Utilization of Lipophilic Ionic Additives in Liquid Polymer Film Optodes for Selective Anion Activity Measurements

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Abstract
Lipophilic anionic and cationic additives are investigated as components for use in liquid polymer film-based optodes. These ionic additives are known to strongly influence the selectivity behavior of anion-selective electrodes. They also make it possible to construct ion coextraction optodes that can measure anion activities. Theoretical, thermodynamic anion−optode equilibria formalisms were derived to help understand the influence these additives have on the overall optode response and on the selectivity behavior. Neutral and charged anion carrier film configurations are described and tested for two anion ionophores with known modes of action, ruthenium(II) octaethylporphyrin and a vitamin B12 derivative (cyanoaquacobyrinic acid heptakis(2-phenylethyl ester)). These film configurations were further tested using a less well-understood ionophore, indium(III) octaethylporphyrin. Notable is the indium(III) octaethylporphyrin optode, which has a dynamic range appropriate for physiological measurements of chloride at neutral pH values. Also of interest is the optode with the vitamin B12 derivative ionophore, which has a dynamic range appropriate for some physiological measurements of nitrite at neutral pH values.