DEVELOPMENT AND VALIDATION OF A GC-HS-FID METHOD FOR DIMETHYL SULFATE IN CLOBAZAM API: INTEGRATION OF (Q)SAR-BASED GENOTOXICITY ASSESSMENT

Objective: To develop and validate a sensitive gas chromatography–headspace method with flame ionisation detection (GC–HS–FID) for trace-level quantification of dimethyl sulfate (DMS) in clobazam active pharmaceutical ingredient (API), supported by an in silico quantitative structure-activity relationship ((Q)SAR) based genotoxicity assessment in accordance with International Council for Harmonisation (ICH) M7(R1). Methods: DMS was derivatised to anisole using phenol under alkaline conditions in a dimethylformamide–water diluent and analysed by GC–HS–FID. The method was validated in accordance with ICH Q2(R1) guidelines. Mutagenicity was evaluated using VEGA (Q)SAR models within their applicability domains. Results: The method demonstrated high specificity with no interference at the anisole retention time. Linearity was observed over the studied concentration range (R² = 0.9993). The limit of detection and limit of quantification were 0.04 ppm and 0.12 ppm, respectively. Precision and accuracy met ICH acceptance criteria, and the method remained robust under minor variations in chromatographic conditions. In silico (Q)SAR analysis consistently predicted dimethyl sulfate as mutagenic within the applicability domain. Conclusion: The validated GC–HS–FID method is sensitive and reliable for routine monitoring of dimethyl sulfate in clobazam API. The in silico (Q)SAR assessment corroborates its classification as a Class 1 genotoxic impurity (GTI), supporting the need for stringent control.