Voltammetric determination of chlorothalonil and its respective reduction mechanism studied by density functional theory

A simple, fast, and direct electroanalytical method has been developed for the pesticide chlorothalonil determination using a boron-doped diamond electrode and square-wave voltammetry technique. In the pH range values between 8.0 and 10.0, the voltammetric results showed three reduction peaks − 1.07, − 1.2, and − 1.4 V (vs. Ag/AgCl) for the chlorothalonil. This reduction mechanism is based on three consecutive dehalogenation steps proposed by density functional theory and the calculation of the Chelpg charge values. The results showed that the most negatively charged carbon was the first dehalogenated and the following dehalogenations for the intermediates occurred by the chloride anions loss from their most respective negative carbon atoms. From the square wave voltammetric behavior of chlorothalonil, an analytical method was developed in which the calibration curve was obtained in a concentration range of 1.2 × 10−7 to 4.0 × 10−6 mol L−1 with sensitivity of 0.29 A/mol L−1 and linear correlation coefficient of 0.997. The limits of detection (LOD) and quantification (LOQ) were 4.0 × 10−8 mol L−1 (10.6 μg L−1) and 1.2 × 10−7 mol L−1 (55.8 μg L−1), respectively, being lower than the maximum values allowed by the Environmental Protection Agency and the Brazilian National Surveillance Agency. Tea infusion samples (lemon grass, spearmint, strawberry, and orchard) were spiked with the chlorothalonil pesticide standard solutions. The results showed recovery values between 98.0 and 103.0% for 1.0 × 10−6 mol L−1concentration, indicating the applicability of this method for different complex matrices.