One-step equilibrium direct-solvent extraction was conducted
by the method of Chen and Bergman (2005a) with some modifications.
Each sample (1 g) was extracted with acetone ratio of 1:10
w/v, vortexed at maximum speed for 1 min then centrifuged at
2500 rpm for 20 min, after which the solvent was removed. The
residual was further extracted twice, and the supernatants were
combined before evaporating them to dryness under nitrogen
gas. The determinations were made in triplicate.