The present disclosure relates to a device for measuring a first analyte concentration and a second analyte concentration in a measuring medium, the device including: a sample cell; a first light source unit; a first detector unit; a functional element; a second light source unit; a second detector unit; and a control unit adapted to analyze a detected first light for determining a first value representing the concentration of the first analyte in the measuring medium and adapted to analyze a detected third light for determining a second value representing the concentration of the second analyte in the measuring medium. A method of using the device is also disclosed.