Characteristic fragmentation of thromboxane B2 in thermospray high-performance liquid chromatography-mass spectrometry.

Cyclo- and lipo-oxygenase metabolites of arachidonic acid have been reported to have very simple thermospray mass spectra. However, thromboxane B2 (TXB) in ammonium acetate-methanol and at interface temperatures below the point of total vaporization shows a mass spectral pattern characterized by abundant ions at low masses. The more abundant TXB fragment ions have been characterized as adducts from four principal fragments with molecular masses of 156, 170, 196 and 326. Positive- and negative-ion mass spectra, and mass spectra obtained with an alternative thermospray buffer (butylammonium acetate) support the molecular masses of these fragments. A tentative assignment of the fragments can be made by comparison of the thermospray mass spectra of TXB, 2,3-dinor-TXB and some of their methyl ester and methyl oxime derivatives. Interface temperature and solvent composition effects on the fragmentation, as well as in the electron-capture processes observed when working in the filament-on mode, are discussed. Fragmentation mechanisms can be related to those observed for monosaccharides, and imply retro-Diels-Alder as well as retroaldolic condensation-type rearrangements.