (683) Zweig, G.j Whitaker, J. li., Eds., “Paper Chromatography atid Electrophoresis,” Vol. 1, Academic Press, New York, 1967. j - . , - - / .
Gas Chromatography Richard S . Juvet, Jr., Department o f Chemistry and Chemical Engineering, University of Illinois, Urbanu, 111. Stephen Dal N o g a r e , Department o f Chemistry, V i r g i n i a Polyfechnic Institute, Blacksburg, V u . 24060
T
lication of the last review in this series (120) and covers the years 1966-67. Gas chromatogra1)liy continues to be one of the most active areas iii alialytical rheniistry. .i recent survey by the Satioiial Ycimce Fouiitlatioii (93) iiitlicates that 15.9y0of all analytical chemists hliecialize i i i the area of chromatogralihic aiialy.~is,second o n l ~ . iii numbers to those specializing iii absorptioii spectroscopy. Oiie marketing groul) (413) has estimated t h a t 70,000 gas cICS a i r and I3oiielli i,5 ai-ailable through Variaii -4erograph Corp. (41.4), atid a nioiiogral~h by Votiz aiid Clark (653) gives detailed procedures used iii the gas chromatographic anal) hormones. Referelice texts iiiclude a coinliilation by 11cReyiiolds (415) of retention data for over 300 solutes, mainly aliphatic compouiids, on 80 commoiily used liquid phases expressed a t two temperatures as specific retentioil volume and retention index; a sequel to ail earlier AISTNcoinpilation by Schup~i aiid Lewis (630) providing data on reteiitioii indices, relative retention, and liquid phases for some 3800 compouiids; and a comprehensive handbook on gas chromatography published in East Germany (866). Four volumes of “.ldvaiices in
6 7 80J
C h r o i i i a t o ~ r a ~ ~ l edited i y ’ ~ by Giddings and I d l e r have appeared during this bieiiiiium (193). Each of these volumes contailis several sections 011 gas chromatography. The pal)ers are generally of a revielv nature writteii by authorities iit the various areas of cliromatogral)hy. .I secoiirl ctlitioii of Heftniaii’s “C1irornatogral)h~”has appeared (242) and 14 of the 20 chapters of the book coiitaiii iiiformation of direct interest to the gas chromatographer. 1he ~iroceediiigsof two major symposia 011 gas chroniatography were pubed including the proceedings of the th Iiiterliatioiial Symposium on Gas Chroiuatogm~~liy :iiitl Aqsociated Techniques held iit Iioiiic, Italy (36‘3),aiid sponsored 11y t’he I{ritish Institute of Petroleum aittl the 1)roceedi~gsof the meetiiig, JouniCes Ilell&nesd’Etude des Met hodes de S i.para t io1i Imm6tlia t e e t de Cliromatograj)hie, sponsored by G.A.1I.S. (Groupeiiieiit pour l’.ivanceinerit des Methodes Spcctrographiques) aiid the union of Greek Chemists (466), Volume I of which cotitailis 30 papers on gas chromatography. Published rev i e w of‘ various sy1iq)osia devoted t o gas chromatography iiiclude the Sixth r ,
VOL. 40, NO. 5, APRIL 1968
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International Symposium at Rome ( 118, 6 4 7 ) , the Third International Meeting on Chromatography and Immediate Separations in Athens (467), the Fifth Eastern Germany Symposium on Gas Chromatography with authors mainly from Russian-bloc countries (249)) a conference in Budapest a t which the state of the a r t of gas chromatographic equipment was discussed along with plans for the manufacture of GC equipment in Hungary ( 7 ) , the Analytical Chemistry Summer Symposium in Edmonton, .Slberta, Canada, on “Separation Techniques” (202, 5181, a t which 14 of the 28 papers presented dealt with or involved gas chromatography, as ell as informal symposia of the British Gas Chromatography Discuwion Group (270,384-386,535). The 1967 applied reviews issue of ASALYTICALCHEMISTRYcites several hundred references to applications of gas chromatography published during 1965 and 1966 in the fields of air pollution (12), clinical chemistry (524), coatings (576),essential oils and related products (209), food (65), pesticide residues (646), petroleum (595),pharmaceuticals and related drugs (586), rubber (625), and solid and gaseous fuels (3). Trace analysis ( 5 7 3 , reaction gas chromatography (49),pesticides ( 5 9 4 ) , and the gas chromatographic separation of iiiorgaiiic compounds (280, 298, 486) were the subjects of other comprehensive reviews. The Preston Technical Abstracts Co. (491) continues its excellent service to workers in the field of gas chromatography by issuing weekly abstracts of all papers and major addresses on 5- X 8inch needle sort cards, often within a matter of weeks following publication of the original article. These abstracts are also now available on 16- or 35-mm microfilm reels or on microfilm reader cartridges and are used in combination with the Thermatrex Index system (491). The 8th and 9th aniiual volumes of “Gas Chromatography Abstracts” edited by C. E. H. Kiiapman were published by the gas chromatography discussioii group of the British Institute of Petroleum and list 1100 abstracts in the 1965 edition (333) and 1200 abstracts in the 1966 edition (334). A cumulative index for “Gas Chromatography Abstracts” covering the years 1958-63 has been edited by Butlin et al. (82). Preston and Gill compiled the fourth annual comprehensive bibliography and index to the GC literature (490) covering 1821 papers abstracted during the period Kov. 1, 1965, to Xov. 1, 1966. Ail annotated bibliography covering 426 papers published during the period 1952-64 on programmed temperature gas chromatography has also appeared (234). Recent surveys list gas chromatographic equipment, acces-
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ANALYTICAL CHEMISTRY
sories, and suppIies from all parts of the world (283, 3 6 4 ) . Sampling devices, pyrolizers, carrier gas equipment, liquid phases, detectors, sample collection devices, recorders, and integraters are included in these lists.
PACKED C O L U M N S
Column Theory. A simplified derivation of the van Deemter equation (464) and a new approach to the rate theory (222) were published. In the latter paper, Hal&sz (222) proposed a substitute for the height equivalent to a theoretical plate designated “relative peak broadening.’’ Some of the shortcomings of the original van Deemter equations were overcome by including a contribution from the cross-section flow profile (548). The van Deemter equation has also been modified by Kambara (301) allowing for diffusion and pressuredrop effects, and pressure-drop considerations were taken into account to characterize flow distribution in the column (300). Giddings reviewed his nonequilibrium theory presenting supporting data from glass bead coluiniis (190). Linear nonequilibrium chromatography was mathematically treated by Kucera (349) in which five moments of the chromatographic peak were calculated and their significance was discussed. Chromatographic peaks were treated mathematically by Kaminskii et a/.(302),and the first six moments of the peaks were derived on the assuinption that diffusion in the mobile phase was overriding. Barr (35) placed emphasiq on liquid phase loading of the solid support and liquid phase mass transfer in a n iiivestigation of GC theory. The coiicentration dependence of elution curves was examined theoretically (221) from which it was established that both adsorption and isotherm nonlinearity must be taken into account to adequately explain peak asymmetry. Xonideal behavior of the carrier gas introduces changes in retention and efficiency at pressures in the vicinity of 200 a t m and temperatures close to critical (524). Giddiiigs and conorkers continued their investigation into turbulent gas chromatography and aiinounced the first well-defined demonstration of the effects of turbulence in capillary and packed columiis at super pressures (195, 4 4 0 ) . Knox (336) obtained clear evidence for coupling in the plate height equation through a study of liquid chromatography and defined the role of turbulence in reducing plate height. Turbulence is also the subject of a paper describing the speed advantage to be gained by operating in this region (492). The advisability of high flow rates for greatest efficiency was
pointed out by Littlewood (582) in a study of the relative contributions of molecular diffusion and radical mass transfer. Kliiikeiiberg ( M i , 332) replied to a previous note of Giddings (189) on the nature of eddy diffusion, to the effect t h a t the relationship of Giddings is not universally valid. Calculatioii of inass transfer coefficients has been carried out (206) from a more exact treatment of gas-solid chromatography 1%ith experimeiital evidence obtained from carbon dioxide-charcoal systems. Pressure changes occurring during dilution and the quantitative measurement of the effect of the solute peak viscosity were the subjects of other publications (142, 620). Crone and coworkers (602) investigated the effect of iioiiliiiear partition coefficients of polar solutes 011 coated and uncoated diatomaceous earth supports. The deactivation of the support, the effect of sample size, and colunni conditioning were particularly considered. Kubin (348) contributed to the theory of chromatography in a detailed discussion of diffusion outside and inside the support particles, and Kiiox and coworkers (267) compared mobile phase dispersion in gas and liquid chiomatographic systerns. The theoietical work of Wicke (639) furiiishes a bet of differential equations for rectangular and Gaussian inl1ut.j to chromatographic s p t e m s and allows a comparison of packed column, capillary colunni, and distillation columii performalice. -4 critical evaluation of resolution expressions has been made by Karger (305, 306) who concludes t h a t existing resolution eupressioiis leave soinething to be desired and proposes a modification of l’urnell’s equation as useful for a wide variation in sepaiation problems. Optimum resolution in iniiiimuin times is the subject of a paper by Guiochon (215) who exlwimentally verified theoretical predictions. Evaluation of limiting GC efficiency, including consideration of time, n a s made by Struppe (565) who confirmed t h a t temperature or flow prograniming does not increase resolving power. Optimum conditions for high-speed gas chromatography were investigated by some Chinese scientists (474), and Giddings (191) summarized his research on basic chromatographic processes. Choviii and Guiochon (98) compared the performance of various chromatographic columns with regard to resolution and efficiency. Klein (330) provided criteria for assessing the purity and identity of chromatographic peaks and has given a theoretical basis for his conclusions. Physical cheiiiical nieasurements by GC were reviewed by Kobayashi and Deans (538) who focused attention, in particular, on the perturbation technique for obtaining such measurements. The
