where ∑A is total peak area, AEI is the peak area that corresponds to methyl heptadecanoate, CEI is the concentration of the methyl heptadecanoate solution (mg/mL), VEI is the volume of methyl heptadecanoate (mL) and m is the mass of the biodiesel sample (mg).
The biodiesel sample was washed with distilled water at a water; biodiesel ratio of 0.5:1 by volume, 3 times at ambient temperature under a stirrer speed of 200 rpm [28]. The properties of the purified biodiesel were then analyzed according to the ASTM standard.