The mixture was vigorously shaken and quantitatively
transferred to a separatory funnel and extracted with 10 ml of n-hexane. The mixture was extracted again and vigorously shakenin duplicate for 2 min and then left to settle for 10 min. Then, the three extracts of hexane were washed with Milli-Q water to remove the sulphuric acid traces. Traces of water from the supernatant were removed with anhydrous sodium sulphate; hexane was
transferred to a vial and directly injected into a GC–FID using the
above-mentioned conditions.