Letters Differentiation of Gunpowders Sir: I read the ANALYTICAL AP
PROACH article entitled "The Differ entiation of Black and Smokeless Gunpowders" by Darwin B. Dahl and Peter F. Lott (Anal. Chem. 1985, 57, 446-54 A) with considerable interest. Among other things, it draws atten tion to the advantages of electro chemical detection of diphenylamine, a smokeless-powder stabilizer. Based on my experience in the quality con trol of propellants and explosives, I would like to comment on the compo sition of propellants (gunpowders) and the electroanalytical determina tion of gunpowder components. It is true that smokeless powder, in its simplest form, is composed of ni trocellulose stabilized with diphenyl amine. But to improve its ballistic properties, the propellant may be sur face treated with a nitrotoluene, a phthalic acid ester, or centralite, for example. Besides nitrocellulose and nitroglycerin, double-base propellants
may contain some plasticizer, e.g., phthalate or urethane, as well as var ious stabilizers (diphenylamine, cen trantes, and acardites) or other com ponents. In addition, smokeless pow ders are subject to change upon aging as a consequence of the slow decompo sition of nitrocellulose. Thus, a propel lant is a complex mixture, and a num ber of methods are available to deter mine its composition. Because gunpowder components are electrochemically active, voltammetry has proven to be a most appropriate method of analysis for smokeless pro pellants (2) and can be used for both qualitative and quantitative determi nations. Compounds such as nitrate esters (nitroglycerin), nitrotoluenes, nitramines, and phthalic acid esters are reduced at a dropping mercury electrode. In multicomponent systems with partly or completely overlapping polarograms, differential pulse polarography is used for the analyses (2). Di-
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phenylamine, centralites, acardites, and urethanes are oxidized at carbon electrodes. This can, of course, be used to advantage in analytical work. The simpler nitro-derivatives of the stabi lizers can also be determined by oxi dation (3). Polarography as a method of analy sis is selective enough for determina tion of nitro-derivatives of diphenyl amine in hot-stored single-base pro pellants (4). HPLC with electrochemi cal detection can thus be used to ad vantage in determinations of individ ual nitrodiphenylamine derivatives. Differential pulse polarography is in itself, however, both a complement and an alternative to chromatographic methods in the determination of up to four components in terms of selectiv ity, accuracy, and number of samples analyzed in a day's work. A differentiation of black and smokeless gunpowder should not be based on an attempt to identify only diphenylamine. The diphenylamine may have been completely trans formed into its nitro(so) derivatives, or a different stabilizer may have been used for the gunpowder in question. Jan Asplund Nobel Kemi AB, Quality Control Explosives S-69185 Karlskoga Sweden References (1) Asplund, J. Int. Jahrestag.-Fraunhofer-Inst. Treib-Explosivst. 1983, 313. (2) Asplund, J., presented at the 1985 Pittsburgh Conference & Exposition, New Orleans, La., Feb. 25-March 1, 1985. (3) Bergens, Α.; Lundstrom, K.; Asplund, J. Talanta, in press. (4) Asplund, J., presented at the Joint Symposium on Compatibility of Plastics/ Materials with Explosives, Propellants, and Pyrotechnic Ingredients, Lake Ozark, Mo., Oct. 31-Nov. 2,1983.
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Reply: We thank J. Asplund for his interesting commentary on our recent article. It came about as an offshoot of our continuing primary investigation on the determination of gunshot resi dues—work aimed at identifying a shooter in a crime situation through the analysis of the discharge residue remaining on a suspect's hand. Be cause of this significant underlying fo rensic consideration, we believe addi tional comments are necessary to
Letters minimize erroneous conclusions that could arise as a result of Asplund's communication. We agree with Asplund that there may be additional constituents in gunpowder such as the phthalates, urethanes, and nitrosodiphenylamines. This is well-known and docu mented in the literature (2). In normal gunpowders and firearm discharges, these constituents are present in very small amounts so as to make their de tection extremely difficult (2, 3). Most of these constituents that Asplund lists are also so widespread as to make their detection meaningless in a foren sic situation. Asplund apparently is concerned with accelerated aging studies of gunpowder, which is an en tirely different situation than that en countered in normal firearm dis charges. It is true that the nitrosodiphenylamines and related degradation products can be detected occasionally in a firearm residue. We also report such information in an article on gun shot residue determinations in the April issue of the Microchemical Journal. The article on which As plund commented gives in general form our thoughts and results on the problem described—the detection of
black powder or smokeless powder in a firearm residue. As stated, it is a summary of a presentation given at a Benedetti-Pichler Symposium. It does not report the conditions for the anal ysis in the detailed manner of a re search article, and it should not be read as such. For example, we did not include the composition of the mobile phase (presently we are using a 52% acetonitrile, 1% triethylamine, 1% phosphoric acid, and 46% water solu tion). Such information as well as ad ditional experimental information would be contained in a research arti cle, but it is not appropriate for the type of article we wrote. We wish to emphatically point out and clear up a possible major misun derstanding. We have never stated that the appearance of a chromato graphic peak by itself under condi tions where diphenylamine is detected can be considered as totally unambig uous and conclusive proof of the pres ence of smokeless powder. We have assiduously refrained from such rea soning and thought that we went into sufficient, extensive considerations to prevent any reader from coming to such a conclusion. This is why we went into the explanation for multiple test
ings and the need for description of the conditions such as the injured shooter and the damaged firearm so as to overcome reasonable-doubt argu ments. Chromatography is a separa tion method, not an absolute method of identification. Only under properly selected conditions can a chromato graphic separation be very persuasive for identification purposes. Again we appreciate Asplund's com ments, although we think they are not pertinent and are actually misleading. Because of future forensic implica tions, we are pleased to be able to offer this additional written commentary so as to hopefully prevent such questions from re-arising. Darwin B. Dahl and Peter F. Lott Chemistry Department University of Missouri—Kansas City Kansas City, Mo. 64110 References
(1) Yinon, J.; Zitrin, S. "The Analysis of Explosives"; Pergamon Press: New York, N.Y., 1981. (2) Mach, M. H.; Pallos, Α.; Jones, P. F. J. Forensic Sci. 1978,23, 446-55. (3) Bratin, K; Briner, R. C; Bruntlet, C. S.; Kissinger, P. T. Anal. Chim. Acta 1981,110, 295-311.
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