In this report we present the feasibility of using analytical and chemometric methodologies to reveal and exploit the chemical impurity profiles from commercial dimethyl methylphosphonate (DMMP) ...samples to illustrate the type of forensic information that may be obtained from chemical-attack evidence. Using DMMP as a model compound of a toxicant that may be used in a chemical attack, we used comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GC × GC/TOF-MS) to detect and identify trace organic impurities in six samples of commercially acquired DMMP. The GC × GC/TOF-MS data was analyzed to produce impurity profiles for all six DMMP samples using 29 analyte impurities. The use of PARAFAC for the mathematical resolution of overlapped GC × GC peaks ensured clean spectra for the identification of many of the detected analytes by spectral library matching. The use of statistical pairwise comparison revealed that there were trace impurities that were quantitatively similar and different among five of the six DMMP samples. Two of the DMMP samples were revealed to have identical impurity profiles by this approach. The use of nonnegative matrix factorization indicated that there were five distinct DMMP sample types as illustrated by the clustering of the multiple DMMP analyses into five distinct clusters in the scores plots. The two indistinguishable DMMP samples were confirmed by their chemical supplier to be from the same bulk source. Sample information from the other chemical suppliers supported the idea that the other four DMMP samples were likely from different bulk sources. These results demonstrate that the matching of synthesized products from the same source is possible using impurity profiling. In addition, the identified impurities common to all six DMMP samples provide strong evidence that basic route information can be obtained from impurity profiles. Finally, impurities that may be unique to the sole bulk manufacturer of DMMP were found in some of the DMMP samples.
► On-matrix derivatization developed for dynamic headspace sampling. ► Targeted analytes were chemical warfare hydrolysis products and amines. ► Substrates included glass, painted wallboard, carpet, ...and concrete. ► Technique was successful for all analytes on all substrates. ► Recoveries reasonable, except low for half-acid methylphosphonic acids on concrete.
The goal of this study is to extend sampling by the field and laboratory emission cell (FLEC) dynamic headspace technique to applications that target nonvolatile residues. On-matrix derivatization of residues to render analytes stable and more volatile is explored to achieve this goal. Results show that on-matrix derivatizations of nerve agent hydrolysis products (monoalkyl methylphosphonic acids and methylphosphonic acid MPA) with diazomethane were successful on glass and painted wallboard (at the 10-μg level). It also was successful on the more difficult concrete (at the 500-μg level) and carpet (at the 20-μg level), substrates that cannot be successfully sampled using swipe techniques. Analysis of additional chemical warfare (CW)-associated residues can be approached by on-matrix derivatization with trifluoroacetic anhydride (TFAA). For example, amines (used as stabilizers or present as decomposition products of the nerve agent VX) or thiodiglycol (hydrolysis product of sulfur mustard) could be sampled as their TFAA derivatives from glass, painted wallboard, and concrete (at the 40-μg level), as well as carpet (at the 80-μg level) surfaces. Although the amine and thiodiglycol are semi-volatile and could be sampled directly, derivatization improves the recovery and chromatographic behavior of these analytes.
We analyzed 21 neat acetone samples from 15 different suppliers to demonstrate the utility of a coupled stable isotope and trace contaminant strategy for distinguishing forensically-relevant samples. ...By combining these two pieces of orthogonal data we could discriminate all of the acetones that were produced by the 15 different suppliers. Using stable isotope ratios alone, we were able to distinguish 8 acetone samples, while the remaining 13 fell into four clusters with highly similar signatures. Adding trace chemical contaminant information enhanced discrimination to 13 individual acetones with three residual clusters. The acetones within each cluster shared a common manufacturer and might, therefore, not be expected to be resolved. The data presented here demonstrates the power of combining orthogonal data sets to enhance sample fingerprinting and highlights the role disparate data could play in future forensic investigations.
•A need exists for fingerprinting starting materials used for illicit synthesis.•Stable isotope and trace contaminant analysis can aid in fingerprinting.•We tested a combined, hierarchical approach using acetone samples.•The results demonstrate enhanced differentiation versus the isotope method alone.•This method could be applied to forensic fingerprinting of wide ranges of compounds.
