. Residual hydrocarbon remaining at the surface of the tube was separated properly and 4 mL were transferred to a clean tube to which 4 mL of hexane was added prior to extraction by vortexing for 2 min. Then,
. Residual hydrocarbonremaining at the surface of the tube was separatedproperly and 4 mL were transferred to a clean tube to which 4 mL ofhexane was added prior to extraction by vortexing for 2 min. Then,