Adsorptive Stripping Anodic Voltammetric Determination of Thioctic Acid in Bulk and Pharmaceutical Formulations

The electrochemical behavior of thioctic acid at the hanging mercury drop electrode was studied in different supporting electrolytes. In Britton - Robinson buffer pH 3.29, the square – wave adsorptive anodic stripping voltammogram of thioctic acid exhibited a single well – defined anodic peak at about -0.21 V vs Ag/AgCl. The peak response was characterized with respect to pH, preconcentration time, accumulation potential, supporting electrolytes, frequency, scan increment and pulse amplitude. Under the optimized conditions, a fully validated, simple, high sensitive, precise and inexpensive square – wave adsorptive anodic stripping voltammetric procedure was described for determination of thioctic acid in bulk form and tablets. The obtained results were in good agreement with those obtained with the reference method. The calibration graph was linear over the range 5 × 10(-8) - 9 × 10(-7) M (r=0.9997) with accumulation for 60 s at –0.4 V vs Ag/AgCl and the detection limit was ca. 1.2 × 10(-8) M.