The investigation of crimes involving chemical or biological agents is infrequent, but presents unique analytical challenges. The protein toxin ricin is encountered more frequently than other agents ...and is found in the seeds of Ricinus communis, commonly known as the castor plant. Typically, the toxin is extracted from castor seeds utilizing a variety of different recipes that result in varying purity of the toxin. Moreover, these various purification steps can also leave or differentially remove a variety of exogenous and endogenous residual components with the toxin that may indicate the type and number of purification steps involved. We have applied three gas chromatography-mass spectrometry (GC-MS) based analytical methods to measure the variation in seed carbohydrates and castor oil ricinoleic acid, as well as the presence of solvents used for purification. These methods were applied to the same samples prepared using four previously identified toxin preparation methods, starting from four varieties of castor seeds. The individual data sets for seed carbohydrate profiles, ricinoleic acid, or acetone amount each provided information capable of differentiating different types of toxin preparations across seed types. However, the integration of the data sets using multivariate factor analysis provided a clear distinction of all samples based on the preparation method, independent of the seed source. In particular, the abundance of mannose, arabinose, fucose, ricinoleic acid, and acetone were shown to be important differentiating factors. These complementary tools provide a more confident determination of the method of toxin preparation than would be possible using a single analytical method.
This paper examines the application of gas chromatography/mass spectrometry (GC/MS) in a comparative experiment to identify volatile compounds from urine that differ in concentration between two ...groups of inbred mice. A complex mixture might comprise several hundred or even thousands of volatile compounds. Because their number and location in a chromatogram are generally unknown, and because components overlap in populous chromatograms, the statistical problems offer significant challenges beyond traditional two-group screening procedures. We describe a statistical procedure to compare two-dimensional GC/MS profiles between groups, which entails (1) signal processing, baseline correction, and peak detection in single ion chromatograms; (2) aligning chromatograms in time; (3) normalizing differences in overall signal intensities; and (4) detecting chromatographic regions that differ between groups. In an application to chemosignaling, we detect differences in GC/MS chromatograms of ether-extracted urine collected from two inbred groups of mice that differ only in genes of the major histocompatibility complex (MHC). Several dozen MHC-regulated compounds are found, including two known mouse pheromones, 2,5-dimethylpyrazine and 2-sec-butyl-4,5-dihydrothiazole.
► Impurity profiling works even after chemical is disseminated into the environment. ► Selectivity is a useful measure of impurity-profile forensic value. ► Guidance provided for optimization and use ...of impurity profiling.
Dimethyl methylphosphonate (DMMP) was used as a chemical threat agent (CTA) simulant for a first look at the effects of real-world factors on the recovery and exploitation of a CTA's impurity profile for source matching. Four stocks of DMMP having different impurity profiles were disseminated as aerosols onto cotton, painted wall board, and nylon coupons according to a thorough experimental design. The DMMP-exposed coupons were then solvent extracted and analyzed for DMMP impurities by comprehensive 2D gas chromatography/mass spectrometry (GC×GC/MS). The similarities between the coupon DMMP impurity profiles and the known (reference) DMMP profiles were measured by dot products of the coupon profiles and known profiles and by score values obtained from principal component analysis. One stock, with a high impurity-profile selectivity value of 0.9 out of 1, had 100% of its respective coupons correctly classified and no false positives from other coupons. Coupons from the other three stocks with low selectivity values (0.0073, 0.012, and 0.018) could not be sufficiently distinguished from one another for reliable matching to their respective stocks. The results from this work support that: (1) extraction solvents, if not appropriately selected, can have some of the same impurities present in a CTA reducing a CTA's useable impurity profile, (2) low selectivity among a CTA's known impurity profiles will likely make definitive source matching impossible in some real-world conditions, (3) no detrimental chemical–matrix interference was encountered during the analysis of actual office media, (4) a short elapsed time between release and sample storage is advantageous for the recovery of the impurity profile because it minimizes volatilization of forensic impurities, and (5) forensic impurity profiles weighted toward higher volatility impurities are more likely to be altered by volatilization following CTA exposure.
