Development and Validation of a Highly Sensitive LC‐MS/MS Method for Quantification of Mutagenic <i>N</i> ‐Nitroso Desmethyl Citalopram in Drug Formulations

Abstract The global pharmaceutical industry is presently apprehensive about nitrosamine impurities and nitrosamine drug substance‐related impurities (NDSRIs), which are known as human mutagens. Citalopram, a selective serotonin reuptake inhibitor, ranks among the most frequently prescribed antidepressants worldwide. It is a primary medicine utilized for the treatment of depression. Based on a theoretical assessment of the structure of Citalopram for the potential formation of an NDSRI, it was determined that it can indeed form an NDSRI, namely N ‐Nitroso Desmethyl Citalopram. The Carcinogenic Potency Category Assessment indicates that the impurity is classified as carcinogenic Category 1, with an acceptable intake limit of 26.5 ng per day (ng/day). Due to their elevated cancer risk, a very sensitive quantitative method is essential. An LC‐MS/MS method was established for quantification utilizing a Poroshell StableBond‐C18 column with dimensions of 150 (length) × 4.6 (internal diameter) mm and a particle size of 2.7 µm, with the column temperature maintained at 30°C. A 50 mM formic acid buffer and acetonitrile are employed in a 50:50 v/v ratio, with a flow rate of 0.5 mL/min in isocratic mode for peak elution. A multiple reaction monitoring program, MRM, was employed in mass spectrometry, utilizing three product ions at m / z 291.1 (quantifier), 138, and 263.1 (qualifier) with electrospray ionization mode. The LC‐MS/MS method was validated in accordance with regulatory criteria and deemed appropriate for its intended application. The employed approach is a highly sensitive analytical technology that will assist the scientific community by offering insights into the mutagenic impurity levels in citalopram drug formulations.