Adsorption
by minerals is a common geochemical process of dissolved
organic matter (DOM) which may induce fractionation of DOM at the
mineral-water interface. Here, we examine the molecular fractionation
of DOM induced by adsorption onto three common iron oxyhydroxides
using electrospray ionization coupled with Fourier-transform ion cyclotron
resonance mass spectrometry (ESI-FT-ICR-MS). Ferrihydrite exhibited
higher affinity to DOM and induced more pronounced molecular fractionation
of DOM than did goethite or lepidocrocite. High molecular weight (>500
Da) compounds and compounds high in unsaturation or rich in oxygen
including polycyclic aromatics, polyphenols and carboxylic compounds
had higher affinity to iron oxyhydroxides and especially to ferrihydrite.
Low molecular weight compounds and compounds low in unsaturation or
containing few oxygenated groups (mainly alcohols and ethers) were
preferentially maintained in solution. This study confirms that the
double bond equivalence and the number of oxygen atoms are valuable
parameters indicating the selective fractionation of DOM at mineral
and water interfaces. The results of this study provide important
information for further understanding the behavior of DOM in the natural
environment
