Aviv Amirav, Tel Aviv University and Aviv Analytical, Tel Aviv Israel.
Hans-Gerd Janssen, Unilever R&D Vlaardingen and University of Amsterdam, Amsterdam The Netherland
- All the triglycerides were eluted with GC-MS with Cold EI and exhibited good peak shape without any ion source tailing. The biggest and last to elute triglyceride was with molecular weight of 1031.0 which has the elemental formula of C67H130O6 (Carbon number CN64). Note that the 130 hydrogen atoms resulted in 1.0 amu high mass shift. Cold EI excels in the elimination of ion source peak tailing and thus all peaks were tail free.
- Cold EI provided molecular ions information for all the triglycerides. The Cold EI mass spectra of all the triglycerides in all the three oils exhibited useful molecular ions with relative abundances in the range of 10-50%. This molecular ions information was not only important for the elucidation of the structure of the triglycerides but it also helped to resolve co-eluting further unsaturated triglycerides in majority of a given triglyceride.
- Cold EI provided informative high mass fragment ions information. As a result it is possible to more accurately obtain the structure of the triglycerides.
- Cold EI provided useful information on diglycerides that eluted among the triglycerides. The Cold EI mass spectra of diglycerides were characterized by having abundant molecular ions plus a nearby high mass fragment of M-18 in view of loss of water.
- The sensitivity was good and ratio of triglycerides signal to column bleed background was very high. This high ratio of signal to column bleed is another beneficial feature of Cold EI.
- The analysis time was relatively short at 20 min.
- Unexpected GC peak broadening was found in olive oil. This observation was particularly evident with olive oil in which the most abundant peak of glycerol trioleate was relatively broad. The common perception is that such broadening emerges from the coelution of several triglycerides with different degrees of unsaturation. However, we found that the majority of the broad peak is triolein with some addition of triglyceride with 4 double bonds but the triolein itself had a broad GC peak. While one explanation is that there can be a few isomers in the fatty acids our speculation is that the position of the double bond in the oleic acids is migrating at the hot (350°C) GC column or alternatively it undergoes quick cis-trans isomerization. This observation is new and to our knowledge unreported and thus requires further investigation about its source.