title: Direct potentiometric determination of sodium ion in blood. II. Influence of cations.
abstract: We measured the emf of NaCl solutions (120-160 mmol/L), with and without the addition of KCl (5-20 mmol/L), CaCl2 (2-8 mmol/L), or MgCl2 (1-4 mmol/L). Measurements were made with a home-built cell in steady-state and with two commercial direct potentiometric analyzers about 20 s after the sample was introduced. We calculated the sodium ion activity in the mixed NaCl-KCl solutions according to different thermodynamic theories and found almost the same results. We conclude that the influence on the emf of physiological concentrations of these cations was negligible when emf measurements were made in steady-state with the home-built cell. Of the three added cations, K+ caused the greatest increase in apparent sodium ion activity (up to about 4%) when emf measurements were made with commercial analyzers, owing to low salt-bridge concentration and the short measuring time of about 20 s.
mesh_terms: D002122:Calcium Chloride; D002412:Cations; D004573:Electrolytes / Q000097:blood*; D006801:Humans; D008274:Magnesium; D015636:Magnesium Chloride; D008433:Mathematics; D008954:Models, Biological; D009994:Osmolar Concentration; D011189:Potassium Chloride; D011199:Potentiometry / Q000295:instrumentation; D012964:Sodium / Q000097:blood*
chemical_list: D002412:Cations; D004573:Electrolytes; D015636:Magnesium Chloride; D011189:Potassium Chloride; D012964:Sodium; D008274:Magnesium; D002122:Calcium Chloride