Electron ionization mass spectrometry fragmentation routes of Chemical Weapons Convention-related organoarsenic compounds: Electron ionization and density functional theory studies

Rationale: For unambiguous identification of Chemical Weapons Convention (CWC)-related chemicals in environmental and biological samples, access to mass spectra and expertise in spectral interpretation is required. As of today, there is no mass spectrum available for dialkyl alkylarsonodithioites in the literature. Therefore, it is essential to obtain spectral information about these compounds. Methods: CWC-related organoarsenic compounds were synthesized and analyzed by gas chromatography combined with mass spectrometry (MS), and their retention index (RI) was calculated by Van Den Dool's method. The relationship between RI and density functional theory (DFT)-calculated polarizability (alpha) and molecular weight was also studied. Electron ionization (EI) mode was used to investigate the general fragmentation patterns of the synthesized compounds. A DFT analysis of some major fragment ions was performed in order to confirm the fragmentation pathways. Results: A linear relationship between RI and alpha is observed. The mass spectra of compounds 5-7 are affected by alkyl groups on sulfur and arsenic atoms. The molecular ions of compounds 5-7 can be observed in their EI-MS spectra with relatively good abundance. EI-MS studies revealed some interesting fragmentation pathways, such as the formation of arsenic analogue of benzylic and tropylium cations in EI-MS of chemicals 6. Conclusions: By analyzing the mass spectra and RI values, it is possible to detect CWC-related chemicals in aqueous, blood and urine samples during an on-site or off-site inspection.