Calibration of ion-selective electrodes for use in biological fluids.

We measured electromotive force at 37 degrees C with pH, sodium glass, valinomycin, and the Simon calcium electrodes in synthetic electrolyte mixtures simulating serum, in cells both with and without liquid junction. Evidently these electrodes respond in a near-Nernstian manner to changes in concentration of the ion sensed. We su-gest that such mixtures may serve as calibrating standards for ion-selective electrodes in clinical analysis. The effect of ionic strength on electrode response can be accounted for almost wholly by alterations in the activity coefficients. The lanthanum fluoride electrode activity coefficients. The lanthanum fluoride electrode shows promise as a reliable reference in cells without liquid junction.