Ultra-sensitive HPLC–ESI–MS/MS quantitation of N-nitroso-phenylephrine in phenylephrine-containing anticold products

Phenylephrine is widely used in anticold medications and contains a secondary amine moiety capable of forming N-nitroso-phenylephrine (NNPE), a potentially carcinogenic nitrosamine impurity. Despite increasing attention to nitrosamine contamination in pharmaceuticals, no dedicated analytical method has been reported for the determination of NNPE at trace levels in complex drug formulations. In this study, a highly sensitive and selective HPLC-ESI-MS/MS method was developed and validated for the quantitation of NNPE in phenylephrine-containing anticold products. Chromatographic separation was achieved using reversed-phase conditions, and detection was performed by triple-quadrupole mass spectrometry operated in multiple-reaction monitoring mode. Method validation followed the ICH Q2(R2) guideline and demonstrated excellent linearity, accuracy, and precision, with a limit of detection of 1.95 pg/mL and a limit of quantification of 3.9 pg/mL. Sample preparation was intentionally kept simple and representative of routine quality control practice, relying on direct aqueous dissolution without extensive clean-up. Matrix effects were systematically evaluated and shown not to compromise quantitative performance due to effective compensation by the isotopically labelled internal standard. The validated method was applied to commercially available anticold products, revealing measurable NNPE levels in all samples analysed, with several products exceeding currently applied acceptable intake limits. The proposed method provides a reliable analytical tool for trace-level NNPE determination and is suitable for routine quality control and safety assessment of phenylephrine-containing pharmaceutical products.