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We compare the electrochemical behavior of cocaine hydrochloride (in acidic medium) and its free base form (in acetonitrile) by a simple, cheap, and fast square wave voltammetry method for cocaine analysis based on carbon paste electrodes without chemical modification. The electrodes performed better than the electrodes obtained for analysis on commercial screen-printed electrodes, which we also tested here. We conducted the analyses in aqueous solution containing 0.1 mol•L-1 NH4ClO4 as supporting electrolyte. For cocaine in acidic medium, the linear correlation coefficient, the LOD, and the LOQ were 0.996, 4.66 10-6 mol•L-1 , and 1.55 10-5 mol•L-1 , respectively. For cocaine in acetonitrile medium, the linear correlation coefficient, the LOD, and the LOQ were 0.994, 9.77 10-6 mol•L-1 , and 3.26 10-5 mol•L-1 , respectively. The specificity of the methodology is advantageous when the response of different interfering substances analyzed in this work (lidocaine, procaine, caffeine and phenacetine) is concerned.

The consequences of consuming and commercializing illicit drugs including cocaine, con­stitute a serious problem for authorities and the whole society. Cocaine is usually identified in the laboratory conditions by chromatographic or spectroscopic methods. Electro­che­mical techniques have also gained prominence because they are fast and easy to use, have many applications, and provide reproducible and reliable results. Therefore, in the present study, a voltammetric method was developed to detect freebase cocaine using carbon paste electrode and methanol as the main cocaine solvent. The developed method was applied to detect cocaine in the artificial saliva by the square wave voltammetry (SWV). The current values increased linearly with the concentration of cocaine, which afforded construction of the analytical curve. The limit of detection (LoD) and the limit of quantify­cation (LoQ) were determined as 0.90 µg/mL and 2.41 µg/mL, respectively. For compa­rison purposes, HPLC-DAD chromatographic method was also applied to detect cocaine. The corresponding analytical curve gave LoD = 0.043 µg/mL and LoQ = 0.130 µg/mL. Although showing better analytical results, HPLC-DAD method could not detect cocaine in saliva samples without previous treatment, what makes the electrochemical method much more attractive for this type of detection.

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