Three-Phase
Electroextraction: A New (Online) Sample
Purification and Enrichment Method for Bioanalysis
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Abstract
The
migration and at the same time enrichment of analytes from
a liquid aqueous sample donor phase through an immiscible organic
solvent layer acting as a filter phase into a liquid aqueous acceptor
phase is enabled by the application of an electric field between the
donor and acceptor phase. The organic filter phase acts as a purification
filter, which prevents, for
example, proteins from migrating into the acceptor phase. Moreover,
the composition of the organic filter phase influences the selectivity
of the extraction. We show that analytes can be rapidly enriched from
a 50 μL donor phase at the bottom of a sample vial, via an immiscible
organic filter phase, into a 2 μL acceptor phase which consists
of a droplet that is hanging from a (conductive) pipet tip in the
organic filter phase. Acylcarnitines spiked to human plasma as a donor
phase were extracted reproducibly with good linearity and a 10-fold
improved limit of detection and, importantly, resulted in a stable,
protein-free nanoelectrospray signal. Finally, a proof of principle
toward the online integration in an automated nanoelectrospray-direct
infusion-mass spectrometry platform has been realized. This makes
3-phase electroextraction (3-phase EE) a novel sample purification
and enrichment method, with straightforward online integration possibility.
We envision that 3-phase EE will enable new possibilities using electrokinetic
sample pretreatment for fully automated, high-throughput bioanalysis
purposes