A method of infrared-optically determining the concentration of at least one analyte in a liquid sample, wherein the infrared absorption of the analyte(s) is measured and compared with a standard, which is characterized in that the liquid sample is sampled with an infrared radiation of high light density, wherein the infrared radiation has a sharp intensity peak at at least one wave length, as well as an arrangement for the infrared-optical transmission determination of the concentration of at least one analyte in a liquid sample, with a sample cuvette flowed through by the sample liquid, the sample cuvette being arranged in the radiation path between a radiation source for providing the infrared radiation and a detector for measuring the infrared absorption induced by the analyte in the sample cuvette.