Sensitive Determination of the Diquat Herbicide in Fresh Food Samples on a Highly Boron‐Doped Diamond Electrode

The highly boron‐doped diamond electrode (HBDD) combined with square wave voltammetry (SWV) was used in the development of an analytical procedure for diquat determination in potato and sugar cane samples and lemon, orange, tangerine and pineapple juices. Preliminary experiments realised in a medium of 0.05 mol L−1 Na2B4O7 showed the presence of two voltammetric peaks around −0.6 V and around −1.0 V vs. Ag/AgCl/Cl− 3.0 mol L−1, where the first peak could be successfully used for analytical proposes due the facility in the electrode surface renovation. After the experimental and voltammetric optimisation, the calculated detection and quantification limits were 1.6×10−10 mol L−1 and 5.3×10−10 mol L−1 (0.057 µg L−1 and 0.192 µg L−1, respectively), which are lower than the maximum residue limit established for fresh food samples by the Brazilian Sanitary Vigilance Agency. The proposed methodology was used to determine diquat residues in potato and sugar cane samples and lemon, orange, tangerine and pineapple juices and the calculated recovery efficiencies indicated that the proposed procedure presents higher robustness, stability and sensitivity, good reproducibility, and is very adequate for diquat determination in complex samples.