Transcript NMR spectroscopy - SPP 1315 Biogeochemical Interfaces in Soil

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 [email protected], [email protected]
2Universität Koblenz-Landau, Institut für Umweltwissenschaften, AG Umwelt- und Bodenchemie,
Fortstr. 7, 76829 Landau [email protected], [email protected]
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
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30
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60
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10
0
10
20
20
30
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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
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40
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5
10
15
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30
35
NMR CPMAS spectra
1,5
NMR spectra
0
5
10
15
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carboxylic
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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)
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22
20
0
(peak distance)
References
90 100
3,0
20
40
60
80
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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
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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).