iiieasureniciit of physical chemical aiid aiinlyticnl quatititics is the subject also ol’ :i 11al)crby Gidtliiigs ailti Malik (194), a l ~ dl’ccsir (471, 472) discussed measru‘ciiiclit of the solution thermodyiianiicx of t\~o-coiiil)oiiciitvolatile nonelectrolyte soliitioiis a t iiifinite dilution by G ( ’ . ‘ h e theriiiodyiiainic functions derivable by C X have been reviewed by several workers (116, 188, 593). Latiger niid l’uriiell (359) discuxscd particularly the thermodynamics of solutioiis in di-?2-l)roi)yltetrachlorophthalate, and hydrogen bond energies \yere eatiniated from GC data (339). Molar cohesion, as a coiicept for t.he explanation of structural effects in retention by G C , was the subject of a paiier by Taylor atid Solins (684),and surface Excess coiiceiitratioiis and coniplex formation were investigated by Puriiell, Wasik. aiid Juvet (497). The iiiatheniatical techiiique of factor analysis was applied to the prediction of iiifiiiite dilutioii activity coefficients of nonelectrolytes (174) and Barker and Hilmi (38) iisetl GC for measuring activity cocfficieiiti aiid second 1-irial equilibria coeffirieiit s. T‘apor-liquid for multiconipoiieiil niiiied by GC i i i coi logging system (48 chloroform Iiiiiary the model mixture vapor-liquid equil activity coefficients of ethanol aiid a iiuni1)er of hydrocarhons iii various liquid phases (4%) aiid the heat of vaporization of several conipouiids (186) were established, while t,he activity coefficients and heat of solution for henzeiie in biphenyl aiid polypheiiyl liquid pliascs were dcterniincd by Clark and Schmidt (105). Ititerdiffusioii coefficients of gases measured by m a n s of (157)> and diffusion coefficients were determiiied in helium aiid argon for a number of compounds by an iiiitial base-line techiiique from the chroniatograinr (232). .I similar techiiique was discussed for diffusion coefficients i n both liquids aiid gases by Hubcr and van T’uglit ( 2 7 2 ) . Liquid Phases. Karger (304) reviewed the iniporiaiit factors leading to selectivity i i i liquid phares aiid covered such topics as complexation equilibria, therinodynainic considerations, mixed solid techniques, liquid crystals, and separatioii of optical isomers. Laiiger (868)also considered the principles of liquid phas:r selectivity placiiig emphasis on soliitioii theory. Tn-enty-two liquid phase;: were characterized by Rohrschneidcr (.509) using a method bared on interinolecular forc‘ea by measurement of the reteiitioii indices of benzene, ethaiinl, methyl ethyl ketone, nitromethane, and pyridine, aiid the relative polarities of several liquid phases were listed (546)and used in predicting
the order of elution of hydrocarbons. Other papers characterizing liquid phases by polarity have also been published (99, 608). VaiidenHeuvel and coworkers (606) used certain straight chain hydrocarbons and steroids in the evaluation of steroid numbers (SS) and methylene units (MU) for establishing the polarity of stationary phases. The polarities of several liquid phases used in GC were also determined through correlation with frequency shifts in the infrared absorption spectra of 10 polar substances dissolved in these liquids
(145). -1series of ester liquid phases was investigated (481) and a correlation was made between the structure of the liquid phase and the activity coefficient at iiifinite dilution of specified solutes. Owing t o differences in relative retention of isomeric alcohols, Littlewood (367) coiicludes that the free energy of interaction of a secondary hydroxyl group n ith another secondary hydroxyl grouii or with a tertiary hydroxyl group is less than the free energy of interaction of a primary hydroxyl group with a secondary or tertiary group. -4 relationship between the logarithm of the “Henry coefficient” and the number of carbon atoms in the alkyl chain of dialkyl phthalates has also been found (543). Diffusion coefficients of several solute‘ on a number of polymeric liquid phases were measured as a function of teinperature by Hawkes and Carpenter (239) and correlations between diffusivity and viqcosity were discusqed. The selectivity of desosyeholic acid for nhydrocai hoiiq relative to their branched homologs was studied by Naczek and Phillip. (398). The advantages of lightly loaded columns in allowing separation far below the boiling point of solutes were once again eiiunierated (307) and applications to the separation of complex biological compounds and inorganic conipouiids including metal atoms suggested. An Orion G Y E N Type 676 derivatograph 11-3s used (379) to determine the upper temperature limits of pure partitioning liquids arid their mixtures. The absence of oxygen was fouiid to be a major factor in the upper temperature limit measured. The first iii a series of articles (182) dealing with the proper kelectioii of liquid phases lists the temperature limitations of 13 liquid phases, aiid the effect on retention of working below the melting point of Carbowax 2011 was studied i n >omedetail (161). An apparatus was designed enabling complete column packing preparation (acid or alkali washing, removal of dust particles, drying and impregnation with liquid phase) in a >ingle one-step procedure (692), and the loss in efficiency of 8-inch and 3/’g-iii~h diameter chromatographic columns caused by deliberate columii overloading when mea-
suring components in low concentration was thoroughly investigated by X k kelsen et al. (424). The use of liquid crystalline melts as stationary phases continues to be a topic of growing interest. Kelker et al. (316, 317) showed once again t h a t positional isomers may be effectively separated using nematic melts as liquid phases. A t temperatures below 100’ C eutectic mixtures of 4,4’-azoxyanisole and -phenetole, and 4-methoxybenzylidine-4’-cyanoanilirie and -4’-acetoxyaniline were studied, while phases most suitable above 200” C were 4,4’-bisbeiizylidinebenzidiiie; 4,4’-bis(p-inethoxybenzylidine) - 4,4’ - diaminostilbene; and bisphenetidineterephthalaldehyde. Studies of the cholesteric mesophase were also carried out using mixtures of cholesterol benzoate and 4,4’-ethoxyazoxybenzene. Barrall and coworkers (36) found slope changes and sharp discontinuities in the liquid crystal temperature range in log retention us. temperature plots of cholesteryl acetate, n-valerate, and n-nanonate liquid phases. -4bel et al. (I) introduced a new concept in column packing by chemically bonding n-hexadecyltrichlorosilaiie to Celite 545 support. Moore and Davison (432) also chemically combined the liquid and solid phases by crosslinking polyester acetals having a spiro structure with the silanol groups of the support to produce a material stable above 300’ C. Organic phases chemically bound to inorganic supports and their application to fatty acid analyses was discussed by Netcalfe (418). -4 new polar liquid phase stable at temperatures as high as 300’ C is a poly(viny1formalpropionitrile) recommended for the separation of polyols, multifunctional alcohols, and fatty acid methyl esters ( 2 2 ) . A new material developed in East Germany has also been tested (262) a t temperatures as high as 300’ C. The commercially available liquid phases OV-1 (a methylsiloxaiie polymer-nonpolar) and OV-17 (a phenymethylsiloxane polymer-more polar) can be programmed to temperatures as high as 320-40’ C before excessive bleeding occurs (269). Patents were issued for a polyester of cyclohexanedimethaiiol and a dibasic acid (568) thermally stable to 250” C, organosilanes (569) , aryl bis(triha1omethy1)carbinols ( 1YO), and a packing for gas-solid chromatography comprised of clathrate crystals formed from a salt of a transition metal aiid a n aromatic nitrogen-containing coordination zompound-e.g., copper di(1,lO-phenanthroline) (NOJz useful a t high temperatures (507). Coating the latter complexes on Chromosorb W increases resistance to crumbling but does not appear to increase the low sample capacity of these packings (10). Zado and VOL. 40, NO. 5 , APRIL 1968
35 R
Juvet (659) used inorganic fused salts as liquid phases for the separation of metal halides and found certain melts, such as neodymium chloride-sodium chloride eutectic, could be used at temperatures as high as 748” C without excessive bleeding or decomposition. A saturated solution of silver nitrate in ethylene glycol proved useful in the separation of deuterated ethylene and butylene (22) and 4- to i-membered cyclic olefins (197). Pecsok and Vary (473) found certain advantages of gas-solid and gas-liquid chromatography could be combined by employing substrates of finely divided metal phthalocyanines in silicone oil. The application of columiis containing mixtures of silicone grease with up to 6% solid Bentone 34 was studied by other workers (617). An optically active ureide formed by condensation of phosgene with L-valine isopropyl ester shows remarkable efficiency for the resolution of the N-trifluoroacetyl derivatives of primary amines when the amine group is directly attached to a n asymmetric carbon (156). A series of polyesters syiithesized from adipic acid and 1-w-glycols ranging from ethylene glycol to 1.15-pentadecanediol was evaluated as liquid phases for terpenoids (29), and a new stationary phase synthesized from maleic anhydride and ethylene glycol proved useful in the separation of a 11t h r a c e 11e-p h e n a n t h r eiie mixtures (574). Free fatty acids to c18, esters, and fatty alcohols may be eluted at temperatures up to 240’ C from a new polyester phase synthesized by reacting phosphoric acid, diethyl-yketopimelate, diethyl succinate, and ethylene glycol (165). Relative retention data for a variety of compounds were measured (4%) 011 Ethofat, a polyoxyethylene monostearate containing approximately 15% ethylene oxide units per molecule with ai1 average molecular weight of 938. Formamide was recommended as an extremely polar liquid phase with advantages of low signal in the flame ionization detector aiid a low resistance to mass transfer term (448). Juvet and Fisher (296) aiid Shinohara et al. (542) found polytrifluoromonochloroethyleiie columns useful in the separation of volatile metal fluorides. Sucrose octaacetate has relatively high thermal stability aiid was recommended (660) for separation of fatty acid methyl esters. A liquid phase mixture consisting of 78 parts nonylphenol glycerol ether, 22 parts isooctylresorcinol glycerol ether and two parts Alkaterge T was recommended for the quantitative determination of ethanol in dilute aqueous solution for forensic purposes (525). Eleven polyesters were tested for separation of CI6-C2ofatty acids esters, and ethylene glycol phthalate polyester
