Electroanalysis of diquat using a glassy carbon electrode modified with natural hydroxyapatite and β-cyclodextrin composite.

The present work reports the development of a low-cost and reliable differential pulse adsorptive stripping voltammetric procedure for the detection of diquat (DQ) in water, using a glassy carbon electrode (GCE) modified with β-cyclodextrin (β-CD)/Natural hydroxyapatite (NHAP) composite material. The structural characterization of the natural hydroxyapatite and its modified counterpart was achieved using several techniques including X-ray Diffraction, Fourier Transform Infrared Spectroscopy and Thermal Analysis. By comparing the physico-chemical characteristics of hydroxyapatite material before and after reaction with β-CD, all of these techniques have demonstrated the successful grafting process of β-CD on the surface hydroxyl groups of hydroxyapatite, using citric acid (CA) as cross linker. The electrochemical features and permeability properties of the obtained materials, coated as thin film onto the GCE surface were characterized using ion exchange multisweep cyclic voltammetry. The β-cyclodextrin modified hydroxyapatite (NHAP-CA-β-CD) was evaluated as electrode modifier for DQ sensing. The electroanalytical procedure followed two steps: the chemical preconcentration of DQ under open-circuit conditions, and the differential pulse voltammetric detection of the preconcentrated pesticide. Various experimental parameters likely to influence the sensibility of electrode were fully investigated and optimized. A linear calibration curve for DQ in the concentration range of 5 × 10 - 4.5 × 10 mol L was obtained at GCE/NHAP-CA-β-CD, with a detection limit of 4.66 × 10 mol L (DL = 3S/M). The proposed method was successfully applied to the determination of DQ in spring water.