Indomethacin ion-selective electrode based on a bis(triphenylphosphoranylidene)ammonium–indomethacin complex

Abstract

The properties of an ion-selective electrode for indomethacin based on the bis(triphenyl-phosphoranylidene)ammonium–indomethacin ion-pair complex in a poly(vinyl chloride) membrane are described. The detection limit found for indomethacin at pH 7.0 was 2 × 10^–5 mol l^–1(6.4 µg ml^–1) and the linear range was determined to be between 5 × 10^–5 and 10^–3 mol l^–1. The selectivity coefficients observed for organic anions of different lipophilicity were 10^–1.1 for naproxenate, 10^–0.75 for salicylate and <10^–4 for tartrate. Cationic organic and inorganic ions showed negligible interference with selectivity coefficients of <10^–4. A strong electrode response was observed for the inorganic anions IO₄^–, ClO₄^– and SCN^– with selectivity coefficients of up to 10^+0.9. Very low detection limits, e.g., 6 × 10^–7 mol l^–1(60 ng ml^–1) for ClO₄^– were found. The selectivity for inorganic anions was close to the Hofmeister series.