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

In solutions containing 160 mmol/l Na+ and K+, respectively, measurements with an ion-selective electrode system (KNA1, Radiometer), showed apparent falls in the respective Na+ and K+ concentrations when C1- was replaced by HCO3-. After correction for the change in liquid junction potential, the fall was 9.2 mmol/l for Na+ and 7.3 mmol/l for K+. On the basis of these findings we conclude that sodium bicarbonate and potassium bicarbonate are not fully dissociated in solution, and that NaHCO3(0) and KHCO3(0) 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/l NaHCO3(0) and 0.03 mmol/l KHCO3(0). Thus NaHCO3(0) 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/l of unknown CO2 species in normal plasma.