96-Well Agarose-Gel Electromembrane Extraction

For the first time, gel electromembrane extraction was demonstrated in a 96-well system. Gel membranes of 3% w/v agarose and with a thickness of 3.5 mm were immobilized in hydrophilic polyvinylidene fluoride (PVDF) filters in a 96-well filter plate. The filters provided mechanical support for the gel membranes, and were important for the stability and robustness of the system. A selection of 90 basic pharmaceuticals in the polarity range -4.2 < log <i>P</i> < 8.1 was used as model analytes (compounds). The compounds were extracted from 200 μL sample (water or human plasma) adjusted to pH 4.0 with dilute formic acid, through the gel membrane, and into 200 μL of 100 mM formic acid as acceptor. The extraction potential was 25 V, and the extraction time was 20 min for careful operation to limit Joule heating and electroendosmosis. The majority of the compounds in the polarity range -4.0 < log <i>P</i> < 3.0 were extracted with high recovery (40-100%). Compounds with log <i>P</i> > 3.0 were discriminated due to interactions with the gel membrane. Proteins and phospholipids were not extracted, and the system therefore provided efficient cleanup from human plasma samples. The 96-well agarose-gel electromembrane extraction (EME) system showed great potential. Selectivity was controlled by interactions with the aqueous gel membrane. This is fundamentally very different from traditional EME with oil membranes, where selectivity is controlled by electro-assisted partition in and out of the oil membrane. 96-Well electromembrane extraction with gel membranes of agarose is favorable in terms of greenness and efficiency for polar analytes, as compared with systems based on oil membranes.