Structural Analyses of Glycolipids by FAB MS/SI MS With Particular Reference to Long Chain Bases in Sphingolipids

Abstract

Glycosphingolipids and phosphonosphingolipids were investigated with f ast atom bombardment mass spectrometry (FABMS) and/or secondary ion mass spectrometr y (SIMS). Application of B/E-constant and B²/E-constant linked scannings in the positive mode made it possible to determine the mass number of long chain bases without ambiguity.
The sphingolipids generally show MH⁺, (MH-H₂O)⁺, (MH-saccharid e or MH-phosphonate)(Y-H₂O)⁺, and +CH, C(NH₂) =CHR(Z⁺), the last one being the k ey ion. Thus, the mass number of a long chain base is determined according to the Z⁺ ion which is easily detectable as an even mass number ion in the region of m/z 200-400.
The method also provides information about the fatty acid m oiety in the ceramide independently through the reverse search of the ceramide by B/E-constant linked scanning of the daughter ion Z. Further linked scanning in the same mode from Y+ may lead to an assignment of the specific MH+ among other MH+s. Confirmation of the assignment is successfully made by sequential B/E-constant linked scannings from MH+→ Y⁺ Z⁺.
Provided that a neutral matrix is used, the method is applicable not only to the sphin genine or sphinganine homologs but also to the phytosphingosines which have an additional hydroxyl group in the long chain base.