Modification of carbon paste electrodes with recrystallized zeolite for simultaneous quantification of thiram and carbendazim in food samples and an agricultural formulation

A simple, inexpensive, highly sensitive, selective novel electrochemical method was developed for simultaneous quantification of the fungicides thiram and carbendazim in samples of honey, fresh grape juice, and an agricultural formulation using a carbon paste electrode modified with recrystallized zeolite. Zeolite was characterized by TG-DSC, XRD, FT-IR, and SEM-EDS before and after recrystallization treatment. The electrodes were electrochemically characterized using cyclic voltammetry, square-wave voltammetry, and electrochemical impedance spectroscopy. Electrode area, standard heterogeneous rate constant, and double-layer capacitance were the electrochemical variables investigated. Recrystallized zeolite had a strong influence on these variables. Development of the method for simultaneous thiram and carbendazim quantification involved optimizing instrumental parameters (frequency, amplitude, and potential step) and experimental parameters (pH, zeolite content, temperature, and recrystallization time). The oxidation peak current for thiram varied linearly in the concentration range of 0.36-4.99 × 10−7 mol L−1, with limit of detection (LD) of 6.74 × 10−9 mol L−1 and limit of quantification (LQ) of 20.17 × 10−9 mol L−1. For carbendazim, the oxidation peak current varied linearly in the concentration range of 0.10-2.35 × 10−6 mol L−1, with LD and LQ of 3.51 × 10−9 and 11.71 × 10−9 mol L−1, respectively. Thiram and carbendazim recovery experiments were performed by adding known amounts of these fungicides to samples of honey and grape juice, yielding recovery rates in the 98.85-101.15% range. In the agricultural formulation, the concentrations measured with the new method were close to those specified on the label, with deviations of below 1.1%. No thiram or carbendazim were found in the grape juice and honey samples. The results demonstrated the method's feasibility for quantifying both compounds simultaneously in these samples.