36 R
ANALYTICAL CHEMISTRY
(mol wt, 6000) was most highly recommended ( 5 ) . Fifteen liquid phases and their mixtures were studied for their application to the separation of polyphenyl mixtures (180). Solid Supports. T h e structure of granular support materials, both spherical and irregularly shaped, was treated mathematically with regard to random and regular packing arrangements, and experimental studies were carried out to show the validity of the theoretical conclusions (515). Grubner and coworkers (207) studied mass transfer phenomena in gas-solid systems with special emphasis on internal porosity of the immobile phase aiid were able to show the coiitributioii of porosity to efficiency. Berezkin et al. (48) demonstrated that the efficieiicy of columns may be materially improved by filling the pore structure of supports with a n inert material. Support properties were extensively studied by Hargrove and Sawyer (233) who also established that the correct van Deemter gas velocity to use in open-structure supports is that derived from total gas rebidence time. Reviews of solid supports have appeared which effectively cover the broad spectrum of standard, modified, and novel GLC supports (458,462). Uroiie aiid Parcher (601j continued their study of support effects aiid demonstrated that silaniziiig produces little change 011 the total support area. Surface active supports were clearly shown to coiitribute to retention in a way dependent on liquid phase loading. Binary liquid phases were used to modify the adsorption properties of supports (627), and an extensive investigation of reduced activity supports, iiicludiiig organic polymers, was carried out by Ioiiescu (276). In another study, the adsorptive properties of supports were modified by the addition of sugar (4SO), and Jeltes (381) clearly demonstrated t h a t active supports could adsorb irreversibly parts-per-million concentratioii of polar solutes. This observation is of some concern in the analysis of trace components in air aiid water pollution studies. Silanized supports were shown to substantially alter the relative retention of ethanol-benzene mixtures (427)). A large variety of solid supports and a number of liquid phases were investigated for their catalytic effect 011 the isomerization of terpenes (241). The silane treatmelit of solid supports has been discussed extensively by Supina and associates (570, 571). Recommendations were made by these authors regarding the best method of preparing silanized supports and complete column packing. The effect of acid washing and several different silanizing treatments and some thermal treatments 011 the gas-liquid separation
of small amounts of drugs mas investigated by McMartin and Street (411). It was demonstrated that alkalized supports gave inferior resolution of hydrazine derivatives relative to unalkalized supports with “Carbowax” liquid phase (N),aiid it was shown that the polyvinyl pyrrolidone-modified support materials resulted in a substantial increase in the retention of alkaloids a t 230’ C ( 7 1 ) . Pretreatment of diatomaceous earth materials with orthophosphoric acid, followed by heating at 200” C for extended periods, is reported to produce a superior support (153). Thermal treatment of supports alters substantially the adsorption characteristics of the material, and the reduction of adsorptive activity appears to he maximum a t a treatment temperature of 1100” C (540). =It higher temperatures, of the order of 1400” C, Blandenet and Robin (59) showed that substantial pore volume loss R as mainly responsible for the reduced adsorption activity but that such supports were roughly equivalent to the original silanized material. Among the novel supports iiivestigated for gas chromatography was vermiculite, which is attractive from a cost and property standpoint and seems to offer potential advantage3 for aqueous samples (410). Graphite \vas studied a i t h respect to its pore distribution and specific surface (58) but is coiisidered inferior to silicate-type supports. Porous silica was demonstrated to be highly effective as a solid support (213). Sponge spicules appear to be a n attractive support material for gas chromatography because of their dimensions and iiiterestiiig textured surface which effectively retains liquid phase (634). “Sephadeu.” the cross-linked dextran polymer, was investigated as a solid support and was found to be stable at elevated temperatures for substantial periods of time and suitable for aqueous samples (108). Sonporous “Teflon” is effective for the separation of watercontaining mixtures (546), and the “Kel-F” type solid supports (542) as well as LLTeflon-6”support (296) may be used for the separation of volatile, inorganic fluorides. Fluoroplasticcoated diatomite gives symmetrical peaks with polar solutes (488) and a randomly entwined metallic felt was recommended as a n effective solid support (445). Adsorbents. A review of GSC b y Scott includes discussion of modified adsorbeiits, the potential of GSC for high molecular weight separations, the influence of structure on adsorption, and the specific interactions between aromatic compounds and adsorbeiits ( ~ 7 3 2 ) Locke ~ (391) described the theoretical aspects of GSC, taking into account the nonideality of carrier gases and nonlinear adsorption isotherms. Others have performed analyses of the
adsorbed state including consideration of a binary adsorbed film (511), the interpretation of adsorption through electrostatic interactions (321), and a theory of lowtemperature separation of hydrogen isotopes (67, 322). Waksmundski and coworkers (626) defined a procedure for estimating the adsorption potential distribution on solid adsorbeiits. Parcher aiid Urone (465) determined nonlinear adsorption isotherms on adsorbents by several procedures, and adsorption enthalpies were measured in other instances (18, 5 6 0 ) . Adsorption isotherms were also measured by employing t h e frontal analysis technique (43), and a n evaluation of several published procedures was made (519). Iiiselev (181) described a simple method for quickly determining t h e specific adsorbent surface. The separation of mixtures of argon and osygen on molecular sieves was studied estensively, particularly from t h e standpoint of t h e required degree of thermal activation of the sieves (309, 629). -4 3O-foot column of molecular sieve 5.1 was satisfactory for separating mixtures of argon, oxygen, and nitrogen a t temperatures near 0’ C (218). Molecular sieves were discussed with respect t o their structure and their physical and chemical composition ( 3 0 ) and modified molecular sieves in which pore diameters were changed by cation exchange were t h e subject of another investigation ( 1 7 5 ) . The degree of hydration profoundly affects t h e separation of permanent gas mixtures on molecular sieve 5-4 with corresponding changes in t’he heat of adsorption ( W ) , and a substantial degree of irreversible adsorption of gases (including water vapor) was observed on molecular sieves in another instance ( 9 0 ) . Adsorption heats of hydrocarbons on assorted zeolites were carefully investigated, including r-bond interactions (%%), and molecular sieve 5.4 was once again shown t o be effective for separating t h e n-paraffins from isoparaffins by exclusion (64). X coinbination of surface and pore adsorption was demonstrated to occur in zeolites by Kiselev and Yashin ( 3 2 9 ) . -4 technique which involves eventual destruction of the zeolite t o recover absorbed 72-paraffins on a n analytical scale appears t o be highly effective (436). Small-diameter aerogel columns (1 p light silica) provides a highly dispersed adsorbent for t h e separation of hydrocarbons (224). High-resolution capillary adsorpt’ioncolumns were prepared by Schwartz and coworkers (551) who applied a colloidal hydrophobic adsorbent t o the inside of plastic and steel capillaries. Porous glasses as adsorbents were discussed with respect to t h e uniformity of their adsorption characteristics and their use for the separation of vapors,
gases, and hydrocarbons (327, 539). The various performance parameters of silicas were discussed by Snyder who also described t h e preparation and standardization of silica adsorbents (557). Various alkanes, alkenes, and alkynes (259) and cis-trans isomeric olefins were resolved on alumina (380, 381). The influence of t h e carrier gas on retention in alumina columns was noted by Hoffman, List, and Evans who separated atmospheric gases a t low temperature (162). A silver nitratealumina precolumn was used t o effectively remove olefins from hydrocarbon samples analyzed on alumina columns (255). Carbons, modified by t h e addition of a liquid phase, were recommended for t h e separation of mixtures of hydrocarbons and carbon dioxide ( 4 7 ) . Manavanese oxide was studied as a n adsorbent (328), and t h e adsorption of polar compounds on amorphous boron was investigated with t h e results indicating chemisorption and reaction (200). Various solids derived from phthalic acid were comprehensively examined as adsorbents in a study of Heveran (250, 251), and a comparison of t h e selectivity of alkali metal halides for organic isomers and homologs was t h e subject of a study by Guran and Rogers (219). Starch was observed to show a high affinity for alcohols with little retentive behavior toward aliphatic and aromatic hydrocarbons (350), and phthalocyanines were investigated as adsorbeiits by varying t h e metal ion in t h e phthalocyanine and employing oxygen- and nitrogen-containing adsorbates as competitive ligands (612). -4 significant discovery was t h a t porous polymers, notably crosslinked polystyrene, are remarkably effective for separating low molecular weight compounds of various classes, including hydrocarbons, halides, ethers, alcohols, acids, amides (264, 265), and gases (663),among others. Finally, it should be noted t h a t water vapor has been used effectively as mobile phase for GSC in t h e separation of alcohols and organic acids on alumina aiid firebrick
(444).
