Generic Liquid Membranes for Electromembrane Extraction of Bases with Low or Moderate Hydrophilicity

Abstract

For the first time, this paper introduces the idea of generic extraction conditions in electromembrane extraction (EME), where the selection of the liquid membrane is based on the charge (z) and hydrophobicity (log P) of the analyte. A broad range of organic solvents were tested as liquid membranes, and 90 basic pharmaceuticals were used as model analytes (−4.2 < log P < 8.1). 2-Nitrophenyl octyl ether (NPOE) was confirmed as a highly efficient liquid membrane for mono-and dibases (+1.0 ≤ z ≤ +2.0) of low polarity in the log P range of 2.2−6.4. This log P range was set as the extraction window (operational range) of NPOE. NPOE provided very high operational stability. At 50 V, the current was at a 1 μA level, and gas formation and drifting pH due to electrolysis were insignificant. 2-Undecanone was discovered as a new and robust alternative. This solvent extracted monobasic analytes (z = +1) in the log P range of 1.0−5.8 and was efficient even for bases of moderate polarity. The current was at the 1−3 μA level when 2undecanone was operated at 50 V. Tri(pentyl) phosphate emerged as another new alternative for bases in the log P range of 0.5 to 5.5, providing greater selectivity differences. This solvent provided a higher current (30−50 μA), but the EME system stability was not compromised. 2-Undecanone and tri(pentyl) phosphate extracted protonated bases mainly by hydrogen bond interactions. NPOE, on the other hand, extracted based on a combination of hydrogen bond and π-type interactions and was consequently less selective.

Optimization of generic conditions for electromembrane extraction of basic substances of moderate or low polarity

“…Recoveries surpassing 85% were considered as exhaustive extraction [11]. Furthermore, based on previous experiences the upper limit for the extraction current was set at 50 μA [11].…”

“…The mobile phase A consisted of 5:95 v/v acetonitrile and MQ-water with 0.1% formic acid, and mobile phase B consisted of 95:5 v/v acetonitrile and MQ-water with 0.1% formic acid. Gradient elution was performed as reported elsewhere [11]. The total run time was 10.0 min, the column temperature was 40 • C, and the injection volume was set to 10 μL.…”

“…The total run time was 10.0 min, the column temperature was 40 • C, and the injection volume was set to 10 μL. S1 and elsewhere [11].…”

“…Recently, a system of generic EME methods was presented [11]. This conceptual framework comprises a limited set of recommended extraction conditions, selected based on the charge (z) and polarity (log P) of the target analyte.…”

“…In previous research, liquid membranes specifically designed for the generic methods referred to as B1 and B2 were introduced for the extraction of mono-and dibasic analytes within the polarity range of 2.0 < log P < 6.0 and monobasic analytes within the polarity range of 1.0 < log P < 4.5, respectively [11]. For the generic method B1; 2nitrophenyl octyl ether (NPOE) was selected as the ideal liquid membrane, while 2-undecanone was designated for use in B2.…”