Use of a Microplate Scintillation Counter as a Radioactivity Detector for Miniaturized Separation Techniques in Drug Metabolism

• Published in: Analytical chemistry (Washington) Vol. 72; no. 16; pp. 3956 - 3959
• Main Authors: Boernsen, K. Olaf, Floeckher, James M, Bruin, Gerard J. M
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.08.2000
• Subjects: Animals; Biological and medical sciences; Drugs; General pharmacology; Medical sciences; Metabolism; Miniaturization; Pharmaceutical Preparations - metabolism; Pharmacokinetics. Pharmacogenetics. Drug-receptor interactions; Pharmacology. Drug treatments; Radioactivity; Radiochemistry; Rats; Scintillation Counting - methods; Urine - chemistry; Dose metabolism relationship; Biological fluid; Chemical analysis; Capillary electrophoresis; Liquid chromatography; Radioactivity detector; Multicomponent analysis; Concentration metabolism relation; Qualitative analysis; Miniaturization; Scintillation counter; Pharmacokinetics; Labelled compound
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac000432s

In miniaturized separation techniques, such as capillary electrophoresis (CE) or capillary liquid chromatography (LC), conventional on-line radioactivity detection of labeled compounds is restricted, because of insufficient sensitivity. It will be shown that a microplate scintillation counter for 96-well plates (TopCount) can be used as a sensitive and easy-to-handle radioactivity detector for capillary LC and CE. The attractive combination of capillary LC, eluent fractionation, and subsequent off-line counting is described. The new method is applied for rapid and sensitive separation and detection of 3H-labeled parent drug and its metabolites at levels between 25 and 700 cpm in rat urine. The advantages of capillary LC coupled to the TopCount, and combined with LC−MS data, can be of benefit in many analytical areas, including the characterization of metabolites at low concentration within complex biological fluids. With the same setup, the fractionation with subsequent off-line counting is equally applicable to CE. This is demonstrated with electrophoretically separated 14C-labeled impurities, nicely resolved from a negatively charged main compound, at low levels.