dence of similarity to the 258, 300, and 370 excitation and 445 mp emission wavelengths recorded for pure p-carboline on glass-fiber paper wet with 5% aqueous HC1. It was noted, however, that the spectra contained bands analogous to the 365 excitation and 535 emission bands reported by Uphaus, Grossweiner, and Katz (10) for l-methyl-3carboxy-3,4-dihydro-~-carboline isolated from the N-acetyl derivative of tryptophan in trifluoroacetic acid. It seems probable that in this reaction decarboxylation does not occur and the end products are rich in 3-carboxy-3,4dihydro-@-carboline. Also, since tryptamine, 3-methylindole, 2,3-dimethylindole, 2,5-dimethylindole, and 2,3,7trimethylindole gave only weak and erratic positives a t concentrations above 20 pg., the test indicates that the method is specific for tryptophan in the presence of less than 200-fold amounts of 3-substituted indoles. The sensitivity for p-nitrophenylacetic acid was not as good as for the other compounds shown in Table I. The dry spot did not fluoresce, but when wet with 2 pl. of toluene a yellow-green fluorescence with a wavelength maximum a t 550 mp was observed. It appears, therefore, that wetting with an
appropriate solvent can be used to enhance fluoresence, reduce noise from scattered light, and obtain fluorescence spectra more compatible with solution spectra. Many organic compounds present in extracts of air particulate matter do not fluoresce. However, using methods in which fluorogens are formed and techniques described in this communication, air samples can now be quickly screened for the presence of precursors of formaldehyde and malonaldehyde. Unstable phenolic aldehydes believed to be present in automotive exhaust fumes should be capable of being identified through the formation of the more stable and fluorescent azine as described in the procedure for vanillin. Since many aza, and some oxy, heterocyclics have been found in contaminated atmospheres, it seems very probable that these techniques can be used for the detection and characterization of many compounds of biological interest, some of which are probably present in polluted atmospheres. These preliminary results show the potentially wide applicability of the method to the fluorometric detection and characterization of aldehydes, amines, amino acids, steroids, hallucino-
gens, and countless other nonfluorescent compounds. These techniques are being applied to air pollution analysis and should find wide use in other areas of analytical chemistry. LITERATURE CITED
(1) Berguer, K. G., Sperlich, H., Deut. Lebensm.-Rundschau 47, 134 (1959). (2) Epstein, E., Maddock, W. O., Boyle, -4.J., ANAL.CHEM.29, 1548 (1957). (3) Hess, S., Udenfriend, S., J . Phavnacol. Ezptl. Therap. 127, 175 (1959). (4) Prochazka, Z., Chem. Listy 47, 1643 (1953). (5) Sawicki, E., Hauser, T. R., McPherson, S., ANAL.CHEM.34, 1460 (1962). (6) Sawicki, E., Stanley, T. W.; Elbert, W. C., Occupational Health Rev. 16, 8 (1964).
( 7 ) Sawicki, E., Stanley, T. W., Johnson, H., Chemist-Analyst 52, 4 (1963). (8) Sawicki, E., Stanley, T. W., Johnson, H., Microchem. J . 8 , 257 (1964). (9) Sawicki, E., Stanley, T. W., Pfaff, J. D., Anal. Chim. dcta 28, 156 (1964). (10) Vphaus, R. A,, Grossweiner, L. I., Katz, J. J., Science 129, 641 (1959).
THOMAS W. STANLEY EUGESESAWICKI
Division of Air Pollution Robert A . Taft Sanitary Engineering Center I:. S. Dept. of Health, Education, and Welfare Cincinnati, Ohio
Polarography of Dithiodimalic Acid SIR: The study of organic sulfhydryl and disulfide compounds is of interest because of their relation to proteins. Kolthoff and coworkers thoroughly studied the polarography of cystine and cysteine (3-5). The polarography of thiomalic acid has also been investigated (2). The present paper summarizes findings on the polarography of dithiodimalic acid (TSST) , a disulfide dimer of thiomalic acid.
EXPERIMENTAL
Reagents. TSST was prepared by the oxidation of thiomalic acid with ferric alum, similar to the method for preparation of dithiodiglycollic acid (7). Apparatus. A Leeds & Northrup Electro Chemograph T y p e E was used throughout. h manual setup with circuit similar to t h a t used by Kolthoff and Lingane was also used a t times. iill potentials were measured against the saturated calomel electrode. The characteristics of the DME were m = 2.403 mg. second-’; t = 3.57 seconds (open circuit); and h = 35 em. The pH was measured with a Leeds & Northrup pH meter using a generalpurpose glass electrode. 940
ANALYTICAL CHEMISTRY
RESULTS
Polarograms of l O - 3 X TSST were taken in buffers of pH 1-9. Well defined cathodic waves were obtained a t pH 1 and 3. The wave height was much reduced a t pH 5 and no wave was observed a t higher p H values. 4 t pH 1 and 3, diffusion currents proportional to the concentration were observed. ht p H 5 alone, a prewave was obtained preceding the main wave. Triton X100 (7.9 x or thymol (4.9 X 10 -5M)completely suppressed the maximum. The diffusion coefficients a t pH 1.3 and 3.1 were 4.81 X lo-* and 4.807 x low8,respectively. The corresponding zero current potentials were 0.07 and 0.09 volt. I n both cases TSST concentration was 5 X 10-4M. DISCUSSION
By following the usual calculations, the value of CY was found to be 0.185. The reduction of TSST ( 1 , 6) can be represented by El/2
=
~
where the different symbols have their usual significance. Applying the equation for perchloric acid buffer a t p H 1.3 cm. the value of KO, is 4.235 X second -I. ACKNOWLEDGMENT
The author expresses his thanks to
R. C. Kapoor, Head, Chemistry Dept., Jodhpur University, for helpful suggestions during the progress of this work. H e is also grateful for the gift of thiomalic acid which was supplied by Evans Chemetics, Inc., New York, N. Y. LITERATURE CITED
( 1 ) Delahay,
P., “New Instrumental Methods In Electro-Chemistry,” Interscience, New York, 1954. ( 2 ) Kapoor, R. C., Tiwari, S. K., Proc. Natl. Acad. Sci. ( I n d i a ) 28, 52 (1959). ( 3 ) Kolthoff, I. &I., Barnum, C., J. Am. Chem. SOC.62, 3061 (1940). (4) Kolthoff, I. M., Barnum, C., Ibid., 63, 520 (1941). ( 5 ) Kolthoff, I. M., Stricks, W., Tanaka, N.,Ibid., 77, 4739 (1955). (6) Koutecky, J., Collection Czech. Chem. Commun. 18, 597 (1953). ( 7 ) Leussing, D. L., Kolthoff, I. &I., J . Electrochem. Soc. 100, 334 (1953).
S. K . TIWARI Prince of Wales Chemical Laboratories Aligarh Muslim University Aligarh, India
