Determination of Acylglycerols and Glycerol in Castor:Soybean Biodiesel Blend Produced by a Base/Acid-Catalyzed Process

This paper describes the production of the methyl biodiesel blend of hydroxylated vegetable (castor oil) and soybean oils by a base/acid-catalyzed process and the first simultaneous determination by gas chromatography of the levels of total and free glycerol, mono-, di- and triacylglycerols based on the standard method ASTM D 6584. Best results were observed for transesterification carried out in 6:1 (methanol:oil), sodium hydroxide 1 % w/w at 60 °C for 1.5 h. The analytical method not only produced curves with good linearity, but also had a coefficient of determination (r ²) above 0.997 and accuracy between 70 and 141 % at relative standard deviations (RSD) lower than 10 %. The matrix effect (ME) was investigated and only diolein was found to have a significant matrix effect. The method was robust when applied to different chemical compositions of biodiesel. Results showed that the acid value and the contents of mono-, di-, and triacylglycerols, total and free glycerol were within the limits set by standardized methods and that biodiesel may be produced from soybean and castor oil blends.