(494) Vaintraub, I. A., Biokhimiya 28, 661 (1963). (495) Valberg, L. S., Holt, J. M., Szivek, J., ANAL.CHEM.36, 790 (1964). (496) Vanden Heuvel, W. J. A., Gardner, \ -
W: L., Horning, E. C., ANAL. CHEM:
36, 1550 (1964). (497) Vanugopalan, M., Kutschke, K . O., Can. J. Chem. 41, 548 (1963). (498) Vithayathil, A. J., Ternbert, J. L., Commoner, B., Nature 207,1246 (1965). (499) Voorspuij, A. J. Z., van der Slik, W., Chem. Weekblad 59, 405 (1963). (500) Vul’fson, N. S., Stepanov, V. M.,
Puchov, V. A., Zyakun, A. M., Zsv. Akad. Nauk SSSR Ser. Khim. 1963, p. 1524; C.A. 59, 15586a (1963). (501) Wacker, W. E. C., Iida, C., Fuwa, K., Nature 202, 659 (1964). (502) Wagner, H., Goetschel, J. D., Lesch, P., Helv. Chim. Acta 46, 2986
(1963). (503) Wainerdi, R. E., Fite, L. E., Steele, E. L., AEC Accession No. 33464, Rept. No. NASA-CR-52997; C.A. 62, 10795e (1965). (504) Walborg, E. F., Jr., Christensson, L., Anal. Biochem. 13, 186 (1965). (505) Walborg, E. F., Jr., Christensson, L.. Gardell. S.,Zbid., D. 177. (506j Wallach, ’D. F.* H., de PerezEsandi, N., Zbid., 7, 67 (1964).
(507) Wallach, D. F. H., Steck, T. L., Zbid., 6, 176 (1963). (508) Walter, C., Arch. Biochem. Biophys. 110, 244 (1965). (509) Walter, H., Selby, F. W Brake, J. M., Biochem. Biophys. Res. 8ommun. 15, 497 (1964). (510) Watanabe, S., Frantz, W., Trottier, D., Anal. Biochem. 5,. 345 (1963). (511) Watson, J. T., Biemann, K., ANAL. CHEM.36, 1135 (1964). (512) Zbid., 37, 844 (1965). (513) Weissblauth, M., ed., “Quantum Aspects of Polypeptides and Poly-
nucleotides,” Interscience (Wiley), New York, 1964. (514) Wells, M. A., Dittmer, J. C., Biochemistry 2, 1259 (1963). (515) Wendlandt, W. W., Southern, T. M., Anal. Chim. Acta 32, 405 (1965). (516) West. C. D.. Hume. D. N.. ANAL. . CHEM.36, 412 (i964). ’ (517) Wevaand. F.. 2. Anal. Chem. 205. 406 (1$6j). ’ ’ (518) Whipple, H. E., ed., “The Lasers,” Ann. N . Y . Acad. Sci. 122, Art. 2 (1965). (519) . . Whitaker. D. R.. Mittelstadt. K. A., Can. J. Blochem. 42, 149 (1964). (520) Whitby, L. G., Brit. Med. J. 2, 895 (1964): (521) Wieme, R. J., “Agar Gel Electrophoresis,” Elsevier, New York, 1964.