Carrier Gases. An extensive discussion of gas flow in porous media was written by Guiochon in which t h e various pressure-flow laws and methods for calculatiiig principal quantities in flow systems are given (217). This discussion includes some practical applications of flow programming and problems associated with this technique. Ultrahigh-pressure GC to about 2000 a t m using small columns was studied by ,Myers and Giddings (441). Highly specialized equipment is needed for operation in this range. As a corollary t o this work, Giddings (192) discussed t h e implications of pressure-induced changes in migration rates and column
selectivity. Specific retention volumes a t nominal pressures were measured by Brookman et al. (74) as a function of t h e nature of the carrier gas. With HP, N 1 , He, and A retention was constant to within 1-3%. B y operating at supercritical conditions using COP as carrier, on t h e other hand, Sie and Rijiiders (549, 550) obtained enhanced volatility for high-boiling solutes. Their technique of “fluid-liquid” or “fluidsolid” chromatography represents the transition region between GC and L C* Another mode of operating entails the step increase of inlet pressure, t h e advantages of which have been enumerated (279). Russian workers (11, 661, 662) discussed a t length the possibility of performing chromatographic separations without carrier gas. In these systems the vapor mixture t o be separated is passed continuously through t h e column, and differential changes in signal are noted with pulsed composition changes or with pulsed displacer addition to t h e column. Sample Introduction. A paper b y LeMoan (367) reviews 78 literature references on t h e sampling of gases, and Johnston (289) discusses loss of volatiles during storage of liquid samples in plastic containers. Some factors affecting the reproducibility of sample injection were covered by Hamilton (228). The preconditioning of septums by heating them overnight a t 260’ C was recommended recently (582). A unique septumless injection system which is rugged and dependable was described by vailSwaay and Bacon (611), and a n apparatus providing for discrete heating of sample was also reported (421) for introducing organic compounds into gas chromatographs. T h e introduction of samples in capsules of fusible metal alloys again was noted (139, 273). Micropipet encapsulation of samples which are then injected into a crusher device has yielded high reproducibility (50). Volatile fatty acids were introduced in a unique way by first absorbing them on a small, sintered-glass pellet which is then inserted into t h e inlet of the column (607). Aqueous samples were successfully introduced directly on the column by means of exchangeable injection-port cartridges (171), aiid dry samples were introduced by means of a modification t o t h e injection port of the chromatograph which involves interrupted gas flow (396). ;in automatic solid sample injector was described by Ruchelman (513) which allows a series of samples to be injected on a predetermined time schedule, t h e solid sample being distributed on small wire gauze pellets. A head-space method for t h e concentration and separation of volatile components was described by Binder (57), and a patent was granted (205) for a device VOL. 40, NO. 5 , APRIL 1968
37 R
for withdrawing vapor samples from stills. Gases may be extracted successfully from mater (431), and from body fluids using another unit (60, 526). Small gas samples, including hydrogenoxygen mixtures (667) and lower hydrocarbons (662), and a device for gas samples in the micron pressure range were developed (14). A system for the removal of samples a t pressures up to 100 psi has been used t o analyze combustion reactions (9). Coaxial sample injection a t supercolumn pressure provides a slug of sample from t h e system described by Ferrin (160). A number of devices for handling samples were patented, including one of the rotary valve type (657), a novel fluid-sampling valve which can be located inside a reactor (l58), a highpressure sampler (@), and a unit which permits easy clean-out for continuous process analysis (159). A large number of publications have dealt with repetitive or automatic sampling devices, including a sequential valve fitted with O-rings (119), an apparatus which automatically transfers samples previously placed on stainless gauze pellets separated from s u c c e d v e samples by glass beads (66),a n automatic apparatus which 15 heated above the condensation temperature to yield representative samples from vapor systems (579), a high-pressure gas-sampling valve for working a t 5000 p i (357)) a repetitive automatic device for use in the medical field ( j a g ) , another automatic device consisting of solenoid valves and electromagnetically transported sample holder3 (484)) and a proceys-stream sampler equipped n i t h a helical displacement pump for 1% ithdrawing samples from the stream (109). The exponential dilution method for obtaining very low concentration calibration standards was evaniined by Kil1iani.s and Winefordner (644), and a new diffusion cell permit, calibration with gas stream5 containing very small amounts of measured components (363). I n the latter device, the components are alloaed to diffuse into t h e pure floiiing gas through a Teflon n-all -1modification of the sample splitter technique which i b designed to overcome the problem of sample fractionation was reported by 13ruderreck et al. (75). A sample system in nhich variation of sample size due to barometric pressure changes is eliminated by compeiisation was also described (597). The littleknown, but ea4ly demonstrated, problem of damage to gas chromatographic column, by large samples has finally appeared in the literature in a n interesting discuision by Mikkelsen and associates (424). This nork clearly shons t h a t as much as one half of t h e theoretical efficiency of a column can be dehtroyed by sample overloading. Trapping. An a p p a r a t u s for t h e
38 R
ANALYTICAL CHEMISTRY
isolation of volatiles from food substances provides for heating of the sample and low-temperature trapping of the volatiles (249). Another technique entails the use of a nitrogen sweep gas and low-temperature collection of the entrained volatiles (260). Activated charcoal traps were shown effective for trapping of volatiles prior to study by mass spectrometry (121). On-column trapping procedures for flavor volatiles were described by Morgan and D a y (433). Two techniques, one involving the total trapping technique of Svoboda, were found effective by other workers (271). A convenient collector for GC fractions consists of a n easily removed U-shaped trap which is friction-fitted to the outlet of the chromatograph (390). Efficient collection of eluate can also be carried out with a device consisting of multiple glass cylinders, containing solvent and fitted with septums to permit withdrawal of final solution (442). A variety of trapping devices for use with commercial chromatographs has been summarized recently (183). Particular emphasis mas given the collection of methyl esters from preparative gas chromatographs by electrostatic precipitation in the work of Borka and Privett (63). A microcollector based on the multiple trap carrousel principle was described by Deck and coworkers (123) and successfully used in the isolation of food volatiles. X preparative-scale collection programmer was also well described with drarvings and circuit diagrams (319). Minimum alteration of existing GC equipment ia claimed for another automatic trapping system (371).
DETECTORS
The application of physical techniques to t h e detection of gases was reviewed for GC and other systems (126, 210). Karmen performed the commendable task of consolidating the literature for t h e most important ionization detectors with the practical and important consideration of t h e effects of GC variables on sensitivity limits and linear range (310). il recent book discusses the many aspects of ionization phenomena in gases (389). We should note t h a t Ettre, in a n early reference (148), made a study of t h e relative molar response of hydrocarbons in ionization detectors, particularly flame and argon detectors, and included some d a t a on the thermal conductivity detector. A review of detectors, applicable particularly to pesticides, includes also discussions of auxiliary techniques (637). Thermal Conductivity. Thermal conductivity (TC) continues t o receive modest attention in the literature, including a quantitative study of t h e
detector response based on the kinetic theory (315), operating characteristics (282), and a review of significant advances in T C detection with comments on proper design and operation (355). The relationship between t h e geometrical, electrical, and chemical parameters of T C was noted by Novcik (44’7). Small-volume detectors with fast response, based on t h e T C principle, were described in detail (342, 4 8 9 ) , and a simple, inexpensive unit t h a t can easily be constructed was also reported (394). A unique T C detector for capillary columns was patented recently (341), and Hoffman and Evans (256) substantially increased the sensitivity of T C devices by operating at low temperatures. The high-pressure applicability of T C is emphasized in a paper by Hawkes and Wheaton (240). The use of nickel-cadmium batteries substantially improves T C performance of t h e Perkin-Elmer Model 154 (230). Ionization. The sensitivity of flame ionization detectors (FID) can be substantially increased by the use of high-quality electrometers as demonstrated in several cases (91, 1’77). These publications include detector modifications which increase the stability of t h e system. Improvement in the sensitivity of t h e F I D was noted when oxygen replaced air for conibustion and when certain other operating precautions were taken (267, 261, ,993). A newly designed dual-flame device was described which operates at a n optimum nitrogen-to-hydrogen ratio of about one (347). The response of the F I D t o organosilicon compounds (368), to nitroaliphatic compounds (464), and to carbon disulfide (628)has been noted. The thermal conductivity of carrier gases and its influence on the F I D senbitivity was reported with the recommendation t h a t nitrogen or carbon dioxide be employed (268). Organic aerosols and vapors in the atmosphere have been quantitatively measured by means of t h e F I D (172), and Ohline (453) used the device for t h e sizing of organic aerosols by passing them directly into t h e detector. Particles as small as 1 micron can be detected in this manner. -4 simple modification involving replacement of resistance with capacitance in t h e detector circuit yields integration of the F I D signal (231). An assembly which could be attached to a conventional F I D t o convert i t t o a thermionic detector was described by Cremer and coworkers (117 ) . Karmen (311) developed a modification of the F I D for application t o liquid-liquid chromatography which includes a n aspiration technique for delivering the vaporized solutes and fragments t o the FID. Triphenyl derivatives of phosphorus-, nitrogen-, arsenic-, and halogeii-contain-
iiig coiiipouiids were studied for their tlicrinioiiic detector response (278). The lxinciplcs of selective detection, with special consideration of t h e thermionic dctixtor for sulfur aiid phosphorus wcrc discussed by Creiiier (116). -A modification of the thermioiiic detector increases sensitivity to nitrogen conipounrls by several orders of magiiitude (24). ;1 new commercial dctcctor gives selective response t o halogen or phosphorus depending on the nature of the fuel applied t o the burner (2). Electron capture (EC) affinities of organic molecules were included in the comprehensive work of Shoemake on ionization detection systems (644). A study of the sensitivity and response of this class of detector with continuous or pulsed polarization, geometry modifications, and other factors was made (129, 130). The importance of temperature aiid concentration variables on the mechanism of E C was the subject of research by Wentworth and Chen (636). The response characteristics of a new high-temperature E C detector using nickel-63 and operable to 300" C was described (656). Various fluorine-, chlorine-, bromine-, and iodine-containing compounds were evaluated with regard t o their respoiise in electron capture detectors (106), aiid dibromoethane in gasoliiies was quantitatively measured with this device (479). Halogeiiated amine derivatives were measured by means of E C . aiid some interesting applications to amino acids and peptides were also noted (104, 356). Tritium foils in E C detectors may be cleaned by a procedure recommended to restore sensitivity (263). hlodifications in the operational mode of the microargon detector and a n investigation of theoretical and esperinieiital responses u-ere made by Collision et d. (110). d triode argon detector was described in detail (137), and a krypton triode device was found particularly sensitive t o compounds with ionization potential below 10 electron volts (470). -4leakproof argon ionization detector cell was described (638))and Hartman and Diniick (287) demonstrated parts-per-billion sensitivity for their helium ionization detector which consists of two closely spaced electrodes in parallel geometry operated at high voltage. Other workers showed t h a t the sensitivity to trace component,s in helium is a direct function of t h e applied voltage (68, 69). dnomalous response of the helium ionization detector was shown by the partially negative peaks obtained for hydrogen, osygeii, and iiitrogen (469).Theoretical and esperimental investigations on t h e operation of argon, helium, and crosssection types of detectors were discussed by Lasa (360). A discharge detector in which t h e ionization cur-
