Mitigation of ionization-induced quantitative bias in LC-MS/MS analysis of N-nitrosamine drug-substance-related impurities in Rasagiline pharmaceutical products

초록

Accurate quantification of N-nitrosamine drug-substance–related impurities (NDSRIs) in pharmaceutical products requires careful control of ionization- induced artifacts during LC–MS/MS analysis. In pharmaceutical matrices where the active pharmaceutical ingredient (API) is present at concentrations several orders of magnitude higher than the target impurity, in-source fragmentation can generate overlapping product ions, leading to significant quantitative bias. In this study, we demonstrate that certain atmospheric-pressure ionization con- ditions induce in-source decomposition of both rasagiline and its correspond- ing nitroso impurity, producing a common fragment ion at m/z 117. This overlap can compromise analytical specificity and potentially result in overesti- mation of impurity levels. To mitigate this ionization-induced quantitative bias, Heated Electrospray Ionization (H-ESI) parameters were systematically opti- mized to preserve the intact protonated molecular ion (m/z 201) while minimiz- ing thermally induced fragmentation. In addition, a gradient LC method incorporating a high-organic wash step and flow diversion strategy was estab- lished to enhance analytical robustness under routine quality control condi- tions. The optimized LC–MS/MS method demonstrated excellent linearity (R2 > 0.998), acceptable precision (RSD ≤ 11.5%), and sufficient sensitivity (LOQ 30 ng/mL) to meet current regulatory requirements. These findings highlight the critical importance of ion-source selection in nitrosamine impurity analysis and provide a practical strategy to reduce the risk of ionization-induced quanti- tative bias in pharmaceutical LC–MS/MS applications.

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