Impurity Analysis for N-Nitroso-Desloratadine by LC-MS/MS Method with HILIC-Based Separation Mode

N-Nitroso drug substance-related impurities (NDSRIs) have raised major safety concerns due to their genotoxic potential in pharmaceutical products. In this study, we developed and validated a sensitive LC-MS/MS method based on hydrophilic interaction liquid chromatography (HILIC) for the quantification of N-nitroso-desloratadine (NO-desloratadine). To minimize matrix effects from excess active pharmaceutical ingredient (API), the method was optimized to elute the NDSRI prior to the API. The method demonstrated excellent specificity, linearity (1–50 ng/mL, r² > 0.999), and sensitivity, with a limit of quantification (LOQ) of 1.0 ng/mL. Validation confirmed acceptable precision, accuracy, robustness, and system suitability in accordance with regulatory guidelines. NO-desloratadine was detected in both APIs and finished dosage forms at levels below the acceptable intake threshold based on the Carcinogenic Potency Categorization Approach (CAPA). Furthermore, the method was successfully applied to other structurally diverse NDSRIs, including NO-fluoxetine and NO-betahistidine, without modification. This HILIC-based LC-MS/MS approach offers a broadly applicable and reliable platform for the routine analysis of trace-level NDSRIs in pharmaceutical matrices.