Direct immersion in-tube microextraction coupled with capillary electrophoresis

Abstract

Solid phase microextraction (SPME) and liquid phase microextraction (LPME) are widely used for sample enrichment and cleanup prior to an instrumental analysis. Compared to simply applicable SPME, LPME usually requires more manual maneuvers. In order to overcome such shortcomings of LPME, we developed in-tube microextraction (ITME). ITME uses a liquid plug inside a capillary as an acceptor phase and thus can be in-line coupled with capillary electrophoresis (CE) with ease. Since the acceptor phase is well protected inside the capillary, ITME can be carried out under severe extraction conditions. Moreover, given that the extraction and injection processes take place simultaneously, the extraction kinetics and efficiency are very high. Using a commercial CE instrument, direct immersion (DI)-ITME was demonstrated for two- and three-phase configurations. In two-phase DI-ITME, acidic analytes of neutral forms in an acidic aqueous donor solution were extracted into a pentanol acceptor plug in the capillary. In three-phase DI-ITME, a small amount of octanol was injected into a capillary containing a basic aqueous acceptor phase and acidic analytes in an acidic aqueous donor solution were enriched into the basic acceptor phase through the octanol layer by the driving force of a pH difference. Due to the lack of a hanging drop, DI-ITME is a quite simple and robust extraction method.