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 electro phoresis (CE) are the limited concentration sensitivity and the applicabili ty to biological samples. An enrichment technique using miniaturised on-lin e solid-phase extraction did enhance the concentration sensitivity by a fac tor 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 m m) 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 capilla ry and glass-fibre filters retained the sorbent. Preparation and performanc e 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 separati on efficiency was excellent as 250 000 plates were obtained in a 58 cm enri chment capillary (550 000 plates m(-1)). The concentration limit of detecti on 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 pr essure injection) without enrichment. The enrichment procedure was successf ully adapted to high efficiency separation of terbutaline enantiomers using cyclodextrin as chiral selector. It was possible to enrich terbutaline fro m directly injected spiked plasma as well. (C) 1999 Elsevier Science B.V. A ll rights reserved.