Miniaturised on-line solid-phase extraction for enhancement of concentration sensitivity in capillary electrophoresis

Two of the most important issues facing the technology of capillary electrophoresis (CE) are the limited concentration sensitivity and the applicability to biological samples. An enrichment technique using miniaturised on-line solid-phase extraction did enhance the concentration sensitivity by a factor of 7000 using W-absorbance detection. The cationic drug terbutaline was used as a model compound. The extractor consisted of a short length (1-3 mm) of a capillary (200 mu m I.D.) packed with C-18 alkyl-diol silica (d(p) 12 mu m). This capillary was connected to a 50 mu m I.D. separation capillary and glass-fibre filters retained the sorbent. Preparation and performance of the enrichment capillary is discussed and described in detail. The on-line enrichment procedure includes washing, wetting, conditioning, sorption, washing, filling and desorption. Then follows CE separation. The separation efficiency was excellent as 250 000 plates were obtained in a 58 cm enrichment capillary (550 000 plates m(-1)). The concentration limit of detection for terbutaline in aqueous solution with on-line enrichment was 0.6 nM (10 min x 140 kPa pressure injection) compared to 4.4 mu M (1 s x 3.4 kPa pressure injection) without enrichment. The enrichment procedure was successfully adapted to high efficiency separation of terbutaline enantiomers using cyclodextrin as chiral selector. It was possible to enrich terbutaline from directly injected spiked plasma as well. (C) 1999 Elsevier Science B.V. All rights reserved.