An aqueous control liquid is provided that contains glucose at a known concentration and cyclodextrin. A method is also provided that binds a wetting agent from a region of a test element that comes into contact with a sample. The method includes contacting the region with a control liquid that has a substance selected from the group of cyclodextrin derivatives and dispersed materials having a specific surface of 100 m.sup.2 /g to over 1000 m.sup.2 /g. A method for controlling the function of a measuring system having test strips and a measuring instrument for the determination of glucose in liquid samples is provided that includes contacting the test strip with a control liquid containing glucose at a known concentration and at least one substance selected from the group consisting of cyclodextrins and cyclodextrin derivatives and detecting a signal caused by the glucose contained in the control liquid.

The invention concerns an analytical element for determining the amount of an analyte in a liquid containing a sample application zone (1) and a detection zone (2) which are in liquid-transferring contact, the latter containing at least one enzyme and an indicator substance, the enzyme catalysing a reaction in which the analyte or a substance derived from the analyte participates and the indicator substance forming a signal when the analyte is present which signal correlates with the amount of analyte, and containing a liquid-permeable interference-reducing layer (3) in direct contact with the detection zone (2) arranged such that liquid does not reach the detection zone until it has passed through the interference-reducing layer, the interference-reducing layer containing at least one enzyme which participates in a reaction of the analyte to be determined or of a substance derived from the analyte, wherein the analyte or the substance derived from the analyte is converted enzymatically in the interference-reducing layer into end products which cannot contribute to the signal formation by the indicator substance, and a method for the determination of an analyte in a liquid by means of such an analytical element.