The present invention relates to a device (1) and a method for determining parameters of fluid-containing samples (2) in a system (3) for individually irradiating the samples (2) with light (4) of a light source (5) in an essentially vertical irradiation direction (6). In this case, this system (3) includes a detector (7) for measuring the light (8) coming from a single sample, and this detector (7) has a detection direction (9'), which lies on an optical axis (9) that is essentially parallel to the optical axis (6) of the light source (5). This device (1) includes at least one reflective surface (10), using which the light (4) coming essentially vertically out of the light source (5) may be at least partially deflected in an essentially horizontal irradiation direction (11). The device according to the present invention and the method according to the present invention are distinguished in that the detection direction (9') of the detector (7)--for measuring the individual light (8) coming from a single sample (2)--is positioned at an angle to the optical axis of the light (4) irradiating the sample (2) in such a way that only the light (8) coming from the individual sample (2), but not this light (4), reaches the detector (7).