Continuous-Flow Microelectroextraction for Enrichment of Low Abundant Compounds

We present a continuous-flow microelectroextraction flow cell that allows for electric field enhanced extraction of analytes from a large volume (1 mL) of continuously flowing donor phase into a micro volume of stagnant acceptor phase (13.4 mu L). We demonstrate for the first time that the interface between the stagnant acceptor phase and fast-flowing donor phase can be stabilized by a phaseguide. Chip performance was assessed by visual experiments using crystal violet. Then, extraction of a mixture of acylcarnitines was assessed by off-line coupling to reversed phase liquid chromatography coupled to time-of-flight mass spectrometry, resulting in concentration factors of 80.0 +/- 9.2 times for hexanoylcarnitine, 73.8 +/- 9.1 for octanoylcarnitine, and 34.1 +/- 4.7 times for lauroylcarnitine, corresponding to recoveries of 107.8 +/- 12.3%, 98.9 +/- 12.3%, and 45.7 +/- 6.3%, respectively, in a sample of 500 mu L delivered at a flow of 50 mu L min(-1) under an extraction voltage of 300 V. Finally, the method was applied to the analysis of acylcarnitines spiked to urine, resulting in detection limits as low as 0.3-2 nM. Several putative endogenous acylcarnitines were found. The current flowing-to-stagnant phase microelectroextraction setup allows for the extraction of milliliter range volumes and is, as a consequence, very suited for analysis of low-abundant metabolites.