The invention relates to a device (1) comprising integrated beam switching systems using corresponding devices (7 and 9) and fibre-optical light guides (10 and 11) for guiding the light (3) used for the analysis of a liquid medium (2), for example in a spectrophotometer, a spectrofluorimeter or a similar measuring device, to a measuring point located on the device (1) and embodied as a receiving surface (4) for the medium, and back therefrom to the detector of the spectrophotometer, spectrofluorimeter or the like. Said receiving surface (4) forms a flat measuring point on the upper side of thedevice (1) and is closed by a cover-type detachable reflector (8) in the position of use. Said reflector is in close contact with the sample or the medium (2) and can be removed before the application of the sample and for cleaning the measuring point.