Detecting sup 13 C in Solid Coals by Nuclear Magnetic Resonance: A Cautionary Note

摘要

T/sub 1rho/ of sup 1 H, concentrations of free radicals and ''percent sup 13 C seen'' in six coals have been determined by standard pulsed NMR and continuous wave ESR experiments. Each coal studied exhibited two values of proton T/sub 1rho/, one being of order of 100 mu sec, and the other of order of 2 msec. Less than 60% of sup 13 C is detected under a single-pulse spin counting experiment in some coals. Free radical concentrations are of order of 10 sup 19 spins g sup -1 , but do not correlate with the fraction of sup 13 C detected under spin-counting conditions. There does appear some correlation between the fraction sup 13 C detected, and the fraction of sup 1 H exhibiting the longer T/sub 1rho/. 13 refs., 2 figs., 2 tabs. (ERA citation 11:055712)