Department of Drugs and Toxicology, National Institute of Criminalistics and Criminology, Brussels, Belgium; AXES Research Group, Chemistry Department, University of Antwerp, Antwerp, Belgium.
Department of Drugs and Toxicology, National Institute of Criminalistics and Criminology, Brussels, Belgium.
Forensic Sci Int. 2021 Feb;319:110534. doi: 10.1016/j.forsciint.2020.110534. Epub 2020 Oct 5.
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.
对缴获的可卡因粉末进行常规筛选通常采用颜色测试。另一种快速筛选技术是中红外（MIR）光谱法。然而，在走私案件中，毒品经常经过加工以逃避检测。在本研究中，对五个走私案件应用了当前的筛选技术（可卡因颜色测试和使用库和化学计量学的 MIR 光谱法）。对于每个案例，所有样品均首先进行可卡因颜色测试和 MIR 分析筛选，然后使用 GC-MS 和 GC-FID 进行确认分析，以识别和定量可卡因和切割剂。最后，对扫描电子显微镜-能量色散 X 射线光谱法（SEM-EDX）分析进行了额外的表征。所有走私样品在现场和实验室均通过可卡因颜色测试对可卡因测试呈阴性。四个走私案件均由有色样品组成。因此，颜色测试结果受到影响，因为测试的变色与粉末的颜色（棕色、绿色、红色或黑色）几乎相同。相比之下，（有色）粉末可以用 MIR 测量，但使用参考库搜索时，MIR 光谱未显示可卡因的命中。此外，在应用化学计量分类模型后，五个案例中有四个未检测到可卡因。GC-MS 分析是鉴定的金标准，所有案例均鉴定出可卡因。这些样品含有 0.8w%至 35w%之间的可卡因。考虑到筛选、色谱和 SEM-EDX 分析的结果，可以假定可卡因被掩盖了。假阴性筛选结果是由化学修饰的可卡因和/或可卡因与有色粉末混合引起的。在额外的实验中，在筛选技术之前进行了样品提取步骤。测试了两种样品制备方法（丙酮和乙酸乙酯），结果可卡因颜色测试和/或 MIR 光谱呈阳性。可以得出结论，颜色测试和 MIR 光谱等筛选技术的结果只是推测性的，应始终予以确认。
