Simultaneous determination of iodide and nitrite by catalytic kinetics

Abstract

Nitrite and iodide can be determined simultaneously by a single experiment using their kinetic effect on the colour fading of the iron(II)–thiocyanate complex in nitric acid solution. The rate of the colour-fading reaction is in proportion to the concentration of iodide and is independent of the concentration of nitrite. The length of the induction period of the indicator reaction is in inverse proportion to the logarithm of the concentration of nitrite and is independent of the concentration of iodide. Under conditions of 1.3 mol l^–1 HNO₃, 0.067 mol l^–1 Fe³⁺ and 2.7 × 10^–4 mol l^–1 SCN^–, concentrations of 4.0 × 10^–5–1.6 × 10^–4 mol l^–1 iodide and 4.1 × 10^–7–6.6 × 10^–6 mol l^–1 NO₂– were determined with mean relative errors of 1.5 and 3.9%, repectively.