(522) Wilcox, W. R., Friedenberg, R., Back, N., Chem. Rev. 64, 187 (1964). (523) Wilks, P. A., Jr., Brown, R. A., ANAL.,CHEM. 36, 1896 (1964). . (524) Wilson, A. T., J. Immunol. 92, 431 (1964). (525) Windle, J. J., Wiersema, A. K., Clark, J. R., Feeney, R. E., Biochemistry 2, 1341 (1963). (526) Winsten, S., Friedman, H., Schwartz. E. E., Anal. Biochem. 6. 404 (1965). ’ (527) Winter, L. N., Albro, P. W., J. Gas C h r m t o g . 2, 1 (1964). (528) Winzor, D. J., Nichol, L. W., Bioehim. Biophys. Acta 1 0 4 , 1 (1965). (529) Winzor, D. J., Scheraga, H. A,, Biochemistrg 2, 1263 (1963). (530) Wood, J. L., Quart. Rev. 17, 362 (1963). (531) Yagi, Y., Onoue, K., Stelos, P., Pressman, D., Science 146, 404 (1964). (532) Yapel, A., Lumry, R., J.Am. Chem. SOC.86, 4499 (1964). (533) Yonda, A., Filmer, D. L., Pate, H., Alonzo. N.. Hirs. C. H. W.. Anal. Biochem. 10. 53 (1965). (534) Yphantfz, D: A.,‘ Biochemistry 3, 297 (1964). (535) Zettner, A., Seligson, D., Clin. Chem. 10, 869 (1964). (536) Zosimovskaya, A. I., Dokl. Akad. Nauk SSSR 151, 687 (1963); C.A. 60, 920h (1964).
Chromatography Erich Heftmann, Western Regional Research laboratory,’ Albany, Calif., and Division of Biology, California lnstifofe of Technology, Pasadena, Cali?.
T
article is based on chromatographic literature that has come to the author’s attention since his last review in 1964 (767), from December 1963 through December 1965. For the sake of completeness, some less original or less important contributions have been included, but articles dealing with routine applications of known methods or with techniques covered by other reviewers in this issue have been omitted. Recent developments in chromatography have been reviewed by other authors (743, 853, 865, 1138, 11.40, 1183, 1257, 1335) and the Second Edition of Heftmann’s “Chromatography” (768) is now in press. Books and review articles on more specific HIS
HISTORY
The history of chromatography has been outlined by Zechmeister (2313), and Hais (717) has written a history of paper chromatography. 1 A laboratory of the Western Utilizazation Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture. Work conducted under a cooperative agreement with the California Institute of Technolog a t the Division of Biology, Pasadena, dhif Requests for reprints should be addressed to Albany, Calif.
topics will be cited under the appropriate headings below. This is the place to record that the recipients of the fifth and sixth American Chemical Society Awards in Chromatography were Stephen Dal Nogare (38) and Kurt A. Kraus (39),who have made important contributions to gas and ionexchange chromatography, respectively. Harold H. Strain (284) was presented the twentieth Midwest Award of the ACS for his role in the development of Chromatography. THEORY
General. Strain (1994) has reviewed differential migration methods and outlined the position of chromatography among them. Although such processes as zone melting may be considered as chromatographic techniques (1545), he includes only those involving the flow of a solvent or electric current (electrochromatography). The principles of chromatography have also been discussed by Senyavin (1838). Giddings as well as Rachinskii have published books (6.30, 1633) and reviews (631, 1632) on the dynamics of chromatography. Theories developed in connection with gas chromatography
have been shown to have general validity in calculating the efficiency of various types of chromatographic systems (629, 639, 652, 825, 1088, 1089, 1163), and a reduced plate height equation was formulated, which may serve to correlate data obtained from them (632, 1923). These theoretical studies show that liquid chromatography has a much greater potential than is realizable with present-day instrumentation, Separability has been considered from the standpoint of interactions between migrants and chromatographic systems (81, 135), and overlapping peaks have been evaluated by analog computers (7) and probability methods (777). Rackow (1634) has discussed the thermodynamic meaning of chromatographic information, while Klein, KunzeFalkner, and Tyler (1009, 1011) have used a computer to analyze the validity of chromatographic data. Pertsev, Krasovs’kii, and Pivnenko (1537) have taken on the problem of the choice of chromatographic methods, a topic which deserves more intensive study. Adsorption. The theory of adsorption in relation t o chromatography was reviewed by Snyder (1914),who has published extensively on linear elution adsorption chromatography (1911,1917, VOL. 38, NO. 5, APRIL 1966
