Ultrahigh Resolution Mass Spectrometry of Leachable Organic Matter yFrom Wood after Progressive Fungal Decay

Dissolved organic matter (DOM) leaching from forest floor coarse woody debris is an yimportant mediator in metal cycling, microbial activity, and mineral dissolution in the yassociated soils. Much research has been directed at characterizing the chemical ycomposition and molecular weight range of DOM to better assess and predict its yreactivity. Unfortunately, these chemical and structural properties of DOM are extremely ydifficult to assess and consequently a wide variety of indirect analytical techniques are ytypically employed. Direct analysis of DOM by High-field Fourier Transform Ion yCyclotron Resonance Mass Spectrometry combined with Electrospray Ionization (ESI yFT-ICR MS) has only recently been applied to a limited number of environmental yorganic matter samples. With a resolving power of greater than 200,000, this is currently ythe only analytical technique capable of fully resolving individual molecules in such ycomplex mixtures. y To simulate leachates from coniferous woody debris samples of red spruce (Picea yrubens) wood were degraded with brown rot fungi over a period of 43 weeks and yextracted with water. Water-soluble fractions of the degraded residue were analyzed yusing a 9.4 Tesla ultra-high resolution FT-ICR MS. Supporting information on the yleachate and solid residue chemistry was obtained using on-line 13C-labelled ytetramethylammonium hydroyide (TMAH) thermochemolysis GC-MS, solid-state NMR yand elemental analysis. y The FT-ICR mass spectra reveal structures at every nominal mass from approximately yy250 to 1200 Daltons as well as molecular families containing ions that differ from each yother in degree of saturation or number of functional group substitutions. There is a yprogressive increase in the number of individual compounds within a nominal mass unit, yfrom 2 compounds at 4 weeks decay to 6 compounds at 32 weeks, resulting in thousands yof discrete extractable compounds at the conclusion of decay. Degradation of wood over ytime does not change the overall molecular weight range of products, however, a shift in ylocation of the data distribution on the Kendrick plot demonstrates changes in yhomologous series with degradation. This data is currently being analyzed using the van yKrevelen diagram to gain additional information.y