Development and Validation of an Electrochemical Screening Methodology for Sulfonamide Residue Control in Milk Samples Using a Graphene Quantum Dots@Nafion Modified Glassy Carbon Electrode

An electrochemical method based on the assembly of graphene quantum dots (GQD) and Nafion onto a glassy carbon electrode (GQD@Nafion/GCE) was developed to detect sulfonamide residues in milk. The resulting modified electrode (GQD@Nafion/GCE) demonstrated a significant increase in sensitivity compared to a bare GCE. Repeatability, reproducibility, and stability studies also indicated the suitability of the electrode used as a sensing probe for sulfonamide residues. Under optimized conditions, the method was validated according to specific performance parameters of screening (qualitative) methods. Six sulfonamides were evaluated: sulfadimethoxine, sulfadiazine, sulfamethazine (SMZ), sulfamethoxypyridazine, sulfapyridine, and sulfathiazole, taking SMZ as the representative analyte in milk samples. No false-positive results were observed, the parameters related to precision presented suitable values, and the detection limit was estimated as 74.8 μg L−1. The screening method demonstrated its applicability for the analytical control of total sulfonamide residues according to international regulations for maximum residue limits.