All solutions were stored in amber flasks at –18 °C. For the injection in the GC-ECD system, the analytical solution mixture at 1 mg L-1 was diluted at the concentrations 5, 10, 20, 50, 75 and 100 µg L-1 in acetonitrile and, also, in the matrix blank extract (matrix matched calibration) prepared by the QuEChERS procedure in order to evaluate the matrix effect.