Concerning the Dissociation of Hypericin: An Atmospheric Pressure Ionization Mass Spectrometric StudyZur Dissoziation des Hypericins: Eine massenspektrometrische Untersuchung mit Atmosphärendruck-Ionisierung

 The dissociation of hypericin (1) was investigated using atmospheric pressure ionization mass spectrometry of 80% ethanolic solutions under variation of their pH values. Thus, it could be unequivocally established that the species predominant within the pH region of 3–10 and 11–13 are the mono- and dideprotonated compounds 1(−) and 1(2−). These results nicely corroborate the hitherto accumulated mostly spectrophotometric evidence for the first deprotonation step occurring at a pKa value in the order of 2 and the second one at about 12. Moreover, this example demonstrates the potential of atmospheric pressure ionization mass spectrometry as a valuable tool to investigate dissociation equilibria.