Fabricação de um dispositivo eletroquímico miniaturizado para a determinação voltamétrica de cloreto

Abstract

The quantification of chloride is quite relevant, as the concentration of this ion is an important parameter in different areas such as environmental monitoring, clinical diagnosis, and food safety. From a clinical point of view, chloride ion is a biomarker for some diseases, high levels of chloride in sweat may be an indicative of a disease called cystic fibrosis, in urine, may indicate kidney malfunctioning. Thereby, analytical methods that allow chloride quantification quickly, reliably, and cheaply and that require low sample volumes are highly desirable. Electroanalytical methods satisfactorily fulfill many of these requirements, as they combine high sensitivity with simple and low-cost instrumentation. Furthermore, because they are based on an interfacial phenomenon, electrochemical sensors can be miniaturized without significant loss of sensitivity. The use of tips for micropipettes and metallic wires is a strategy that allows the manufacture of miniaturized and very low-cost electrochemical devices, which require low volumes of sample and chemical reagents, generate little amount of waste, and can be used for analysis in biological samples (such as sweat and tears), for which it is impossible to obtain high volumes. Thus, in this study, a miniaturized electrochemical device for the quantification of chloride was fabricated with an Ag wire as the working electrode. The technique of cyclic voltammetry was used, using an electrochemical cell containing 500 µL of supporting electrolyte. Three supporting electrolytes were evaluated: acetate (pH 4.74); phosphate (pH 6.0) buffer solutions and H2SO4. The best voltammetric response for chloride was observed in H2SO4 in which well defined, intense, and repetitive voltammetric peaks were obtained. When the cathodic peak corresponding to the reduction of AgCl preconcentrated onto electrode surface during the anodic scan was used as the analytical signal, a linear range for chloride was observed from 0.25 to 10 mmol L-1 with a limit of detection and limit of quantification of 0.05 and 0.17 mmol L-1, respectively Thus, the miniaturized device described in this study provided satisfactory responses for chloride being promising to develop reliable, cheap, and environmentally friendly methods for the quantification of chloride ions in different matrices.