ATTEMPTS TO IMPROVE SOLID STATE <sup>13</sup>C NMR SPECTRA OF WHOLE MINERAL SOILS

Arshad, Muhammad; Ripmeester, John A.; Schnitzer, M.

doi:10.4141/cjss88-057

Cited by 75 publications

(39 citation statements)

References 3 publications

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“…This may produce fractions that are more sensitive to change, as well as enriched in C and N content for NMR and other analyses. Treatment of whole soils and low-carbon fractions with HF is very effective in dissolving mineral matter, usually with little loss of organic components (Arshad et al 1988;Preston et al 1989a;Newman 1992, 1995;Skjemstad et al 1994;Schmidt et al 1997). It has also Fig.…”

Section: Modifying the Samplementioning

confidence: 99%

Carbon-13 solid-state NMR of soil organic matter - using the technique effectively

Preston¹

2001

Can. J. Soil. Sci.

112

104

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).Preston, C. M. 2001. Carbon-13 solid-state NMR of soil organic matter -using the technique effectively. Can. J. Soil Sci. 81: 255-270. Solid-state 13 C CPMAS NMR offers many options for characterizing carbon in soil organic matter (SOM). Its effectiveness, however, is often limited by a poor understanding of the techniques, and lack of hands-on access and training opportunities for students. Of nearly 250 modern NMR systems in Canada, approximately one is genuinely available for SOM studies, and there is poor communication between NMR operators and SOM users. While quantitative reliability can be addressed to some extent by multiple contact-time experiments or single-pulse (Bloch decay) spectra, it is also important to consider the effects of spectrometer background, spinning sidebands (especially with higher magnetic fields) and processing operations such as linebroadening, phasing and baseline correction. In many studies, more consideration needs to be given to instrument specifications, the type of information needed, and whether sample fractionation or pretreatment should be used. Structural information can be greatly enhanced by dipolar-dephasing and sideband suppression sequences. Sequences based on relaxation differences can reveal pools of carbon with different structures. Data analysis can be enhanced by principal component analysis, spectrum deconvolution and difference spectra. Studies of xenobiotics and C metabolism can be greatly aided by 13 C-labeling. However, a key limitation to SOM applications remains the gap in culture and expectations of the users.Key words: Soil organic matter, 13 C CPMAS NMR, Bloch decay, dipolar dephasing, spinning sidebands Preston, C. M. 2001. Analyse de la matière organique du sol par RMN au 13 C électronique -de l'importance de bien utiliser la technique. Can. J. Soil Sci. 81: 255-270. La RMN CPMAS 13 C électronique permet de caractériser le carbone présent dans la matière organique du sol (MOS) de diverses manières. Il arrive souvent cependant que cette technique perde de son efficacité parce qu'on la connaît mal et parce que les étudiants n'ont pas eu la chance de l'examiner ou de l'expérimenter. Sur les 250 systèmes modernes de RMN existant au Canada, un seul, à peu près, est vraiment réservé à l'étude de la MOS; de plus, la communication passe mal entre les opérateurs de systèmes RMN et les utilisateurs de MOS. Bien qu'on puisse remédier dans une certaine mesure au problème de la fiabilité quantitative en multipliant les expériences sur la durée de contact ou en recourant au spectre obtenu après une seule impulsion (décroissance de Bloch), il ne faut pas négliger les effets de l'arrière-plan du spectromètre, de la rotation des bandes latérales (surtout quand le champ magnétique est puissant) et des opérations de traitement comme l'élargissement des lignes, la mise en phase et la correction de la ligne de base. Dans de nombreux cas, on devrait accorder plus d'attention aux paramètres de l'instrument, au genre de données requises et à la nécessité de fractionner et...

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Section: Modifying the Samplementioning

confidence: 99%

Carbon-13 solid-state NMR of soil organic matter - using the technique effectively

Preston¹

2001

Can. J. Soil. Sci.

112

104

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“…The Ap horizon of the Culp soil, a loamy sand from northwestern Alberta, classified as Gray Luvisol has a pH of 5.5, contains 21.8 g kg -1 organic C and 2.9 g kg -1 total N. This soil contains 15.0 g kg -1 total Fe, so that the C/Fe ratio is 1.5 (Arshad et al 1988). The 13 C NMR spectrum of the air-dried Culp soil is shown in Fig.…”

Section: Analysis Of Som In Whole Soils By 13c Nmrmentioning

confidence: 99%

“…If the C/Fe ratio is >>1, the quality of the spectrum will be good; if the ratio is >1, a reasonable spectrum will be obtained, but if the ratio is <1, the spectrum will be poor. According to Arshad et al (1988), acceptable 13 C NMR spectra can be obtained on untreated soil particle size-fractions, non-magnetic portions of whole soils, fractions enriched in OM by flotation, especially after chemical reduction, and whole mineral soils with C/Fe ratios >1.…”

Section: Analysis Of Som In Whole Soils By 13c Nmrmentioning

confidence: 99%

“…Some of these difficulties can be overcome by the isolation of OM-rich soil fractions by flotation, particle-size separation (Arshad et al 1988), removal of paramagnetic metal ions (Skjemstad et al 1994), and chemical reduction of paramagnetic metal ions (Wilson 1987). Useful indicators for obtaining satisfactory 13 C NMR spectra of whole mineral soils are C/Fe ratios.…”

Section: Analysis Of Som In Whole Soils By 13c Nmrmentioning

confidence: 99%

“…This procedure has been used by most soil scientists over the past 200 yr. In recent years, two new methods, 13 C NMR (Wilson, 1987;Arshad et al 1988;Skjemstad et al 1994;Cook and Langford 1999;Xing et al 1999) and pyrolysis-field ionization mass spectrometry (Schnitzer and Schulten 1992) have become available, making it possible to determine the chemical composition of SOM directly in the soil, that is, in situ. This means that it is no longer necessary to extract OM from the soil, fractionate, and purify it.…”

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The in situ analysis of organic matter in soils

Schnitzer¹

2001

Can. J. Soil. Sci.

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0C6.Schnitzer, M. 2001. The in situ analysis of organic matter in soils. Can. J. Soil Sci. 81: 249-254. Traditionally, studies on soil organic matter (SOM) begin with the extraction of SOM from soils, its fractionation into humic acid, fulvic acid, and humin, followed by de-ashing of each fraction. These are tedious, laborious and inefficient procedures that do not provide any chemical information on these materials. Instead, recently developed methods such as solid-state 13 C NMR and pyrolysis -field ionization mass spectrometry (Py-FIMS) can now be used for the in situ analysis of SOM in soils. These methods identify the major chemical components of SOM without extractions and fractionations, and yield valuable information on the main chemical structures in these materials. A better knowledge of the structural chemistry of SOM will help SOM chemists and other soil scientists to better understand the complex chemical and biochemical reactions that occur in soils, and will enable them to develop practices that will improve soil management and soil productivity.

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