Generic conditions for electromembrane extraction of polar bases

Abstract

The current paper reports the first generic conditions for electromembrane extraction (EME) of polar bases within -2.0 < log P < 1.0 from human plasma. Generic conditions are important for inter-lab transferability and reproducibility, and were accordingly developed in commercially available EME equipment. In previous work, generic methodology was proposed for the extraction of bases of moderate and low polarity in the range 1.0 < log P < 6.0. The current paper extends this range of hydrophobicity downward. For polar bases, the composition of the liquid membrane is critical, in order to obtain high extraction recoveries, and to keep the extraction current as low as possible. The final liquid membrane was based on the deep eutectic solvent formed upon mixing 6-methyl coumarin and thymol in a 1:2 w/w ratio. The deep eutectic solvent was mixed with 2-undecanone in a 1:1 volumetric ratio. The latter decreased the extraction current, and improved the stability of the EME system. Finally, di(2-ethylhexyl) phosphate (DEHP) was added as ionic carrier to the liquid membrane to improve the mass transfer of polar bases. With this liquid membrane, the following generic conditions were established for mono- and dibases in the range -2.0 < log P < 4.5; plasma samples were diluted with an equal volume of 900 mM HCOOH, the acceptor was 450 mM HCOOH, voltage was 40 V, and the extraction time was 30 min. With this development, generic EME methods are now available for mono- and dibases in the polarity range -2.0 < log P < 6.0.