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Solvent extraction and thin-layer chromatography

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  274

2026-10-24

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Solvent extraction and thin-layer chromatography

In general, the choice of solvent is dictated by the wide range of drugs to be covered, or the need to extract a specific drug as in confirmatory analysis procedures. The classic extraction–TLC methods used primarily by North American laboratories for drug testing in animal sports provide coverage for a wide range of basic, acidic and neutral drugs. Individual aliquots of urine, in some cases following pre-treatment, are extracted at various pH values and with a range of organic solvents. The extracts are applied to TLC plates run in a variety of solvent systems, and the TLC plates are sprayed with a range of reagents, often in sequence. Ion pair (IP) extraction can be used to optimise the extraction of weak acids, weak bases and zwitterionic compounds. The ion pairing buffer (phosphate buffer with bromothymol blue) is added to the urine and the pH adjusted to 7.4. Drugs are extracted with dichloromethane: 2 propanol (3: 1) and aliquots of the extract are applied to two TLC plates. The developed plates are examined under UV light and subjected to a range of visualisation reagents. Steroids are extracted from urine using ethyl acetate after adding saturated sodium borate solution and washing the extract in 15% sodium sulfate in sodium hydroxide solution. The extract is run in a TLC system of chloroform: ethyl acetate: methanol (50: 45: 5 v/v); the plate is dried and then re-run in Davidow reagent. The steroids are visualised by spraying with a mixture of sulfuric acid: ethanol (50: 50 v/v) and heating (high heat) with a hot-air blower or hot plate to develop dark oxidation spots.