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

Author(s)

Castro, Alex Soares ^[1] ; de Azevedo, Larissa Silva ^[2] ; Bruni, Aline Thais ^{[3, 1]} ; Teles de Menezes, Matheus Manoel ^[4] ; Dockal, Edward Ralph ^[5] ; de Oliveira, Osmair Vital ^[4] ; Ferreira, Bruno ^[1] ; de Oliveira, Marcelo Firmino ^{[1, 2]}

Affiliation

^[1] Univ Sao Paulo, Fac Filosofia Ciencias & Letras Ribeirao Preto, Dept Quim, Grp Eletroquim Eletroanalit & Quim Forense, Ave Bandeirantes 3900, Ribeirao Preto, SP - Brazil

^[2] Univ Sao Paulo, Inst Quim Sao Carlos, Ave Trabalhador Sao Carlense 400, Sao Carlos, SP - Brazil

^[3] Inst Nacl Ciencia & Tecnol Forense INCT Forense, Ribeirao Preto, SP - Brazil

^[4] Inst Fed Educ Ciencia & Tecnol Sao Paulo, Campus Catanduva, Catanduva, SP - Brazil

^[5] Univ Fed Sao Carlos, Ctr Ciencias Exatas & Tecnol, Dept Quim, BR-13565905 Sao Carlos, SP - Brazil

• Document type: Journal article
• Source: FORENSIC CHEMISTRY; v. 26, DEC 2021.
• Web of Science Citations: 0

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((+/-)-t3MeOsalcn)] 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 mu mol.L- 1and 2.04 mu mol.L- 1, respectively. As for HC@({[}Cu((+/-)-t-3MeOsalcn)] the LOD and the LOQ were 0.58 mu mol.L-1 and 1.92 mu mol.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((+/-)-t3MeOsalcn)] 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. (AU)

• FAPESP's process: 16/23825-3 - Development of voltammetric sensors for determination of cocaine and delta-9-tetrahydrocannabinol in samples seized by the police
• Grantee: Marcelo Firmino de Oliveira
• Support Opportunities: Regular Research Grants
• FAPESP's process: 16/01447-7 - Development of chemically modified electrodes (NDEs) with complexes of Schiff base for determination of cocaine: voltammetric studies and application of density functional theory (DFT)
• Grantee: Alex Soares Castro
• Support Opportunities: Scholarships in Brazil - Scientific Initiation