ANALYTICAL CHEMISTRY
970 minute, the current becomes appreciable a t -1.5 volts, while a t 6.0 volts per minute a potential of only about -0.9 volt can be attained. ACKNOWLEDG.MENT
The authors gratefully acknowledge the support of the U. S. Air Force in this work. LITERATURE CITED
(1) Clark, W. Jl., and Lubs, H. A., J . Bacterial., 2, 1, 109, 191 (1 917). (2) Day, R . A., and Kirkland, J. J., J . Am. Chem. Soc., 72, 2766 (1950).
(3) Kolthoff, I. M., Lee, T. S., Stocesova, D., and Parvy, E. P., ANAL.CREM., 22,521 (1950). (4) Kolthoff, I. M., and Lingane, J. J., “Polarography,” Kew York, Interscience Publishers, 1952. (5) Marple, T. L., and Rogers, L. B., ANAL.CHEM., 25, 1351 (1953). (6) Page, J. E., Smith, J. W., and Waller, J. G., J. P h y s . & Colloid Chem., 53,545 (1949). (7) Pearson, J., Trans. Faraday Soc., 44, 683 (1948). (8) Randles, J. E. B., Zbid., 44, 327 (1948). (9) Sevcik, A., Collection Czechoslov. Chem. Communs., 13, 349 (1948). (10) Streuli, C. .4.,and Cooke, W. D., ANAL.CHEY.,25, 1691 (1953). (11) Ibid., 26, 970 (1954). ~~
RECEIVEDf o r review Sovember 10, 1953. Accepted March 30, 19.54, Research performed under Contract -4F 18(600)-486 and monitored by Office of Scientific Research, A i r Research a n d Development Command.
Polarographic Determination of the Gamma Isomer Of HexachIo rocyclohexane In the Presence of Other Isomers and Higher Chlorinated Material CARL A. STREULI and W. DONALD COOKE Baker Laboratory, Cornell University, Itbaca, N. Y. In the usual polarographic determination of the gamma isomer of hexachlorocyclohexane, difficulties are experienced from other compounds which are normally present. In particular, heptachlorinated compounds are reduced at a half-wave potential which overlaps that of the gamma isomer. If the dropping mercury electrode is replaced by a mercury pool electrode, the reduction potentials are shifted in such a way that interferences are eliminated. This method has a greater sensitivity than the conventional polarographic method and has been applied to pure lindane, natural isomeric mixtures, concentrates, dusts, and alpha-beta cakee.
T
HE widespread use of lindane as a pesticide has aroused
recent interest in its analytical determination. Because of the difficulty of determination in the presence of the usual impurities, a solution to this problem has been attempted by a wide variety of analytical methods. Simple colorimetric tests have been devised ( 7 , 9), but these are not specific for the gamma isomer, and all other isomers interfere. Bioassay methods which employ the toxic effect of lindane on houseflies have been tried ( 5 ) . These methods lack precision and have inherent uncertainties in any one determination. Polarographic methods have been proposed ( 2 , 4, 6, 10) and are useful, because the alpha, beta, delta, and epsilon isomers yield no diffusion wave, but the gamma isomer is reducible. I n the presence of hepta- and octachlorocyclohexane, the method is difficult to apply. These more highly chlorinated products give a wave which merges into the polarogram of the gamma isomer. Draght ( 3 ) has devised an empirical procedure for surmounting this difficulty if only small amounts of heptachlorocyclohexane are present. Infrared methods have been used for this analysis ( 2 ) , but the other compounds absorb radiation at all wave lengths within the spectrum of the gamma isomer. Higher chlorinated material causes further uncertainties in the analysis. When the method is applicable, however, each individual isomer in a mixture can be determined. All components in the pesticide mixtures can be separated chromatographically ( 1 , 8). I n such procedures, the gamma isomer can be separated and weighed and, therefore, is not dependent on
