Physicochemical properties of a liquid ion exchanger microelectrode and its application to biological fluids

Double-barreled potassium or chloride ion-selective microelectrodes were constructed using a liquid ion exchanger. Technical details of the fabrication of double-barreled microelectrodes, having a PD sensor as one barrel and an ionic sensor as the other, are described. The sensitivity of K+ or CI- ion-selective microelectrodes exhibited an approximately Nernstian response over a temperature range of 7 degrees-37 degrees C, and the electromotive force (EMF) was stable within +/- mV for a few hours. The rise time was less than 1 sec. The effect of pH on the electrode response was negligible over a physiological range of pH 5.6 to 7.8. The selectivity constants of the K+ microelectrode to other cations were 0.011 for Na+, 0.200 for NH+4, and less than 0.002 and 0.001 for Ca++ and Mg++, respectively, while that of the CI- microelectrode was 0.067 for HCO-3. Glucose or urea has no effect on the EMF. Protein has a significant effect on ion exchanger membrane only when the concentration of the tested ion is low and protein is high. On the basis of this background the determination of K+ and CI- activity was carried out both in vivo and in vitro on several biological samples, such as serum, tissue and cellular fluids, and other protein-containing fluids. The values obtained with the microelectrode were consistent with those obtained with the other conventional methods or with the current theory on electrolyte solutions. These results were taken to assure the practical application of these electrodes to biological studies in many fields.