A simple, sensitive, and stability indicating isocratic reverse phase high performance liquid chromatography method has been developed, optimized and validated for the separation and quantification of S-enantiomer in linagliptin (R-enantiomer) drug substance. Enantiomeric separation was achieved on a Cellulose tris(4-chloro-3-methylphenylcarbamate) stationary phase. Mobile phase consists of aqueous diammonium hydrogen phosphate buffer and acetonitrile in the ratio of 35:65 v/v. Isocratic elution was performed at a flow rate of 1.0 mL/min, the column oven temperature was set at 40°C and detection was at 226 nm. The resolution between R and S enantiomers is found to be more than 4.0. The impact of mobile phase composition, pH of buffer and temperature on the resolution has been studied. The detector response is found to be linear over the concentration range of 0.17-1.7 g/mL. LOD and LOQ levels of S-enantiomer are found to be 0.057 and 0.172 g/mL respectively. The recovery of S-enantiomer is 99.8% w/w. The proposed method is validated for specificity, precision, linearity, accuracy and robustness.

A simple and sensitive method based on capillary electrophoresis with UV detection was developed, optimized, and validated for the determination of five membered heterocyclic polar compound, imidazole in pharmaceutical drug substances. Separation was achieved on bare fused silica capillary using a simple running buffer, potassium dihydrogen phosphate at pH 4.0. Capillary temperature set at 25°C. The applied voltage was 25 kV across the capillary and the samples were injected by hydrodynamically at a pressure of 50 mbar for 5 s. Analyte was monitored at 210 nm. The achieved limit of detection value was 0.005%w/w, limit of quantification value was 0.014%w/w, and the average accuracy value was 98.4% for imidazole. The aim of present study is to develop a specific and sensitive method for the determination of imidazole to overcome the void volume and sample matrix interferences.

A simple, sensitive, selective and reproducible stability indicating reverse phase HPLC method has been developed and validated for the determination of related substances of linagliptin drug substance. Separation of impurities was carried out on a YMC Pack ODS-AQ, 5 μm (250 × 4.6 mm) column. Column eluent consists of gradient mixing of phosphate buffer at pH-3.7 as mobile phase A and a mixture of acetonitrile, methanol and water in the ratio of 600:250:150 v/v/v as mobile phase-B. Gradient elution at a flow rate of 1.0 mL/min and injection volume is 10 μL. The UV/vis detector is set to a wavelength of 226 nm and the column oven is set at 30 ºC. The detector response was found to be linear over the concentration range of 0.07-1.1 μg/mL with correlation coefficients greater than 0.999 for linagliptin and its related substances. LOD values for specified impurities range from 0.004-0.005% w/w and LOQ values from 0.013-0.015% w/w. The accuracy obtained by the proposed method was found to be in the range of 93.2-101.3%. Degraded and process impurities are well separated and the method has been validated for specificity, precision, ruggedness, linearity, accuracy and robustness as per ICH guidelines.