rent is measured downstream from t h e escelleiit sensitivity (253). Water in discharge was developed (428) as was hydrocarbon samples was determined by a n electrodeless dkcharge detector (19). combination of gas chromatography and a n electrolytic water detector (522). Miscellaneous. Considerable interest has developed on the use of flame detector having a high selectivity for photometric detectors during this bienhalogen aiid sulfur is based 011 a solidnium. The flame photometric detector state electrochemical cell which requires was shonn to be highly sensitive and the osidatioii or reduction of the solute before detection (42). selective in the aiialyais of metal halides and chelates and wa3 characterized in The combination of mass spectromdetail t heriiiodyiiamically by Juvet and etry and gas chromatography has produced some remarkable analyses and Durbiii (140, 295). h modified flame has been discussed in a number of photometric detector of verbatile design, developed by Zado and Juvet publications (76, 246). The high res(659, can be operated in either a olution of natural products using this selective or nonselective mode, t h e iiistrumental combination is noteworthy nonselective mode permitting detec(56). The ionization produced by t h e tion of organic compounds as TI ell as those inorganic compounds s h o w catalytic combustion of hydrocarbons on a heated platinum filament above 500°C ing broad oyide band \pectra. Braman (70) described the characteristics serves as the detection principle in anof a flame emission-flame ion izaother device (652). Both a n acoustical whistle detector which responds t o tion dual detector also useful for varying gas density (247), and a fluid organic materials. Element-specific detection has been employed in gas oscillator (686) which can be employed chromatography by coupling atomic as a GC detector have been patented. absorption spectroxopy with the chro*A thin-film semiconductor on which the matograph (840). Brody aiid Chaney solutes are adsorbed has been employed as a detector of high sensitivity (537) (73) developed a flame photometric detector with high specificity for phosand the piezoelectric detector developed by King was used to measure oxidation phorus and sulfur compounds as a result of cheiiiilumiiie~ceiice e m i 4 o n . Tong stability of elastomers (163). described the detection of organic comI n chromatographic pounds containing halogen, phosphorus, are used repetitively, and sulfur by means of their emiz-' .bion can be compensated for bj- t h e device (691), and a servo-operated microwave described by Levy and Nikkelsen (370), detector of modest sensitivity showed aiid a high-senFitivity electronic in1% linearity over a 20-fold concentrategrator for storing detector signals was tion range (285). developed which may be constructed for -A radio-frequency detector was pata nominal cost (38). The gas density ented (229), and some comments were balance originally invented by A. J. P. made concerning the modification of a Martin was evaluated in some studies by direct current discharge detector (504). Walsh and Rosie (631) and was used for Radioactil e compounds containing trithe determination of molecular weights tium aiid carbon-14 were discussed in a of suitable compounds (503). A continreview of means for their detection by uation of their study on t h e gas density Karmen (312). -A Geiger counter debalance has been made by Guilleniiii tector applicable to gab chromatographs and coworkers (212) in which it is conhas also been deqigned (643). Tracer cluded t h a t t h e gas density balance is pulbe chromatography with scintillation approximately equivalent t o T C in liquid counting was described by Petersensitivity and linearity. A pneumatic son et al. (480), aiid the instrumentation, detector related to t h e gas density balcalibration, and application of radioance was devised (449),and l'horburn active analysis in GC mas discussed aiid Bevan (588)received a patent for a gravimetric mass detector. These (443)' -1specific detector for nitrogen comn-orkers discussed applications and pounds is based on the coiiversion of t h e advantages of this detector in a n addinitrogen t o ammonia and electrolytic tional publication (63). Hydrogenmeasurement of this material (92, 212). atable materials have been measured by X bimilar detector mas advantageously a closed loop H2 generator-hydrogenaapplied to t h e measurement of traces of tioii detector (388). nitrogen in petroleum products (6, 402). Electrical conductivity detection was QUANTITATIVE AND used in the analyses of the lower fatty QUALITATIVE MEASUREMENTS acids (493). A microcoulometric cell effective for sulfur compounds was Quantitative Studies. X recent described ( 4 ) and niicrocoulometry was survey by Varian .Aerograph of over used to measure chlorine, sulfur, aiid 1,600 practicing gas chromatographers phosphorus in pesticides ( 7 8 ) . The shows t h a t quantitative measurements determination of traces of osygen from are made using the following procedures : t h e chromatographic column can be peak height, 28.07,; disc integrators, carried out with a Hersch cell with 20.870 ; triangulation, 16.9%; planimVOL. 40, NO, 5, APRIL 1968
39 R
eter, 15.5%; digital integrators, 8.5%; cut and weigh, 6.4%; computers, 2.4%; and tape systems, 1.4% (198). Errors occurring with t h e various manual integration techniques were evaluated by Ball, Harris, and Habgood (28) while digital integrators were considered by Uaumann and Tao (41) and peak detection logic systems by Karohl (313). Mikkelsen (423) and Seher (536) considered the main sources of error in quantitative GC analysis and tabulated the normal reliability of analyses for the various type detectors and injection methods. Mikkelsen (423) reports precision at the 95% confidence level of &0.5% relative mith indium tube injection and i l % relative error with syringe injection. The characteristics and significance in quantitative gas chromatography of potentiometric recorders (87) and ionization detectors and electrometers (199) were considered in some detail. An automatic processor for GC d a t a which uses voltage-tofrequency conversion plus counting as its basic area measuring technique has optional tape recording facilities allowing d a t a from as many as eight gas chromatographs to be processed (538). McCullough (407) described a system used for interfacing a digital computer directly to several gas chromatographs for on-line monitoring with a digital computer. The standard addition method was eyamined in some detail by NovAk and Janitk (450),who showed this procedure can lead t o erroneous results. Reproducibility checks using the linear 0ring type gas valves for 98 runs over a 22-day period showed precision on the order of 0.5% (420). The importance of providing sufficiently high air flow rates for reproducible results with the flame ionization detector n as emphasized by Batt and Cruickshank (40). D p o n and Littlewood (142) warn, following a study of t h e effect of viscosity of a solute vapor on quantitative analysis, t h a t errors of u p t o 10% in quantitative GC analysis can occur as a consequence of the perturbaiice of the flow rate by the peaks in the column, and evidence is presented t h a t detector calibrations can depend on the absolute sample size. AIeasurement of molar response factors for various detectors continues. Dietz (132) measured the response factors of a variety of compounds for both the flame ionization detector and the thermal conductivity detector. Other workers (248) suggest t h a t measurement of response factors for a thermal conductivity detector should be performed during temperature programming of the column t o reduce differences in response factors observed under different isothermal conditions. Relative molar response factors for Cg to C24 fatty acid methyl esters were 40 R
ANALYTICAL CHEMISTRY
reported using the flame ionization detector (649) and for CI t o C6 amines, cyclic amines, and hydrocarbons using a thermal conductivity detector (616). Maher recommends a reactioii-subtraction method for the semiquantitative determination of Olefiii5, aromatics, isoparaffins, and naphthenes (399), and the precise quantitative analysis of isomeric materials was performed using the reverse isotope dilution method in conjunction with preparative scale GC (83). The quantitative determination of mixtures containing high-boiling compounds gives special problems. One approach has been the use of the internal standard method (363). -4proceure was developed (521) t o avoid errors in calculating detector response at high column temperatures where liquid phase bleeding may cause detector saturation. Displacement of the calibration curve for high-boiling compounds along the ordinate and failure of the curve to extrapolate through the origin wa$ attributed (419) to flashing of a lowboiling solvent from the syringe needle leaving a significant residue in the needle. The use of higher boiling solvents apparently eliminates this problem. Qualitative Studies. Although t h e collection of retention data, particularly retention indey data, continues to be important in qualitative analysis (122, 290, 291, 335, 343, 578, 640), emphasis during this biennium has been on combining GC with other techniques such as mass spectrometry, thin-layer chromatography, infrared spectro>copy,and other spectrochemical methods. Several reviews of the combination of GC and mass spectrometry have appeared (364, 408, 578). An important consideration in combining these t\$o techniques involves the methods of sample introduction (409) and the molecular separator used to remove excess carrier gas before introduction into t h e mass spectrometer. Ryhage (517) reported further studies of his jet-orifice design molecular separator now commercially available on a n instrument of Swediih make. Lipsky, Horvath, and 1IcAlurray (377, 378) used a 7-fOOt length of thin-ualled (0.005-inch) Teflon FEP (a copolymer of tetrafluoroethylene and hesafluoropropylene) capillary tubing as a niembrane interface for t h e selective permeation of helium with efficiencies ranging from 40-70%,. The fritted glass molecular separator developed by T.liatson and Biemann (633) and t h e Teflon FEP tubing separator of Lipsky et al. (377), were evaluated by Grayson and Wolf ( 2 0 4 , who stated a preference for t h e fritted glass separator. Foltz et al. (165) warned against the use of PTFE for certain systems because they found trimethylfluorosilane was
formed by reaction of the solutes trimethylchlorosilane, hexamethyldisilazane, bii(trimethyldyl)acetamide, and bis(trimethylGly1) lactate with a Teflon sleeve positioned between the gas chromatograph and the mas? spectrometer. rZ new type ieparator developed by Varian A4siociatesusing a liquid phase ab a barrier for the carrier gas looks very promiiing (641). In order to reduce the need for a rapid-scan mass spectrometer, Scott et al. (534) used a stop-start interrupted flow technique with only minor spreading of peaks retained in the column during spectral studies. ;1 patent was issued to Coates and Delany (107) for a n apparatus which reduces column temperature while the eluted component is being scanned by the mass spectrometer, effectively freezing the remaining components on the column until the spectrometer is ready to receive another component. Other authors (121) recommend trapping eluted solutes prior to study by mass spectrometry in >mall capillary tubes, I-inch x 0.070-inch i.d., packed with 20 mg of activated coconut charcoal, 70-100 mesh, and plugged at each end n i t h glass ~ o o l . An electrical scan system for a fast scan, high-resolution mass spectrometer n a s evaluated (412)allowing monitoring of GC effluents by recording spectra on analog magnetic tape at a resolving power of 1 :10,000 a t scan rates down to 8 seconds per mass decade. Hitec and Biemann (254) described a digital computer-compatible recording system for fast-scaiining, *ingle-focusing mass spectrometers which allou s recording of the spectra in 1-3 seconds and preients the mass and abundance data directly in tabular or graphical form. Capillary columns have been used with both a high-resolution mass spectrometer (245) and a compact quadrupole mass spectrometer (600). Sweeley and coworkers (577) showed t h a t a tmo-component miyture producing unresolved chromatographic peaks may be evaluated analytically by observing the changing intensities of two selected mass peaks characteri4c of the compounds under study during their elution from t h e chromatographic column. The two mass peaks are produced by rapid switching of t h e accelerating voltage with a time-actuated relay and a voltage-dividing circuit. The combination of GC and infrared spectroscopy has also proved useful. Low and Freeman (393) applied t h e Block Model 200 infrared interference spectrometer t o GC effluents using a scan rate of 1 sec for the wave number range 2500 to 250 cm-l and a resolution of 18 cm-'. A patent was auarded (39) t o t h e Dow Chemical Co. for a heated IR cell of use with GC effluents, and King and O'Connor showed t h a t aerosol samples could be analyzed (323).
