where C: Total fatty acid methyl ester content (mg mg ); A: sum of peak area of fatty acid methyl ester 
from C14 to C24:1 ; AEI : peak area of internal standard, heptadecanoic acid acid methyl ester; CEI : 
concentration of heptadecanoic acid methyl ester (mg ml
-1
); VEI : Volume of heptadecanoic acid acid 
methyl ester (ml
-1
); and m: mass of input biodiesel (mg). Then, biodiesel yield was calculated relative to 
the initial amount of waste cooking oil by weight. Similar calculations were used by others [19-22].