Chemometrically assisted development and validation of LC-UV and LC-MS methods for simultaneous determination of torasemide and its impurities.

Complete evaluation of chromatographic behavior and establishment of optimal experimental conditions for determination of torasemide and its four impurities are determined by experimental design. Fractional factorial and 3(n) full factorial design were employed for efficient and rapid optimization of liquid chromatography-ultraviolet and liquid chromatography-mass spectrometry (LC-MS) methods. Separation is achieved on a Zorbax SB C(18) analytical column (250 x 4.6 mm, 5 µm) with mobile phase consisting of acetonitrile and 10 mM ammonium formate (pH 2.5 with formic acid) in gradient mode. The flow rate is 1 mL min(-1), the temperature of the column is 25 °C and UV detection is performed at 290 nm. The efficiency of ionization in electrospray ionization is higher than in atmospheric pressure chemical ionization mode; therefore, it is further used for analysis of torasemide and its impurities. Both methods meet all validation criteria. The calibration curves show high linearity with the coefficients of correlation (r) greater than 0.9982. The obtained recovery values (95.78-104.92%) and relative standard deviation values (0.12-5.56%) indicate good accuracy and precision. Lower limit of detection (LOD) and limit of quantitation (LOQ) values are obtained with the LC-MS method, indicating higher sensitivity of the proposed method.