Method for determining ion concentration or concentration of a substance in a solution

A method for determining ion concentration or concentration of a substance in a solution by means of an ion selective, field effect transistor, or an ion sensitive sensor, with an EIS structure, thus an Electrolyte Insulator Semiconductor structure, which includes at least one semiconductor substrate, a layer of substrate oxide and a sensor layer, wherein at least in an intermediate region between the substrate oxide and the sensor layer an externally accessible electrode is provided, wherein the method comprises the steps of:

• at least at a predetermined point in time of a first measuring phase, the potential lying on the electrode is sensed relative to a reference potential;
• before beginning a sterilization- and/or cleaning phase following the first measuring phase, the last voltage sensed during the first measuring phase is stored;
• and
• at the beginning of a second measuring phase following the sterilization- and/or cleaning phase, the voltage stored during the sterilization phase is applied to the electrode.

An ion selective, field effect transistor, or ion sensitive sensor for performing a method at least at a predetermined point in time of a first measuring phase, the potential lying on the electrode is sensed relative to a reference potential;

• at least at a predetermined point in time of a first measuring phase, the potential lying on the electrode is sensed relative to a reference potential;
• before beginning a sterilization- and/or cleaning phase following the first measuring phase, the last voltage sensed during the first measuring phase is stored;
• and at the beginning of a second measuring phase following the sterilization- and/or cleaning phase, the voltage stored during the sterilization phase is applied to the electrode, the transistor comprising:
• a controlled circuit arrangement having an impedance converter, on whose first input the electrode potential is applied during the first measuring phase and on whose inverting input a reference potential is applied;
• and
• a sample/hold circuit connected in series with said impedance converter for storing and freezing in a memory element during the cleaning- and/or sterilization phase the last voltage applied during the first measuring phase on an electrode, and for applying on said electrode at the beginning of the second measuring phase following the sterilization phase the stored, frozen voltage.