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 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 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 nerve agent-related compounds were present and
of which type they were. 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.
Comprehensively, the elemental composition of pseudomolecular ions,
fragment ions, MS/MS spectra, and isotope pattern information were
obtained from the full scan MS/data dependent-MS2 experiments
and elucidated for identification of the candidates selected in the
screening step. This strategy was 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 are applicable
for trace forensic investigations in cases of the alleged use of nerve
agents.