The spectrum of light, inelastically scattered by a sample (16) is measured. The light is guided through a capillary (12) from and to the sample, at least in one of these directions, through the channel no inelastic scattering of light occurs which can form an interfering background when measuring on the sample. By guiding the light through the channel, inelastic scattering of this light is prevented and it becomes possible to guide scattered light back through the channel to spectral analysis equipment (14) without problems with inelastic scattering during the guidance of the light. Preferably, the light is guided through the channel of the capillary in both directions.