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1919, 1920, 1924). An equilibrium separation factor for liquid phase adsorption chromatography (1955)and the minimum amount of adsorbent required for separation (575) have been calculated. Other theoretical work includes: a study of the interaction of adsorption and diffusion effects (1087),a theory of double zoning (577), as well as some work on frontal analysis (651, 1082). h-iederwieser and Brenner (1423) have presented both theory and practice of polyzonal thin layer chromatography (TLC)-Le., TLC with multicomponent solvent systems that separate in the course of development. A theoretical treatment of repeated development in spread-layer chromatography was published by Starka and Hampl (1974). Partition. Theoretical aspects of liquid-liquid partition (633) and particularly of paper chromatography (PC) (452)have been reviewed. Vink (2167)used a digital computer to simulate the operation of a partition column. The selection of solvent systems has been the subject of several theoretical studies (150, 297, 784, 1655, 2080). The results from P C may be applied to bulk extraction methods (922, 1933). Studies have been made of the water content of the paper (2091),of changes in the stationary phase during development (2232), and of the diffusion of solvents into the paper (1719). The mechanisms of zone spreading (1162) and of the partial separation of solvent systems (1314)have also been investigated. Solvent effects on RF values in PC have been correlated by Connors (329), and equations for the optimum separating conditions in repeated development have been derived (1716, 2081). A relation between RF and temperature gradient in thermal PC was established (641),the validity of Martin’s equation in reversed-phase PC was demonstrated (3%’),and a general method for the identification of unknown spots from the R p values of two reference spots was proposed (587). Bush (238) has discussed applications of the RMtreatment in chromatographic analysis, and correlations of RMvalues with other parameters continue to be published (729, 1141, 1927, 1929,1932). Several studies have been concerned with the effect of the pH of the solvent system on the efficiency of separating organic electrolytes (43,1928,1931,2206). Gel Filtration. Theory and practice of gel filtration have been reviewed by Determann (411) and by Gelotte and Porath (612). The nature of the process has been discussed (1347),and an analog computer was constructed t o simulate it (1132). Ackers (11) has calculated separation coefficients for macromolecules, Squire (1951) established relations between molecular weights of macromolecules 32 R
ANALYTICAL CHEMISTRY
and their elution volume, and Winzor and Nichol (2256)found that the elution volumes are a function of concentration. A general transport equation was derived for crystallization chromatography, in which solvent and temperature gradients are combined (1805). TECHNIQUES AND APPARATUS
Two introductory texts on chromatographic techniques have appeared (1, 657). Wohlleben (2160)has written an introductory article on chromatographic apparatus and Taylor (2068) has expounded some simple chromatographic demonstrations for the classroom. Columns. Review articles on techniques of liquid column chromatography have been written by Snyder (1915) and Wohlleben (2261), and three reviews have dealt with automation of these techniques (491, 752,1399). I n addition, one book has been published on industrial methods of adsorption chromatography (2139), one on molecular sieves and their uses (1934, and several reviews on gel filtration methods (308, 411, 612, 809, 1551). Other reviews have been concerned with cellulose powders (692) and silver nitrate-impregnated adsorbents (918) for column chromatography, with reversed-phase partition chromatography (75,766), and with chemical changes induced by the passage through adsorption columns (788). A student experiment in column chromatography has been published (1263). The determination of the activity of alumina by spread-layer