NITRATE-SELECTIVE ELECTRODES WITH POLYMER MEMBRANES CONTAINING IMMOBILIZED SENSORS

Several ion-selective electrodes for the determination of nitrate have been fabricated using polymer membranes containing covalently bound quaternary ammonium salts as sensor groups. Of the two sensor groups compared triallylbutylammonium bromide gave superior results to triallylethylammonium bromide. Hot-pressed membranes gave superior performance to solvent-cast membranes, producing more robust, cross-linked membranes into which a mediator group could be introduced. The best electrode was fabricated with a membrane containing triallylbutylammonium bromide (5.6% m/m), 2-nitrophenyl octyl ether (39.7% m/m) and dicumyl peroxide (7.3% m/m) in poly(acrylonitrile - butadiene) using hot pressing at 150°C for 10 min at a pressure of 15 tons on a 5 in diameter ram. The cross-link density was 1.7 × 10-5 mol cross-link cm-3. The response to nitrate was Nernstian in the range 1 × 10-1-1 × 10-4M nitrate, with a limit of detection of 3 × 10-5 M. The selectivity for chloride (kNO3-,Cl-pot) was 1.2 × 10-2 and for a range of other ions was comparable to commercially available electrodes. The covalently bound sensor electrode offered superior mechanical strength.