Direct determination of boscalid in grape samples by differential pulse voltammetry using a carbon paste electrode

A new methodology to determine directly the fungicide boscalid (BSC) was developed and successfully applied in red grape 100% juice, peel extracts, pulp and purple grape seeds (Vitis labrusca L.) with a working carbon paste electrode (CPE) without sample preparation. Cyclic voltammetry (CV) indicated the presence of an irreversible cathodic process of BSC at -1.21 V vs. Ag|AgCl (KCl 3.0 mol L^-1) in a solution of 0.100 mol L^-1 HCl/acetone 70 : 30 (v/v). This behavior was also observed using Square Wave Voltammetry (SWV). The Differential Pulse Voltammetry (DPV) technique proved to be more sensitive and with higher selectivity for BSC quantification. The influence of pH on the reduction of BSC was investigated in Britton-Robinson Buffer (BRB), 0.01 mol L^-1 (pH 2.00-12.00). The limit of detection (LOD) values obtained from calibration curves for different samples were as follows: 0.107 mg L^-1 for deionized water; 0.146 mg L^-1 for red grape 100% juice; 0.922 mg kg^-1 for peel extracts; 0.818 mg kg^-1 for grape pulp and 0.691 mg kg^-1 for grape seeds. The corresponding Limit of Quantification (LOQ) values for the same samples were as follows: 0.358 mg L^-1; 0.486 mg L^-1; 2.87 mg kg^-1; 2.73 mg kg^-1 and 2.51 mg kg^-1, respectively. In addition, the recovery rates for the different concentration levels in the investigated range varied between 97.13 and 103.4%. All tests performed with the samples did not require extraction or pre-concentration steps of BSC, resulting in a fast, simple and cheap methodology.