Liquid-phase microextraction in a microfluidic-chip – High enrichment and sample clean-up from small sample volumes based on three-phase extraction

Abstract

In this work, a microfluidic-chip based system for liquid-phase microextraction (LPME-chip) was developed. Sample solutions were pumped into the LPME-chip with a micro-syringe pump at a flow rate of 3–4μLmin−1. Inside the LPME chip, the sample was in direct contact with a supported liquid membrane (SLM) composed of 0.2μL dodecyl acetate immobilized in the pores of a flat membrane of polypropylene (25μm thickness). On the other side of the SLM, the acceptor phase was present. The acceptor phase was either pumped at 1μLmin−1 during extraction or kept stagnant (stop-flow). Amitriptyline, methadone, haloperidol, loperamide, and pethidine were selected as model analytes, and they were extracted from alkaline sample solution, through the SLM, and into 10mM HCl or 100mM HCOOH functioning as acceptor phase. Subsequently, the acceptor phase was either analyzed off-line by capillary electrophoresis for exact quantification, or on-line by UV detection or electrospray ionization mass spectrometry for time profiling of concentrations. The LPME-chip was found to be highly effective, and extraction efficiencies were in the range of 52–91%. When the flow of acceptor phase was turned off during extraction (stop-flow), analyte enrichment increased linearly with the extraction time. After 10min as an example, amitriptyline was enriched by a factor of 42 from only 30μL sample solution, and after 120min amitriptyline was enriched by a factor of 500 from 320μL sample solution. This suggested that the LPME-chip has great potentials for very efficient analyte enrichments from limited sample volumes in the future.