Comparison of UV- and second derivative-spectrophotometric and LC methods for the determination of valsartan in pharmaceutical formulation.

UV- and second derivative-spectrophotometric and high-performance liquid chromatographic methods for the determination of valsartan in pharmaceutical formulation have been developed. For the first method, UV-spectrophotometry, standard solutions were measured at 205.6 nm. The linearity changes were found to be 2.0-10.0 microg ml(-1) in ethanol and the regression equation was A=1.05 x 10(-1)C+4.26 x 10(-2) (r=0.9997). For the second method, the distances between two extremum values (peak-to-peak amplitudes), 221.6 and 231.2 nm were measured in the second order derivative-spectra of standard solutions. Calibration curves were constructed by plotting d(2)A/dlambda(2) values against concentrations, 0.5-4.0 microg ml(-1) of valsartan standards in ethanol. Regression equation of linear calibration graph was calculated as D=2.9 x 10(-2)C-2.37 x 10(-3) (r=0.9996). The third method was based on high-performance liquid chromatography on C18 column using acetonitrile, phosphate buffer as a mobile phase and losartan as internal standard. Detection was carried out at 265 nm with a UV-detector. The assay was linear over the concentration range at 1.0-5.0 microg ml(-1) and regression equation was found to be A=2.74 x 10(-1)C+2.06 x 10(-2) (r=0.9991). Commercial capsules containing 160 mg valsartan were analysed by the developed methods and the results obtained were compared statistically at 95% confidence level.