A method for filtering spurious resonances from an NMR dataset comprises the steps of: (a) creating a first, non-oscillating magnetic field of a predetermined field strength across a sample, (b) intermittently exposing the sample to a second, oscillating magnetic field orthogonal to the first to generate an NMR signal, (c) detecting the NMR signal from the sample, (d) adjusting the first magnetic field to a different predetermined field strength and repeating steps (a) to (c), and (d) comparing the detected signals to obtain an NMR dataset from the sample from which spurious resonances have been filtered.