Role of octanol–water partition coefficients in extraction of ionisable organic compounds in a supported liquid membrane with a stagnant acceptor

Abstract

The correlation between the logarithm of the octanol–water partition coefficients (log K ow) and the logarithm of partition coefficients in di- n-hexyl ether–water and n-undecane–water (log K D) which are used as organic solvents in a supported liquid membrane extraction method with a stagnant acceptor was studied for a group of 17 s-triazines. A linear relationship between log K ow and log K D was found. A plot of the extraction efficiency obtained in a supported liquid membrane and their octanol–water partition coefficients of the above compounds together with phenoxyacids, phenols and local anaesthetics resulted into an approximately bell-shaped relationship. Maximum extraction efficiency was obtained for those compounds with log K ow values ∼3.0. Those compounds with high octanol–water partition coefficients were easily dissolved in the supported liquid membrane but were difficulty to strip into the acceptor solution, thus giving lower extraction efficiency. In contrast, those compounds with low octanol–water partition coefficients gave low extraction efficiency due to poor dissolution in the membrane liquid. Implications of log K ow values on the analytical application of the SLM technique are discussed.