Practice of solid-phase extraction and protein precipitation in the 96-well format combined with high-performance liquid chromatography-ultraviolet detection for the analysis of drugs in plasma and brain

C-18 Empore 96-well extraction disc plates have been employed for the analy sis of three drugs with different polarities in plasma in conjunction with HPLC-UV, rufinamide, ICL670 and an anticonvulsant agent (AA1) in an early s tage of development. With the most polar compound (AA1), ion-pair extractio n at pH 12 was applied. The method developed for the assay of AA1 in plasma was applied to its determination in brain using an Oasis HLB plate followi ng homogenisation in a pH 7.4 buffer and protein precipitation with NaOH-Zn SO4, thereby saving time for method development. Protein precipitation in t he 96-well format with filtration of the precipitate was applied to the det ermination of ICL670, a highly protein-bound compound (>99.5%), with a good recovery (78%). Reversed-phase chromatography was applied using a short 5 cm column packed with 3 mum particles for the determination of ICL670 and A A1 and two parallel columns (15 cm long) for the determination of rufinamid e. The methods were used routinely, one plate per analysis day being proces sed, resulting in increase in sample throughput and saving in solvents. (C) 2001 Elsevier Science B.V. All rights reserved.