LC and LC–MS/MS study of forced decomposition behavior of anastrozole and establishment of validated stability-indicating analytical method for impurities estimation in low dose anastrozole tablets

Anastrozole tablets were subjected to different ICH prescribed stress conditions of thermal, hydrolysis, humidity, photolysis and oxidation stress. The drug was found to be stable for all the stressed conditions except for oxidation. Separation of anastrozole from its potential impurities, degradation products and five anastrozole related compounds as main impurities were achieved on Inertsil ODS-3V, 250 mm × 4.6 mm i.d, 5 μm analytical column using reversed phase high performance liquid chromatography (RP-HPLC). The elution of impurities employed time dependent gradient programmed mobile phase consisting of water as mobile phase-A and acetonitrile as mobile phase-B at column flow rates of 1 ml/min and at 215 nm UV detection. The same method was also extended to LC–MS/MS studies which were carried out to identify the degradation product. The method developed was established to have sufficient intermediate precision as similar separation was achieved on another instrument handled by a different operator. The LOQ for anastrozole related compound-A (RC-A), related compound-B (RC-B), related compound-C (RC-C), related compound-D (RC-D), related compound-E (RC-E) and anastrozole were 0.05, 0.03, 0.03, 0.06, 0.06 and 0.06 μg ml −1 respectively. The linearity of the proposed method for all the above related compounds was investigated in the range of LOQ to 0.600 μg ml −1 respectively. The specificity was established through peak purity testing using a photo-diode array detector. Method was validated according to ICH guidelines and statistical analysis of the data proved to be suitable for stability testing at quality control.