Determination of glyceride and free fatty acid residuals in biodiesel by thin layer chromatography combined with on-line pyrolytic methylation gas chromatography

A novel method on basis of thin layer chromatography (TLC) combined with on-line pyrolytic methylation gas chromatography (OPM-GC) in the presence of trimethylsulfonium hydroxide (TMSH) was developed and applied to the determination of glyceride and free fatty acid residuals in biodiesel. Both glycerides and free fatty acids in biodiesel were separated by TLC alumina sheets, and then the cut spots were analyzed directly by pyrolytic methylation gas chromatography method in a pyrolyzer at 350 °C without complex pretreatment. In this process, glycerides and free fatty acids were converted into their corresponding fatty acid methyl esters, and quantified well by the total peak areas of formed esters. Thus obtained calibration curves of monostearin, distearin, tristearin and oleic acid exhibited good linearity with the regression coefficients from 0.9766 to 0.9950 at the concentrations ranged from 300 to 5000 mg L−1. The limits of detection were in the range of 100-200 mg L−1, and the RSDs (n = 3) ranged from 3.7% to 12.5%, calculated for monostearin, distearin, tristearin and oleic acid at the concentration level of 2000 mg L−1. The potential of the proposed method was assessed by the determination of glycerides and free fatty acids in real biodiesel samples. The results prove that this TLC-OPM-GC technique is a simple, accurate and low solvent consuming method for the simultaneous determination of glyceride and free fatty acid residuals in biodiesel.