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A SENSITIVE NMR THERMOMETER FOR MULTINUCLEI FT NMR
Citation:
Levy, G., J. Bailey, AND D. Wright. A SENSITIVE NMR THERMOMETER FOR MULTINUCLEI FT NMR. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-80/375.
Description:
A pernicious problem in multinuclei FT NMR is accurate measurement of sample temperature. This arises from several factors including widespread use of high-power decoupling, large sample tubes (with potentially large temperature gradients across the sample volume), and lack of suitable compounds having temperature-dependent shielding characteristics. The use of proton shieldings is generally precluded as a result of 1H decoupling. Use of thermocouples or thermistors to monitor sample temperature involves either measurement of flow gas temperature (which may not be the same as the sample temperature) or insertion of the device into the sample. Although the latter practice may give an accurate temperature reading at any one point in the sample, it is not sensitive to gradients in temperature. Stopping an experiment and placing one of these devices in a sample necessarily perturbs the temperature of the sample. In addition, there is evidence of thermocouple thermometry errors resulting from large magnetic fields.