The layers were then separated and the hexane layer was collected in an Erlenmeyer flask. An
aliquot of 25 ml from hexane layer was evaporated in a
rotatory evaporator at 37 C. The residue was dissolved
in 2 ml of hexane containing 0.2 mg/ml of 5a-cholestane,
as internal standard, and then 3 ll were injected into the
gas chromatograph.