Spectrophotometric Determination of Telmisartan by Its Reaction with Cresol Red

In B-R buffer medium of pH 6.6, an ion association complex was formed by the reaction between Telmisartan (TMST) and cresol red. When measuring against a reagent blank, a positive and a negative absorption maxima were found at the wavelengths of 572 nm and 428 nm respectively. Linear relationships between values of concentration of TMST and the absorbance were obtained either at 572 nm (the color-enhancing reaction) or at 428 nm (the color-fading reaction), on the base of which determination of TMST could be performed. In the proposed method, 572 nm was selected as the measuring wavelength. Under this condition, linearity range was obtained between 4.6×10-7 and 1.3×10-5mol·L-1 of TMST, and the apparent molar absorptivity found was 5.34×104L·mol-1·cm-1. This method was used for determination of TMST in its capsules and tablets, giving results in comformity with the labelled values, and values of RSD′s (n=11) less than 2.5%.