PHOTO-CURED AMMONIUM AND HYDROGEN-ION SELECTIVE COATED-WIRE ELECTRODES USED SIMULTANEOUSLY IN A PORTABLE BATTERY-POWERED FLOW-INJECTION ANALYZER

Nonactin and N,N-dioctadecylmethylamine ionophores, each in an epoxydi acrylate polymer, were photo-cured on silver wires (0.8 mm i.d.) and e valuated as ammonium and hydrogen (pH) coated wire electrodes. The pho to-cured membranes prepared in this study exhibited excellent adhesion to the metal substrate and improved mechanical strength compared to P VC based membranes. The ammonium electrode exhibited a Nernstian respo nse over a concentration range between 0.01 mM and 100 mM with a detec tion limit of 0.0005 mM. The ammonium electrode exhibited improved sel ectivity against most common interfering ions, including potassium com pared to previous studies. The hydrogen selective electrode exhibited a near-Nernstian slope of 55.9 +/- 0.8 mV change/log a((H+)) between p H 4.0 and pH 11.0 in the steady-state mode. The ammonium and pH sensor s each responded quickly reaching 90% of steady-state value in<5s, mak ing these coated wire sensors ideal for flow injection potentiometry m easurements. In the FIP mode, both the photo-cured ammonium and pH ele ctrodes exhibited near-Nernstian responses of 49.2 +/- 1.0 mV change/a ctivity decade and 50.2 +/- 0.4 mV change/log a((H+)), respectively, o ver a similar concentration range as in the steady-state mode. The pho to-cured ammonium and pH electrodes were used simultaneously in the an alysis of hydroponic nutrient solutions and waste water samples obtain ed from a local greenhouse grower in the dow injection potentiometric mode.