Calibration-Free Measurement of Sodium and Potassium in Undiluted Human Serum with an Electrically Symmetric Measuring System

Abstract

The limitations of ion-selective electrodes (ISEs) presently in use mainly concern the stability of the calibration values. By applying optimal membrane technologies and optimized reference electrodes a perfectly symmetric measuring system including a symmetric ISE membrane has been developed. Thus, stable standard potentials of the cell assembly, both before and after serum contact, as well as theoretical slopes of the electrode response have been obtained. Results of calibration-free assays of K⁺ and Na⁺ concentrations in aqueous calibration solutions and in undiluted human serum are presented. The precision required in fully met for K⁺ measurements in aqueous solutions and in sera of the normal as well as pathological concentration range. In addition, the precision of Na⁺ assays in aqueous calibration solutions and in serum samples of the normal concentration range is close to the required values.