title: Use of a microplate scintillation counter as a radioactivity detector for miniaturized separation techniques in drug metabolism.
abstract: 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.
authors.affiliation: Drug Metabolism and Pharmacokinetics, Novartis Pharma AG, Basel, Switzerland. k_olaf.boernsen@pharma.novartis.com
authors.forename: K O
authors.initials: KO
authors.lastname: Boernsen
authors.forename: J M
authors.initials: JM
authors.lastname: Floeckher
authors.forename: G J
authors.initials: GJ
authors.lastname: Bruin
mesh_terms: D000818:Animals; D008904:Miniaturization; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D011854:Radiochemistry; D051381:Rats; D012588:Scintillation Counting / Q000379:methods*; D014556:Urine / Q000737:chemistry
chemical_list: D004364:Pharmaceutical Preparations