A detector arrangement, which comprises a rotatable microfluidic disc and a spectrophotometric detector unit. The arrangement is characterized in that the detector unit is based on surface plasmon resonance (SPR) and is capable of measuring an analyte within the detection microcavities, each of which is part of a microchannel structure.A microfluidic disc having an axis of symmetry and comprising microchannel structures, each of which has an upstream functional part that is at a shorter radial position than a downstream functional part. The disc is characterized in that there are detection microcavities (DMCs) in at least a part of said microchannel structures, and that each of said DMCs has an SPR surface on an inner wall and a detection detection window extending from the SPR surface to the surface of the disc.The use of the detector arrangement and microfluidic disc described above for determining: a) if the content in one or more of the DMCs is a liquid or a solid state or a gas, and/or b) a feature of an analyte that may be present in a liquid which is present in one or more of the DMCs.