Nuclear magnetic resonance in the earth's magnetic field using a nitrogen-cooled superconducting quantum interference device

The authors recorded nuclear magnetic resonance (NMR) spectra of water, benzene, fluorobenzene, and 2,2,2-trifluoroethanol in the earth's magnetic field (EMF) using a nitrogen-cooled superconducting quantum interference device (SQUID). In trifluoroethanol, the broadband detection characteristics of the SQUID with a noise floor of about 70 fT/root Hz enabled authors to simultaneously observe fluorine and proton spectra at 1940 and 2060 Hz Larmor frequency, reflecting their heteronuclear J coupling in the high-field limit without showing a measurable chemical shift. To reduce the noise in EMF-NMR, the authors suggest the use of frequency-adjusted averaging, which compensates line broadening due to EMF fluctuations. (C) 2007 American Institute of Physics.