Mapping Glyceride Species in Biodiesel by High-Temperature Gas Chromatography Combined with Chemical Ionization Mass Spectrometry.

Accurate and comprehensive identification of residual glycerides in biodiesel is an important part of fuel characterization due to the impact of glycerides on the fuel physicochemical properties. However, analysis of bound glycerol in biodiesel samples faces challenges due to lack of readily available standards of structurally complex glyceride species in nontraditional biodiesel feedstocks and a risk of misannotation in the presence of impurities in gas chromatographic separations. Here, we evaluate methane and isobutane chemical ionization-single quadrupole mass spectrometry combined with high-temperature gas chromatography separations for mapping monoacylglycerols, diacylglycerols, and triacylglycerols in biodiesel. Unlike electron impact ionization, which produces mostly in-source fragments, isobutane chemical ionization spectra of tetramethylsilyl-derivatized monoacylglycerols and diacylglycerols are dominated by molecular ions and M-SiO(CH3)3+ ions, which provide important diagnostic information. We demonstrate the utility of isobutane chemical ionization in identifying structurally complex glycerolipid standards as well as species in biodiesel samples from different plant and animal feedstocks.