2.2. Instrumentation
The analysis of CPs was performed by a Shimadzu GC- 2010 GC-ECD system. The GC was fitted with BPX5 capillary column (30 m × 0.25 mm i.d., 0.25m film thickness, 95% methyl–5% phenyl) from SGE (Victoria, Australia). The injection port was held at 250 ◦C and used in the splitless mode with splitless time of 0.50 min. Ultra pure helium (99.9999%, Air Products, West Sussex, UK) passing through a molecular sieve trap and oxygen trap (Chromatography Research Supplies, Louisville, USA) was used as the carrier gas at constant linear velocity of 30 cm s−1. The analysis was performed with an initial column temperature of 100 ◦C, held for 2 min and followed by heating to 210 ◦C at 5 ◦C min−1 (held 1 min). The ECD temperature was maintained at 300 ◦C. Ultra pure nitrogen (99.9999%, Air Products), as makeup gas for ECD, was passed through molecular sieve trap and oxygen trap (Chromatography Research Supplies) at the flow of 30 mL min−1. A Centurion Scientific (West Sussex, UK) model 1020D centrifuge was used.