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Sensitive Untargeted Screening of Nerve Agents and Their Degradation Products Using Liquid Chromatography-High Resolution Mass Spectrometry.

Nerve agents (NAs) are notorious chemical warfare agents that pose a serious threat to national security and public health. The total number of theoretical chemicals of NAs and their degradation products (DPs) exceeds 410,000, according to 1.A.01-1.A.03 in the Schedules of Chemicals of the Chemical Weapons Convention, which poses great challenges for identification and verification. A three-step integrated untargeted screening strategy was developed based on a high-resolution mass spectrometry. First, an extensible homemade library for targeted screening of common classical agents was established. Second, a set of in-source collision-induced dissociation mass spectrometry (MS)-Alerting Ions was extracted and concluded based on the fragmentation behavior studies, which included 40 specific alerting ions and 10 types of characteristic structural fragments from total NAs and their DPs. A novel "Alerting Ion" searching method was developed to rapidly and sensitively screen whether or not there were nerve agent-related compounds and which type. Third, we built a theoretical exact mass database including 202 accurate masses or molecular formulas, which could cover all structural possibilities of the NAs and their DPs. Com-prehensively, the elemental composition of pseudomolecular ions, fragment ions, MS/MS spectra and isotope pattern information were ob-tained from the full scan MS/data dependent-MS2 experiments and elucidated for identification of the candidates selected in the screening step. This strategy had been successfully applied to the identification of unknown chemicals in real samples with good stability and a low limit of detection of 1-10 ng/mL. These procedures would be applicable for trace forensic investigations in cases of alleged use of nerve agents.