Pseudophase-to-solvent microextraction for in-line sample concentration of anionic analytes in capillary zone electrophoresis

Abstract

We present pseudophase-to-solvent microextraction (PSME) as a simple pressure-driven in-line sample concentration technique in capillary zone electrophoresis (CZE) for small organic anions. The developed technique is like solid-phase extraction; however, the chromatographic phase is a pseudophase, i.e., in-situ cetyltrimethylammonium bromide (CTAB) interfacial micelles. A large volume of sample (e.g., > 12 capillary volumes) prepared in [CTAB] ∼critical micelle concentration was injected into the capillary. The elution and enrichment of analytes trapped in the CTAB coating was facilitated by the high concentration of methanol in the background solution, which was introduced from the outlet end. Co-electroosmotic flow CZE was conducted after the concentrated analytes reached the tip of the inlet. Parameters such as sample loading time and elution time were optimised. Under optimised conditions, the SEFs of 187–573 achieved for the model anions (4-nitrophenol, 4-vinylbenzoic acid, mecoprop, indoprofen, sulfamethizole and sulindac) were comparable to previously reported off-line microextraction techniques. The calculated LOD (S/N = 3), LOQ (S/N = 10), intra-/inter- (n = 6/n = 9, 3 days) day repeatability and linearity (R2s) values in PSME-CZE were 4.2–20.1 ng/mL, 13.8–67.1 ng/mL, 5%, 10% and > 0.990, respectively. The PSME-CZE of fortified urine samples showed % recovery values of 93–108% with %RSDs (n = 3) of 4–10% for the model analytes.