Are sodium bicarbonate and potassium bicarbonate fully dissociated under physiological conditions?

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Abstract
In solutions containing 160 mmol/1 Na+ and K+, respectively, measurements with an ion-selective electrode system (KNA1, Radiometer), showed apparent falls in the respective Na+ and K+ concentrations when CI- was replaced by HCO-3. After correction for the change in liquid junction potential, the fall was 9.2 mmol/1 for Na+ and 7.3 mmol/1 for K+. On the basis of these findings we conclude that sodium bicarbonate and potassium bicarbonate are not fully dissociated in solution, and that NaHCO3d` and KHCO3d` do exist as chemical components with association constants of 0.72 and 0.55, respectively. Using these association constants, normal plasma will contain 1.2 mmol/1 NaHCO3d` and 0.03 mmol/1 KHCO3d`. Thus NaHCO3d` accounts for virtually the same amount of CO2 as the physically dissolved fraction. A review of all the currently known CO2 species in plasma suggests that there may be a residue of about 2 mmol/1 of unknown CO2 species in normal plasma.