Four methods namely, first-derivative of ratio spectra, bivariate, thin layer chromatography and high performance liquid chromatography were used to determine valsartan and hydrochlorothiazide simultaneously in their pharmaceutical dosage forms. The derivative ratio spectra method was based on measuring the peak amplitudes for valsartan at 233 nm and 253 nm using 0.4μg mL-1 hydrochlorothiazide as a divisor. Bivariate method is used for simultaneous determination of both drugs by measuring the absorbance at the selected wavelengths. A TLC separation with densitometric detection of both drugs was achieved using chloroform: methanol: ammonia [8:2:0.1, v/v/v] as developing solvent. Furthermore, a high performance liquid chromatographic procedure with ultraviolet detection at 225 nm was developed for the separation and determination of the studied drugs using a C18 column. The mobile phase is composed of 0.02 M phosphate buffer (pH 2.9): acetonitrile: methanol [50: 40: 10, v/v/v]. The proposed methods were successfully applied for the determination of the studied drugs in their mixtures and in pharmaceutical formulations containing them.
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