A compositional and solid-state nuclear magnetic resonance study of humic and fulvic acid fractions of soil organic matter

Wilson, Michael; Vassallo, Anthony M.; Perdue, Edward M.; Reuter, J.H.

doi:10.1021/ac00131a004

Cited by 87 publications

(59 citation statements)

References 46 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, caution should be exercised in deriving quantitative information from solid state CP/MAS 13 C NMR spectroscopy since this method is based on polarization transfer from protons to carbon atoms and the efficiency of this transfer decreases with the sixth power of the carbon to proton distance. As a result, carbon atoms too far from protons are hardly detected and it is well documented that aromatic moieties in complex mixtures can be markedly underestimated via solid-state CP/MAS 13 C NMR spectroscopy [16,17,18]. Similarly, as recently illustrated by studies on synthetic humic substances [18], carbon atoms in highly cross-linked structures are markedly underestimated as well.…”

Section: Resultsmentioning

confidence: 99%

Characterization and comparison of two ligno-cellulosic substrates by 13C CP/MAS NMR, XPS, conventional pyrolysis and thermochemolysis

et al. 2002

View full text Add to dashboard Cite

Ligno-cellulosic substrates (LCSs) isolated from wheat straw and bran exhibit high complexing capacities and may have important applications for metal removal from industrial effluents. These two LCSs were examined in the present work by spectroscopic and pyrolytic methods (solid state cross polarization magic angle spinning (CP/MAS) (13)C NMR, XPS, conventional Curie pyrolysis (Cupy)/GC/MS, and TMAH thermochemolysis/GC/MS). This combined study highlighted the limitation of some of the above methods when applied to ligno-cellulosic materials and the resulting biases and the usefulness of TMAH thermochemolysis. A large difference in composition was observed between bran- and straw-LCS due to a much higher contribution of alkyl moieties in the former. These moieties correspond to fatty acids esterified to the ligno-cellulosic macromolecular structure and such carboxylic functions should play an important role for metal complexation.

show abstract

Section: Resultsmentioning

confidence: 99%

Characterization and comparison of two ligno-cellulosic substrates by 13C CP/MAS NMR, XPS, conventional pyrolysis and thermochemolysis

et al. 2002

View full text Add to dashboard Cite

show abstract

“…Clearly, finding an apparently linear relationship between ln(intensity) and contact time [2,3,29,32,33,44,45,49,50,56] is not sufficient to guarantee that an accurate T 1r H value can be determined. Fitting an exponential decay function to the decay phase of VCT data [16,52], essentially an equivalent procedure, suffers from the same problem when slowly cross-polarizing nuclei are present. The VCT experiment will only give accurate T 1r H values when the absence of slowly cross-polarizing nuclei can be assured [46].…”

Section: Vsl and Vct Experimentsmentioning

confidence: 99%

“…The apparent lack of correlation of T 1r H with free radical content [15] is likely to result from the biases of the VCT experiment. Over-estimation of T 1r H values determined from VCT experiments is also a likely cause of apparently inhomogeneous T 1r H in natural organic matter samples, in which T 1r H is reported to be longer for non-protonated carbons [44,49,52].…”

Section: Vsl and Vct Experimentsmentioning

confidence: 99%

Determination of T1ρH Relaxation Rates in Charred and Uncharred Wood and Consequences for NMR Quantitation

Smernik

Baldock

Oades

et al. 2002

Solid State Nuclear Magnetic Resonance

View full text Add to dashboard Cite

“…3,4,25,77,87 This yields the theoretical maximum CP intensity at zero tc if T CH were infinitely short and T 1ρH infinitely long. A simplified version can be used to extrapolate intensities back to tc = 0 or to determine T 1ρH using only the decaying part of the curve mainly controlled by T 1ρH relaxation.…”

