Determination of Residual N ‐Nitroso Desmethyl Chlorpromazine in Chlorpromazine HCl Injection by Liquid Chromatography–Tandem Mass Spectrometry

A selective, robust, and sensitive liquid chromatography–tandem mass spectrometry analytical procedure was developed to monitor trace amounts of potentially carcinogenic N ‑nitroso desmethyl chlorpromazine (NNO‑DM‑CPZ) impurity in chlorpromazine hydrochloride injection (25 mg/mL). Using specific multiple reaction monitoring (MRM) in positive electrospray ionization mode and a multistep gradient elution program (mobile phase A and B: 0.1% formic acid and methanol, respectively) employing an XBridge C18 column from Waters, the method achieved acceptable separation from chlorpromazine, its related substances, and matrix components. Validation was performed at the 0.1325 µg/mL specification limit in accordance with International Council for Harmonisation guidelines, evaluating specificity, sensitivity, accuracy, precision, and linearity. The limit of detection and limit of quantification (LOQ) were established as 0.0066 and 0.0133 µg/mL, respectively, with excellent linearity across 0.0133–0.1988 µg/mL (LOQ to 150% of specification). This method ensures reliable detection of NNO‑DM‑CPZ impurity at trace levels in chlorpromazine HCl injection (25 mg/mL).