NITRATE-SENSITIVE CORRODING METAL-ELECTRODE

The electrode potential of Devarda's alloy in phosphate solutions buff ered at pH=12 containing different amounts of nitrate ions has been me asured. A proportional relation between the electrode potential and th e concentration of nitrate ions [NO3-] is observed when [NO3-] is less than 40 mg l(-1). When [NO3-] is larger than 200 mg l(-1), log[NO3-] is linearly related to the electrode potential, with a slope of about 120 mV decade(-1) up to [NO3-]=10000 mg l(-1). The presence of chlorid e, sulfate and perchlorate ions has almost no effect on the above rela tions. The sensitivity and selectivity of the above metal electrode ex ceed those of nitrate-ion-selective electrodes. Since the electrical i mpedance of the corroding metal/solution interface is much lower than that of other methods, the potential measurement should be easier.