POTENTIOMETRIC ANION SELECTIVITY OF POLYMER MEMBRANES DOPED WITH PALLADIUM ORGANOPHOSPHINE COMPLEX

The potentiometric anion selectivity of polymer membrane-based electrodes formulated with a palladium organophosphine complex (benzylbis (triphenylphosphine)palladium(II) chloride) as the membrane active component is examined. The electrode is shown to exhibit a non-Hofmeister selectivity pattern with a significantly enhanced response toward nitrite over the concentration range of 10 mu M-10 mM (log-linear range) and a detection limit 5.0 mu M. The effect of lipophilic anionic (tetraphenylborate derivatives) and cationic (tetraalkylammonium) site additives within the membrane on the anion selectivity is examined in detail. Addition of both cationic and anionic sites is shown to improve potentiometric anion selectivity, suggesting that the palladium complex may operate simultaneously as a neutral and charged carrier-type ionophore within the polymer membrane phase. Using optimal membrane formulations (with added 20-30 mol % cationic sites), the sensors prepared with the palladium complex do not exhibit proton/hydroxide response in the range of pH 3.5-12, a potential advantage over previously reported nitrite electrodes prepared with Co(III) corrins and porphyrin complexes.