The natural line width of low field nuclear magnetic resonance spectra.

The authors suggest a procedure for the determination of the natural nuclear magnetic resonance line width Delta nu of liquids using an air coil system at flux densities from 25 microT to 150 microT. Even if the line broadening caused by instrumental field inhomogeneity is much higher than Delta nu, Delta nu can be found by extrapolating the measured line width's field dependency. For pure water this procedure yielded Delta nu=0.125 Hz+/-0.005 Hz. This is shown to be consistent with the smallest line width found for this sample below 25 microT using a superconducting quantum interference device-based spectrometer.