Challenges for cocaine detection in smuggling samples

Abstract

Screening of seized cocaine powders is routinely performed by means of colour tests. An alternative fast screening technique is Mid-InfraRed (MIR) spectroscopy. In the context of smuggling cases, however, drugs are often processed to circumvent detection. In this study, the current screening techniques (cocaine colour test and MIR spectroscopy using libraries and chemometrics) were applied to five smuggling cases. For each case, all samples were first screened with a cocaine colour test and MIR analysis, followed by confirmation analyses with GC–MS and GC-FID to identify and quantify cocaine and cutting agents. Finally, Scanning Electron Microscopy-Energy Dispersive X-ray spectroscopy (SEM-EDX) analyses were performed for additional characterization. All smuggling samples tested negative, both on-site as in the laboratory, for cocaine with the cocaine colour test. Four smuggling cases consisted of coloured samples. Consequently the colour test result was influenced because discolouration of the test showed almost the same colour as the colour of the powders (brown, green, red or black). In contrast, the (coloured) powders could be measured with MIR, but the MIR spectra showed no hit for cocaine using a reference library search. Moreover, cocaine was not detected in four out of the five cases after application of a chemometric classification model. GC–MS analysis, the golden standard for identification, resulted in a positive identification of cocaine in all cases. These samples contained cocaine ranging between 0.8w% and 35w%. Taking into account the results of the screening, the chromatographic and the SEM-EDX analyses, it could be presumed that cocaine was masked. False negative screening results were caused by chemically modified cocaine and/or cocaine mixed with coloured powders. In additional experiments, a sample extraction step prior to the screening techniques was performed. Two sample preparation methods (acetone and ethyl acetate) were tested and resulted in a positive screening of cocaine with the colour test and/or MIR spectroscopy. It can be concluded that the outcome of screening techniques such as colour tests and MIR spectroscopy is only presumptive and should always be confirmed.