Direct characterization of iodine covalently bound to fulvic acids by electrospray mass spectrometry.

Numerous studies have demonstrated that humic substances (HS) react with iodine to form iodo derivatives and thereby can control the bioavailability of radioisotopes. Unfortunately, none of these studies have provided detailed insights into product compounds and so far, to our knowledge, the direct analysis of these species by electrospray ionization (ESI) mass spectrometry has not been explored. The reactivity of iodine with fulvic acids (FA) present in HS was investigated by means of ESI coupled with a quadrupole time-of-flight (Q-TOF) mass spectrometer. ESI spectra of solutions, that were indicated by MS/MS analysis to have formed iodinated species, apparently displayed singly charged ions corresponding in m/z to hypothesized species, viz., [RI - H](-), R = (substituted FA compound). MS/MS analysis based on the diagnostic fragment ions for FA compounds and their iodo derivatives suggests that FA undergo aromatic substitutions. Furthermore, significant differences in mass profiles are observed that presumably result from extended redox reactions. The ESI-MS technique opens up new opportunities to understand the scavenging properties of HS towards radionuclides and heavy metals for environmental studies. Copyright 2001 John Wiley & Sons, Ltd.