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Impure forms of illicit drugs are almost as big a problem as the drugs themselves. Now, researchers in Spain have used diffuse reflectance near-infrared spectroscopy (DR-NIR) to quickly determine the purity of heroin. Their approach could save lives by allowing drug enforcement investigators to identify impure and more toxic forms of the drug being sold on the street. Unlike conventional tests, it does not destroy the original drug sample, the researchers say. Salvador Garrigues, Javier Moros and Miguel de la Guardia, of the Department of Analytical Chemistry, at the University of Valencia, and Nieves Galipienso and Rocío Vilches, of the Pharmacy and Drug Control Inspection Unit of the Valencia Health Department, explain that heroin, the 3,6-diacetyl derivative of morphine, is an opiate drug synthesized from opium-derived morphine. The purity of heroin being supplied illegally to users worldwide can vary widely. Pushers often mix, or cut, the drug with other materials including chalk, flour, talcum powder, paracetamol, and caffeine. However, it is not uncommon to use "cutting agents" such as household cleaning agents, bleach and scouring powders. Pure heroin is a white, bitter powder whereas street heroin can be anything from white to dark brown depending on what production impurities it contains and what cutting agents have been used. The average heroin user is not usually made aware of the precise concentration of the drug itself and certainly will not learn of the presence of any toxic or harmful cutting agents. As such, they can be at serious risk of overdose and even death irrespective of the fact that they are using a highly addictive and harmful drug. The researchers explain that conventional tests for determining the purity of street heroin usually involve destructive and time-consuming sample preparation. Techniques such as high-performance liquid chromatography (HPLC), gas chromatography (GC) with and without derivatization procedures, and capillary electrophoresis are commonly used for separation. The US Drug Enforcement Administration (DEA) has used capillary technique since 2003. However, the researchers point out that, while these methods can be highly sensitive, they are destructive, and "involve a tedious and solvent-consuming sample preparation". Moreover, not all techniques are suitable for all heroin samples. This situation makes it very difficult for drug enforcement authorities to keep track of trends in cutting and abuse of the drug among pushers and so makes it difficult to predict where overdoses or toxic side-effects might become more common because of particularly toxic batches of heroin hitting the streets. A simple, non-destructive test would allow a much more rapid response to be made by the authorities. "Vibrational spectroscopy-based methods, like Raman, mid-infrared (MIR), or near-infrared (NIR) spectroscopy can be applied to determine the concentration of compounds present in complex samples at percentage levels without any sample preparation," the researchers explain. It is puzzling then, that their bibliographic search, revealed only a few references to the determination of heroin by vibrational spectroscopy. As long ago as 1987, researchers had suggested that infrared spectroscopy might be a viable technique for the analysis of cocaine and heroin samples. Raman techniques have also been used on both these two drugs, and amphetamine. The team adds that NIR spectroscopy is being used increasingly for the quantitative analysis of solid samples, but only one preliminary study for its use in the analysis of heroin, 6-acetylmorphine, and codeine has been published. "The main objective of [our] study was the development of a fast, non-destructive, and well-validated method for the quantitative determination of heroin in seized illicit street drugs using previously analysed actual samples to build the calibration model in order to model the behaviour of heroin and to minimize the possible spectral contribution of cutting agents," the researchers explain. Garrigues and colleagues have now studied 31 illicit drug samples from Spain that contained between 6% and 34% heroin by weight. They used DR-NIR to determine the chemical composition of the cut heroin. From a hierarchical cluster analysis of all samples considered in the study, the authors selected 21 representative samples to build a partial least-squares (PLS) calibration model, working with zero-order NIR spectra in the interval between 1111 and 1647 nm. In these conditions only eight factors are required for calibration and the remaining samples were used to validate proposed method. This model could be useful in verifying the nature of newly seized samples as well as correctly predicting heroin concentration in unknown samples, they explain. Reference:
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