After the aqueous phase had been acidified to pH 2 with HCl (5 mol/L), the FFA were finally extracted 3 times with 5 mL of chloroform/methanol (2:1, vol/vol). The combined solution was dried with anhydrous Na2SO4 and brought to near dryness by passing a stream of nitrogen across. Thereafter, the FFA were methylated with 1 mL of BF3/CH3OH (14%, wt/wt) for about 20 min in a water bath at 80°C. After cooling the methylated FFA to room temperature, 1 mL of hexane and 1 mL of saturated aqueous NaCl were added, mixed thoroughly, and left overnight at −40°C for phase separation.