Voltammetric study of valsartan–Ni complex: application to valsartan analysis in pharmaceuticals and in vivo human urine profiling

Abstract

Valsartan (VAL) can be analyzed at the mercury electrode in the presence of nickel (II) yielding a sensitive cathodic peak at − 0.7 V which may be attributed to the reduction of the complex formed between nickel and VAL. Low LOD and LOQ were achieved (7.6 and 23 nM, respectively) permitting the analysis of VAL not only in its pharmaceutical formula, but also in human urine. The influence of adding transition metal, Ni(II), to the electrolyte containing VAL, on the voltammetric response was studied. Differential-pulse voltammetry, using working electrode: hanging mercury drop electrode (HMDE), was applied to elucidate and confirm the possible complexation reaction that could occur between VAL and nickel which aids in the determination of VAL in tablets and human urine. A simple cleanup procedure was applied for urine samples that involves the use of solid-phase extraction with the elution of VAL with methanol. The polarographic peak, which corresponds to the reduction of Ni(II) in the formed complex with VAL, was a function of the concentration of VAL, pH of the medium and Ni(II) concentration at the electrode surface. At Britton–Robinson buffer pH 6 and using 800 µM Ni(II), the reduction peak current linearly varied with the VAL concentration over the ranges of 25–150 and 25–200 nM in tablets as well as urinalysis, respectively.