[sup 13]C-NMR spectra and contact time experiment for Skjervatjern fulvic and humic acids

The T[sub CP] and T[sub 1[rho]] time constants for Skjervatjern fulvic and humic acids were determined to be short with T[sub CP] values ranging from 0.14 ms to 0.53 ms and T[sub 1[rho]] values ranging from 3.3 ms to 5.9 ms. T[sub CP] or T[sub 1[rho]] time constants at a contact time of 1 ms are favorable for quantification of [sup 13]C-NMR spectra. Because of the short T[sub CP] values, correction factors for signal intensity for various regions of the [sup 13]C-NMR spectra would be necessary at contact times greater than 1.1 ms or less than 0.9 ms. T[sub CP] and T[sub 1[rho]] values have a limited non-homogeneity within Skjervatjern fulvic and humic acids. A pulse delay or repeat time of 700 ms is more than adequate for quantification of these [sup 13]C-NMR spectra. Paramagnetic effects in these humic substances are precluded due to low inorganic ash contents, low contents of Fe, Mn, and Co, and low organic free-radical contents. The observed T[sub CP] values suggest that all the carbon types in Skjervatjern fulvic and humic acids are fully cross-polarized before significant proton relaxation occurs. The [sup 13]C-NMR spectra for Skjervatjern fulvic acid is similar to most aquatic fulvic acids as it is predominantly aliphatic, low in aromaticity (fa[sub 1] = 24), low in phenolic content, high in carboxyl content, and has no resolution of a methoxyl peak. The [sup 13]C-NMR spectra for Skjervatjern humic acid is also similar to most other aquatic humic acids in that it is also predominantly aliphatic, high in aromaticity (fa[sub 1] = 38), moderate in phenolic content, moderate in carboxyl content, and has a clear resolution of a methoxyl carbon region. 10 refs., 6 figs., 3 tabs.