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Solvent Resonance Decoupling in Carbon/13 NMR

IP.com Disclosure Number: IPCOM000052243D
Original Publication Date: 1981-May-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 3 page(s) / 49K

Publishing Venue

IBM

Related People

Bleich, HE: AUTHOR [+2]

Abstract

In high resolution nuclear magnetic resonance (NMR), the samples are dissolved in solvents containing the isotopes of deuterium or fluorine. An electronic signal derived from these isotopes is used to stabilize the static magnetic field and/or the sources of radio frequency fields. This method is called field-frequency lock. The carbon-13 resonances of the solvent often cover a certain range of frequencies due to nuclear coupling between the carbon-13 isotopes and the solvent isotopes used for field-frequency stabilization. These complex resonances often overlap the carbon-13 resonances of the sample being investigated. The strong radio frequency irradiation of the deuterium (or fluorine) resonances is called decoupling, and it produces single resonances for carbon-13 resonances due to the solvent.

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Solvent Resonance Decoupling in Carbon/13 NMR

In high resolution nuclear magnetic resonance (NMR), the samples are dissolved in solvents containing the isotopes of deuterium or fluorine. An electronic signal derived from these isotopes is used to stabilize the static magnetic field and/or the sources of radio frequency fields. This method is called field-frequency lock. The carbon-13 resonances of the solvent often cover a certain range of frequencies due to nuclear coupling between the carbon-13 isotopes and the solvent isotopes used for field-frequency stabilization. These complex resonances often overlap the carbon-13 resonances of the sample being investigated. The strong radio frequency irradiation of the deuterium (or fluorine) resonances is called decoupling, and it produces single resonances for carbon-13 resonances due to the solvent. The resonances of interest are thereby revealed. However, this decoupling also destroys the signal used for field-frequency stabilization.

The method described herein allows both solvent decoupling and field-frequency stabilization. It makes use of the fact that only a slowly varying signal is needed for field-frequency correction and that the signal used for field-frequency lock is proportional to field (or frequency) deviations and is therefore near zero for a stabilized instrument. A sample-and-hold circuit 1 at the output of a lock receiver 2 holds the field-frequency error signal to the fixed value present at the instant when the deuterium (or fluorine) decoupling is applied and allows the solvent signal to be passed to a field-frequency stabilization circuit 3 when the deuterium (or fluorine) decoupling is turned off. In practice, a deuterium (or fluorine) decoupler 4 is turned on during data acquisition (the data acquisition time) and is turned off otherwise (the relaxation delay time), as shown in Fig. 2. This delay time provides the time interval required to regenerate the lock signal which was destroyed during the time interval of solvent decoupling. The new feature of this method is the use of the sample-and-hold circuit which allows for routine use of solvent decoupling in carbon-13 spectroscopy. In Fi...