Disposable Stencil-Printed Carbon Electrodes for Electrochemical Analysis of Sildenafil Citrate in Commercial and Adulterated Tablets

Abstract

Forensic studies are extremally important to investigate suspected adulterations of consumable products, such as Viagra®. This report describes the determination of sildenafil citrate (SC) in commercial and adulterated tablets based on square-wave voltammetry (SWV) measurements using disposable stencil-printed carbon electrodes. The conductive ink used for the manufacture of integrated electrodes was produced by combining graphite powder and glass varnish. To promote a reusable strategy for limiting the geometric area of the electrodes, a 3D-printed holder was constructed. Detailed morphological and electrochemical characterization studies revealed well-defined graphite flakes incorporated on the polymeric substrate and a fast heterogeneous electron-transfer rate constant (Ks = 1.3 × 10–3 cm s–1). Based on the analytical performance, a linear behavior was observed in a SC concentration range from 1 to 20 µmol L–1 with limit of detection equal to 0.2 µmol L–1. The selectivity of the proposed method was evaluated and the presence of potentially interfering compounds like phosphate, lactose, paracetamol and tadalafil and no difference higher than 15% was observed. The analysis of SC was performed in commercial and seized tablets and the achieved values were 50 ± 1 mg for Viagra® tablet, 54 ± 1 mg for generic formulations 38 ± 1 mg for seized tablet. In addition, the proposed method offered satisfactory accuracy (98.2 – 102.0%) no noticeable matrix effect. Lastly, considering the achieved results, the use of stencil-printed carbon electrodes and SWV has demonstrated to be a powerful and robust analytical tool for forensic investigations.