PREPARATION OF A DOUBLE-MEMBRANE NITRATE-SELECTIVE ELECTRODE - ESTIMATION OF ITS ESSENTIAL ANALYTICAL CHARACTERISTICS

A double -membrane nitrate- selective electrode was prepared with an internal conductor membrane made of tetrabutylammonium bromide (BrTBA) and nitrobenzene (PHINO2) in naphtalene as an inert matrix, and an external active membrane (Aliquat - NO3- in paraffin), on a Pt electrode. The electrode exhibits Nernstian response over the range 1 - 10(-3.5) M of nitrate, with a slope of 56.60 +/- 0.3 mV decade-1 at 25.0 +/- 0.2-degrees-C. The detection limit was 10(-3.5) M of nitrate. The reproducibility (coefficient of variation) was 0.11% (n - 10 determinations, for [NO3-] - 10(-3) M). The stability of its potential is 0.5 mV/12 h. The effects of the active membrane composition, the thickness of the membranes and the pH of solution on the electrode response were also investigated.