Cocaine electrooxidation behavior, mechanism, and kinetics on a carbon paste electrode chemically modified with a cobalt or copper Schiff base complex

Abstract Cocaine is one of the most abused drugs worldwide. Therefore, it is crucial to develop and improve cocaine identification techniques. This article describes two new electrodes chemically modified with ([Co((±)-t-3MeOsalcn)] or ([Cu((±)-t-3MeOsalcn)] and their use in free-base cocaine (FB) and cocaine hydrochloride (HC) identification. The electrodes were not active toward FB, but cyclic voltammetry analysis revealed an increase of 0.1 V (vs Ag/AgCl) (Eoxi) for HC. The square-wave voltammetry results showed that FB@([Cu((±)-t-3MeOsalcn)] and HC@([Cu((±)-t-3MeOsalcn)] presented higher amperometric sensitivity than FB@([Cu((±)-t-3MeOsalcn)] and HC@([Cu((±)-t-3MeOsalcn)]. The limit of detection (LOD) and the limit of quantification (LOQ) for FB@([Cu((±)-t-3MeOsalcn)] were 0.61 μmol.L−1and 2.04 μmol.L−1, respectively. As for HC@([Cu((±)-t-3MeOsalcn)] the LOD and the LOQ were 0.58 μmol.L−1 and 1.92 μmol.L−1, respectively. The higher chemical stability of the cocaine@([Cu((±)-t-3MeOsalcn)] complexes and the lower binding energy of FB and HC with ([Cu((±)-t-3MeOsalcn)] predicted by theoretical calculations explain the results of the voltammetric analyses. Moreover, the topographic and compositional results confirmed that HC adsorbed onto the surface of the electrodes chemically modified with [Co((±)-t-3MeOsalcn)] or ([Cu((±)-t-3MeOsalcn)]. Overall, our results demonstrated that the electrodes chemically modified with [Co((±)-t-3MeOsalcn)] or ([Cu((±)-t-3MeOsalcn)] developed in this study have promising application in cocaine detection and quantification. At the end of the study, we propose a schematic mechanism for the HC oxidation process at the modified electrodes.