Eletrodos quimicamente modificados por complexos de rutênio (II) com fórmula Cis- [RuCl2(N-N)(P-P)], onde N-N = (bipy); P-P = Dppe, Dppp e Dppb, para a determinação do íon nitrito.

Abstract

The present work portrays the use of Ru(II) complexes with the generic formula cis-[RuCl2(NN)(PP)] where NN = bipy ; PP = Dppe, Dppp and Dppb used as modifiers of carbon paste electrodes for the determination of nitrite through its electrochemical oxidation. The characterizations of the same were carried out by the spectrometry technique in the ultraviolet visible region, around 320 and 380 nm, the bands corresponding to the transfer of metal ligand charge attributed to the “d” orbital of ruthenium and the transfer of internal charge of the binders. For the manufacture of modified electrodes, the amounts of modifier were evaluated, and the following proportions were adopted: 65% (m/m) of graphite, 32% (m/m) of paraffin and 3% (m/m) of modifier. During the cyclic voltammetry studies, the electrodes were sensitive to nitrite quantification, emphasizing the cis-[RuCl2(bipy)(dppb)] electrode, which showed the best response, especially in comparison to the non-modified one, demonstrating a linear range between 2,0 x 10-4 and 1,4 x 10-3 mol L-1, detection limit of 3,92 x 10-5, quantification limit equal to 1,31 x 10-4 and high repeatability. It was found that the best condition for the quantification of the analyte in these electrodes is at pH 4,6, 0,1 mol L-1acetate buffer, due to its greater supply of H3O+ ions in the medium. By scanning speed analyses, it was found that the process indicates an irreversible and diffusion-controlled electron transfer. Before the analyzes by differential pulse voltammetry and square wave voltammetry, the electrodes again showed good linear ranges and promising detection and quantification limit values, showing the applicability of the electrodes in other electroanalytical techniques, highlighting the cis-[RuCl2( bipy)(dppe)] with a detection limit of 1,0 x 10-5 and quantification equal to 3,4 x 10-5 for differential pulse voltammetry and the cis-[RuCl2(bipy)(dppb)] electrode with 1,1 x 10-5 and 3,6 x 10-5 for the limit of detection and quantification, respectively, for square wave voltammetry. In addition, studies for the determination of nitrite in a sample of bacon are satisfactory, resulting in a concentration of 6,23 mg/kg, below the recommended by the Ministry of Health, however, other techniques must be used for the purpose of comparison.