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

Abstract

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.

Mass transfer in electromembrane extraction—The link between theory and experiments

“…In relation to the theory discussed in Section , the pH changes alter the distribution coefficients included in the equations. Drop in recovery due to long extraction times has also been explained by partial degradation of the liquid membrane, either by dissolution into the sample or by water penetration into the liquid membrane .…”

Impedometric monitoring of the behavior of the supported liquid membrane in electromembrane extraction systems: An insight into the origin of optimized experimental parameters

“…Later, the magnitude of the released heat was found to be insufficient to cause severe problems [23]. Another factor attributed to the performance loss is the propagation of double layer capacitance caused by the ambulation of charged species on both sides of the SLM [24]. Kuban and coworkers introduced another limiting feature of EME.…”

“…While the main driving force of the extraction in EME is the applied voltage, the overincreasing of voltage results in loss of recovery and instability problems [28]. It has been reported that the mass transfer resistance, double layer capacitance, increased current and bubble formation are responsible for the above problems [24,29]. Generally, pH of donor/acceptor solution is adjusted to keep the analyte in its ionized form [30] and to make a pH gradient between the two phases [12].…”

Electromembrane extraction of polar basic drugs from plasma with pure bis(2-ethylhexyl) phosphite as supported liquid membrane

“…Alternatively, tris(2-ethylhexyl) phosphate (TEHP) has been used as an non-ionic carrier [27]. TEHP is expected to improve mass transfer of polar basic drugs based on dipole and hydrogen bonding interactions.…”

“…Non-polar basic drugs in their protonated form are easily transferred into the SLM under the influence of an electrical field, based on strong dipole and hydrogen bonding interactions with NPOE [27]. On the other hand, EME of polar basic drugs (log P < 2) is more challenging due to their low affinity to the M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 5 relatively high extraction recoveries have been reported with DEHP [31], this carrier increase the electrical conductance of the SLM, and also facilitate transfer of back-ground electrolyte ions and sample matrix ions across the SLM.…”