At the present time, it is possible to carry out identification and quantification of a wide variety of drugs, ranging from those which are entirely herbal or fungal in origin (Cannabis and its products), through those which are semi-synthetic (cocaine and diamorphine), to those which are entirely synthetic (the amphetamines). A wide variety of techniques can be applied for their analysis and it is rare that an issue of sensitivity becomes apparent. In terms of drug identification and quantification, the drug analyst is in a particularly strong position.
However, the position changes with respect to the comparison of drug samples. Such comparison (profiling) procedures can be considered to consist of five stages, as follows:
• sample selection
• sample homogenization
• sample preparation for analysis
• sample analysis
• data interpretation and reporting
Even with the (apparently) simple task of sample selection, we are presented with a great number of difficulties which still remain to be resolved. These include the following:
• How many samples should be taken and what proportion of the whole should these represent?
• Should it be assumed that there is one drug, two drugs or more than this present in a sample, or that the accused is innocent and that there are no drugs present?
Each of the above aspects have been studied in great detail and a number of mathematical models proposed for evaluation studies, but there is currently no universally adopted method (apart from the United Nations recommendations)^ However, the latter themselves present their own problems - how are random numbers assigned to individual doses in a batch of thousands so that the samples can be chosen truly randomly?
A further question that might be asked is how should drugs be homogenized once selected? Large batches may be treated by using blenders or grinders, but in this case there is the associated difficulty of ensuring that the equipment is clean before use. Small samples can be handled by the cone-and-square method, but what of medium-sized samples which may be too large for the latter technique but too small for the former?
Much is known about sample preparation for comparison purposes in cases of the more commonly encountered materials, for example, heroin, and Cannabis and its products. However, considerably less information is available concerning the stabilities of the newer 'designer' drugs in the solvents used to prepare them, what the extraction efficiencies are for the different impurities, and whether, for example, artefacts are formed as a consequence of a particular preparation process. Research is clearly needed in these areas and this has only really just begun.
Another issue is whether or not the analytical techniques themselves are optimized. Have the methods used been fully scrutinized? Are they valid for the synthetic drugs made by the routes encountered today, plus are they separating the anticipated impurities without the expected artefacts?
There is also the issue of which numerical method should be used for drug comparison investigations. This has been well studied for heroin, but the arena is wide open for analysis and numerical comparison of Cannabis and its products, cocaine, amphetamines, tryptamines and other synthetic or semi-synthetic drugs. How these methods should be reported has still not been fully explored.
There are also a number of new analytical techniques available for the comparison of samples. Traditionally, drugs are compared on the basis of their impurity content. Little attention, until recently, had been applied to the use of DNA profiling for drug identification and comparison - such an approach offer great
potential for application in this area. A wide variety of alternative methods, involving the analysis of e.g. metal ion concentration, stable isotope ratios and occluded solvent content, to name just a few, have been reported in the scientific literature, although these have not yet found widespread application in casework studies. The question must be raised - are these approaches worth further investigation?
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