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This work describes a new specific, sensitive, and rapid stable isotope dilution method for the simultaneous detection of the organophosphorus nerve agents (OPNAs) tabun (GA), sarin (GB), soman (GD), cyclosarin (GF), VR, VX, and VM adducts to tyrosine (Tyr). Serum, plasma, and lysed whole blood samples (50 μL) were prepared by protein precipitation followed by digestion with Pronase. Specific Tyr adducts were isolated from the digest by a single solid phase extraction (SPE) step, and the analytes were separated by reversed-phase ultra high performance liquid chromatography (UHPLC) gradient elution in less than 2 min. Detection was performed on a triple quadrupole tandem mass spectrometer using time-triggered selected reaction monitoring (SRM) in positive electrospray ionization (ESI) mode. The calibration range was characterized from 0.100-50.0 ng/mL for GB- and VR-Tyr and 0.250-50.0 ng/mL for GA-, GD-, GF-, and VX/VM-Tyr (R(2) ≥ 0.995). Inter- and intra-assay precision had coefficients of variation of ≤17 and ≤10%, respectively, and the measured concentration accuracies of spiked samples were within 15% of the targeted value for multiple spiking levels. The limit of detection was calculated to be 0.097, 0.027, 0.018, 0.074, 0.023, and 0.083 ng/mL for GA-, GB-, GD-, GF-, VR-, and VX/VM-Tyr, respectively. A convenience set of 96 serum samples with no known nerve agent exposure was screened and revealed no baseline values or potential interferences. This method provides a simple and highly specific diagnostic tool that may extend the time postevent that a confirmation of nerve agent exposure can be made with confidence.

The analysis of biomedical samples such as urine and blood can provide evidence of exposure to chemicals for a range of applications including occupational exposure monitoring, detection of drugs of abuse, performance enhancement in sport and investigations of poisoning and incapacitation. This paper reports the development of an analytical method for two suspected urinary metabolites of the riot control agent 2-chlorobenzylidene malononitrile (CS): 2-chlorohippuric acid and 2-chlorobenzyl-N-acetylcysteine. 2-Chlorohippuric acid was identified in all 2 h post-exposure samples from a set of urine samples taken from army recruits exposed to low levels of thermally dispersed CS during training. 2-Chlorobenzyl-N-acetylcysteine, a metabolite known to be formed in the rat, was not identified in any of the samples. The lower limit of detection (LLOD) for 2-chlorohippuric acid and 2-chlorobenzyl-N-acetylcysteine was 1 ng/ml and 0.5 ng/ml in pooled urine from the pre-exposed subjects. 2-Chlorohippuric acid was rapidly excreted but was detectable in the urine of 17 of the 19 subjects tested 20 h after exposure.

Organophosphorus nerve agents inhibit the activity of cholinesterases by phosphylation of the active site serine. In addition, sarin, cyclosarin, soman and tabun have been shown to phosphylate a tyrosine residue in albumin. Therapies against nerve agent poisoning include the use of oximes to reactivate inhibited cholinesterases by displacement of the phosphyl moiety and hence detectable levels of adducts with cholinesterases may be reduced. Adducts with tyrosine have been shown to be persistent in the guinea pig in the presence of oxime therapy. Plasma samples obtained from an animal study aimed at improving therapy against nerve agent poisoning were used to compare the suitability of tyrosine and butyrylcholinesterase (BuChE) adducts as biomarkers of nerve agent exposure after treatment with therapeutic oximes. Under the terms of the project licence, these samples could be collected only on death of the animal, which occurred within hours of exposure or when culled at 23 or 24 days. Tyrosine adducts were detected in all samples collected following intra-muscular administration of twice the LD50 dose of the respective nerve agent. Aged BuChE adducts were detected in samples collected within a few hours after administration of soman and tabun, but not after 23 or 24 days. No BuChE adducts were detected in animals exposed to sarin and cyclosarin where samples were collected only after 23 or 24 days.