any interpretive procedures. The disadvantages of this method are the time and technique necessary and the fact that a large sample must be used. A new polarographic procedure has been proposed, using a mercury pool cathode (11), in which a wave is obtained for the gamma isomer of hexachlorocyclohexane. None of the other isomers contributes to this wave nor do the hepta- and octachlorinated compounds. The method is rapid and has a sensitivity more than ten times the conventional polarographic procedure. I n applying the recently developed mercury pool cathode to organic polarography, distinctly different results from those found with the dropping mercury electrode were often obtained (12). Reduction potentials mere shifted, sometimes in a positive direction and, a t other times, toward negative potentials. I n some instances, even the number of waves obtained was different. Because such results might be obtained a t the mercury pool
60-
Volts vs. SCE
Figwre 1. Mercury Pool Polarogramsof Hexachlorocyclohexane8
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V O L U M E 2 6 , N O . 6, J U N E 1 9 5 4
cedure was successful because of this difference between the two electrodes. The octachlorocyclohexanes also were found to give two waves a t the mercury pool. The first wave apparently occurred a t a positive potential, because the polarogram begins a t a high current value. The second wave is close to the hydrogen discharge and is not fully developed. Because the difference between the reduction potentials of the various compounds indicated the feasibility of a n analytical method, the linearity of the height of the gamma isomer wave was first checked against concentration. Lindane, which assayed 99.9% pure, was used in these analyses. Only the first reduction wave was considered, because the alpha isomer and the more highly chlorinated compounds interfere with the second peak. The wave height was measured a8 o c t a chloro isomers illustrated in Figure 4. The current was found to be linear within 5% over the range of 1 to 25 y 0 0 per ml., as shown in Figure 3. I n more concenresidual trated solutions, the current values increase more 0' rapidly than would be predicted. The peak 2 6 -1.0 1.4 1.8 heights also vary with the square root of thevoltage V O L T S vs. SCE scanning rate, a behavior noted with other organic Figure 2. Polarograms of Hepta- and Octachlorocyclohexanes molecules and inorganic ions (11, l a ) . The greatest difficulty, in the application of the conventional dropping mercury electrode to the determination of electrode, it was hoped that a solution to the problem of deterlindane, is involved with the interference of the heptachlorinated mining the gamma isomer might be found. compound. Synthetic mixtures of the gamma isomer of hexaA solution of 20% ethyl alcohol with 1% potassium chloride chlorocyclohexane with heptachloro- isomers were therefore anawas chosen as the supporting electrolyte for the analyses. Polarolyzed for lindane content. The results are shown in Table I. grams were run in this medium, both a t the dropping mercury It may be seen that the first wave of lindane shows no interferelectrode and the mercury pool cathode on the alpha, beta, and gamma isomers of hexachlorocyclohexane, as well as the heptaand octa- compounds. The gamma isomer was found to give one long wave a t the Table I. Effect of Heptachlorocyclohexanes on the Wave dropping mercury electrode a t -0.94 volt vs. S.C.E. This potenHeights of Gamma Hexachlorocyclohexane tial is considerahly more positive than the half-wave values usually Approximate recorded a t higher alcohol concentrations. I n contrast, two Gamma HeptachloroCurrent before Isomer, cyclohexane, Correction by Wave Height, Error, waves were found a t the mercury pool electrode. The first had +v$l. Estrapolation, pa. pa. % a half-peak potential of -0.83 volt, and the second occurred at 16.5 ... .. 