Mark L. Tracy, Xiaodong Liu, and Linda Lopez. Consumables Research & Development, Dionex Corp., 1228 Titan Way, Sunnyvale, CA 94085
In the production of ester-type biodiesel fuels, analysis for glycerides has two important functions: one is to characterize the natural lipids for carbon-chain length and unsaturation in the feedstock, and the other is to measure residual glycerides after transesterification. New methods based on liquid chromatography (LC) are displacing earlier methods based on gas chromatography (GC). Even so, there is room for improvement. The well-known ASTM method for residual glycerides in biodiesel by LC requires long run times and a chlorinated solvent because of the type column used in the separation. A variation of the method may be used to get a high-resolution profile of the triglyceride composition of natural lipids. Newer LC columns with particle sizes in the range of 1.5—2.5 µm and the instrument systems that support them permit the optimization of lipid analysis in ways that were previously not available. For these analyses, we demonstrate short run times, reduced solvent consumption and elimination of chlorinated solvent by using 2.2 µm C18 columns, temperature control and replacement of dichloromethane by alcohol or ester solvents.
