ABSTRACT
A novel voltammetric screening method has been developed for the rapid determination of fipronil (FPN) residues in lactose-free milk samples with the use of a carbon-paste electrode (CPE) by differential-pulse voltammetry (DPV). Cyclic voltammetry indicated the occurrence of an irreversible anodic process at approximately +0.700 V (vs. Ag|AgCl, 3.0 mol L-1 KCl) in a 0.100 mol L-1 NaOH supporting electrolyte prepared as a 30% (v/v) ethanol-water solution. Quantification of FPN was carried out by DPV and analytical curves were constructed. In the absence of a matrix, the limits of detection (LOD) and quantification (LOQ) were 0.568 mg L-1 and 1.89 mg L-1, respectively. In the presence of a lactose-free skim milk matrix, the values of LOD and LOQ were 0.331 mg L-1 and 1.10 mg L-1. The recovery percentages for three different concentrations of FPN in lactose-free skim milk samples ranged between 95.3% and 109%. All assays could be conducted with milk samples without any prior extraction steps or pre-concentration of FPN, making this novel method rapid, simple, and relatively cheap.
Subject(s)
Carbon , Milk , Animals , Cattle , Carbon/chemistry , Electrochemistry/methods , ElectrodesABSTRACT
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.
