Abstract
Electromembrane extraction is affected by acid-base equilibria of the extracted substances as well as coupled equilibria associated with the partitioning of neutral substances to the supported liquid membrane. A theoretical model for this was developed and verified experimentally in the current work using pure 2-nitrophenyl octyl ether as supported liquid membrane. From this model, extraction efficiency as a function of pH can be predicted. Substances with log P<0-2 are generally extracted with low efficiency. Substances with log P>2 are generally extracted with high efficiency when acceptor pH<pKaH - log P. Twelve basic drug substances (2.07<log P<6.57 and 6.03<pKaH <10.47) were extracted under different pH conditions with 2-nitrophenyl octyl ether as supported liquid membrane and fitted to the model. Seven of the drug substances behaved according to the model, while those with log P close to 2.0 deviated from prediction. The deviation was most probably caused by deprotonation and ion pairing within the supporting liquid membrane. Measured partition coefficients (log P) between 2-nitrophenyl octyl ether and water, were similar to traditional log P values between n-octanol and water. Thus, the latter have potential for pKaH - log P predictions.
Highlights
Electromembrane extraction (EME) was introduced in 2006 and offers rapid and selective extraction properties with the addition of an electrical field to a three-phaseArticle Related Abbreviations: EME, electromembrane extraction; FA, formic acid; Nitrophenyl octyl ether (NPOE), 2-nitrophenyl octyl ether; SLM, supported liquid membrane microextraction system [1]
EME is affected by acid–base equilibria of the extracted species as well as coupled equilibria associated with the partitioning of neutral species into the SLM
EME is affected by acid–base equilibria of the extracted species as well as coupled equilibria associated with the partitioning of neutral species to the SLM
Summary
Electromembrane extraction (EME) was introduced in 2006 and offers rapid and selective extraction properties with the addition of an electrical field to a three-phaseArticle Related Abbreviations: EME, electromembrane extraction; FA, formic acid; NPOE, 2-nitrophenyl octyl ether; SLM, supported liquid membrane microextraction system [1]. Conventional EME comprises an aqueous sample solution, which is separated from another clean aqueous solution (acceptor) by a porous membrane coated with an organic solvent. This membrane is termed supported liquid membrane (SLM) and acts as a barrier between the two aqueous solutions. For compounds to migrate from the sample solution, through the SLM, and to the acceptor solution, they need to be ionized. This is achieved by adjusting the pH of both sample and acceptor. In order to promote efficient extraction, the EME system needs to be agitated
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