Simultaneous Estimation of Telmisartan and Amlodipine by Second Derivative Spectrophotometric Method and First Derivative Ratio-Spectrophotometric Method

Two simple, specific, precise and accurate spectrophotometric methods have been developed for the simultaneous estimation of Telmisartan (TEL) and Amlodipine besylate (AML) involving: second derivative Spectrophotometric method (I) and first derivative Ratio -Spectrophotometric Method (II). Method (I) is based on measurement of amplitude of second derivative spectrum absorbance at two wavelengths; 329 nm and 368 nm for Telmisartan and Amlodipine besylate respectively. The latter (method II) depends on measurement of amplitude of the first derivative of the ratio spectrum at two wavelengths, 319 nm and 288 nm for Telmisartan by using 2 µg/mL of AML as a divisor and 393 nm for Amlodipine besylate by using 4 µg/mL of TEL as a divisor. Beer's law obeyed in concentration range of 1 - 35 µg/ mL and 2- 16 µg/ mL for Telmisartan and Amlodipine besylate respectively for both methods. The proposed methods are recommended for routine analysis since they are rapid, simple and specific. The described UV methods were successfully employed for the analysis of each drug in their combined dosage form. For method (I), the mean% recoveries were found to be 100.49±0.15 for Amlodipine besylate and 98.99±1.83 for Telmisartan. For method (II), the mean% recoveries were found to be 99.55±0.92 and 100.48±1.69 for Telmisartan at 319 nm and 288 nm respectively and 99.92±1.69 for Amlodipine besylate at 393 nm. The validation of methods was carried out utilizing ICH guidelines.