Perfiles amperométricos obtenidos por electrogeneración amperostática de reactivos en reacciones de cinética lentaPosibilidades Analíticas

Abstract

Amperometric monitoring of the concentration of a reagent during its amperostatic electrogeneration in the presence of one or more analytes, with which it reacts, gives a current-time curve which has been called the amperometric profile of the electrogenerated reagent. This profile contains information of stoichiometric as well as kinetic nature about the reactions taking place between the electrogenerated reagent and the analytes present in the solution, and this information can be useful for analytical purposes. Algorithms to obtain the theoretical profiles of electrogenerated reagent in the presence of one or two analytes have been developed through the numerical integration of the differential equations that represent the rate of electrogeneration of the reagent and the rates of the chemical reactions between the reagent and the analytes present. Equations for the addition of low- and high-frequency random noise to reagent profiles, as well as algorithms for evaluating the stoichiometric coefficient and the second-order rate coefficient of the chemical reactions involved have also been developed. By means of the proposed algorithms, electrogenerated reagent profiles in the presence of one and two analytes have been simulated. The algorithms for evaluating the stoichiometric coefficient and the rate coefficient of the chemical reaction have been applied to the simulated profiles in the presence of one analyte. On the other hand, the possibilities of using simulated profiles in the presence of two analytes for the resolution of the mixture by multivariate calibration (PLSR) have been studied, and the effects of the calibration region, the ratio of the rate coefficients and the amplitude of low- frequency noise in the results obtained have been critically analysed. Experimental amperometric profiles of the electrogenerated reagent have been obtained for the following systems: electrogenerated Ce (IV) in the presence of oxalic acid and/or oxaloacetic acid, as well as in the presence of cysteine and/or homocysteine; electrogenerated Fe(CN)63- in the presence of fructose and/or sorbose and electrogenerated Br2 in the presence of phenol and/or resorcinol. The algorithms proposed for evaluating the stoichiometric coefficient and the rate coefficient of the involved chemical reactions have been applied to these experimental profiles, and the possibilities of using the profiles in the resolution of binary mixtures using PLSR have been explored. The results obtained are critically discussed.