Electrospray ionisation mass spectral studies on hydrolysed products of sulfur mustards

Abstract

Off-site detection of the hydrolysed products of sulfur mustards in aqueous samples is an important task in the verification of Chemical Weapons Convention (CWC)-related chemicals. The hydrolysed products of sulfur mustards are studied under positive and negative electrospray ionisation (ESI) conditions using an additive with a view to detecting them at trace levels. In the presence of cations (Li⁺, Na⁺, K⁺ and NH), the positive ion ESI mass spectra of all the compounds include the corresponding cationised species; however, only the [M+NH₄]⁺ ions form [M+H]⁺ ions upon decomposition. The tandem mass (MS/MS) spectra of [M+H]+ ions from all the hydrolysed products of the sulfur mustard homologues were distinct and allowed these compounds to be characterised unambiguously. Similarly, the negative ion ESI mass spectra of all the compounds show prominent adducts with added anions (F^-, Cl^-, Br^-, and I^-), but the [M-H]- ion can only be generated by decomposition of an [M+F]^- ion. The MS/MS spectra of the [M-H]^- ions from all the compounds result in a common product ion at m/z 77. A precursor ion scan of m/z 77 is shown to be useful in the rapid screening of these compounds in aqueous samples at trace levels, even in the presence of complex masking agents, without the use of time-consuming sample preparation and chromatography steps. An MS/MS method developed to measure the detection limits of the hydrolysed products of sulfur mustards found these to be in the range of 10-500 ppb.