Trace‐level determination of potential genotoxic impurities in quetiapine fumarate using LC–MS

A novel LC-MS method was developed and validated to determine three potential genotoxic impurities, namely 2-(2-aminophenylthio)benzoic acid hydrochloride, 2-aminothiophenol, and 2-(2-aminophenylthio)benzonitrile, at trace level (~1.6 ppm) in quetiapine fumarate drug substance, an antipsychotic drug. These impurities are potentially genotoxic and therefore should be controlled at or below specific acceptance limits. An InertSustain AQ-C18 column (250 × 4.6 mm, 5 μm) in reversed-phase mode with the column temperature at 45°C was used. The mobile phase was 0.1% trifluoroacetic acid in water and acetonitrile with gradient elution mode, and the run time was 45 min. The flow rate was 0.8 ml/min. A mass spectrometer was used to quantify the amount of impurities using electrospray ionization mode at specific m/z 245.9, 126.0, and 226.9 for 2-(2-aminophenylthio)benzoic acid hydrochloride, 2-aminothiophenol, and 2-(2-aminophenylthio) benzonitrile, respectively. The method was found to be sensitive and possessed excellent linearity in the concentration ranges from the limit of quantification to 150% of the permitted level (0.47-2.36 μg/ml) with correlation coefficients above 0.999. The results showed that the method was specific, precise, linear, and accurate for the estimation of these three impurities in quetiapine fumarate.