Abstract
Drugs incorporated into hair are exposed to the environment, and cosmetic and chemical treatments, with possible decreases in their content. Knowledge concerning the effect of sunlight on drug content in hair can be helpful to forensic toxicologists, in particular, when investigating drug concentrations above or below pre-determined cut-offs. Twenty authentic positive hair samples were selected which had previously tested positive for amphetamines and/or ketamine. Washed hair were divided into two identical strands, with the former exposed at 765 W/m2 (300–800 nm spectrum of irradiance) for 48 h in a solar simulator, and the latter kept in the dark. Hair samples were extracted and analyzed by liquid chromatography high-resolution mass spectrometry detection. The percentage of photodegradation was calculated for each analyte (i.e., amphetamine, methamphetamine, methylendioxyamphetamine, ketamine, and norketamine). In parallel, photodegradation processes of standard molecules dissolved in aqueous and organic solutions were studied. In 20 hair samples positive for the targeted analytes, exposure to artificial sunlight induced an appreciable decrease in drug concentrations. The concentration ranges in the non-irradiated hair samples were 0.01–24 ng/mg, and 65% of samples exhibited a decrease in post-irradiation samples, with reduction from 3% to 100%. When more drugs were present in the same hair sample (i.e., MDMA and ketamine) the degradation yields were compound dependent. A degradation product induced by irradiation of ketamine in aqueous and methanol solutions was identified; it was also found to be present in a true positive hair sample after irradiation. Ketamine, amphetamines, and their metabolites incorporated in the hair of drug users undergo degradation when irradiated by artificial sunlight. Only for ketamine was a photoproduct identified in irradiated standard solutions and in true positive irradiated hair. When decisional cut-offs are applied to hair analysis, photodegradation must be taken into account since sunlight may produce false negative results. Moreover, new markers could be investigated as evidence of illicit drug use.
Highlights
The main advantage of hair as a testing matrix is the ability to provide information relating to historical drug exposure
Methamphetamine, both in methanol and water (Figures S1B1 and B2, respectively), presented curves similar to AMF, with the unique difference being the absorption at 205 nm in water which increased under irradiation
Amphetamine, MA MDA, MDMA, KET, and NKET incorporated in hair undergo degradation when irradiated by artificial sunlight, suggesting that they can suffer photodegradation under natural sunlight
Summary
The main advantage of hair as a testing matrix is the ability to provide information relating to historical drug exposure. The stability of drugs in hair, is affected by exposure to sunlight and weathering, cosmetic chemical treatments (i.e., oxidative dyeing, bleaching, or permanent wave), and physical damage [5,6,7]. In order to better understand the role and underlying mechanisms of solar light exposure on decreasing concentrations of drugs in hair, and following our previous [10] photodegradation studies on UVA- and UVB-induced changes, the aim of the present work was to evaluate the photodegradation of several common stimulant drugs (i.e., amphetamines and ketamine (KET))
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