Electrocatalytic determination of sulfite at immobilized microdroplet liquid - Liquid interfaces: The EIC' mechanism

N Katif, S M MacDonald, A M Kelly, E Galbraith, T D James, A T Lubben, M Opallo, F Marken

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)

Abstract

Liquid I liquid interfaces provide a natural boundary and a reactive interface where an organic phase is in contact with an aqueous analyte. The selectivity of ion transfer processes at liquid I liquid interfaces can help to provide sensitivity, introduce reactive reagents, or allow analyte accumulation at the electrode surface. In this study, microdroplet deposits of the organic liquid 4-(3-phenylpropyl)-pyridine (PPP) with the ferrocenylmethyl-dodecyldimethyl-ammonium(+) (FDA(+)) redox system are deposited onto a basal plane pyrolytic graphite electrode and employed to transfer anions from the aqueous into the organic phase. A clear trend of more hydrophobic anions transferring more readily (at more negative potentials) is observed and an ESI-mass spectrometry method is developed to confirm the transfer. Subsequently, the electrocatalytic oxidation of sulfite, SO32-, within the organic phase and in the presence of different electrolyte anions is investigated. Competition between sulfite transfer and inert anion transfer occurs. The electrocatalytic sulfite oxidation is suppressed in the presence of PF6- and occurs most readily in the presence of the hydrophilic nitrate anion. The resulting process can be classified as an electrocatalytic EIC'-process (E: electron transfer; 1: ion transfer; C: chemical reaction step). The effectiveness of the electrocatalytic process is limited by i) competition during anion transfer and ii) the liquid I liquid interface acting as a diffusion barrier. The analytical sensitivity of the method is limited to ca. 100 mu M SO32- (or ca. 8 ppm) and potential approaches for improvement of this limit are discussed.
Original languageEnglish
Pages (from-to)469-475
Number of pages7
JournalElectroanalysis
Volume20
Issue number5
DOIs
Publication statusPublished - 2008

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