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+/S2- 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 X 10-6 mol dm-3 ≤ [Cl-] ≤ 1.6 x 10-4 mol dm-3, 1.0 x 10-6 mol dm-3 ≤ [Br-] ≤ 8.3 x 10-5 mol dm-3, 2.0 x 10-6 mol dm-3 ≤ [I-] ≤ 1.0 x 10-4 mol dm-3, 8.4 x 10-7 mol dm-3 ≤ [Mn2+] ≤ 8.3 x 10-5 mol dm-3, 3.8 x 10-7 mol dm-3 ≤ [malonic acid] ≤ 2.1 x 10-5 mol dm-3 and 1.5 x 10-8 mol dm-3 ≤ [quercetin] ≤ 3.7 x 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.