Accurate Quantifcation of Aromaticity and Nonprotonated Aromatic Carbon Fraction in Natural Organic Matter by 13C Solid-State Nuclear Magnetic Resonance.
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| Title: | Accurate Quantifcation of Aromaticity and Nonprotonated Aromatic Carbon Fraction in Natural Organic Matter by 13C Solid-State Nuclear Magnetic Resonance. |
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| Authors: | Mao, J.-d.1, Schmidt-rohr, K.1 srohr@iastate.edu. |
| Source: | Environmental Science & Technology. 5/1/2004, Vol. 38 Issue 9, p2680-2684. 5p. |
| Subjects: | Aromatic compounds, Carbon, Organic compounds, Nuclear magnetic resonance, Polarization (Nuclear physics), Anisotropy, Humic acid |
| Abstract: | An improved approach for accurately determining the aromatic carbon fraction (fa) and nonprotonated aromatic carbon fraction (faN) in natural organic matter by solid- state 13C NMR is described. Quantitative peak areas are obtained from direct polarization 13C nuclear magnetic resonance (NMR) under high-speed magic angle spinning (MAS). The problem of overlap between aromatic and alkyl carbon resonances around 90-120 ppm in 13C NMR spectra is solved by a 13C chemical shift anisotropy (CSA) filter technique. After correction for residual spinning sidebands, an accurate value of the aromaticity fa is obtained. To obtain a quantitative faN fraction, dipolar dephasing was adapted for high-speed MAS 13C NMR; the separation of the signals of nonprotonated alkyl and aromatic carbons was achieved by CSA filtering plus dipolar dephasing. The method is demonstrated on a peat humic acid, yielding fa = 45 ± 2% and faN = (0.64 ± 0.07) x 45%. [ABSTRACT FROM AUTHOR] |
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| Database: | Engineering Source |
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