The extraction was centrifuged
at 4000rpm for 5min to separate the supernatant from
the soil or plant. Then, 2ml of the supernatant was filtered through
2 g of silica gel column and was eluted consecutively with 10 ml of
the mixture of 1:1 hexane and dichloromethane (v/v). The extract
was concentrated by evaporation of the dichloromethane under a
stream of nitrogen and the residue was dissolved in hexane with a
final volume of 1.0 ml for GC analysis.