DEVELOPMENT OF ELECTROCHEMICAL SENSOR USING GRAPHITE POWDER AND STAINED-GLASS VARNISH FOR SULFANILAMIDE ANALYSIS IN EGGS

Sulfanilamide (SFA) is an antibiotic widely used in the veterinary sector, with a maximum allowable limit of 100 µg/kg in eggs to ensure the quality and safety of the animal product. [1] This work aimed to develop an electrochemical sensor for determining SFA in egg samples using square wave voltammetry (SWV). The sensors were fabricated using a stencil mold on a pre-polished acetate surface, incorporating a mixture of graphite (conductive material) and stained-glass varnish (polymeric binder) in a 30:70% (w/w) ratio.  After a 24-hour curing period, the electrodes were polished with 2000-grit wet sandpaper, and a mixture of silver powder and stained-glass varnish (50:50% w/w) was applied to the pseudo-reference electrode. The electroactive area of the working electrode was determined using 2.5 mmol L⁻¹ of [Fe(CN)₆]³⁻/⁴⁻, resulting in an area of 24.2 mm². Electrochemical impedance spectroscopy was employed to determine the charge transfer resistance of 652.61 Ω. The effect of pH on the SFA oxidation process was evaluated using a BR buffer solution (0.1 mol L⁻¹) with pH values ranging from 2.0 to 10.0, with pH 4.0 ultimately selected as the optimal condition. A method using the SWV was optimized with a frequency of 10 Hz, an amplitude of 40 mV, and a step potential of 7 mV. This optimization resulted in a linear working range of 2.0 to 10.0 µmol L⁻¹, demonstrating excellent analytical performance (LOD = 1.46 µmol L⁻¹) and high accuracy. The method showed recovery rates ranging from 90% to 105% for detecting the analyte in egg samples.

Acknowledgements. We would like to acknowledge the universities UFJF and UFGD, and the funding agencies CAPES, CNPq, and FAPEMIG.

References. [1] ZEXIANG, W. et al., Journal of the Science of Food and Agriculture, 101, 684-692 (2020).