a method for at least partially applying a hydrophilic polymer to a measurement channel of a sensor cartridge is provided , which sensor cartridge can be replaceably inserted in an analyzer . the measurement channel comprises at least one sensor element . the method comprises inserting the sensor cartridge into the analyzer , introducing an aqueous solution containing chitosan or a chitosan derivative into the measurement channel of the sensor cartridge , and following a residence time replacing the aqueous chitosan solution with a gaseous or liquid medium , wherein residues of the chitosan or chitosan derivatives remain on the inside surface of the measurement channel and hydrophilize the surface .