Signature-Discovery Approach for Sample Matching of a Nerve-Agent Precursor Using Liquid Chromatography−Mass Spectrometry, XCMS, and Chemometrics

Abstract

This report demonstrates the use of bioinformatic and chemometric tools on liquid chromatography-mass spectrometry (LC-MS) data for the discovery of trace forensic signatures for sample matching of ten stocks of the nerve-agent precursor known as methylphosphonic dichloride (dichlor). XCMS, a software tool primarily used in bioinformatics, was used to comprehensively search and find candidate LC-MS peaks in a known set of dichlor samples. These candidate peaks were down selected to a group of 34 impurity peaks. Hierarchal cluster analysis and factor analysis demonstrated the potential of these 34 impurities peaks for matching samples based on their stock source. Only one pair of dichlor stocks was not differentiated from one another. An acceptable chemometric approach for sample matching was determined to be variance scaling and signal averaging of normalized duplicate impurity profiles prior to classification by K-nearest neighbors. Using this approach, a test set of seven dichlor samples were all correctly matched to their source stock. The sample preparation and LC-MS method permitted the detection of dichlor impurities quantitatively estimated to be in the parts-per-trillion (w/w). The detection of a common impurity in all dichlor stocks that were synthesized over a 14-year period and by different manufacturers was an unexpected discovery. Our described signature-discovery approach should be useful in the development of a forensic capability to assist investigations following chemical attacks.

Profiling of volatile impurities in tetramethylenedisulfotetramine (TETS) for synthetic-route determination

“…However, unexpected trace contaminants are always possible and are dependent upon the reaction conditions and environment of a specific batch. These compounds may therefore help to fingerprint a specific batch or source of TETS as previously shown for other chemical-threat related compounds [16,18]. The detection of 1,3,5-trioxane in TETS 1 and TETS 2, which were not produced using 1,3,5-trioxane, and its absence in the TETS 3, which was produced using 1,3,5-trioxane, was unexpected.…”

“…The impurity profiling work described here has precedence in previous forensic research on other chemical-threat agents and precursors [16][17][18]. In those studies, the feasibility of obtaining forensic information from impurity profiling for sample matching and possible route and source determination were demonstrated.…”

The identification and evaluation of two different color variations of tea

“…Peaks with a signal to noise ratio were extracted using Masslynx, version 4.1 (Waters). Unprocessed MS files were firstly converted into the NetCDF format and sequentially handled by XCMS (http://www.bioconductor.org) software running under the R environment, version 2.3.1 (R Foundation for Statistical Computing, Vienna, Austria) for detection of metabolic features, chromatographic matching and aligning all metabolite peaks in the LC/MS data. In the end, all peak areas were normalized by sum and then subjected to statistical analysis.…”

Identification of Endogenous Substrates of Orphan Cytochrome P450 Enzymes Through the Use of Untargeted Metabolomics Approaches

“…The extract was then incubated with the recombinant P450 in the presence of NADPH and redox partners, with subsequent metabolite profiling by LC-MS. The metabolic profile obtained after the reaction was compared with that before the reaction using specialized metabolomics software, e.g., XCMS (4, 5). Molecules that were depleted due to the enzymatic reaction were identified as potential substrates.…”