FIG. 8.

ESI-linear-ion-trap-MS profile spectra of lithium-adducted ceramide-containing lipid fractions. (A) Constitutive ceramide fraction. The major ion is at m/z 690, and minor ions (3 to 9% relative abundance) were observed at m/z 618 and at m/z 662, 676, 704, and 718, which are consistent with phytoceramides differing from the major molecular species by the number of CH₂ units. Odd m/z adduct ions are most likely diacylglycerol lipid components. (B) Inducible ceramide fraction. Even m/z values indicate ceramide MLi⁺ adduct ions confirmed by collision-induced-dissociation-MS² analysis; odd m/z values indicate confirmed nonceramide (probably phospholipid) MLi⁺ adduct ions. The asterisk indicates a residual MNa⁺ adduct from the major ceramide component (m/z 16 increment from m/z 690).