Abstract
A simple, selective, and sensitive high-performance liquid chromatographic method is described for the simultaneous determination of amlodipine and valsartan combined tablets in rat plasma, using losartan as internal standard. The assay was based on protein precipitation with acetonitrile then reversed phase chromatography with fluorescence detection. In order to delay the rapid elution of amlodipine and to obtain acceptable relative retention value, sodium hexane sulfonate was used as ion pairing reagent and a gradient elution mode was applied. The separation was performed on an Agilent Zorbax Eclipse XDB C18 column, using gradient elution with aqueous 0.02% sodium hexane sulfonate-glacial acetic acid (500:1,v/v) (solvent A) and acetonitrile (solvent B). The fluorescence detector was on-line switched to measure each analyte and internal standard at their optimum excitation and emission wavelengths. The assay was linear over the concentration ranges 0.01-0.80 and 0.10-20 mu g/mL for amlodipine and valsartan, respectively, with recoveries of 97.80 and 99.35%, respectively. The method was successfully applied to a pharmacokinetic study involving a single oral dose of combined (10/160mg) tablet.