Headspace-no drop microextraction for capillary electrophoresis

Abstract

In liquid phase microextraction, high enrichment factors can be obtained using an acceptor phase of small volume. By hanging an acceptor drop at the separation capillary tip, single drop microextraction (SDME) can be in-line coupled with capillary electrophoresis (CE). The small surface-to-volume ratio of the drop enables high enrichment factors to be obtained in a short time. One practical issue in SDME is how to keep the drop attached to the capillary stably. Here, we present novel but extremely simple no drop microextraction (NDME) using the liquid inside the capillary as an acceptor phase, without forming a drop at the capillary tip. As a first example, NDME has been combined with headspace (HS) extraction. Simply by placing a capillary filled with a basic run buffer in the HS above an acidic donor solution, volatile acidic analytes were extracted into the acceptor phase in the capillary. After extraction, electrophoresis of the extracts in the capillary was carried out. Owing to the robust nature of the acceptor phase, the extraction temperature and time ranges of HS-NDME can be extended significantly, compared to HS-SDME. The enrichment factors for chlorophenols in a standard solution were up to 1100 under an optimal HS-NDME condition of 80°C for 15 min. For a complex sample such as red wine, an acceptor phase with an increased buffer capacity was used obtaining detection limits of about 20 nM. The whole procedures of HS-NDME-CE were carried out automatically using built-in programs of a commercial CE instrument.