Levamisole: a Common Adulterant in Cocaine Street Samples Hindering Electrochemical Detection of Cocaine

Abstract

The present work investigates the electrochemical determination of cocaine in the presence of levamisole, one of the most common adulterants found in cocaine street samples. Levamisole misleads cocaine color tests, giving a blue color (positive test) even in the absence of cocaine. Moreover, the electrochemical detection of cocaine is also affected by the presence of levamisole, with a suppression of the oxidation signal of cocaine. When levamisole is present in the sample in ratios higher than 1:1, the cocaine signal is no longer detected, thus leading to false negative results. Mass spectrometry and nuclear magnetic resonance were used to investigate if the signal suppression is due to the formation of a complex between cocaine and levamisole in bulk solution. Strategies to eliminate this suppressing effect are further suggested in this manuscript. In a first approach, the increase of the pH of the sample solution from pH 7 to pH 12 allowed the voltammetric determination of cocaine in the presence of levamisole in a concentration range from 10 to 5000 μM at nonmodified graphite disposable electrodes with a detection limit of 5 μM. In a second approach, the graphite electrode was cathodically pretreated, resulting in the presence of oxidation peaks of both cocaine and levamisole, with a detection limit for cocaine of 3 μM over the linear range of concentrations from 10 to 2500 μM. Both these strategies have been successfully applied for the simultaneous detection of cocaine and levamisole in three street samples on unmodified graphite disposable electrodes.

Simple Strategy for Selective Determination of Levamisole in Seized Cocaine and Pharmaceutical Samples Using Disposable Screen‐printed Electrodes

“…Jong et al . (2018) investigated the reasons for this overlapping or suppression of the peaks and showed that this process is not related with interactions between the molecules in bulk solution (formation of complexes or adducts), but by the electrochemical processes at the electrode surface (electrode passivation or adsorption of oxidation products) . The BR buffer solution pH 8.0 was chosen for further experiments, since provided higher oxidation currents.…”

“…Therefore, this process was applied for LEV determination in a street cocaine sample. On the other hand, the same behavior was not observed for COC, which probably is not related to the deconvolution process, but to matrix effect caused by the presence of LEV, as reported in the literature .…”

“…Levamisole (LEV) is one of the most common adulterants found in cocaine street samples, i. e. around 69 % of seized cocaine samples contained this adulterant. It also may be used due to synergetic effects and increase in the drug action duration . LEV is also an anthelmintic agent used in veterinary medicine and its use associated with cocaine can cause neutropenia and agranulocytosis .…”

“…Recently, Jong et al . (2018) solved this problem by applying a cathodic pretreatment (−0.8 V for 360 s before each SWV scan) on unmodified graphite disposable electrodes, resulting in a separation of the peaks for the determination of cocaine in the presence of LEV . A similar approach was demonstrated to eliminate the interference of the most common cutting agents on the colorimetric detection of cocaine .…”

Profiling cocaine residues and pyrolytic products in wastewater by mixed‐mode liquid chromatography–tandem mass spectrometry

“…The aim of this study was to develop a new analytical method combining SPE and mixed‐mode LC coupled to MS/MS for the determination of COC and its related compounds in wastewater. The analytes selected were the parent drug, its metabolites BE and COE, the pyrolytic products AE and AEME, and levamisole (LEV), one of the main pharmaceuticals used in the adulteration of COC hydrochloride . To the best of our knowledge, this is the first application of RP ion‐exchange mixed‐mode LC for the determination of drugs of abuse.…”