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 (logP) 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 <
logP< 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 logPrange of 2.2–6.4. This logPrange 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 logPrange
of 1.0–5.8 and was efficient even for bases of moderate polarity.
The current was at the 1–3 μA level when 2-undecanone
was operated at 50 V. Tri(pentyl) phosphate emerged as another new
alternative for bases in the logPrange 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.