Then the mixed working standard solutions
of 5 mg/L, 10 mg/L, 100 mg/L were made with methanol as
solvent. The mixed standards solutions (1 mL) were filtrated into
glass vials through 0.22 mm nylon membrane. OFM samples were
diluted by 20 folds with water. Then 1 mL diluted samples was
filtered into the glass vial through 0.22 mm nylon membrane, and
1 mL was injected into GC with a split ratio of 25 being used.