Liquid chromatography/electrospray mass spectrometry of mustard-related sulfonium ions

The detection and identification of degradation products of the chemical blister agent bis(2-chloroethyl) sulfide, commonly known as mustard or HD, is important for the future destruction of the mustard stockpile for safety and environmental reasons. Because stored mustard tends to degrade via intramolecular substitution forming stable sulfonium ions, conventional gas chromatographic/mass spectrometric analysis does not give a true picture of sample composition. In this study, liquid chromatography/electrospray ionization mass spectrometry (LC/MS) was applied for the detection and identification of six synthesized mustard related cyclic and open-chain sulfonium ions to demonstrate the applicability of the technique. The technique was then applied to confirm the identification of the major component of unknown solid heels isolated from mustard ton containers as the six-membered ring cyclic 1-(2-chloroethyl)-1,4-dithianium ion by comparison of spectra obtained by LC/MS and LC/MS/MS for a mustard heel and a reference standard. A mechanism to account for this sulfonium ion formation under long-term ton container storage conditions is provided. The technique was also applied to monitor open-chain sulfonium ion formation during the hydrolysis of 0.01 M mustard in 0.05, 2.3 and 10 vol.% thiodiglycol–water at 20°C. © 1997 John Wiley & Sons, Ltd