chromatography has been described (783)and also the preparation and use of new types of alumina (1578)and of specific silica gels (488, 1515). Other sorbents studied include: carbon black (1365), silk fibrion (24),factice ( a polymer derived from soybean oil) (799), porous glass (728),spherical agarose (800),and a three-dimensional polymethacrylate (2248). Methods were described for packing alumina columns (1303), for preparing permanent silica gel columns (425), and for automatic packing of Sephadex columns (2246). For alumina of standardized activity the water content of the eluents must be properly adjusted (789). A (3:2) mixture of CF3CCl3-CHzClz is recommended for eluting volatile materials from alumina or silica columns (59). A modified method of Celite partition chromatography was published (1645),and an interesting partition column was constructed from compartments separated by differentially permeable partitions (98). The dry column technique uses TLC adsorbents; resolution comparable to TLC is claimed when development is stopped before the solvent reaches the bottom of the column (1180). Extru-
sion of a microcrystalline cellulose column is said to yield resolution superior to elution (2269). Sample applicators have been devised for liquid column chromatography (241, IlZO), and also a number of solvent feeders (534,1168, 1673) and pressure regulators (257,346, 2295). New designs have been published for automatic stepwise elution (227,793,1179, 1728) and gradient elution (771, 780a, 1125, 1694, 1699, 1775, 2027, 2 0 6 8 ~2274, ~ 2297). The principles of gradient elution have been reviewed by Dorfner (439) and by Snyder (19131,who also published on its theoretical aspects
(1918). Column designs were developed for reversed-flow gel filtration (1706), for remote control handling of radioactive materials (1136)and for automatically stopping (1S07) or dividing (248) the effluent stream. For many applications, specially constructed multiple columns, either in series (137,598, 525 2072, 2117) or in parallel ($140,2277), have been recommended. A large number of new automatic fraction collectors have been described (162,278, 782,943, 11 23, 1208, 1366, 1613, 1868, 1869,1925,2101,2266). It is also possible to absorb the effluent on a moving strip (399),which can then be attached to sheets of filter paper for monitoring by PC (1900). While eluates may be assayed by a great variety of chemical, physical, and biological (2022) methods, those which most readily lend themselves to automation will be the most important ones in the future. These include: recording colorimetry (660,1552,1806,1891,2069, 2162), fluorimetry (1069),and refractometry (189,1119), and the continuous determination of radioactivity (1178, 1381, 1891, 2119). Chromatopolarography has been reviewed (890, 1862), and the use of voltammetry (2060), controlled-potential coulometry (903,2044), and high-frequency methods (66,879)in automatic analysis have been reported. The application of gas chromatography detectors, such as ionization detectors (712,884,885,1818, 1992) and the katharometer (1381), to liquid chromatography is in the beginning stages, but shows great promise. Paper Chromatography. “Paper Chromatography, A Comprehensive Treatise,” edited by Hais and Macek (723), has appeared in English, and the laboratory manual on “Paper and Thin-layer Chromatography and Electrophoresis” by Smith and F’einberg (1902)is now in its second edition. I n addition to reviews on techniques of PC in general (502,691, 1210), articles have appeared which cover, more specifically, circular (1251), centrifugal (417 , 2289), and preparative PC (1616), equipment (2262) and paper (694, 1225) for PC, sample application (718), development