23 16.2 -1.8 - 1.40 volts. The initial wave was different in shape from those 17.0 +3.0 32 16.8 +1.8 usually obtained a t the mercury pool in that the peak was flat39 A typical polarogram is shown in Figure 1. tened (12). .. . S o reduction wave was found for the alpha isomer a t the dropping electrode. A wave was obtained a t the quiet mercury pool, which occurred shortly after -1.0 volt. The wave was not fully developed in this medium, because of the appearance of the hydrogen discharge shortly after its initiation. The beta isomer did not give a wave with either electrode, and neither of the two other isomers was available for study. Polarograms are shown in Figure 1 for each of these samples 12.9 % gamma a t a concentration of 10 y per ml. 65 % alpha A mixture of the heptachlorocyclohexane isomers was also studied. A single wave was 8 % beta obtained a t the dropping electrode with an 2 % hepta approximate half-wave potential of -0.6 volt. This polarogram was drawn out over the long range of -0.2 to -1.0 volt. A t the mercury pool electrode, two reduction potentials were found (Figure 2). The first, a positive value, had already begun to develop a t zero applied e.m.f. ; the estimated half-peak .4 -.6 -.8 -1.0 1.2 potential was about -0.1 volt. The second Volts vs. SCE wave occurred a t negative values merging into the hydrogen wave. The proposed praFigure 3. Polarogram of Lindane in a Natural Isomeric Mixture
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ANALYTICAL CHEMISTRY
912
ence from the heptochlorinated compounds. There n a s a considerable contribution to the second wave, however. A minor difficulty was experienced with large amounts of the heptacompounds. The recorded currents from the 13.0 % gamma first \rave of heptachlorocyclohexane did not I O % alpha level off before the lindane wave appeared, and straight-line extrapolation was not possible. I % bet a This difficulty could be easily avoided by ap7 % hepta plying a potential of -0.2 volt and not starting the voltage scanning until the current had reached a steady value. This usually occurred in 2 or 3 minutes. Under these conditions, the base line preceding the lindane wave could be easily extrapolated. According to the preliminaiy lvork, the alpha isomer appeared to be the only one Volts vs.SCE Tvhich might cause difficulty. This comFigure 4. Polarogram of the Gamma Isomer in a Dust pound gave a reduction wave, which was initiated shortly after the wave for lin. __ ____ dane, as shown in Figure 1. If the amount Table 11. Analysis of Technical Samples of the alpha isomer was very large, the iniGamma Isomer, R Other Isomers tiat'ion of its wave occurred a t more posiType of By pool B y chromatog- Differ(Chromatographic Analysis) tive voltages. K h e n the amount of the Material electrode raphy ence Alpha, 70 Beta, 70 Heptachloro-, Yo alpha compound \\+as greater than thirty S a t u r a l isomer 1 11,2+0.5(6) 11.11.0.3 +O.l 05 8 2 times the gamma isomer, this wave en2 1 2 . 9 i 0 . 5 (10) 1 2 . 3 + 0 . 3 +O.ii ti5 8 2 crouched upon the lindane peak, t,hr Concentrate 1 3 4 . 9 i O . 8 (4) 33.0 + 0.5 -0.7 25 3 21 length of the current plateau was consid2 35.61.1.2(4) 36 t i z t O . 6 -1.0 25 3 21 erably shortened, and a n uncertainty was 3 42 1 1 1 . 1 ( 4 ) 42.7+0.tj -0.6 20 2 17 Dust introduced in measuring its magnitude. 1 11.2 +OO.5(4) 11 1 i o . 3 f0.1 10 1 7 This may be seen in the error introduced 2 1 3 . 0 i 0 . 5 (4) 12.4 1.0.3 +O.Ii 10 1 7 in the analysis of the slpha-11et:r rake a s 3 2 4 . 5 3= 0 . 8 (2) 2 2 . 9 i. 0 . 4 +I . t i Alpha-beta rake shown in Table 11. 1 3 . 9 i0 . 2 3 ( 2 ) 2.3 + 0 . 