A method of characterising particles in a sample, comprising: obtaining a scattering measurement comprising a time series of measurements of scattered light from a detector, the scattered light produced by the interaction of an illuminating light beam with the sample; producing a corrected scattering measurement, comprising compensating for scattering contributions from contaminants by reducing a scattering intensity in at least some time periods of the scattering measurement; determining a particle characteristic from the corrected scattering measurement.