Desenvolvimento de eletrodo 3D a base de carvão e grafite para a detecção de ácido oxálico em forrageiras

Abstract

Oxalic acid (OXA) is a compound naturally present in plants such as grasses, spinach, and tomatoes, and can cause toxic effects—including irritation and the formation of kidney stones—especially in ruminants. Conventional methods for its determination, such as High-Performance Liquid Chromatography (HPLC) and titrimetry, present limitations associated with high costs, long analysis times, and significant reagent consumption. In this work, a low-cost 3D electrode composed of graphite, activated carbon, and nail polish was developed for the electrochemical detection of oxalic acid in forage. Different proportions of the constituent materials were evaluated, focusing on the adsorptive and conductive properties of the activated carbon. The sensors were characterized by Scanning Electron Microscopy (SEM), Raman spectroscopy, and Electrochemical Impedance Spectroscopy (EIS) to analyze morphology, surface structure, and charge transfer resistance. The electrode was optimized based on current density, peak potential, and sensitivity, using cyclic voltammetry with the potassium ferricyanide redox probe. Analyte quantification was performed via amperometry with Flow Injection Analysis (FIA), optimizing parameters such as supporting electrolyte, ideal pH, applied potential, and flow volume. The method was applied to real grass samples (Setaria sphacelata) provided by EMBRAPA; recovery values between 91 and 96% were obtained with good precision, showing a relative standard deviation of 6%. Furthermore, the results passed statistical evaluations and showed no significant differences between the proposed method and the validation method.