Direct derivatization and gas chromatography–tandem mass spectrometry identification of nerve agent biomarkers in urine samples

• Screening, unequivocal verification and quantitation of nerve agent biomarkers in urine samples.
• Direct derivatization of alkylalkylphosphonic acids using a new fluorinated diazomethane reagent.
• ‘Dilute and shoot’ sample preparation and water tolerance of the reagent minimizes matrix effects.
• Conditions were optimized using statistical experimental design and multivariate data analysis.
• GC–MS/MS gives detection limits at low-ppb levels.

Rapid determination of nerve agent biomarkers at low-ppb levels in urine samples was achieved by direct derivatization and sample analysis using gas chromatography–tandem mass spectrometry. The studied biomarkers were alkylphosphonic acids (APAs), as they are specific hydrolysis products of organophosphorus nerve agents that can be used to verify nerve agent exposure. The sample preparation technique employed involves rapid direct derivatization (5 min) of acidified urine samples (25 μL) using a highly fluorinated phenyldiazomethane reagent [1-(diazomethyl)-3,5-bis(trifluoromethyl)benzene]. The derivatization conditions were optimized using statistical experimental design and multivariate data analysis. The APA derivatives were analyzed by GC–MS and MS/MS using negative ion chemical ionization. The selectivity and sensitivity of analyses performed by low and high resolution single ion monitoring MS-mode were compared with those performed by multiple reaction monitoring MS/MS-mode. The MS/MS technique offered the greatest sensitivity and selectivity of the tested mass spectrometric techniques, with limits of detection ranging from 0.5 to 1 ng APAs/mL of urine. The method's robustness was evaluated using urine samples from the OPCW 2nd biomedical confidence building exercise and all APAs present in the samples were conclusively identified. The method thus offers excellent performance and is viable for the simultaneous trace determination of a wide range of nerve agent markers.