18.104.22.168 Powder Samples
If the samples are powdered materials, they should be sorted into groups, where the members of the groups cannot be distinguished from each other. Having achieved this, the items in each group should be counted and a good physical description prepared. This should include weight, colour, odour and any other physical characteristic that the scientist considers to be important. Depending upon the number of items in the group, the following sampling strategy, based upon the United Nations Drug Control Programme (UNDCP) recommendations, may be adopted. If there are between 1 and 10 items, all of them should be examined. If there are between 10 and 100 items, then 10 items should be examined, while if there are more than 100 items, the square route of the number of items f May, 2002.
should be examined. These should be chosen at random from among the items, by, for example, assigning each of them a number and then choosing the items to be examined from a random-number table.
What advantage is there in using a random-number table or generator to determine which of the samples should be analysed?
The advantage of this is that it removes any bias which might be imparted by the operator in sample choice.
Other sampling protocols exist, but a discussion of these is beyond the scope of this present text. There are, however, a number of problems associated with sampling procedures in general. If, for example, the sample comprises 1000 items, then a large number of expensive and time-consuming analyses will be required. If it is assumed that there is only one drug type in the seizure, then recent work using 'probabilistic reasoning' has shown that it may be possible to analyse as four or six individual items, depending upon the degree of certainty required . However, the difficulty arises when more than one type of drug or drug mixture is present, but the different mixtures are visually identical. Whether this occurs or not depends upon the area in which one is working. In some areas, the problem (in amphetamines, at least) is reported not to arise , while in parts of mainland Europe, it is known to exist . As a consequence, such a model, where reduced numbers are sampled, may only be applicable after a great deal of work to establish that multiple visually identical drug types do not occur within seizures. In essence, the number of items to be analysed depends upon the drug in question, the experience of the analyst and the jurisdiction in which he is working.
Once the samples to be analysed have been identified, physical descriptions, homogenization and sampling, presumptive testing, TLC and confirmatory testing should be undertaken.
If the items are tabletted, then a different approach is required. The items should be divided into visually indistinguishable groups and the number of items in each group should be counted, if necessary estimating the number from the mean weight of tablet and the total mass of the tablets, if very large numbers are involved. A good physical description of the tablets should be made, including recording of the size, colour, shape, logo and score marks (if present), while the ballistics (physical characteristics) of the tablet should be examined and detailed. Photography is particularly helpful in this respect. This latter includes recording of all of the physical damage to the tablets which may be present.
What is the advantage of recording the ballistic features of tabletted drug units?
Having recorded all of the physical data, the items to be examined chemically should be chosen. At the time of writing^ there is no agreed best-practice protocol for undertaking this and the analyst should work within the requirements of the judicial system in which he/she is operating. The theory applied to powdered amphetamines can be equally applied to amphetamine tablets. The latter should be sampled and presumptive tests, TLC and confirmatory tests then carried out.
If the samples are trace samples, that is, the drug present is likely to be easily contaminated, the approach should be that the operators, laboratory equipment and reagents to be used should be demonstrably free of drug residues prior to the commencement of the analysis. This can be achieved by washing the glassware, work surfaces and operator's hands with a small amount of methanol and concentrating the dissolved materials. The same batch of solvent should be used for this procedure and for the analysis of the drug items themselves. The control extract should be analysed in the same run sequence as the materials from the case samples (it is not usually possible to carry out the control analyses prior to commencing further work because of time and cost constraints). If the controls are drug-free, then any drug observed in the casework samples can only have come from the latter materials themselves.
Having carried out the control procedures, the item(s) to be examined should then be swabbed, individually, by using a clean swab soaked in a suitable solvent. A suitable solvent should freely dissolve the drug material, not cause decomposition of the drug or react with it, and be amenable to subsequent analytical procedures. It should be remembered that the swabbing process should leave enough material intact for a second and subsequent analysis. If the swab is not to be used immediately, it should be dried and stored until needed.
Why should the swab be dried prior to storage if it is not going to be used immediately?
Homogenization of powdered samples can be achieved by using a number of different methodologies. One of the best methods for samples likely to be encountered 'on the street' is the use of the 'cone-and-square' method. In this technique, f May, 2002.
the materials are mixed and the larger fragments reduced in size. The material is poured onto a flat, clean surface and then divided into four; opposite quarters are removed and the two remaining quarters recombined. The process is repeated until the desired sample size is achieved. For larger samples, a 'core' may be taken and then subjected to further homogenization by using this cone-and-square methodology.
For tabletted materials, homogenization is more problematic since if the tablet was homogenized, it would also be destroyed. For this reason, a sample is taken from the tablet and gently scraped from the dose form, away from any ballistic features which are likely to be of use in subsequent examinations. The powder is then thoroughly homogenized prior to testing.
Why is it important to retain the ballistics features where possible?
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