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

The properties of an ion-selective electrode for indomethacin based on the bis(triphenylphosphoranylidene)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 x 10(-5) mol l-1 (6.4 micrograms ml-1) and the linear range was determined to be between 5 x 10(-5) and greater than or equal to 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 less than 10(-4) for tartrate. Cationic organic and inorganic ions showed negligible interference with selectivity coefficients of less than 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 x 10(-7) mol l-1 (60 ng ml-1) for ClO4- were found. The selectivity for inorganic anions was close to the Hofmeister series.