Kuksis (351) reviewed more t h a n one hundred papers in which thin-layer chromatography and gas chromatography were used in combination. JanBk (516) combined G C and T L C in a unique two-dimensional manner by eluting fatty acid esters from a gas chromatograph onto a logarithmically travelling start line of a silica gel-silver nitrate thin layer. The gas chromatograph separated t h e acids according t o chain length (firqt dimension) and T L C separated the acids according t o degree of unsaturation (second dimension). Another novel combination of these techniques was developed by Padley ( 4 6 1 ) , who detected components separated by T L C by passing t h e plate through the flame of a flame ionization detector. Tumlinson and coworkers (425, ,596) made derivatives of carbonyl compounds and alcohols on T L C plates as the solutes were eluted from t h e exit port of t h e gas chromatograph. Other combinations of techniques useful in qualitative analysis include coupling of GC 15 ith neutron activation analysis (lis), differential thermal analyqis (463), ultraviolet spectroscopy (168), and time-average proton magnetic reqonance spectroscopy (595). In the latter study, a 50-pl cell was used and time averaging of the spectrometer output over a period of 1 d a y permitted use of a sample containing 0.3 pmole of hydrogen. A new micromethod for the simultaneous determination of carbon, hydrogen, and nitrogen was developed using gas absorption chromatography with decomposition of the solutes by nickel oside (loo),and Juvet, Tanner, and Tsao (297) developed a new procedure combining mercury-sensitized photolysis with P T G C for organic structural identifications. SPECIALIZED OPERATIONS
Preparative Scale. A review of preparative G C covering such aspects as apparatus, packing methods, effects of column overloading, and solute trapping was prepared by Rijnders (505). British and C . S. patents (27) were issued to I>r. R . F. Baddour of M.I.T. and assigned to Abcor, Inc., for a system of alternate diik and annular baffles incorporated transversely within the packing bed of the column t o induce lateral flow and improve t h e separating ability of large diameter columns. A system u i t h a 6-inch column is priced a t $49,500 and is complete with feed injection and fraction collection subsystem, automatic sequencer and controller unit, carrier gas recycle and purification subsystem, and a column of Carbowax 20M on Chromosorb P ; a second pilot plant with columns 1 foot in diameter is priced at $150,000 (95). Ilarker and Huntington (53, 34) described a circular chromatograph using
the moving bed principle but elimiiiating the problem of mechanical handling as there is no relative movement between the packing and the column, and this device can be used either for continuous separations or for preparative scale batch separations. Guillemin and Wetroff (214)were awarded a patent for a fluidization procedure of packing large diameter columns by passing a gas upward through the packing at a velocity sufficient to fluidize the filling and then reducing the flow rate t o allow t h a t packiiig material to gradually settle into a fixed bed. Guillemiii (211) apnlied t h e fluidization technique to columns 6-em in diameter and obtained efficiencies of 500 theoretical plates per meter for 0.25-nil injections. Carel and Perkins at Continental Oil Co. developed (85) a preparative scale unit which will accommodate up to 30 feet of a .&inch column or 16 feet of a 6-inch column, pressurized chambers allowing sample injections of up to 200 ml, and a special sample trap equipped with porous stainless steel plates to provide large condensing surface. Carel mas also awarded a patent (84) for a chromatographic system using cylindrical annular columns in which vapor sample is fed uniformly to the column at several points circumferentially spaced around the upper end of the column annulus and component collection takes place at a plurality of point3 spaced around the bottom of the effluent collection manifold. A patent was issued (314) to Rewlett-Packard Co. for a fully automatic preparative scale gas chromatograph accepting columns up to 3/4-inch in diameter and providing for automatic and repetitive injection of samples and temperature programming. Another commercial instrument was described by Fischer and Eberle (164) capable of separating mixtures up to 150-ml volume in approximately 30 minutes in one passage using columns up to 20 cm in diameter with up to 10 1-meter columns in series and operated a t temperatures up to 30OOC. Perry (477) reported experimental conditioiis which led to a decrease in HETP with increase in column length in a preparative scale unit and formulated a yield index for comparinq preparative scale columns (475). Hargrove and Sawyer (281) report that gas-phase mass transfer is a principal band-broadening factor in large diameter colunins while Guiochon and coworkers ( 1 3 4 ) , in a thorough study of the factors influencing efficiency and productivity, found that use of a high diffusivity carrier gas such as helium or hydrogen gives greatly improved column productivity and Verzele (618, 620) showed that sample size is the most important factor determining relative band width. Finned columns OF 1.5- and 3-inch diameter were compared with columns of
the same diameter without fins and were shown t o give considerably higher efficiency and resolution (502). A novel countercurrent distribution device may be used in gas chromatography with samples as large as 0.35 ml (236) and Borka and Privett (64) employed a n ac electrostatic precipitator for preparative GC trapping. A few interesting applications of preparative scale GC include the purification of 14C-labeled conqiourids using a T C and a modified end-window Geiger Muller tube as detector (31),the quantitative ewhange labeling of imine, hydroxyl, and enolizable compounds by passing the sample through a prep-scale column pretreated with D20 (299), and the reported separation of the two stereoisomers of methyl 2 - ~ ~ - , 4 - ~ - d i methylhexanoate (452). Open Tubular Columns. The history and development of capillary columns including sample introduction and column coating were reviewed by Desty (121). Although Wilhite (642) recommends micro-packed columns over support-coated packed capillaries because of increased sample capacity and lower HETP, Halitsz (223) considers HETP values a n unsuitable basis of column comparison and coiicludes better resultscan be obtainedwith packed capillary columns, pointing out that loadability depends not only on column type but also on the capacity of the liquid phase. Factors affecting the efficiency of glass capillary partition and adsorption columns were reviewed by Liberti (376), and procedures were discussed uselul for producing high efficiency glass columns coated with polar liquid phases and adsorption columns etched with sodium hydroxide. Support-coated open tubular columns received considerable interest during this biennium owing to increased sample capacity of this type column over t h a t of simple open tubular columns (direct injection of 0.1-0.2 p l ) , comparable performance, and reduced analytical time. Patents have been awarded to Halitsz and Heine (225) and Halitsz and Horvath (226) dealing with the preparation and characterization of supportcoated open tubular columns. Purcell and E t t r e (495) applied support-coated open tubular columns to trace analysis and pointed out these columns can be used in a n integrated GC-MS system and in combination with flow programming. Performance characteristics of support-coated open tubular columns were compared with wall-coated open tubular columns and with conventional packed columns (150), and the effect of large changes in t h e ratio of column gas t o liquid volume was investigated (151). New techniques applicable to capillary column technology include the use of multichannel open tubular columns providing a high-capacity, low-pressureVOL. 40, NO. 5, APRIL 1968
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drop column useful in direct coupling with a mass spectrometer (630) ; the use of infrared spectrometry for micro amounts of effluent from capillary columns (45) ; a two-stage temperatureprogrammed capillary column and splitter unit (44);and a n injector insert used in conjuction with on-column injection into open-tubular columns (646). A patent was issued (648)t o t h e Regents of the University of California for a new type capillary column of variable length comprised of a cylinder with helical groove circumscribed by a second cylinder connected in a gas-tight manner. lletcalfe (41 7 ) recommends addition of the long-chain quaternary ammonium compound, trioctadecylmethylammonium bromide, to the liquid phase t o aid in uniform coating of a stainless steel column. Different degrees of adsorption between packed and capillary columns can cause differences in observed relative retention (429). Addition of Igepal CO 880 is recommended to reduce adsorption and peak tailing and effectively improves resolution (430), and potassium hydroxide was used (103) as a n additive in Carbowax-coated capillary columns in the separation of organic amines.
