Spectra contributions from organic acids

The C-NMR spectmm of HMW DOM also includes contributions from carboxyl (CO-(OH or NH), 5% of total carbon), and alkyl (CH 14% total carbon) functional groups, which may derive from proteins, lipids, or carbohydrates (deoxy-and methyl sugars). Hydrolysis of HMW DOM followed by extraction with organic solvent yields 4-8% of the total carbon in HMW DOM as acetic acid. Acetyl is easily recognized in the H-NMR spectra of HMW DOM, where it appears as a broad singlet centered at 2 ppm (Figure 6(b)). Free acetic acid and its derivatives are not retained by ultrafiltration, and the acetyl in HMW DOM must be covalently bound to macromolecular material, most likely as an A-acetyl amino sugar. Acetyl contributes up to half the carboxyl carbon in the C-NMR spectrum. 

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