*3.4. Analytical Procedure*

Biodiesel was analyzed by gas chromatography, using a gas chromatograph with an FID detector (VARIAN 3900, Varian, Palo Alto, CA, USA). A polyethylene glycol column (Zebron ZB-WAX PLUS, Phenomenex, CA, USA) was used with the following characteristics: length, 30 m; film thickness, 0.5 μm; and i.d., 0.32 mm. Helium (1.4 mL·min−1) was used as a carrier gas, and the temperature oven for each run was 220 ◦C for 34 min and at 245 ◦C for 29 min with a ramp of 20 ◦C·min−1. The injector and detector temperatures were 270 and 300 ◦C, respectively. Methyl heptadecanoate and methyl erucate were used as standards for the internal standard method for most methyl esters and methyl ricinoleate, respectively. Ethyl acetate was used as a solvent for the standards, and calibration curves were carried out for each standard.
