Abstract: The invention relates to a sensor for determining a concentration of a substance contained in a fluid-containing matrix, with a measurement chamber (5), a sender (3) for the emission of optical radiation (6) into the measurement chamber, and a receiver (4) for receiving optical radiation which has traversed the measurement chamber, wherein the measurement chamber is designed for bringing into the matrix and is filled with a specific fluid, and the wall (12, 13) is at least sectionally permeable to the diffusion of the substance. A control and evaluation circuit (7) is connected to the sender (3) and controls the sender (3), and is connected to the receiver (4) for selecting the receiver signals and determines, from the receiver signal, a measurement for the concentration of the substance in the matrix.

Abstract: The invention relates to a sensor for determining a concentration of a substance contained in a fluid-containing matrix, with a measurement chamber (5), a sender (3) for the emission of optical radiation (6) into the measurement chamber, and a receiver (4) for receiving optical radiation which has traversed the measurement chamber, wherein the measurement chamber is designed for bringing into the matrix and is filled with a specific fluid, and the wall (12, 13) is at least sectionally permeable to the diffusion of the substance. A control and evaluation circuit (7) is connected to the sender (3) and controls the sender (3), and is connected to the receiver (4) for selecting the receiver signals and determines, from the receiver signal, a measurement for the concentration of the substance in the matrix.

Abstract: The invention relates to a method for the long-term stable and well-reproducible spectrometric measurement of the concentrations of components of aqueous solutions, especially of dialysates of interstitial tissue fluids, especially the glucose concentration. The inventive method comprises splitting a measuring beam into two partial beams by means of a beam splitter (2), and guiding one partial beam through a measuring cuvette (3), that is separated from the solution to be measured for example by a diaphragm, or that is connected to a pump system with an exchange path that is separated from the solution to be measured by a diaphragm. The other partial beam is guided through a reference cuvette (4) that is filled with a reference solution. The light intensity of both partial beams is measured and the measured signals are subjected to a symmetrical signal processing, optionally after suitable amplification.