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 shaken
in 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 re-
move the sulphuric acid traces. Traces of water from the superna-
tant were removed with anhydrous sodium sulphate; hexane was
transferred to a vial and directly injected into a GC–FID using the
above-mentioned conditions.