Ion-selective electrode potentiometry in protein-containing solutions

Abstract

The variations in the potentials of the sodium-selective glass-membrane and potassium-selective valinomycin-based electrodes in various concentrations of albumin were investigated. These protein solutions serve as a simple model for measurements of electrolytes in whole blood, plasma, or serum with such electrodes. The results indicate that electrode drift increases with increasing protein concentration whereas electrode response time is unaffected by protein. Also, the results indicate that albumin-sodium and albumin-potassium binding and variations in liquid junction potentials are of negligible importance. Mostly, the effect of albumin on the membrane potential is attributable to variations in the activity of sodium and potassium, determined by the water content of the solutions. The apparent fractional protein volumes in albumin solutions were calculated from measurements of membrane potentials and they compare well with the classical McLean-Hastings formulation. The results indicate the need to correct experimentally determined potentiometric electrolyte concentrations for protein volumes.