Section: Toward Quantitative Reliabilitymentioning

confidence: 96%

“…34,57,65,85,86 Spin counting is also possible with internal standards mixed in with the sample, but these introduce other complexities, including overlap with sample peaks or alterations in the relaxation properties of the standard because of interactions with the sample. 87 Sensitivity also varies with position within the rotor, 34,55,88 and even wellmixed materials may migrate to different parts of the rotor with spinning. Inserts have been used to center a capillary of standard along the axis of a large rotor 72 or to place samples at different points along the rotor axis; 34 presumably, the latter could be used to position a layer of standard separated from the sample.…”

Section: Toward Quantitative Reliabilitymentioning

confidence: 99%

Environmental NMR: Solid-state Methods

Preston

1996

eMagRes

View full text Add to dashboard Cite

Solid-state NMR is widely used to characterize organic matter (OM), including litter inputs, peat, composts, and mineral soil, and to understand the fate of environmental contaminants. The combination of high-power decoupling, magic-angle spinning (MAS), and cross polarization (CP) to enhance sensitivity has greatly facilitated applications to 13 C, with lesser use of 15 N and 31 P. Focusing on 13 C, this article summarizes the development of the field and presents basic concepts of solid-state NMR, pulse sequences commonly used [direct polarization (DP), CP, dipolar dephasing (DD), and total sideband suppression (TOSS)], sample preparation and hydrofluoric acid pretreatment, general approaches to spectral acquisition and FID processing, removal of background signal, and data analysis including correction for spinning side bands (SSBs) and interpretation through a molecular mixing model of representative biopolymers. As CP NMR is inherently nonquantitative, and nuclei may be undectectable even with DP, techniques to improve quantitative reliability are discussed. More complex experiments can reveal spatially heterogeneous domains by generating subspectra of 13 C associated with protons with different relaxation times, and more recent developments allow spectral editing and two-dimensional (2-D) applications such as heteronuclear correlation (HETCOR). Applications of solid-state 15 N NMR are much more challenging, because of its low sensitivity and low natural abundance. Similarly, despite 100% natural abundance and high sensitivity, solid-state 31 P NMR is also limited by the small chemical shift range of phosphate minerals, and peak broadening and large higher order sidebands because of their close association with paramagnetics and large chemical shift anisotropy (CSA). However, studies with these nuclei can still provide much insight into OM cycling and the fate of fertilizers and contaminants in the environment. Introduction Principles of NMRThe basis of NMR spectroscopy is that only certain atomic nuclei have a nuclear spin I, and thus a magnetic moment μ, which interacts with a static magnetic field. These nuclei include 1 H, 13 C, 15 N, and 31 P (Table 1 1 ). In an external magnetic field B 0 , which is represented as a vector in the z direction, such nuclei split into 2I + 1 energy levels, with the splitting proportional to the field strength B 0 and γ , a constant for each nucleus. Nuclei with I = 1 / 2 , such as 1 H and 13 C, therefore, split into two populations. The very slight surplus of nuclei in the lower energy level, as determined by the Boltzmann equation, results at equilibrium in a macroscopic sample magnetization M 0 (Figure 1a). In fact, each nuclear spin is not statically aligned, but precessing around B 0 at the Larmor frequency ω, which corresponds to the energy gap ΔE:Rather than the laboratory (static) frame of reference, Figure 1 uses a reference frame rotating at the Larmor frequency, which simplifies the picture. In NMR, transitions between the energy levels are induced by a very bri...

show abstract

A compositional and solid-state nuclear magnetic resonance study of humic and fulvic acid fractions of soil organic matter

Cited by 87 publications

References 46 publications

Characterization and comparison of two ligno-cellulosic substrates by 13C CP/MAS NMR, XPS, conventional pyrolysis and thermochemolysis

Characterization and comparison of two ligno-cellulosic substrates by 13C CP/MAS NMR, XPS, conventional pyrolysis and thermochemolysis

Determination of T1ρH Relaxation Rates in Charred and Uncharred Wood and Consequences for NMR Quantitation

Environmental NMR: Solid-state Methods

Contact Info

Product

Resources

About