2 +1 . o 90 The method was test'ed on analyzed samples generously supplied hy the Perinsylvania Salt Manufacturing Co. These inrluded natural isomers, concentrates, dusts, and alpha-beta cake, ethyl alcohol and 1% potassium chloride. About 15 ml. of the solution were placed in the polarographic cell and deareated for R hich had been analyzed bya chromatographic method tentatively 10 minutes with an applied voltage of -0.2 volt. Five milliapproved by the Association of Official Agricultural Chemists. liters of mercury were then added and deaeration was continued The polarograms were run a t a quiet mercury pool electrode, and for an additional 5 minutes. I n later models of the electrolysis the amounts in each mixture n ere determined by reference to the cell, a small side arm with a ground-glass cap was supplied for int'roduction of the mercury. The nitrogen was then bypassed calibration curve. Polarograms are shox n in Figures 3 and 4 for over the surface of the solution, and the polarogram xyas run from a natural isomeric mixture and a sample of dust. The results of -0.2 to about - 1.4 volts a t a rate of 200 volts per minute. Wave these analyses, as m ~ 1 1as the mean deviation and the number of heights Tvere obtained bj- extrapolation of the base line, as shown analyses, are shon n in Table 11. in Figure 4, and the gamma isomer content was obtained by comparison with the calibration curve prepared from pure lindane. ~
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APPARATUS AND REAGENTS
The polaro raphic cell and circuit employed have been described (11). %he area of the pool was calculated as 2.86 + 0.04 sq. cm. A saturated calomel electrode was used as the reference electrode, and the temperature control &as maintained a t 25" f 0.1" C. The polarograph n a s a Leeds and Sorthrup Electrochemograph n i t h a voltage scanning rate of 200 mv. per minute. The cell was deaerated with Seaford nitrogen from Air Reduction Sales Co. Before entering the cell, it was passed through a scrubber containing a 20% by volume solution of ethyl alcohol. The mercury for the pool was obtained from the Bethlehem Apparatus Co. I t s use eliminated the troublesome transients probably caused by traces of grease, sometimes observed in polarograms where mercury from other sources had been employed. Reagent grade potassium chloride was used rrithout further purification. iibsolute ethyl alcohol was better than 95% alcohol in eliminating errors from impurities in the solvent. .411 water used was redistilled. The various isomers of hexachlorocyclohexane were supplied by Pennsylvania Salt llanufacturing Co. and were used without further purification. T h e heptachloroand octachloro- compounds had been recrystallized from heptane and undoubtedly were mixtures of the various isomeric forms. They had a wide melting point range and analyzed slightlx- h e low the theoretical valiie for chlorine.
.4CKNOWLEDGRIENT
The authors are grateful to llohindra Chadha for arousing the initial interest in this problem. They are also thankful to Pennsylvania Salt Manufacturing Co. for kindly supplying all the analyzed samples used in this work, and particularly to IValter Claven, of their research laboratory, for much helpful advice and information. Special thanks are due to the U. S. Air Force. LITERATURE CITED
(1) Boiven, C. V., J . Assoc. Ofic. A g r . Chemists, 33, 774 (195Oj
(2) Daasch, L. W., ASAL.CHEM.,19, 779 (1947). (3) Draght, G., Ibid., 20, 737 (1948). (4) Grass, H., and Spencer, E. Y.. Can. J . Research, 27,368 (1949).
(5) Hoskins, W. AI., Witt, J. AI,, and Erwin, W.R., ANAL.CHEM.. 24. 558 (1952). (6) Inpram, J. B., and Southern, H. K., Sature, 161,437 (1948). (7) Phillips, W. F., d s a r . . CHEM.,24, 1976 (1952). (8) Rosin, Jacob, and Raddan, G. B., Ibid., 25,817 (1953). (9) Schechter, AI. S., and Hornstein, Irwin, Ibid., 24, 544 (1952). (IO) Schwabe, K., 2. .Vaturforsch., 3, 217 (1948). (11) Streuli, C. A , , and Cooke, W. D.. A N ~ LCHEM., . 25, 1691 (1953). (12) Ibid., 26, 963 (1954). RECEIVED for review November
PROCEDURE
A sample of appropriate size was dissolved in hot, absolute ethyl alcohol, cooled, and diluted to vield a solution of 20%
10, 1953 Accepted February 16, 1954 Work Derformed under Air Force Contract S o A F 18(600) 486 a n d monitored by Office of Scientific Research, A i r Research and Development Command