Temperature and Flow Programming. Recent advances in programmed-temperature chromatography were reviewed by hlikkelsen (422). Interest continues in flow programming as demonstrated by the work of TakAcs and coworkers (581). I n this work, the carrier gas inlet pressure was prqgramrned and pertinent equations describing this mode of operation were included. The application of double programmed gas chromatography-column temperature and carrier gas flow rate-was also investigated (406) and recommended particularly when performed near the upper temperature limit of the liquid phase. Substantial attention was paid to obtaining reproducible retention d a t a under programmed-temperature conditions by Guiochon (216) and Schmit and Wynne (528). -1computer procedure for determining retention temperature was described by Rowan (512). An inexpensive demonstration dualdetector gas chromatograph with temperature programming was constructed (476), and a careful study of temperature gradients in P T G C columns revealed the existence of large temperature inhomogeneities (275). Nonlinear or otherwise modified temperature programming was discussed in two publications (527, 5 8 0 ) . Temperature programming with a high degree of flexibility is possible with the interesting circuits by Amy and Soderholm (13). Thermachromatography using serially connected columns represents a modification of temperature programming and is described in a patent issued to Burow (80).
42 R
ANALYTICAL CHEMISTRY
Noteworthy applications of P T G C include the separation of phenylethoxysilanes at temperatures up to 310' C (176) and investigation of motor fuels over a wide temperature range (44). Pyrolysis. Trends in t h e pyrolysis technique, including apparatus, were discussed in reviews by Levy (379,373). Other reviews are directed toward the application of pyrolysis to polymers and copolymers (623), t o the investigation of thermal stability and microstructure of these materials (478), and t o structural identification (320). Papers presented at the International Symposium on Pyrolysis and Reaction Gas Chromatography held in Paris in September 1966 were published in the January, February, and hlarch 1967 issues of the Journal of Gas Chromatography. Specific apparatus discussed includes the familiar platinum spiral filament (345), a modification to a syringe which allows the injection of the volatile pyrolyzate into a standard chromatograph injection port (535). and a n improved pyrolysis furnace with reported 10.5' C control (128). *\ small induction furnace and necessary electronic circuitry was designed by Simon and Giacobbo (555), and a simple pyrolyzer, costing less than $100 also was described (266). Fragmentation chromatography, in which the organic material is decomposed in a n electrical discharge, was discussed by Sternberg and others in several publications (88, 286, 563, 5 6 4 ) . This system is commercially available, and its reproducibility is carefully assessed in these publications. h pyrolysis device was devised (494) in which the carrier gas is heated t o pyrolysis temperature before contacting the sample. Another unit incorporates a magnetic temperature oven (141). Juvet and coworkers (297) recommend photolytic degradation as more reproducible than standard pyrolysis techniques, less complex in degiadation patterns, applicable to gas, liquid, and solid samples, and useful, when combined with retention data, in structural identifications. Pyrolysis was carried out on different support materials such as glass wool, quartz, steel,.gold, and silica to evaluate catalytic activity (619). Or6 and associates (455) investigated the products from the pyrolysis of isoprene by coupling a mass spectrometer to the pyrolysis-GC apparatus, while a similar combination was used to investigate the pyrolysis of peptides (624). Dual column analysis of pyrolyzates from proteins is expected to be useful in characterization work (503). Wolf and Rosie (651) investigated the pyrolysis of simple organic molecules and determined t h a t the main products were hydrogen, carbon monoxide, water, methane, and lower molecular weight oxygenated compounds at the tempera-
ture of operation investigated. A tubular thermolysis unit was used by Cramers and Keulemans (114) to investigate the pyrolysis of volatile organic materials with the purpose of relating the decomposition pattein to the structure of the parent molecule. Structure elucidation by pyrolysis has been applied to various compounds, including amino acids (556) and the phenothiazines (166). Steric effects on the pyrolysis of tertiary octyl alcohols was the subject of another study (401), and the benzalkonium salts were observed to pyrolyze mainly into amines, olefins, and aldehydes ( 5 9 9 ) . Anionic and nonionic surfactants were pyrolyzed in a n acid medium to give characteristic pyrograms (374). Metal chelates, amino acids, and alkylbenzene sulfonates were pyrolyzed from dilute solution (79), and the pyrolysis of cyclopropene fatty acids on silica yielded a number of olefin isomers which were subsequently ozonized and hydrogenated for further identification (287). -4queous solutions of quaternary fatty acid salts were almost quantitatively converted to their methyl esters by injection into a 300'C injection port ( I % ) , and microorganisms were differentiated by their unique pyrograms, (501). The pyrolysis of bone was carried out with a temperature-programmed pyrolyzer to distinguish it from other materials (650),and proteins, peptides, and amino acids were investigated by the combinations of pyrolysis, GC, and mass spectrometry (416). Oyama and Carle (459) utilize pyrolysis-GC for the qualitative detection of life in space by means of typical protein pyrolysis patterns. Antibiotics were differentiated by pyrolysis a t two temperatures (72), and Kirk (525) indicated the degree to which a crime laboratory can make effective use of pyrolysis-GC including the identification of poisons, plastics, paints, bacteria, and proteinaceous matter. Lehrle and Robb (S65), pioneers in the pyrolysis field, made a quantitative study of polymer degradation using pyrolysisGC in which they calibrated with known mixtures and utilized characteristic peaks for determining the composition of homopolymers, random copolymers, and block copolymers. A theory of hydrocarbon chain degradation was presented by Zulaica and Guiochon (66?),and a review of the pyrolysis of polymeric organic materials also was presented ( 5 2 ) . The problems of pyrolysis were discussed by Lebel (362) who noted limitations in applying the technique t o the analysis of rubber and copolymers. The pyrolysis-GC of synthetic and natural rubbers provide a rapid means of identification when used in conjunction with a n HzS04 column to differentiate unsaturated products (8). Instrumentation of pyrolysis was
( i i w u w d by Dimbat and Eggertsen (133) \\ itli particulai application t o the nicahuieiiiciit of co1)olynier coatings on pfilwr. .liiotlicr publicatioii from this lnlioi atory dibcuwd the determination oi thcrmal qtability of polymers by iiicaii4 of a l)yrolyzcr attachment and a chiomatogralih (146). A large number of pyrol) sis 1)roducts derived from hydrocai boil polymers and copolymers IT eie identified by multiple-column chi omatography (666),and additional identification work on macromolecular compouiids n as performed by Ciaiietti aiid Pecci (101) and Vacherot (603). Elucidation of polymer microstructure and degradatioii niechaiiisms through a study of model polymers has been carried out (292). Polystyrene was polymerized in the 500-1000°C range (138, 595) and qhowed no significant difference in pyrolyzate compositions for different molecular weight polystyrenes. Polystyrene-l)olyethyleiie graft copolymers, however, were decomposed reproducibly to yield the styrene content in a n analytical procedure involving pyrolysis (284), and polymers have been studied by the pyrolytic technique after oxidative degradation (529). Pyrolysis was also effectively used to study polyester resins (46), in the identification of elastomers (IO$), and in the investigation of various natural and synthetic fibers ($3S). Flame retardants on cellulose mere investigated using pyrolysis by Byrile and associates (82), and differences between commercial automotive brake linings were established by pyrolysis-GC (162). Soiivolatile petroleum fractions were investigated (369),and a method was proposed for the analysis of sulfolenes by this technique (405). MISCELLANEOUS
X number of new applications for GC were developed during the past two years including the determination of high molecular weights (Cod,, the determination of relative humidity (622), estimation of the effective diffusivities of catalysts (392))a n automated method for evaluating the gas phase efficiency of cigarette filters (632), a gas chromatograph for nionitoring tract contaminants within the Xpollo space craft (274, 590), the separation of isotopes aiid isotopic molecules (61, 7 7 ) ,and the separation of diastereoisomeric compounds (196,227, 308). Schopf (94),in the study at SASd's Ames Research Center, separated the S-trifluoroacetylbutyl esters of 22 amino acids extracted from a sample of Pre-Cambrian sedimentary rock and showed the formation was at least 3.1 billion years old by rubidium-strontium isotopic dating techniques. The hydrocar boils present in Pre-Cambrian rock (456)and in five different types of meteorites (457),including noncarbonaceous