Detection of small quantities of agar associated with spores of
Bacillus anthracis could provide key information regarding its source or growth characteristics. Agar, widely used in growth of ...bacteria on solid surfaces, consists primarily of repeating polysaccharide units of 3,6-anhydro-
l-galactose (AGal) and galactose (Gal) with sulfated and
O-methylated galactoses present as minor constituents. Two variants of the alditol acetate procedure were evaluated for detection of potential agar markers associated with spores. The first method employed a reductive hydrolysis step, to stabilize labile anhydrogalactose, by converting to anhydrogalactitol. The second eliminated the reductive hydrolysis step simplifying the procedure. Anhydrogalactitol, derived from agar, was detected using both derivatization methods followed by gas chromatography–mass spectrometry (GC–MS) analysis. However, challenges with artifactual background (reductive hydrolysis) or marker destruction (hydrolysis) respectively lead to the use of an alternative agar marker. A minor agar component, 6-
O-methyl galactose (6-O-M gal), was readily detected in agar-grown but not broth-grown bacteria. Detection was optimized by the use of gas chromatography-tandem mass spectrometry (GC–MS–MS). With appropriate choice of sugar marker and analytical procedure, detection of sugar markers for agar has considerable potential in microbial forensics.
A solvent extraction approach was developed and examined for extraction of targeted organophosphorus compounds as well as nerve agent simulants from painted wallboard (PWB). Painted wallboard was ...chosen as a substrate due to its presence as large surface area media in an indoor environment that is applicable to a chemical agent release scenario. Three different solvent systems were examined with a 1:1 methylene chloride: acetone mixture having the most robust and consistent extraction for four target organophosphorus compounds dimethyl methyl phosphonate (DMMP), diethyl methyl phosphonate (DEMP), diethyl methyl phosphonothioate (DEMPT), and diisopropyl methyl phosphonate (DIMP). An average extraction efficiency of approximately 60% was obtained for these four compounds. The extraction approach was further demonstrated by extracting and detecting the chemical impurities present in neat DMMP that was vapor deposited onto painted wallboard tickets as a simulant to an agent release. Five chemical impurities that were present in DMMP – dimethyl phosphate, trimethyl ester phosphoric acid, ethyl methyl methylphosphonate, O,O,S-trimethyl ester phosphorothioic acid, and biphenyl were detected on the PWB and were utilized to determine the source/supplier of the DMMP.
Abstract This study investigated the feasibility of using volatile impurities from the rodenticide tetramethylenedisulfotetramine (TETS) for the discrimination of TETS produced by three synthetic ...routes. Each route was used to make one batch of TETS by reacting sulfamide with one of three formaldehyde analogs in the presence of either trifluroacetic acid (TFA) or hydrochloric acid. Ten impurities useful for differentiating the three TETS batches were discovered and tentatively identified by headspace solid-phase microextraction comprehensive two-dimensional gas chromatography–mass spectrometry (HS-SPME/GC × CG–MS). Of the ten identified impurities, the alkyl trifluoroacetate and alkyl chloride impurities distinguished TETS routes based on their use of either TFA or HCl as catalyst. On the other hand, four 6-carbon ketone impurities appeared to be batch specific rather than route specific and hence potentially useful for sample matching. Interestingly, 1,3,5-trioxane was not found in the TETS batch where it was used as a reactant, but instead was found in the two batches that did not have 1,3,5-trioxane as the reactant. In brief, the limited work discussed in this paper supports: (1) the feasibility of sampling and detecting volatile organic impurities from a solid chemical-threat agent, (2) the probable forensic benefit of catalysts acting as reactants in side reactions, (3) the uniqueness of a synthetic batch's impurity profile for potential sample matching, and (4) the possibility that some impurities, such as formaldehyde analogs, are not forensically helpful and may lead to an incorrect estimate about the synthetic route if not supported by sound chemical knowledge.
PDF
