Chemical footprints of sulfur mustard: GC-MS profiling of methylated degradation products

Sulfur mustard, a Schedule 1 chemical under the Chemical Weapons Convention (CWC), poses a significant threat to human health, animals, plants, and the environment due to its persistent nature. Bis(2-methoxyethylthio)alkanes (compounds 10-14), along with Bis(2-methoxyethyl)sulfide (compound 8) and related disulfide Bis(2-methoxyethyl)disulfide (compound 9), were synthesized and investigated using gas chromatography-mass spectrometry (GC-MS) under both electron ionization (EI) and positive chemical ionization (PCI) conditions. These compounds are structurally analogous to known degradation products of sulfur mustard, such as thiodiglycol and its derivatives, making them of particular interest for environmental analysis and chemical forensics. EI mass spectra revealed consistent fragmentation behavior, including α cleavage and neutral losses. Diagnostic ions at m/z 45 (C₂H₅O⁺), m/z 59 (C₃H₇O⁺), m/z 61 (C₂H₅S⁺), and m/z 75 (C₃H₇S⁺) were observed across the series. A generalized fragmentation pathway is proposed to support structural elucidation and homologous trend interpretation. PCI with isobutane and ammonia provided molecular ion confirmation via [M+H]⁺, [M+39]⁺, and [M+18]⁺ adducts. Due to their chemical resemblance to vesicant degradation products, these sulfur-containing compounds, along with their comprehensive mass spectral data, contribute to the spectral libraries essential for off-site analysis, substance verification, and participation in official proficiency tests conducted under the framework of the CWC by the Organization for the Prohibition of Chemical Weapons (OPCW).