Electrochemical behavior of 5-type phosphodiesterase inhibitory drugs in solid state by voltammetry of immobilized microparticles

Abstract

Evaluation of electrochemical behavior of 5-type phosphodiesterase inhibitory drugs is of major concern since they have been added illegally as adulterants in dietary supplements. Then, for the first time, the solid-sate electrochemistry of sildenafil and tadalafil is described using voltammetry of immobilized microparticles (VIMP). An electrochemical cell was designed and printed in a fused deposition modeling (FDM)-based 3D printer for VIMP measurements. The 3D-printed cell designed with a distance of 5 mm between the working and reference electrode presented better voltammetric response and decrease in the uncompensated resistance of the electrochemical system. Cyclic and square wave voltammograms of the individual compounds were recorded in a paraffin-impregnated graphite electrode in contact with 0.01 mol L−1 H2SO4. The electrochemical oxidation/reduction products were characterized by Raman spectroscopy and scanning electron microscopy (SEM). Different voltammetric responses were detected for the solid compounds depending on the solubility of the parent compound and their products of oxidation/reduction. Moreover, significant crystal re-structuring was also observed after voltammetric scan of the solid compounds. Under optimized conditions, sildenafil and tadalafil could be electrochemical identified and distinguished in dietary supplements.