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Title
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Qualitative and quantitative determination of cocaine using mid-infrared spectroscopy and chemometrics
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Author
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Abstract
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| Worldwide, cocaine is commonly one of the most seized and used drugs. Currently, the screening of cocaine in seized powders is performed by means of colour tests. The major drawbacks of these tests are a lack of specificity and a subjective colour interpretation (‘50 shades of blue’). The high prevalence of cocaine and the limitations of colour tests have led to widespread interest in developing a fast method for identification and quantification of cocaine. In this thesis, a new approach was established using Mid-InfraRed (MIR) spectroscopy in combination with Support Vector Machines (SVM). The SVM models resulted in a clear output (cocaine detected/not detected) and a reliable estimation of the purity of cocaine in a wide variety of street mixtures. Combined with SVM, the MIR technique is a simple, user-friendly and fast method to identify and quantify cocaine. The developed chemometric models were tested in practice for the analysis of large cocaine seizures. A strategy was developed to obtain information about seizure homogeneity, the presence and concentration of cocaine and its most common adulterant, levamisole. Applying this method, the sample size as well as the number of confirmation analyses could be reduced. It was also investigated whether the developed models could be applied to another MIR instrument of the same brand. Various strategies to perform a calibration transfer were compared. A mixed model, using data of both instruments, was the most successful and could be used on both instruments to detect cocaine. A comparative study was conducted to determine if other spectroscopic techniques such as Raman and Near-InfraRed [NIR], in addition to MIR, could be used to classify and quantify cocaine. These techniques performed quite similar and could be considered as good alternatives for the MIR technique. Finally, the current screening techniques (colour tests and MIR spectroscopy) were evaluated for the detection of cocaine in complex smuggling samples. Detection of cocaine was only possible after an extraction step prior to screening analysis. It can be concluded that spectroscopic techniques combined with chemometric methods are an important added value for initial screening of cocaine. Moreover, an estimation of the purity is possible without wet chemistry. The obtained knowledge of this work can be applied for the detection of other illicit drugs, such as heroin and amphetamines. |
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Language
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English
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Publication
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Antwerp
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University of Antwerp, Faculty of Sciences
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2020
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Volume/pages
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184 p.
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Note
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De Wael, Karolien [Supervisor]
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Janssens, Koen [Supervisor]
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Meert, Natalie [Supervisor]
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