Simple and Efficient Method for the Analysis of Transesterification Reaction Mixtures for Biodiesel Production by Reversed-Phase High Performance Liquid Chromatography

Isocratic reversed-phase high performance liquid chromatography (HPLC) methods have been developed for the analysis of biodiesel methyl esters and intermediate species associated with transesterification reactions. While most HPLC methods for biodiesel analysis employ gradient elution and ultraviolet (UV) detection, these methods employ isocratic elution with refractive index detection (RID). For the separation of methyl esters, monoglycerides, and free fatty acids, a mobile phase of 85% acetonitrile + 15% deionized water is used. Diglycerides can be separated using 100% methanol, and triglycerides can be quickly analyzed using a mixture of 60% 2-propanol + 40% methanol. While previous HPLC methods for methyl ester analysis have been shown to successfully separate components found in biodiesel mixtures, the use of UV detection is inadequate for the detection of species with saturated carbon chains. Many of the common feedstocks used for biodiesel synthesis contain a significant percentage of species with saturated carbon chains, for example, soybean, sunflower, palm, and palm kernel oils. The use of RID, however, allows for both saturated and unsaturated methyl esters to be detected. Additionally, the use of HPLC for the analysis of biodiesel methyl esters and the intermediate species associated with transesterification reactions, as opposed to the more commonly employed gas chromatography (GC) method, has the advantage that samples can be directly analyzed without any sort of sample derivatization, as is required when GC is used.