Analytical approaches for of Soil Organic Matter Alexander 1 Jäger , Marko 1 Bertmer , Gabriele E. 1H NMR wide line spectra 2 Schaumann 1Universität Leipzig, Institut für Experimentalphysik II, Abteilung MQF, Linnéstr. 5, 04103 Leipzig ajaeger@physik.uni-leipzig.de, bertmer@physik.uni-leipzig.de 2Universität Koblenz-Landau, Institut für Umweltwissenschaften, AG Umwelt- und Bodenchemie, Fortstr. 7, 76829 Landau schwarzj@uni-landau.de, schaumann@uni-landau.de Implications from humidity experiments (sapric peat) static 1H NMR spectrum * before heating after heating 70 40 larger fraction of water with higher mobility heating event Lorentzian line, water with higher mobility 30 min @ 110° C mobilizable fraction: “water molecule bridges” (WAMBs) Gaussian line, organic matter Lorentzian fraction / % • 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): moisture content * / % Introduction 1H NMR 35 30 25 60 50 40 30 20 10 0 10 20 20 30 40 50 60 70 80 90 100 relative humidity / % 15 10 5 0 0 • 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 1H 50 40 30 5 10 15 20 25 30 35 NMR CPMAS spectra 1,5 NMR spectra 0 5 10 15 20 carboxylic 25 30 35 40 moisture content / % (dry matter basis) analysis broad Lorentzian: aliphatic component poly-methylene aromatic compounds broad Lorentzian: aliphatic component poly-methylene aliphatic compounds only one Lorentzian: no poly-methylene high-order Pake doublet: crystalline carbohydrates assignment & line width: water 1.9 kHz carbohydrates 42 kHz poly-methylene 40 kHz water 1.9 kHz carbohydrates 42 kHz poly-methylene 49 kHz 2,5 2,0 1,5 1,0 0 5 10 15 20 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 [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): 1H and 13C Solid-State NMR based structural mobility and water adsorption studies of Soil Organic Matter, in preparation. SPP 1315 annual colloquium 2012, October 10th – 12th, Dornburg, Jena Printed at Universitätsrechenzentrum Leipzig 25 30 35 40 moisture content / % (dry matter basis) Improved, extended line fitting model applied to long term data sapric peat (moisture content: 7 %, dry matter basis) 48 46 Gaussian: carbohydrates + WAMBs 44 34 32 second Lorentzian (poly-methylene) 30 28 26 first Lorentzian (water molecules) 24 22 20 0 (peak distance) References 90 100 3,0 20 40 60 80 100 120 • Lorentzian lines show individual behavior: quick return to initial value for second Lorentzian; slow re-formation for first Lorentzian respective line ratio / % O-alkyl carbohydrate 80 3,5 time / days no Gaussian: no/small amount of carbohydrates 70 total signal • moisture uptake leads to characteristic adsorption isotherm (upper right), also reflected in 1H NMR Lorentzian fraction (insert in upper right figure) • 1H 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 1H 60 4,0 line shapes from carbon structural components 13C 50 2,0 40 moisture content / % (dry matter basis) 40 * dry matter basis 2,5 1,0 20 30 relative humidity / % Lorentzian line width / kHz NMR 60 20 3,0 respective line ratio / % 13C Lorentzian fraction / % • 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 change in Lorentzian fraction / % after heating 70 10 140 48 46 44 34 32 30 28 26 24 22 20 1E-3 0,01 0,1 1 10 100 time / days Conclusions & Outlook • improved model for 1H wide line data [2] is derived out of combined humidity and 13C 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 please note the project outcome poster: “Dynamic and Structural Effects in SOM after Thermal Treatment observed with 1H, 13C NMR Spectroscopy & DSC” Acknowledgements We thank the German research foundation (DFG) for funding within the SPP1315 ‘Biogeochemical Interfaces in Soil’ (SCHA849/8-1).