Carbon-13 isotopologue distribution

In general, the isotopologue distribution of each species of a class mainly depends on the number of total carbon atoms in the species. This is due to the following facts. First, all the species of a class of interest should contain identical numbers of O, N, P, or other atoms if the lipid species of interest is not a modified one. This means that these atoms equally contribute their isotopologues to all the species of the class. Therefore, their contribution to the ion intensities does not cause any difference for relative comparison to the selected internal standard(s). Second, the natural... 

As described in Chapter 15, correction for different stable isotopologue distribution due to differences in the number of carbon atoms between the species of interest and the selected internal standard(s) and correction for baseline should be performed prior to the comparison of the intensities. It should be recognized that in the majority of the studies in plant lipidomics after direct infusion, MDMS-type analysis is generally not conducted thus, the isobaric or isomeric species are not resolved as regrettable. A detailed protocol for profihng of polar hpids in plants after direct infusion can be found [9]. 

Each lipid class in a cellular lipidome comprises a variety of lipid species that contain an identical head group but various fatty acyl chains containing a differential number of carbon atoms and differential degrees of unsaturation. Therefore, if an equal molar mixture of lipid species of a class is analyzed by MS, the monoisotopie peak intensities of these species displayed in the mass spectrum decrease as the number of carbon atoms in the species increases. This is due to the differential distribution of isotopologues in those species. 

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