C-13 NMR SPIN-LATTICE RELAXATION PROPERTIES AND QUANTITATIVE ANALYTICAL METHODOLOGY OF C-13 NMR-SPECTROSCOPY FOR COATS

The quantitative reliability of C-13 NMR spectroscopy is examined and discussed. Studies were performed on eight Argonne Premium coals, usin g the nonoverlapping carbonyl peak of 4-(N-methylpyrrolidino)bicyclo[3 .2.1]-octan-8-one triflate as an intensity reference. C-13 spin-lattic e relaxation times measured by cross-polarization (CP) detection depen d on the CP contact time. A series of experiments with different CP co ntact times yielded observed C-13 spin-lattice relaxation times that a re significantly larger than those previously reported in the literatu re. The relaxation time characteristic of the most slowly relaxing car bons, T-1s, was determined for the aromatic carbons and for the alipha tic carbons of each coal. Then, if one uses repetition delays that are >5T(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 t he fraction of carbon spins that are 81-97% of those present in the sa mple. A relationship was observed between the number of unpaired elect ron spins and the fraction of C-13 spins detected. The role of unpaire d electron spin dynamics on the effective electron magnetic moment is considered, and the corresponding influence on C-13 NMR detection is d iscussed.