تسجيل الدخول

تسجيل

Specimen preparation and extraction

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  p199-200

2026-10-12

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Specimen preparation and extraction

The first stage of the analytical process involves separation of the drug or compound of interest from the biological matrix in which it is contained. Urine and other non-viscous fluid specimens do not usually require treatment prior to extraction. However, even for relatively fluid blood samples, volumetric measurement with a positive displacement pipette designed for viscous samples, or gravimetric sampling, is preferred. The use of standard glass pipettes is discouraged as being inaccurate with viscous samples. Liquid–liquid extraction or solid-phase extraction (SPE) are both appropriate procedures for extracting drugs from urine and blood. Clotted blood may be homogenised in water or buffer prior to analysis.

The extraction of drugs from solid tissues requires the tissue matrix to be broken down to release drugs into an environment from which they are accessible for solvent extraction. This can be achieved by homogenisation, acid or alkaline hydrolysis, or enzyme digestion. Direct solvent extraction before or after acid or enzymatic digestion has almost superseded the classic protein-precipitation methods. The more sensitive detection methods of GC-MS and LC-MS mean that much smaller amounts of tissue can be processed. Consequently, any emulsion problems that arise are resolved more easily than in the past, when several hundred grams of liver and large volumes of solvent were required. The use of protein-precipitation reagents, such as barium chloride, zinc sulfate and tungstic acid, is discouraged for quantitative work because a significant portion of the analyte may be co precipitated with the coagulated protein and therefore lost to the analysis.