A mechanistic study on ion pair extraction using single microdroplet injection and microelectrochemical techniques

Abstract

Ion pair extraction from water into oil in a (ferrocenylmethyl)trimethylammonium bromide (FcTMABr)–sodium hexafluorophosphate (NaPF₆) system was studied kinetically by injection and manipulation of a single oil droplet of 10⁻⁸ cm³ and electrochemistry of the single droplet contacting a microelectrode. The FcTMA⁺ concentration extracted into the oil phase at the distribution equilibrium was dependent on the FcTMABr, NaPF₆, and NaCl concentrations in the water phase. The initial rate of the ion pair extraction was directly proportional to the FcTMABr concentration in water, while it was independent of the NaPF₆ and NaCl concentrations in water. These results indicate that the ion pair extraction rate is governed by the ion transfer of FcTMA⁺ from water into the droplet, maintaining the electroneutrality in the droplet by the PF₆⁻ transfer.