Differentiation of Gunpowders

Among other things, it draws atten- tion to the advantages of electro- chemical detection of diphenylamine, a smokeless-powder stabilizer. Based...
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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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866 A · ANALYTICAL CHEMISTRY, VOL. 57, NO. 8, JULY 1985

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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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ANALYTICAL CHEMISTRY, VOL. 57, NO. 8, JULY 1985 · 867 A