Unveiling Impurity Profiling of Synthetic Pathways of Organophosphorus Chlorpyrifos Through LC-HRMS...

Sourcing in chemical forensic science refers to the attribution of a sample to a specific source using a characteristic signature. It relies on the identification of chemical attribution signatures (CAS), including chemical markers such as residual synthetic precursors, impurities, reaction by-products and degradation products, or even metabolites. Undertaking CAS for chemical threat agents (CTA) can be used to provide an evidentiary link between the use of a given chemical and its precursor(s) to support forensic investigations. Organophosphorus compounds, a class of nerve agents, can be produced by different, more or less complex synthesis routes that can lead to specific CAS. Chlorpyrifos (CPF), an organophosphorus pesticide, was selected as model compound. To assess the specificity of impurity markers originated from a chemical synthesis, untargeted fingerprints of crude CPF from different synthesis pathways were analyzed as a first use-case using metabolomics-based trace discovery strategies. Seven different CPF synthesis routes were considered, and their crude mixtures were analyzed with a minimal sample preparation. Analyses were performed on a trapped ion mobility spectrometry (TIMS) coupled to liquid chromatography (LC) and high-resolution mass spectrometry (HRMS). Chemometrics analyses were conducted with multivariate methods to extract discriminating features (i.e., relevant impurities), annotate, and identify them. Then, unknown samples were analyzed in blind conditions without any information of the synthesis pathway employed. The aim is to validate the methodology seeking some discriminating impurities identified in the first section to attribute and classify them according to the synthesis route.