Simultaneous estimation of cilnidipine hydrochloride and chlorthalidone in its combined dosage form by absorbance ratio method

In the quantitative assay of Cilnidipine hydrochloride and chlorthalidone in the mixture by absorption ratio method, absorbance was measured at two wavelengths. One is the iso-absorptive point of the components (233 nm). And the other being wavelength of maximum absorbance of cilnidipine hydrochloride (241 nm). From the overlay spectra of the drugs 233nm was selected as iso-absorptive point for absorption ratio method. Different concentrations of cilnidipine hydrochloride and chlorthalidone were prepared in the range of 2 – 10 µg/ml respectively. The absorbance and molar absorptivities were determined at 233 nm and 241 nm for the components and concentrations of cilnidipine and chlorthalidone in combined dosage form were determined. The percentage label claim was found to be 103.16 for cilnidipine hydrochloride and 98 % w/w for chlorthalidone. The validation of the developed method was performed in accordance with ICH guidelines. The accuracy of the proposed method was studied by recovery at three levels. The precision of the proposed method was studied by intraday precision and inter-day precision. The % RSD of the proposed method was found to be < 2%. The linearity was obtained in the concentration range of 2 - 10 µg/ml for cilnidipine hydrochloride and chlorthalidone at 233 nm. The proposed method was found to be accurate and precise, so this method can be used for routine analysis of cilnidipine hydrochloride and chlorthalidone in combined dosage form.