Partition of amines and lysine oligomers between organic solvent and water under a controlled interfacial potential difference

Abstract We examined the partition of two amines, procaine and metoprolol, in ionic and charge-neutral forms between organic solvent (O) 1,2-dichloroethane and water (W) phases, each of which contained a common ion, [(C n F 2n+1 SO 2 ) 2 N] − , as tetrabutylammonium and Li + salts, respectively, to control the potential difference at the O|W interface, Δ O W ϕ. The interfacial system would be useful in the study of the partitioning of ionic species, which depends on Δ O W ϕ. With different pH levels, the dependence of the distribution ratio on Δ O W ϕ satisfied the prediction from the theoretical equation, giving the formal potentials for the transfer of the ionic forms at the O|W interface. We also examined the partition of nourseothricin, a mixture of streptothricin antibiotics with different sizes of lysine oligomers. They would exist as di-, tri-, tetra- and pentavalent cations in fully protonated forms. The distribution ratio for each ionic species could be determined simultaneously using an HPLC technique. The dependence of the distribution ratio on Δ O W ϕ for each species also satisfied the prediction, giving their formal potentials. Therefore, the present interfacial system can be applied when both ionic and charge-neutral species are partitioned and when the sample is of low purity or is a mixture.