Trace analysis forensic samples

For trace analysis, this means that small bore columns should be used and low retention factors are advantageous if the sample volume is limited, as is often the case in clinical or forensic chemistry. If enough sample is available, e.g. in food analysis, it is not necessary to use small-bore columns and low retention factors. However, the analysis time, solvent consumption and column overload by accompanying substances (not discussed here) need to be kept in mind. 

The value of the limit of detection In forensic work Is shrouded In details not usually present In other trace analysis efforts. In this area the performance of the analyst relates to samples submitted as legal evidence, perhaps for some crime. The sample may often be In such short supply that only limited analyses can be performed on It. In these cases the limit of detection can be greatly affected. 

In the late 1960s and the 1970s, neutron activation analysis has received much attention in forensic science because of its ultimate sensitivity combined with specificity. The early optimism has been dampened by the difficulty in interpreting results due to the variation of trace elements within samples at a given time and over a length of time. It has been used mainly in... 

Kolia, P. Trace analysis of explosives from complex mixtures with a sample preparation and selective detection. J. Forensic Sci. 1991, 36, 1342-1359. 

Solid-phase microextraction (SPME) is a recent sample preparation technique for trace analysis by GC (12). It is a simple, solvent-free method that uses a polar or nonpolar coated fused-silica fiber to directly extract analytes from various matrices (usually aqueous). It can be used in a headspace mode as well. After the fiber is removed from the sample, it is transferred to the heated inlet of a chromatographic system and the analytes are thermally desorbed for analysis. The technique works well for the analysis of trace analytes in water or urine. It has been applied in the field of forensic science in the analysis of fire debris, explosives, and drugs in biological fluids (13-15). 

Neutron activation analysis is an attractive method in many trace element problems, or where the total amount of sample is limited. Many geochemical studies of trace constituents and semi-conductor developments have used the technique, whilst in recent years pollution investigations have provided a new focus. In forensic science small flakes of paint, single hairs and a variety of other small samples have been analysed and identified by activation analysis. In recent years activation analysis has lost further ground to ICP-MS which provides more comprehensive information and is more readily operated. Sensitivity is also comparable in many cases. 

The study of obsidian by NAA has proved to be particularly fruitful because of the relatively limited number of sources and the extent to which it was traded (Beardsley et al. 1996, Cook 1995, Darling and Hayashida 1995, Kuzmin et al. 2002, Leach 1996). Studies have also extended to include other volcanic materials such as pumice (Bichler et al. 1997, Peltz et al. 1999). NAA has also been used for the analysis of flint as OES is insensitive and not reproducible due to the effect of the high silica content, and AAS requires significant sample preparation (Aspinall and Feather 1972). The wide range of appropriate materials extends to organic materials such as human bone (Farnum et al. 1995), and its exceptional sensitivity to trace elements has led to its wide use in geochemistry (for example in determining trace [ppb] contaminants in waters) and more recently in forensic chemistry. 

Figure 3.1 A hair sample from a suspected drug user is prepared for forensic analysis. As hair grows, it incorporates small amounts of chemicals that are produced when drugs are broken down in the body. To identify these drugs, the hair is first cut into pieces and soaked in a liquid solvent The solvent removes the traces of drug metabolites from the hair so that they can be identified by chromatography and mass spectrometry.

The use of activation analysis in criminal investigations (forensic activation analysis) is also well established. The basic idea here is to match the trace-element distributions found in bullets, paint, oil, and so on found at the scene of a crime with the trace-element distributions in objects found with criminal suspects. Such identification is rapid and nondestructive (allowing the actual evidence to be presented in court). Moreover, the probability of its correctness can be ascertained quantitatively. Other prominent examples of the use of forensic activation analysis involve confirmation of the notion that Napoleon was poisoned (by finding significant amounts of arsenic in hair from his head) and the finding that the activation analysis of the wipe samples taken from a suspect s hand can reveal not only if he or she has fired a gun recently but also the type of gun and ammunition used. 

Finally, the Auschwitz State Museum itself ordered an expert report to be compiled. The Institute for Forensic Research, Toxicology Division, of Cracow, Poland, named after Prof. Dr. Jan Sehn, prepared this report under Prof. Dr. J. Markiewicz on September 24, 1990, which confined itself to the analysis of masonry samples.56 The report concluded that the reason why Leuchter s samples from the homicidal gas chambers were mostly negative with respect to traces of cyanide was because the cyanide compounds had been exposed for more than 40 years to weathering, which these compounds allegedly could not have withstood. Three of these authors from the Jan Sehn Institute later published additional findings,57 which were, however, based on a veri-fiably incorrect analytical method—as was the first series of analy-... 

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