I. The Separation of Sodium From Potassium in Human Blood Serum by Ion Exchange Chromatography

The experiments to be described were undertaken to devise a simple and rapid technique for the separation of sodium from potassium in human blood serum in order to facilitate the simultaneous measurement of exchangeable sodium and potassium in man by the isotope dilution technique. This technique requires the intravenous admini- stration of a known amount of radioactive sodium (Na24) and radioactive potassium (K'2), followed by the determination, after a twenty-four hour equilibration period, of the individual sodium and potassium radioactivities and concentrations in the serum. The general principles underlying the application of the isotope dilution technique to the measurement of body constituents have been outlined by Edelnan, Olney, James, Brooks, and Moore (1). The data presented here are pri- marily concerned with the separation of sodium from potassium in aqueous solutions and serum. The results of our measurements in man are pre- sented in Part II of this study (2).