{sup 13}C NMR spin-lattice relaxation properties and quantitative analytical methodology of {sup 13}C NMR spectroscopy for coals
- Colorado State Univ., Fort Collins, CO (United States)
The quantitative reliability of {sup 13}C NMR spectroscopy is examined and discussed. Studies were performed on eight Argonne Premium coals, using the nonoverlapping carbonyl peak of 4-(N-methylpyrrolidino)bicyclo[3.2.1]-octan-8-one triflate as an intensity reference. {sup 13}C spin-lattice relaxation times measured by cross-polarization (CP) detection depend on the CP contact time. A series of experiments with different CP contact times yielded observed {sup 13}C spin-lattice relaxation times that are significantly larger than those previously reported in the literature. The relaxation time characteristic of the most slowly relaxaing carbons, T{sub 1S}, was determined for the aromatic carbons and for the aliphatic carbons of each coal. Then, if one uses repetition delays that are >5T{sub 1S}, quantitative results can be expected for the NMR-observable carbons in a direct polarization (DP) experiment. Carbon spin counting experiments performed by using DP instead of CP yielded numbers for the fraction of carbon spins that are 81-97% of those present in the sample. A relationship was observed between the number of unpaired electron spins and the fraction of {sup 13}C spins detected. The role of unpaired electron spin dynamics on the effective electron magnetic moment is considered, and the corresponding influence on {sup 13}C NMR detection is discussed. 42 refs., 9 figs., 2 tabs.
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FG22-93PC93206
- OSTI ID:
- 81356
- Journal Information:
- Analytical Chemistry (Washington), Vol. 67, Issue 13; Other Information: PBD: 1 Jul 1995
- Country of Publication:
- United States
- Language:
- English
Similar Records
Advanced NMR approaches in the characterization of coal
A bicyclic ketone as a solid-state [sup 13]C NMR intensity reference