Chromatographic analyses were performed using a GC-ECD system Varian CP 3800 (USA), equipped with CP 8410 autosampler; injector model 1079 with electronic pneumatic control (EPC); capillary column DB-5MS (30 m × 0.25 mm × 0.25 µm); electron capture detector and data acquisition system through the Star Workstation 6.0 software.