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Quality control and quality assurance , Unusual specimen matrices

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  207

2026-10-13

59

Quality control and quality assurance

Unusual specimen matrices

 One of the unique aspects of postmortem toxicology work is that often specimens are received in various states of decomposition or putrefaction. Specimens may be denatured by heat, or mummified. All of these sample types create problems. Samples that are heat denatured are probably the easiest to deal with because the lipid content and concentrations of any putrefactive amines are not much higher than those in relatively fresh postmortem specimens. Heat denatured samples usually require homogenisation, and for accurate quantitative work may require some type of protease treatment, since a proportion of the analyte may be occluded by coagulated protein. Decomposed and mummified tissues probably create the biggest challenge, because the presence of high concentrations of lipids and putrefactive amines may obscure or interfere with the detection or accurate quantification of target analytes. Even if there is no obvious interference using a specific MS method, there may be a sufficient matrix effect to influence quantitative measurement adversely. Overcoming the effects of specimen decomposition is very difficult and attempts often have limited success. Finding a matrix-matched sample to act as a blank for the preparation of calibrators or controls is difficult, because samples vary tremendously in the nature or extent of decom position. As noted in the section on calibration methods, the method of standard addition may avoid difficulties in terms of finding a matrix matched sample. The quantitative determination of analytes in decomposed or other deteriorated samples is invariably less accurate than that in fresher samples. Robust, well validated methods inevitably produce more reliable results than those that are not.

Other matrices, such as bone, nails and hair, have been analysed successfully for a variety of substances. As with any other matrix, the appropriate use of internal standards (at least for chromatographic assays) and calibrators is important. The more difficult issue may be interpretation of the quantitative results due to lack of suitable databases in these matrices for comparison purposes. It must also be recognised that drugs and toxins typically take time to be incorporated in bone, nails and hair and therefore the results may not provide information about recent intake.