The stressors, choice of their

concentration and preparation of samples were based http://www.selleckchem.com/products/VX-770.html on guidelines in the publication.12 As the drug was insoluble in water, it was dissolved in a mixture of acetonitrile and water in a ratio of 50:50 (v/v) to a final concentration of 2 mg/ml. The stock was diluted 50:50 (v/v) with the stressor (e.g. HCl, NaOH, H2O2 and water etc.). Hydrolytic decomposition of the drug was carried out in 0.2 N HCl and 0.2 N NaOH at 80 °C for 24 h and in water, refluxing at 80 °C for 4 days. The oxidative study was carried out in 30% (v/v) H2O2 at room temperature for 9 h. For thermal stress testing, the drug was sealed in glass vials and placed in a thermostatic block at 50 °C for 21 days. Photolytic studies on the drug in the solution state were carried out in 0.01 N HCl, water, and 0.01 N NaOH by exposing it for 14 days to a combination of Fluorescent and UV light in a photostability chamber at 1.2 million lx and 200 W/m2, respectively. Parallel set was kept in dark for 14 days. Photolytic studies in the solid state were performed by exposing a thin layer of the drug to light under similar condition as that of solution state. The stressed samples of acid and alkali hydrolysis were neutralized with NaOH

and HCl, respectively to obtain 500 μg/ml solutions. Neutral hydrolysis, thermal and photolytic samples were diluted with mobile phase to obtain 500 μg/ml solutions. The oxidative stress sample was diluted with mobile phase composed of methanol and ammonium formate buffer (pH 4.0; 0.01 M) CDK inhibitor (50:50, v/v) to obtain 100 μg/ml solution. All the prepared samples were passed through 0.45 μm membrane filter before HPLC and LC–MS analysis. The stressed solutions, in which sufficient amounts of products were formed, were combined in equal proportions

to prepare a mixture containing all degradation products in one solution. This mixture was subjected initially to LC–PDA and further to LC–MS analyses for characterization of degradation products. During the optimization all process, preliminary studies were carried out on Hypersil Gold C-18 column (4.6 × 250 mm, 5 μm) using water: methanol (90:10, v/v) as a mobile phase. Initial separation studies were carried out on samples of different stress conditions individually and later on resolution of drug and degradation products was studied in a mixture of those stressed samples, where different degradation products were observed. The peaks corresponding to degradation products did not resolve completely and tailing was noticed. To get acceptable separation between the drug and its degradation products, ammonium formate buffer (0.01 M) was used instead of water. The pH of the buffer, flow rate and composition of the mobile phase were systematically varied to optimize the method.