VOLTAMMETRIC ION-SELECTIVE ELECTRODE FOR THE DETERMINATION OF NITRATE

A sensor which uses an anion-exchange membrane to enclose a small volume electrolysis cell has been demonstrated to be suitable for nitrate determinations. The three-electrode cell includes a constrained mercury column indicator electrode; filter paper, which is impregnated with a 0.1 M KCI-0.01 M ZrOCI2 electrolyte, serves as the constraining barrier and as the spacer for the thin-layer electrolysis chamber. The anion-exchange membrane sheath permits transfer of nitrate from the sample into the electrolysis chamber by Donnan dialysis and excludes several species which would otherwise interfere. Controlled potential electrolysis at -1.25 V vs. Ag/AgCI provides the sensing current, the value of which is proportional to the sample concentration of nitrate. As a steady-state current is not developed with the present design, a defined current sampling time is used. Linear response over 3 or-ders-of-magnitude nitrate concentration is obtained. The detection limit using the current at 8 min is 6.7X10-6 M N03-. © 1979, American Chemical Society. All rights reserved.