Fig. 3. Identification of isotopologue peaks.
Change from a molecular mass [M]+ to a mass of [M+2]+ can be the result of substitution of various isotopes (i.e., 15N for 14N, 13C for 12C, 18O for 16O, 17O for 16O, or 2H for 1H) or can result from the addition of hydrogens to the molecule as in the case of changing the degree of unsaturation in a lipid. Here the differences in mass from substitution of the indicated isotope are shown. The change in mass from addition of two hydrogens (+H2) is also presented.