Microfluidic device for electromembrane extraction with a micro-pillar stabilized liquid membrane

Electromembrane extraction (EME) is a microextraction technique where charged analytes are transferred across a liquid membrane, under the influence of an electrical field, and enables selective and efficient sample cleanup. In this paper, we present for the first time a microfluidic device for electromembrane extraction where the liquid membrane was held in place by rows of micro-pillars. This design allows rapid membrane replacement, low-voltage extractions, and extended reuse, addressing key limitations of conventional EME formats. The microchip was fabricated in a stoichiometric thiol-ene polymer, offering a balance between hydrophobic and hydrophilic properties and supporting controlled flow of both aqueous and organic phases. Lidocaine was selected as the test substance for the experiments. Extraction parameters were optimized, and with a sample flow of 0.5 µL min^-1, acceptor flow of 2.0 µL min^-1, 0.1 µL 2-nitrophenyl octyl ether (NPOE) as the liquid membrane, and a 10-min extraction time, recoveries up to 50% were obtained. Linearity was demonstrated from 5 to 20 µg mL^-1 (R²≈0.99), repeatability was acceptable (16.0% RSD), and carryover was minimal (1.3%). The system remained stable for at least 60 min of continuous extraction, and the liquid membrane could easily be replenished without chip disassembly. The miniaturized design and low solvent consumption yielded a high AGREEprep greenness score of 0.79, confirming the greenness and sustainability of the method. This work is a first step towards a versatile, reusable, and sustainable EME microchip and represents a key step towards a highly flexible device with potential for on-site analytical applications.