Method for operating a measuring device having at least one probe, which has at least one ion selective electrode

A method for operating a measuring device having at least one probe, which has at least one ion selective electrode, and which is embodied to output a measurement signal dependent on concentration of a measured ion in a liquid, wherein the measuring device is embodied to represent a measured value of concentration of the measured ion from the measurement signal output by the probe, based on a calibration function;

• the method comprising the steps of:
• providing a first sample of the liquid;
• ascertaining an updated calibration function by means of a standard addition method, wherein the first sample is supplemented at least once with a standard solution, which has a known concentration of the measured ion;
• determining a measured value of concentration of the measured ion in the first sample as an apparent measured ion concentration based on the updated calibration function;
• providing a second sample of the liquid, wherein the composition of the second sample corresponds to the composition of the first sample;
• ascertaining a measured value of concentration of the measured ion in the second sample as a reference measured ion concentration by means of a reference method;
• and
• determining a difference between the apparent measured ion concentration and the reference measured ion concentration and deriving a correction value therefrom for future measured values of concentration of the measured ion in the liquid, as ascertained by the measuring device.