chondrites, graphite nodules from iron meteorites, and Wiik Types I, 11, and 111, were evaluated by Or6 and Sooner. Hydrocarbons in Jfoonie crude oil from Queeiisland, Australia, weie identified by G C and shown to be 200,000,000 years old (60g). The possible abiogenic origin of naturally occurring hydrocarbons has also received some attention (487). Physical-Analytical Applications. Wurst (655) found a close correlation between the parachor and chroinatographic elution d a t a for organic and silico-organic materials. Sumerous authors have applied GC measurements to the evaluation of thermodynamic quantities (337, 403), kinetics (97,201, 208, 608), and chemical equilibria (154,500, 610). Johnston (288) described a n experiment for the physical or analytical undergraduate laboratory for which kinetic-GC d a t a can be collected in three hours. Purnell (496) summarized various approaches to the study of compleviiig reactions by GC and developed a generalized retention theory for each. il novel approach for evaluating the structure of nonvolatile metal chelates from GC d a t a was outlined by Juvet (294). Separation of Metallic Compounds. Owing t o the rapid growth of research in the separation of inorganic compounds, a separate section will be devoted t o the subject in this review. Two comprehensive reviews covering advances in the separation of inorganic compounds, including permanent gases as well as transition metal halides, alkyls, chelates, and halides were published in this biennium (298,486). A U. S. Patent was issued (37) for the purification of metallic or semimetallic substances by passing the solute through a suitably packed column a t a temperature normally between 500-3000" C, and the procedure mas illustrated by the production of high purity cadmium from a cadmium and mercury mixture. Uranium and thorium mere determined bv a n indirect method (523) involving formation of the metal hydrides followed by selective decomposition of UH3 and Th4H15 at 325" C and 600" C, respectively, and qliantitative measurement of hydrogen released by GC. A number of papers have appeared on the separation of metal chlorides and fluorides. Zado and Juvet (659) studied the elution characteristics and thermodynamics of 11transition metal chlorides on 12 inorganic fused-salt liquid phases and showed, among other things, t h a t ?jbCl6 and TaC15 are readily separated on a 2-inch column containing the InClrTICl eutectic mixture as liquid phase. Stumpp reported briefly (566) on the separation of binary mixtures of A1C13, GaC13, TaC16, SbC15, SbOC13, ZrC14,aiid HfC14 at temperatures ranging from 210450" C using a 2.5-meter
column filled with synthetic:, highly purified graphite. Halocarbon 6-00 was recommended as liquid phase in the separation of certain lowboiling metal chlorides (125). Rijnders and coworkers (547) eluted 19 inorganic chlorides boiling between 50-250" C using 15yoKel-F 40 on Haloport F as column packing and a gas density balance as detector. Akxuracyapproaching lYOwas obtained by Sievers ct a!. (553) in the quantitative determination of titanium, as the tetrachloride, in oxide mixtures such as hauvite using a stainless steel column packed with 15y0 Histowax on GasPack F. A homologous series of chlorosilanes with the general formula Si,C~?,+Z prepared by chlorolysis of silicon dichlorides under pressure may be separated on a column containing 20y0 silicon oil 550 on Celite (46'8). T h e silicon phosphorus, and boron chlorides and bromides present in the atmosphere formed upon epitazial deposition of silicoii in semiconductor processes weie analyzedby GC (451). Metals, alloys, metal oxides, carbides, sulfides, and nitrate and acetate salts of certain metals including tungsten, molybdenum, rhenium, osmium, silicon, uranium, boron, qulfur, selenium, tellurium, and vanadium were quantitatively determined bv Juvet and Fisher (296)by 111 situ fluorination in a reactorsample inlet port and separation on a column packed with 15Y0 Kel-F 10 oil (a polytrifluoromoiiochloroethylene) on Chroniosorb T (polytetrafluoroethylene). Tellurium, molybdenum, and uranium hexafluorides were also separated by Shinohara et al. (&Z), on a polytrifluoromonochloroethyleiie column. By a combination of transpiration and gas chromatographic techniques, phosphorus, carbon, nitrogen, and sulfur fluorides were separated by Rudzitis (514). Chlorine trifluoride, a propellant used in some naval misqiles, was separated gas chromatographically from potential interferences aiid the amount present owing to leakage was monitored a t the 0.01-ppm level using a n electron capture detector containing a 13O-nici tritium source (665). Following the significant work of Eisentraut and Sievers (147) in which 15 trivalent rare earths were eluted from a column of hpiezon on Gas-Pack F a s the 2,2,6,6,- tetramethyl - 3,5 - heptaiiedione chelates (i'thd") a t coluniii temperatures near 185' C, it was reported (552) chelates of 1,1,1,2,2,3,3-heptafluoro7,7-dimethy1-4,6-octanedione ("fod") formed lanthanide compounds of even greater volatility than the "thd" chelates, although several were kolated as hydrates. I n a later publication (551) this ligand was shown t o forin chelates with iron(III), nickel(II), palladium (11), chromium(III), copper(II), aluminum (III), yttrium (I I I ) , and beryllium(I1) stable enough to be eluted ~
VOL. 40, NO. 5, APRIL 1968
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without apparent decomposition, and a n analytical procedure was developed which allowed the quantitative determinations of the iroii in Mesabi iron ore. A comprehensive review in Japanese (16) and several research papers have appeared on the elution of metal fluoroacetylacetonates. As the trifluoroacetylacetonate derivatives, metals eluted include iron, copper, and aluminum (434, 437) , beryllium in trace amounts (510), beryllium, copper, magnesium, manganese, zinc, aluminum, chromium, iron, rhodium, indium, gallium, cobalt, and thorium (583). Fujiiiaga and Ogiiio (173) made the interesting observation that a plot of the logarithm of the relative electron capture coefficients of metal trifluoroacetylacetonates us. the wavelengths of masimumabsorption of these compounds in the ultraviolet region is linear. X number of papers were also published on separation of metal hesafluoroacetylacetonates. Elution of the hesafluoroacetonates of cobalt and ruthenium (615) aiid of beryllium, cobalt, copper, manganese, nickel, lead, aluminum, chromium, iron, gallium, rhodium, and even the alkaline earth, magnesium, has been claimed ( 1 7 ) . Aluminum 2-thenoyltrifluoroacetonate was also eluted without appreciable decomposition (135) as were the copper and nickel /+ketoimine derivatives, bis(4-imino-2-pentanono)copper and -nickel and bis(N-methylsalicylaldimine) copper (439). A third major approach to the GC separation of metallic compounds is elution in the form of metal alkyls. Papers have appeared on the determination of lead alkyls in gasoline using the electron capture detector (344), the conventional flame ionization detector (558), and atomic absorption spectroscopy as the detector ( 3 4 0 ) . I n the latter work, it was noted that the atomic absorption detector waq less sensitive for lead alkyls than the ionization detector but had the advantage of a high degree of selectivity. The various methyl ethyl lead alkyl., hIprPb, MesEtPb, hlezEtJ’b, AleEt3Pb, Et4Pb as well as EtCl?and EtBr2were separated on a 150-cin column containing 20% on 1,2,3 - tris(2cyaiioethoxy)propaiie Chromosorb P precoated with 1% potassium hydrovidc and operated at a column temperature of 83” C (559). The gas chromatographic separation of organosilicon compounds also received considerable investigation. Linear aiid cyclic methylsiloxanes with molecular weights up to appro.;imately 3000 were separated using a diphenylsilosanedimethylsilosane copolymer L gum as liquid phase (S6). Czech workers determined the pyrolmis products of a number of 1)hciiylmethylsilaiies (400) aiid list retention data for 33 polyorganosilosane compounds on Apiezoii and E-301 silicone rubber columns (167). 44 R
ANALYTICAL CHEMISTRY
Garz6 and Fritz (179) modified a flame ionization detector by continuously adding methane to the hydrogen carrier gas and found organosilicon compounds were selectively detected as negative peaks. Gars6 and coworkers (178) also compared the retention indices for silicon, germanium, and tin organometallic compounds on a number of liquid phases. Retention data were tabulated (162) for the methyl, ethyl, and propyl selenides and diselenides on polynietapheiiyl ether, Carbowas 20h1, aiid silicone oil DC-550. The separation of organomercury compounds (277) and organotin cornpounds (654) were also reported. Biochemical Applications. Over 200 papers have been published during this biennium on the application of GC to the analysis of st,eroids and related compounds. Several reviews covering the analyses of steroids have appeared (668, 35.?, 653). D r y injection devices were dev.eloped (16, 396) to overcome limitations in accurate measurement of steroids when fluid injection is used. Knights (555) determined retention indices of various steroids on six columns and discussed application of this technique to structure analysis, Sterols are often separated as the dimethylsilyl and trimethylsilyl derivatives (361, 578, 60.5), but chloromethyldimethylsilyl (687) and bromomethyldimethylsilyl (143) ether derivatives are recommended to increase sensitivity toward the electron capture detector. Other derivatives studied iiiclude enol hept’afluorobutyrates (89), ethylene-thioketals (664), sulfonates and the effect of structure upon the nature of their elimination reaction (604). Free sterols were also quant,itatively separated on XE-60 and JXR (a dimethylpolysiloxane) liquid phases. ‘C‘rinary steroid excretion at levels as low as 0.025 mg/24 h r were studied in normal subjects aiid subjects with various disorders (506). Urinary testosterone determinations made ou men, women, and children (621) were compared with those from hirsut,e and virilized females ( l , 9 4 ) . Measurement of the sterols present in seafood (346), algae (,?6)]Irish moss (Chondrus crispus) (560), ovulation control tablets (169), and lactating and ketosed cows (243) are but a few examples of the many applied studies involving GC analysis of steroids. Gas chromatography has proved useful in the aitalysis of many drugs (541) including vitamin .4 and its isomers (614) aid vitamin C (61s) as the trimet,hylsil!;l ether derivatives, vitamiil D2 and DS (25), vitamin E ( 4 8 3 ) , vitamin K1 (375), vitamin Ks (111), amino ac,ids (144, 18.4, 155, 287, 485, 561) and peptides (635), and alkaloids (397). GC has also been used in the detec-
tion and identification of 29 strain.; of bacteria (244), and Mitruka and Xlexaiider (466) in a very recent article report t h a t by sensing certain bacterial products a t iiano- or picogram levels with the electron capture detector, as few as 10 bacterial cells can 3ometimes be detected. Carbohydrates are most often determined as the trimethylsilyl derivatives (96, 4 3 5 ) , but alkyl ethers, acetals, ketals, and acetate esters of earbohydrates have also been chromatographed (.51, 4 4 6 ) . The saccharine present as an artificial sweetening agent was determinpd as the S-methylsaccharin derivative (205). Finally, a few iiovel applications, including the determination of differences in milk composition from water buffalo, goats, cows, and northern fur seals (go), the determination of the composition of larval blood of silkworms (573), and the evaluation of the sex attractants of the black carpet beetle, Attagenus megatoma (554), are a n indication of the great versatility of gas chromatography LITERATURE CITED
(1) Abel, E.
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