Influence of acid-base dissociation equilibria during electromembrane extraction

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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.

Original languageEnglish
JournalJournal of Separation Science
Issue number15
Pages (from-to)3120-3128
Publication statusPublished - 2020

    Research areas

  • acid–base equilibria, electromembrane extraction, microextraction, sample preparation

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