Determination of Cl–, Br–, I–, Mn2+, malonic acid and quercetin by perturbation of a non-equilibrium stationary state in the Bray–Liebhafsky reaction

Abstract

A new method applying a non-linear chemical system under conditions far from thermodynamic equilibrium in microvolume/microconcentration quantitative analysis is described. The chemical system used as a matrix is the Bray–Liebhafsky reaction in a non-equilibrium stationary state close to a bifurcation point. The method is based on monitoring the response of this system to perturbations by Cl^–, Br^–, I^–, Mn²⁺, malonic acid and quercetin analyte solutions, which are followed potentiometrically either by an Ag⁺/S^2– ion-sensitive or by a Pt electrode. A linear response of the potential shift versus the logarithm of the analyte concentrations is found in the following ranges: 1.3 × 10^–6 mol dm^–3 ≤ [Cl^–] ≤ 1.6 × 10^–4 mol dm^–3, 1.0 × 10^–6 mol dm^–3 ≤ [Br^–] ≤ 8.3 × 10^–5 mol dm^–3, 2.0 × 10^–6 mol dm^–3 ≤ [I^–] ≤ 1.0 × 10^–4 mol dm^–3, 8.4 × 10^–7 mol dm^–3 ≤ [Mn²⁺] ≤ 8.3 × 10^–5 mol dm^–3, 3.8 × 10^–7 mol dm^–3 ≤ [malonic acid] ≤ 2.1 × 10^–5 mol dm^–3 and 1.5 × 10^–8 mol dm^–3 ≤ [quercetin] ≤ 3.7 × 10^–5 mol dm^–3. Under the investigated conditions an improved detection limit for all halides tested is obtained. Unknown concentrations of the analytes can be determined from a standard series of calibration curves to an accuracy within ±5%. In addition, the application of potentiometric measurements in microvolume/microconcentration quantitative analysis is diversified.