(1224, 1226). detection (718, 1223), determination ( 7 1 S j lZ24), and radiochemical methods (119). Xew chromatography sheets include a special short-fiber paper (1227) and a polymeric carrier of nonpolar stationary phases (1555). A nen- micropipet (1991) and a large number of saniple aplilicators (72, 163, 332, 393, 400,683, 1310, 1548, 1725, 1960, 2102), suitable for both P C and T L C , have been described, Other equipment in the recent literature on P C includes: spot driers (82, 31 1 , 2074), a constant-temperature box (ZOO), devices for equilibrating the paper (624, 1072, 1321) and starting the development automatically (1012, 13S4 , 1534), apparatuses for centrifugal chromatography (1210, 118S, 12.42, 2161), spraying equipment (229, 429, 516, l g g ? ) , rulers for measuring RF values (1066, 17S3), a nuniber of elutors (31, 1056, 1S02, 2141) and densitometers (26, 50, 95’1, 1197, 1609, 1661, 1996, 2039), a scaiiiiing fluorometer (1624), and several radioclironiatograiii scanners (125, 90G, 16’65, 1949), including autoniatic equipment for the evaluation of two-diniensiolial radiochroiiiatograiiis (1844,2161). Various techniques of P C have been espounded for beginners (34, 2203) and several ne\\- ones have been described. Aerosol saiiiples niay be spotted by placing the origin of the chromatographic paper in the collector (2324) and products of bacterial nietabolisiii may be directly transferred to the paper (1989). The solvent flow may be accelerated in awending chromatography by keeping the paper inclined (239) aiid reduced by cutting the paper into certain shapes (1 i 3 4 ) . Development a t elevated temperature is more rapid and gives better results than at room temperature (288). One nen- preparative technique is based on radial development (1688) and another one, called stereochroiiiatography, on ascending developiiieii t in a block of compressed cellulose powder ( I 546). The reproducibility of R F determinations has been examined (211, 523) and the relative advantages of several RP scales have been compared (103). Calibration standards for tno-dimensional P C may be run siniultaneously in separate areas of the same sheet (226). Chromatographic spect,ra are not only suitable for identification purposes, but niay even give clues to structural details of aromatic compounds (538). Systematic chromatography involves the use of a preconceived set of solvent’ systems, which serve to classify organic conipounds (I3 ; s ) . ~ltraviolet-absorbiiig conipounds niay be detected by photography (942) or by printing on photocopying (1330)or diazo (1947) paper. Fluorescent zones are documented by color photography (1701) and nonfluorescent coiiipounda are determined by spectrofluorometry after treatment with an appropriate
reagent (1970). Impurities interfering with sl:ectrcphotoiiietric analysis may be removed by preliminary estraction procedures (386,917),but TLC obviates this interfeieyce (540). Photonietric evaluatiocs in transmitted and reflected light have been compared (164, 776,895, 1610, 1784) and transmission measurenieiits were generally found to be superior; accurate reflectance iiieasurenieiits requiie strictly controlled conditions (10). Gravinietiic analyais of separated zones has been proposed (826). and organic compounds lyhich absorb iodine may be eluted and deteriiiined iodometrically (452). For radioactive conipounds, new methods of autoradiography (280, 1182, 1587, 2254) and quantitative determination in situ (794, 913, 2240) have been described. Seutron activation of paper chromatograms, reviewed by Rakovic (1649), is applicable to biological compounds after conversion to derivatives with activatable atoms (133, 1981). Thin-Layer Chromatography. Stahl’s “Thin-Layer Chromatography” has finally been translated into English (1962), and another monograph on T L C has recently appeared in Russian (20). The proceedings of a T L C symposium held in 1963 were published in book forin (1255’). A great nuniber of review articles on TLC are now available, dealing with general techniques (21, 643, 592, 735, 868, 882, 1002, 1 0 3 9 , 1 1 8 ~1235,1246, , 1351,1402, l 4 7 9 , 1 5 5 0 , 1 S l ~1722,1S82,1963,1965, , 2070,2210, 2283), advantages over other chromatographic methods (901), apparatus (1961, 2262), circular technique (1?78),T L C n-ithout binders (461, 798, 1111 , 1331), various sorbents (1801), hydroxylapatite layers (808), cellulose layers (695,2271),impregnated sorbents (1357), particularly silver nitrate-inip r e p i t e d silica gel (181, 918), TLC of radioactive materials (1063, 1861), and combination with infrared spectroscopy (1907). Student experiments (218, 1239) and a lecture demonstration (515) of T L C have been published. Various siniple and inespensive pieces of equipment have been described (684, 221 7 ) . Several adsorbent spreaders have been proposed (124, 155, 270, 514, 433, 519, 1713, 1155)) including a type producing an adsorbent gradient (threedimensional TLC) (1956, 1967, 1959). Plates may also be coated by spraying them with the adsorbent slurry (1352) or allonkg it to sedinient on iiiiniersed plates (1889). Thin layers are prepared from Silica Gel G, slurried with acid, base, or Iyater (520), to which alcohol may be added to improve reproducibility (1505), alumina of constant activity (606), hydrated silica gel (1564), homemade niistures of silicates and plaster (591), microcrystalline cellulose (2210), starch (St??),Sephades with agar (1586), urea-formaldehyde resin (53),polvdered
