Stability and efficiency of supported liquid membranes in electromembrane extraction--a link to solvent properties

The current work presents a large systematic screening of 61 possible organic solvents used as supported liquid membranes (SLM) in electromembrane extraction (EME). For each organic solvent, recovery, current across the SLM, and stability considerations have been investigated and correlated to relevant solvent properties through partial least square regression analysis. The five unpolar basic drugs pethidine, haloperidol, methadone, nortriptyline, and loperamide were used as model analytes. Efficient EME solvents were found to have a low water solubility (<0.5 g L(-1)) and belonged to cluster 2 of a Kamlet-and-Taft-based solvent classification system (high dipole moments and proton acceptor properties). These parameters were especially found in nitroaromatic compounds and ketones. Small molecules with low log P value and high water solubility were unsuitable, as they tended to give unstable extractions, caused by a high current across the SLM. This was often combined with substantial solvent-related interferences and the generation of an electroosmotic flow across the SLM, with resulting acceptor solution expansion. Large molecules with a high log P value were classified as inefficient. For these solvents, no current was measured across the SLM and no analytes were extracted. This is the first time systematic knowledge on the SLM in EME has been gathered and investigated, and the presented results could be highly beneficial for future development and optimization of EME.