Determination of sodium in urine by specific ion electrode.

A method has been developed for determination of sodium concentration (activity) in urine using a glass electrode designed to be especially sensitive to sodium ion activity. The urine is diluted 2:20 with Tris buffer (pH 8.0) and sodium activity measured by dipping a sodium electrode and calomel reference electrode in the diluted specimen and obtaining a millivolt reading with a sensitive pH meter. The sodium concentration is then calculated from a predetermined standard curve. Concentrations of 0-200 mEq./L. may be read using the same dilution. Blind comparisons of sodium concentrations obtained by flame photometry and by sodium ion electrode showed excellent agreement.