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 epoxydiacrylate polymer, were photo-cured on silver wires (0.8 mm i.d.) and evaluated as ammonium and hydrogen (pH) coated wire electrodes. The photo-cured membranes prepared in this study exhibited excellent adhesion to the metal substrate and improved mechanical strength compared to PVC based membranes. The ammonium electrode exhibited a Nernstian response over a concentration range between 0.01 mM and 100 mM with a detection limit of 0.0005 mM. The ammonium electrode exhibited improved selectivity against most common interfering ions, including potassium compared to previous studies. The hydrogen selective electrode exhibited a near-Nernstian slope of 55.9± 0.8 mV change/log a(H+) between pH 4.0 and pH 11.0 in the steady-state mode. The ammonium and pH sensors each responded quickly reaching 90 % of steady-state value in < 5 s, making these coated wire sensors ideal for flow injection potentiometry measurements. In the FIP mode, both the photo-cured ammonium and pH electrodes exhibited near-Nernstian responses of 49.2 ± 1.0 mV change / activity decade and 50.2 ± 0.4 mV change / log a(H+), respectively, over a similar concentration range as in the steady-state mode. The photo-cured ammonium and pH electrodes were used simultaneously in the analysis of hydroponic nutrient solutions and waste water samples obtained from a local greenhouse grower in the flow injection potentiometric mode.