Voltammetric determination of cocaine in confiscated samples using a cobalt hexacyanoferrate film-modified electrode

Abstract 

In this work, a fast, non destructive voltammetric method for cocaine detection in acetonitrile medium using a platinum disk electrode chemically modified with cobalt-hexacyanoferrate (CoHCFe) film is described. The deposition of CoHCFe film at platinum disk (working electrode) was carried out in aqueous solution containing NaClO₄ at 0.1molL⁻¹ as supporting electrolite. Stability studies of the film and subsequent voltammetric analysis of cocaine were made in acetonitrile medium with NaClO₄ at 0.1molL⁻¹ as supporting electrolite. A reversible interaction between cocaine and CoHCFe at the film produces a proportional decrease of original peak current, due to the formation of a complex between cocaine and cobalt íons, with subsequent partial passivation of the film surface, being the intensity of current decrease used as analytical signal for cocaine. A linear dependence of cocaine detection was carried out in the range from 2.4×10⁻⁴ to 1.5×10⁻³molL⁻¹, with a linear correlation coefficient of 0.994 and a detection limit of 1.4×10⁻⁴molL⁻¹. The analysis of confiscated samples by the proposed method indicated cocaine levels from 37% to 95% (m/m) and these results were validated by comparison to HPLC technique, being obtained good correlation between both methods.

Keywords: Cocaine, Cobalt hexacyanoferrate, Forensic chemistry, Chemically modified electrodes