Analytical Sciences

Determination of Losartan and Triamterene in Pharmaceutical Compounds and Urine Using Cathodic Adsorptive Stripping Voltammetry

Ali Asghar ENSAFI and Reza HAJIAN

Department of Chemistry, Isfahan University of Technology, Isfahan 84156-83111, Iran

A square-wave voltammetric procedure for the electroanalytical determination of losartan and triamterene in Britton-Robinson buffer (pH 3.0, 0.1 mol L^-1) as a supporting electrolyte containing 30 ng mL^-1 of copper ions was developed. Opposite to the case of triamterene, losartan can not be reduced at a mercury electrode alone, but a new peak appears at -0.25 V in the presence of copper due to the formation of a complex between copper(II) and losartan. An accumulation potential of -0.30 V during 80 s for the prior adsorption of losartan-copper(II) and triamterene on the electrode surface was used. The response of the system was found to be linear in the range of 30.0 - 270.0 nmol L^-1 for losartan and two linear dynamic ranges containing 0.5 - 200.0 and 200.0 - 400.0 nmol L^-1 of triamterene. The limits of detections were 9.7 and 0.3 nmol L^-1 for losartan and triamterene, respectively. The relative standard deviations for five replicate analyses of 100.0 and 10.0 nmol L^-1 losartan and triamterene were 5.5%. Applicability to assay the drugs in urine and pharmaceutical formulations was illustrated with satisfactory results. The direct-current polarography of triamterene indicates that the reduction of a related drug is strongly dependent on the pH of the solution. A linear segment was found with slope value of -63.6 mV pH^-1 in the pH range of 2.0 - 6.0. The stoichiometry and complex formation constant (β) for losartan-Cu(II), number of transfer electrons (n), transfer coefficients (α) and number of proton transfers were also estimated.

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