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Tackling Poor Specificity of Cocaine Color Tests by Electrochemical Strategies

de Jong, Mats, Florea, Anca, Eliaerts, Joy, Van Durme, Filip, Samyn, Nele, De Wael, Karolien
Analytical chemistry 2018 v.90 no.11 pp. 6811-6819
cobalt, cocaine, color, cutting agents, drugs, electrochemistry, electrodes, false negative results, graphene, pH, prediction, screening, thiocyanates
This paper presents electrochemical strategies for the fast screening of cocaine and most common cutting agents found in seized drug samples. First, a study on the performance of Scott color tests on cocaine and a wide range of cutting agents is described. The cutting agents causing false positive or false negative results when in mixture with cocaine are identified. To overcome the lack of specificity of color tests, we further propose a fast screening strategy by means of square wave voltammetry on disposable graphite screen printed electrodes, which reveals the unique fingerprint of cocaine and cutting agents. By employing a forward and backward scan and by a dual pH strategy, we enrich the electrochemical fingerprint and enable the simultaneous detection of cocaine and cutting agents. The effectiveness of the developed strategies was tested for the detection of cocaine in seized cocaine samples and compared with the color tests. Moreover, we prove the usefulness of square wave voltammetry for predicting possible interfering agents in color tests, based on the reduction peak of cobalt thiocyanate. The developed electrochemical strategies allow for a quick screening of seized cocaine samples resulting in a selective identification of drugs and cutting agents.