Identification of photodegradation product of amisulpride by ultra-high-pressure liquid chromatography-DAD/ESI-quadrupole time-of-flight-mass spectrometry.

Photostability of amisulpride under UVA irradiation in methanol solution was investigated and structural elucidation of its photodegradation products was performed. For the purpose of the quantitative and qualitative analysis of amisulpride and the stress degradation products elucidation, the reversed phase UHPLC-DAD system coupled with accurate mass hybrid ESI-Q-TOF mass spectrometer was used. During one run (10 min) with the use of auto MS/MS mode all essential data for the determination of photodegradation kinetics and for the structural formulas elucidation of the products was collected. Four degradation products were found and their masses with high accuracy (0.53-3.05 ppm) and formulas were obtained--258.0666 (C(10)H(14)N(2)O(4)S), 367.1564 (C(17)H(25)N(3)O(4)S), 341.1412 (C(15)H(23)N(3)O(4)S) and 385.1665 (C(17)H(27)N(3)O(5)S). For all the analyzed compounds MS/MS fragmentation spectra were obtained (collision energy 19.8-26.1 V) allowing structural elucidation of unknown degradation products and indicating photodegradation pathways of amisulpride. UHPLC-DAD/ESI-Q-TOF system was found to be a powerful analytical tool for the fast and accurate stability analysis of pharmaceutical substances.