A rapid method for the structural characterization of sulphated phlorotannins by negative ion fast atom bombardment mass spectrometry and acetylation on the target

Abstract

A method for a rapid and direct structural determination of sulphated phlorotannins has been developed by using a combination of negative ion fast atom bombardment mass spectrometry and acetylation on the target. The structural variations of sulphated phlorotannins include: (i) the number of monomeric phloroglucinol units involved; (ii) the mode of their connectivity; (iii) the orientation of hydroxy groups on aromatic carbon atoms; (iv) the presence of the substituents other than hydroxy groups on aromatic carbon atoms; and (v) the number of sulphate esters on the hydroxy groups. Additionally, the acidic protons on the sulphate groups can be easily substituted by sodium or potassium cations, depending on the mode of isolation. In the negative ion mode, several ions were observed and a determination of molecular size and molecular parameters (i)–(v) appeared to be rather speculative. After adding diluted hydrochloric acid to the sample in order to substitute alkali ions for protons, the hydrolysis of sulphate groups has been observed. The acetylation on the target, however, represents a rapid method to observe the molecular ions, and from the mass differences the molecular parameters can be easily calculated. This procedure also demonstrates the general possibility of studying rapid chemical reactions by fast atom bombardment mass spectrometry.