C-13-NMR SPECTRA AND CONTACT TIME EXPERIMENT FOR SKJERVATJERN FULVIC AND HUMIC ACIDS

The T(CP) and T1p time constants for Skjervatjern fulvic and humic acids were determined to be short with T(CP) values ranging from 0.14 ms to 0.53 ms and T1p values ranging from 3.3 ms to 5.9 ms. T(CP) or T1p time constants at a contact time of 1 ms are favorable for quantification of C-13-NMR spectra. Because of the short T(CP) values, correction factors for signal intensity for various regions of the C-13-NMR spectra would be necessary at contact times greater than 1.1 ms or less than 0.9 ms. T(CP) and T1p 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 C-13-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(CP) values suggest that all the carbon types in Skjervatjern fulvic and humic acids are fully cross-polarized before significant proton relaxation occurs. The C-13-NMR spectra for Skjervatjern fulvic acid is similar to most aquatic fulvic acids as it is predominantly aliphatic, low in aromaticity (fa1 = 24), low in phenolic content, high in carboxyl content, and has no resolution of a methoxyl peak. The C-13-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 (fa1 = 38), moderate in phenolic content, moderate in carboxyl content, and has a clear resolution of a methoxyl carbon region. After the consideration of the necessary C-13-NMR experimental conditions, these spectra are considered to be quantitative. With careful consideration of the previously determined C-13-NMR experimental conditions, quantitative spectra can be obtained for humic substances in the future from the HUMEX site. Possible changes in humic substances due to acidification should be determined from C-13-NMR data.