Ionic activities of sodium, potassium, and chloride in human serum.

Ionic activities of sodium, potassium, and chloride in serums of 26 hospitalized patients were determined with ion-specific electrodes. Comparison of the activities with the corresponding concentrations shows that the two most important parameters influencing the molar activity coefficients of these ions are the water content of serum and the binding between albumin and chloride. Quantitative expressions for activity-concentration conversion factors are given. Calculations show that the conversion factors vary significantly in disease states due to changes in protein.