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 1-1 (6.4-mu-g 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 < 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-, CIO4- 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 CIO4- were found. The selectivity for inorganic anions was close to the Hofmeister series.