Impedance effect of an ion-sensitive membrane: characterisation of an EMIS sensor by impedance spectroscopy, capacitance-voltage and constant-capacitance method

The impedance effect of a thin polymer membrane on the characteristics of a capacitive electrolyte–membrane–insulator–semiconductor (EMIS) sensor has been investigated using a K+-sensitive EMIS sensor with a valinomycin-containing PVC membrane as a model system. The developed EMIS sensor has been studied by means of impedance spectroscopy, capacitance–voltage and constant–capacitance method. It is shown, that an improvement of the accuracy of the measurements can be achieved by means of correcting the capacitance–voltage curves using preliminary defined values of the membrane resistance and capacitance as well as by choosing an optimal working frequency range. The sensors’ behaviour in terms of ion-sensitivity, stability, hysteresis, linear concentration range, detection limit and response time have been investigated, too.

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