Extra information helps inspectors
Site inspections by the Organisation for the Prohibition of Chemical Weapons (OPCW) require unambiguous detection of a range of compounds, including parent compounds, degradation products and synthetic precursors. Scientists at the Defence R&D Establishment at Gwalior, India, have identified a series of important precursors of nerve agents that is not fully represented in the databases used by inspectors.
The main technique used in chemical weapons verification is GC/MS and identification relies on comprehensive reference databases. The master OPCW analytical database contains information on more than 1900 chemicals.
The three major types of nerve agent are O-alkyl alkylphosphono-fluoridates (eg sarin), O-alkyl N,N-dialkylphosphoramido-cyanidates (eg tabun) and O-alkyl-S-2-diisopropylaminoethyl alkylphosphonothiolates (eg VX). N,N-dialkylphosphoramidic difluorides and dichlorides, and alkylphosphonic difluorides containing methyl, ethyl, propyl and isopropyl groups, are covered by the Chemical Weapons Convention, but only the mass spectra of some of them are in the OPCW database. So, Devendra Dubey and colleagues synthesised the series of synthones to obtain comparable sets of mass spectra.
Generalised fragmentation routes for the synthone groups were proposed to account for the major characteristic ions and to aid differentiation between the members of each series.
However, Gary Mallard from the National Institute for Standards and Technology, US, with responsibility for the NIST MS database, is concerned that not all spectral ions have been presented, which makes interpretation difficult. Nevertheless, 'the data are broadly consistent with the data accepted by the OPCW and its review process is very rigorous,' he says.
The data primarily provide more information to compare the data that are currently available, says Mallard.