The surrogate and 30 ml of pure water was added to the sample under stirring. The muddy mixture was poured into a l-l round-bottom flask and then steam distilled until 200 ml of aqueous distillate were collected. The NBS were distilled together with a great part of the first 100 ml fraction. It is preferable to set the outlet of distillate near the bottom of the receiver and to cool it with ice water, in order to prevent volatilization loss of them. The distillate was poured into a separating funnel and 10 g of NaCl was added. Then, analyte was extracted twice with
20 ml of hexane, dehydrated and concentrated to 5 ml of hexane solution which was subjected to the Florisil column. The column was washed first with 30 ml of hexane-benzene (506) and then the 10 NBS were eluted with 100 ml of benzene. The eluate was concentrated to 1.0 ml and subject to the GC- MS-SIM system.