A reverse-phase high-performance liquid chromatographic (RP-HPLC) method was developed for the simultaneous estimation of amlodipine besylate (AMB), valsartan (VAL), and hydrochlorothiazide (HCT) in pharmaceutical formulation using RP-C 18 column. The mobile phase (acetonitrile:methanol:50 mM phosphate buffer adjusted to pH 3 with orthophosphoric acid) was pumped at a flow rate of 1.0 mL min −1 in the ratio of 20:50:30% v/v and the eluents were monitored at 239 nm. Linearity was obtained in the concentration range of 0.5-5 μg mL −1 for AMB, 4-40 μg mL −1 for VAL, and 1-10 μg mL −1 for HCT. The method was validated as per International Conference on Harmonization (ICH) guidelines and statistically. The method was validated for accuracy and precision. For precision, the coefficient of variance (COV) was found to be 0.3794, 0.1703 and 0.0578, and for accuracy, it was found to be 0.6351, 0.7688 and 1.1305 for AMB, VAL, and HCT, respectively. The COV values for all the drugs were found to be less than 2%, indicating high degree of precision and accuracy of the proposed highperformance liquid chromatographic (HPLC) method. Owing to its simplicity, rapidness, high precision and accuracy, the proposed HPLC method can be applied for determining AMB, VAL, and HCT in bulk and in pharmaceutical dosage form.

A simple, efficient, precise and accurate absorbance ratio method have been developed for the estimation of eprosartan mesylate and hydrochlorothiazide in pure and in fixed dose combination. In this method, UV spectra of eprosartan mesylate and hydrochlorothiazide were overlayed which involves the formation of Q-absorbance equation at 249.1 nm (isobestic point) and 274.5 nm, the max of hydrochlorothiazide. Both the drugs obeyed Beers law in the concentration range of 6-36 μg/ml and 1-10 μg/ml for eprosartan mesylate and hydrochlorothiazide, respectively. The accuracy of the method was determined by recovery studies and was found to be in the range of 102.29-103.10% and 99.52-101.60% for eprosartan mesylate and hydrochlorothiazide, respectively. The method was validated as per ICH guidelines and statistically. The method showed good reproducibility and recovery with % RSD less than 2. The method was found to be simple, economic, accurate and reproducible and can be used for routine analysis of eprosartan mesylate and hydrochlorothiazide in pure and in fixed dose combinations.

A simple, precise and accurate difference spectroscopic method has been developed for the estimation of balsalazide in bulk and in pharmaceutical dosage form. The proposed method is based on the principle that balsalazide can exhibit two different chemical forms in basic and acidic medium that differ in the absorption spectra in basic and acidic medium. Since the drug was freely soluble in distilled water, a stock solution (1 mg/mL) was prepared with distilled water. Further dilution was made by using 0.1 M sodium hydroxide and 0.1 M hydrochloric acid separately. The maxima and minima in the difference spectra of balsalazide were at 460 nm and 354 nm, respectively. Difference in absorbance between these maxima and minima was calculated to find out the amplitude. This amplitude was plotted against concentration. Beer's law is valid in the concentration range of 2-20 µg/mL. The results of analysis have been validated statistically and by recovery studies.