glass (219, 1074, 1639), or anodically osidized aluminum (395). Inorganic phosphorescent materials (11911 or pyrene derivatives (2106) may be incorporated in the layer. Carbosymethylcellulose appears to have some advantages over plaster as a binder for silicic acid (1463). Systematic changes in mobility have been produced by changing the itioii ( I T d l ) , and the ica gel is shortened by mixing it n-ith Celite (2133). The use of plates with different layers, side-by-side, has been proposed (139). Adsorbent layers are applied to frosted glass plates (2263),metal plates (215), aluminum foil (1062, 1631): or plastic sheets (1030, 1621). Reuseable plates have been prepared by spraying iiiolten adsorbents onto rigid supports (604). Special equipment for TLC includes: various sample applicator.< ( 7 7 , 321, 496, 1345, 1760, 2057) and application chambers ( 1 7 , 365) 1421), narrow developing chambeys (909, 739, 5’81, 1591, 1724, 2117) aiid an adsorbent sandwich (195S), self-contained chambers of adsorbent layers in test tubes ) or funnels (13S2), sorbentcovered microscope slides (92, 1390, 1860) and glass rods (509), apparatus for starting and stopping development (2054) and for circular (2110) or centrifugal TLC (106S, 1703), a cover plate for staining a t elevated temperatures (1693), a high-resolution zonal scraper (1908-1910), suction apparatus for collecting zones (648, 1785), and elution set-ups (648, 1207, 1760, 2142). Several useful techniques of TLC have been esplained (216). For the application of a saniple in the form of a line, especially in preparative work, it niag be run up to the origin in a solvent in which it migrates Tyith the front (512, 2105) or applied between tn-o parallel cuts, which are later filled in (328). The effluent from gas chromatographs has been collected directly on thin-layer plates for further analysis (886, 926, 1405). TLC was also conibined with the ring oven iiiethod (1478, 1781), and organic conipounds have been subjected to various reactions prior to development (1280). The efficieii-y of thin-layer plates is said to be increased by coating them on both sides ( 1 100) or by siniultaneously developing a stack of plates (chromatostack), appropriately spaced (1449). Several techniques of preparative TLC have been devised (130, 1484, 1827), including the chroniatostick (89), a bar cast from Silica Gel G and sectioned after ascending development, which is entirely analogous in principle to the stereochromatography (l546), mentioned above. If t’he sample is sniall, iiiipurities in the adsorbent may interfere (605). Honegger (817 ) has produced activity gradients on activated silica gel plates by dipping them into successively VOL. 38, NO. 5 , APRIL 1966
33 R
shallower layers of aqueous methanol. Eluotropic series for TLC have been published (473, 844). Continuous separation of a mixture, introduced near the apes of a triangular thin-layer plate, is produced by feeding two solvent systems to its sides (2115). Continuous development may be achieved by allowing the solvent to evaporate from the end of the plate (1142, 2106). -4 gradient elution method of TLC has been devised (1424). Factors that affect RF values in TLC have been evaluated (372, 1852). Siniultaneou reduces the variabi (96). A standardized method of expressing chromatographic data has been suggested (209). Systematic TLC is, of course, analogous to systematic PC, iiientioned above, in establishing a classification system for organic conipounds (2377). Many organic compounds are revealed by quenching the fluorescence nith iodine (1326). During exposure to iodine vapors, a portion of the chroniatoplate may be protected by a cellophane sheet (1412 ) , and self-adhesive cellulose acetate films may be used to peel off and preserve chroniatogranis (1024). For documentation, printing on diazo (468, 1636, 2316) or zinc oxide (1948) paper has been recommended, but chroniatogranis may simply be traced on acetate sheets with a wax pencil (1817). Various quantitative methods have been critically evaluated (1006, 1329,1623),and a densitoiiietric method for transparent’ photographs (2169) as well as direct methods for fluorescelit’ substances (531, 1769, 1830) have been described. Radioactive materials niay be analyzed by a variety of radioautographic methods (546, 908, 1666, 1809), or by scanning (197, 1363, 1807, 1809). Tritium-labeled compounds induce a fluorescence if an equal weight of anthracene has been used in the preparation of the silica gel layer; they niay be detected by keeping it in contact with x-ray film a t low temperatures (1196). APPLICATIONS
Applications of TLC have been reviewed in tabular foriii (223251) and two reviews have been devoted to the application of this technique in organic chemistry (593, 1229). Chroniatography has many important uses in biology (99, 182), in clinical (1496, 1518, 2208) and forensic (6176) laboratories, and in the control of food products (246, 247, 532,690, 2138). Inorganic Compounds. Ritchie’s book, “Chromatography in Geology,” (1679), and the chapter by Nickless and Pollard (1422) cover inorganic chroiiiatography in general. More specific topics recently reviewed include :
34R
ANALYTICAL CHEMISTRY
coluiiin partition chromatography ( 9 @ ) , precipitation chromatography (434), TLC (594, 1580, 2053), PC (927, 1856, 2 l 4 3 ) , TLC of metal complex salts (2048) and of organometallic conipounds (2284),and the chromatography of rare earth elements (476, 1837) and of Be (1521). Coluiiins suitable for cation separations were prepared from aluniina (663, 1890), silica (843, 2171), ferric hydroxide (1164), phosphorites (1348)) hydroxylapatite (982), calcium carbonate (661), sulfides (6‘62)) or adsorbents treated n-ith complesing agents (27, 28, 940). Precipitation chroniatography in gels, containing complexing agents, n-as carried out in colunins or on plates (1856). Sulfur-nitrogen conipounds were separated by adsorption chromatography on aluniina (2166). Many difficult separations were achieved by what is often referred to as reversed-phase partition on colunins, but may also be regarded as liquid ion exchange, especially in cases d i e r e the stationary phase is bis(2-etliylhesy1)phosphoric acid (195>689, 1046, 15&j1 4) nionododecylphosphoric acid (1905),trioctylaniine (1323, 1326), or dipicrylaniine (2076). A4niong neutral stationary phases, tributyl phosphate (513, 711, 929, 2205, 1466, 1604) and other neutral organophosphorus compounds (1322, 1324, 1466, 1467, 2075) enjoy great popularity. Rarely used stationary phases are : tetraphenylboron (2779, methyl isobutyl ketone (555, 556), methyl ethyl ketone ( 1 8 4 , ether (1603), and a film of Hg (172). TLC is applicable to the systematic analysis of all the coninioii cations (649, 760, 2051, 2052) and to their quantitative de t erniina t ion (1828). The layers used are usually either adsorbents (250, 588, 1308, 2278) or carriers of stationary phases, such as triisooctylamine (1261), tributyl phosphate (834, 836), or bis(2-ethylhexy1)phosphate (1553), but the latter has also been used as the mobile phase (377). Salts of heteropolyacids are suitable sorbents for alkali metal ions (2147) and fission products of U (228). Some noble iiietals (827, 828, 2281) and transition nietals (2105) have been chromatographed as complexes. Organotin conipounds (?73), triphenyl derivatives of arsenic, an timony , bisniu t h , and phosphorus (Bl75), and zinc o,o-dialkyl dithiophosphates (608) are readily separated by TLC. TLC is liken-ise used for the systematic analysis of anions (960). A great deal of work has been done on the various acids of phosphorus (64, 111, 112, 251, 315, 1121, 1691). For TLC of halides, the adsorbent is impregnated with silver nitrate (1386, 1980). Methods have also been published for TLC of the acids of sulfur (1829), for thiocarbonates and isotrithiones ( I 702), for chromic acid ~
(1873),and for some radioactive anions (1341 2066). ~
976, 1265, 1547, 1794, 1799). -4s in the other technique.
