THE DETERMINATION OF SODIUM IN BODY FLUIDS BY THE GLASS ELECTRODE*

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Abstract
Until recently there has been no method for the direct determination of activity of alkali ions in biological fluids, physiological data having been expressed solely in terms of concentration. The mathematical and electrochemical techniques for the determination of pH have been applied to the potentiometric determination of Na ion in body fluids by selective glass electrodes. The method is rapid, highly reproducible, and requires no dilution or alteration of the sample. Na activity in urine, serum, cerebrospinal fluid, whole blood, and plasma was linearly related to Na concentration as determined by flame photometry. Electrode data could also be expressed in terms of concentration by derivation of appropriate empirical activity coefficients for each fluid. Results agreed with flame photometer values within about 2%. Protein, erythrocytes, urea and uric acid has no apparent adverse effect on electrode potential.