Quantitative analysis of the Uncompahgre National Forest soil and its extracts by carbon-13 DP- and CP-MAS solid state NMR methods (Colorado)

We have carried out the first absolutely quantitative solid-state 13C NMR study on a soil and its separated components. The Uncompahgre National Forest soil was collected and separated into a humin fraction, humic acid, and fulvic acid using a classic soil separation method. The soil separation was performed in a quantitative manner such that all the organic carbon in the soil and its separated fractions was accounted for by elemental analysis. The peak areas for spin counting spectra generated by DP- and CP-MAS were corrected to account for relaxation and cross-polarization processes to yield NMR peak integrals that are directly proportional to the amount of carbon in a particular functional group that the peak represents. Compared to the carbon detected by elemental analysis, 1H-to-13C CP-MAS and 13C DP-MAS spin-counting accounted for substantially less than 100 percent of the carbon, from a low of 48 percent of the carbon, to a high of about 86 percent of the carbon, depending on the method and particular soil fraction. The role of paramagnetic and ferrimagnetic iron in spin-counting by 13C MAS NMR in these samples was investigated using VSM, ESR, elemental analysis, and various chemical treatments.; The quantitative 13C MAS NMR analysis was accompanied by an extensive error analysis of the regressions, calibrations, and deconvolution procedures used in this dissertation. The B₁ field inhomogeneity of the large-volume NMR coil employed in this study and its relationship to the systematic error associated with spin counting was investigated. The B ₁ field profile for the large-volume NMR coil was measured and subsequently modeled using the law of Biot-Savart. The effect on the B₁ field inhomogeneity of two theoretical coil modifications were explored using the law of Biot-Savart, with one modification yielding a nearly uniform field profile.