1. Analytical approaches for 1 H NMR wide line spectra of Soil Organic Matter Alexander Jäger 1, Marko Bertmer 1, Gabriele E. Schaumann 2 References Introduction 1 H NMR Implications from humidity experiments (sapric peat) Improved, extended line fitting model applied to long term data 1 Universität Leipzig, Institut für Experimentalphysik II, Abteilung MQF, Linnéstr. 5, 04103 Leipzig ajaeger@physik.uni-leipzig.de, bertmer@physik.uni-leipzig.de 2 Universität Koblenz-Landau, Institut für Umweltwissenschaften, AG Umwelt- und Bodenchemie, Fortstr. 7, 76829 Landau schwarzj@uni-landau.de, schaumann@uni-landau.de moisture uptake leads to characteristic adsorption isotherm (upper right), also reflected in 1 H NMR Lorentzian fraction (insert in upper right figure) 1 H Lorentzian fraction shows deviation from linear moisture dependency mobilizable fraction is decreasing with higher moisture content  higher general mobility with higher moisture content expressing in decreasing Lorentzian line width (right figure), water molecules in WAMBs less rigid, line width of Gaussian fraction is not affected by moisture content 1 H line shapes from carbon structural components [1] Jäger, Alexander et al. (2011): Optimized NMR spectroscopic strategy to characterize water dynamics in soil samples; Organic Geochemistry 42, 917–925. [2] Jäger, Alexander et al. (2012): 1 H and 13 C Solid-State NMR based structural mobility and water adsorption studies of Soil Organic Matter, in preparation. We thank the German research foundation (DFG) for funding within the SPP1315 ‘Biogeochemical Interfaces in Soil’ (SCHA849/8-1). Acknowledgements Printed at Universitätsrechenzentrum Leipzig SPP 1315 annual colloquium 2012, October 10 th – 12 th, Dornburg, Jena 13 C NMR wide line NMR is rarely used, but sensitive to mobility of protons and is a fast measurement protons fixed in SOM structure show broad lines, protons in mobile components (e. g., water) show narrow lines since dipolar interaction is cancelled out by motion, DEPTH pulse sequence is used to remove probe background signal (two 180° defocusing pulses): spectra are decomposed using NMR fitting program (dmfit), calculating Gaussian / Lorentzian ratio [1] all measurements performed at 400.15 MHz (9.4 T magnet) using solid-state NMR probe spectra obtained with cross polarization technique under magic angle spinning (CPMAS) average measurement time (SOM) 5-20 h measurements at temperatures up to 100° C are possible spectra are analyzed for chemical composition and structural conformations (phase transitions) correlation spectroscopy (two dimensional) can be performed addressing proton-carbon connectivity and proton wide line of individual functional groups Conclusions & Outlook improved model for 1 H wide line data [2] is derived out of combined humidity and 13 C NMR results individual effects of aging on certain soil components expected further analysis of different SOM types with changing parameters (moisture content, composition) planned advanced mechanistic model required for deeper understanding of soil aging * dry matter basis 13 C NMR CPMAS spectra aliphatic compounds aromatic compounds carboxylic O-alkyl carbohydrate 1 H NMR spectra assignment & line width: water 1.9 kHz carbohydrates 42 kHz poly-methylene 40 kHz analysis water 1.9 kHz carbohydrates 42 kHz poly-methylene 49 kHz water 5.9 kHz poly-methylene 19.5 kHz water 3.6 kHz carbohydrates 44.8 kHz water 1.8 kHz carbohydrates Pake doublet 28.2 kHz (peak distance) broad Lorentzian: aliphatic component  poly-methylene broad Lorentzian: aliphatic component  poly-methylene no Gaussian:  no/small amount of carbohydrates only one Lorentzian:  no poly-methylene high-order Pake doublet:  crystalline carbohydrates before heating after heating Lorentzian line, water with higher mobility Gaussian line, organic matter static 1 H NMR spectrum * 30 min @ 110° C mobilizable fraction: “water molecule bridges” (WAMBs) larger fraction of water with higher mobility heating event total signal first Lorentzian (water molecules) second Lorentzian (poly-methylene) Gaussian: carbohydrates + WAMBs sapric peat (moisture content: 7 %, dry matter basis) Lorentzian lines show individual behavior: quick return to initial value for second Lorentzian; slow re-formation for first Lorentzian please note the project outcome poster: “Dynamic and Structural Effects in SOM after Thermal Treatment observed with 1 H, 13 C NMR Spectroscopy & DSC”