Stability Indicating High‐performance Liquid Chromatography Method for Quantification of Amoxapine and Characterization of Forced Degradation Products Employing Quadrupole‐Time of Flight Mass Spectrometry

ABSTRACT Amoxapine, a tricyclic antidepressant, has been widely used for long‐term treatment of depression along with other psychiatric disorders involving neurosis, agitation, and anxiety. The drug may undergo degradation during manufacturing, transportation, and storage. To ensure drug safety, both identification and characterization of the degradation products (DPs) should be considered. Accordingly, a sensitive and selective stability‐indicating assay method was developed for amoxapine using high‐performance liquid chromatography (HPLC). The amoxapine drug was subjected to acidic hydrolysis, basic hydrolysis, and oxidation separately. The degradation susceptibility of the amoxapine was found to be in the order of Acid hydrolysis > Oxidation > Base hydrolysis. The developed method was validated as per the International Council for Harmonization Q2(R2) guideline. Further, LC‐electrospray ionization‐quadrupole‐time of flight‐tandem mass spectrometry was employed for the identification and characterization of the DPs formed under stress conditions. The study revealed that under accelerated stress conditions, three hydrolytic DPs and one oxidative DP were formed. Three of the four DPs were found to be novel and never reported before. In addition, a plausible mechanism representing the formation of all DPs has also been established.