Mass spectral characterization of three anthracycline antibiotics: a comparison of thermospray mass spectrometry to particle beam mass spectrometry.

Mass spectral results for three anthracyclines, doxorubicin, daunorubicin, and carminomycin are compared by using thermospray (TS) or particle beam (PB) [electron ionization (EI) and chemical ionization (CI)] instruments. Typically, positive ion TS mass spectrometry (MS) provided intense [MH]+ ions and some fragment ions, while PBMS in the EI mode provided only fragment ions. Significant [MH]+ ions were observed for carminomycin and daunorubicin when analyzed using PBMS in the positive ion CI mode. Under negative ion detection, TSMS yielded intense [M-H]- ions for these compounds while PBCIMS resulted in significant M- ions. Fragment ions observed in all three anthracyclines under positive and negative ion detection by TSMS and PBCIMS are due mainly to the cleavage of glycosidic bond, loss of H2O, and the loss of the side chain (COCH2R2) from the aglycone.