Interlaboratory comparison study of a chemical profiling method for methylphosphonic dichloride, a nerve agent precursor

Abstract

An interlaboratory evaluation of a chemical profiling method for a nerve agent precursor was performed by eight chemical analytical laboratories with a wide global distribution. A set of chemical attribution signatures (i.e. impurities) present in methylphosphonic dichloride (DC) were analysed by gas chromatography-mass spectrometry (GC/MS). The GC/MS analyses were performed with the individual instrumentation and analytical methods used by the laboratories in proficiency tests organized by the Organisation for the Prohibition of Chemical Weapons (OPCW). Two batches of DC, produced by two different production routes, were dispatched together with one reference sample. By the use of a targeted MS-library, sixteen chemical attribution signatures were analysed in the DC samples. Retention indices, mass spectra and relative peak areas of the GC/MS data were evaluated. When the within batch-data of the eight laboratories were compared, similarity values of 0.720–0.995 were obtained. In addition, the two different batches had clearly unique chemical attribution profiles, as indicated by a large between batch-distance similarity values of 0.509–0.576. Retention indices showed less than ± 14 retention index unit variation for the 16 chemical attribution signatures. This study showed the potential of getting consistent chemical profiling data over multiple laboratories by the use of retention indices for alignment of GC/MS-data. The results indicate that the GC/MS instrumentation and methods used at most OPCW designated laboratories are valid tools for the acquisition of chemical profiling data of importance for the attribution analysis to study suspected production or use of chemical warfare agents.