Question

If the precision of the measurement of the potential difference between a selective electrode and its reference electrode is +0.1 mV, what is the precision of the pH measurement and the concentrations of sodium, potassium and ionized calcium in a plasma sample of a healthy person whose pH is equal to 7.40 and whose concentrations of sodium, potassium and ionized calcium are respectively equal to 150, 4 and 1.4 mmol / L?

b) A sodium selective electrode is calibrated with a standard solution whose composition is similar to the plasma, it contains 70 g of protein, 140 mmol of sodium per liter of solution. Let V_{0} be the difference in potential measured between the selective electrode and the reference electrode when this standard solution is used. When the electrode system is inserted into a plasma sample from a patient whose protein is also 70 g / L, the potential difference is less than V_{0} at 1.3 mV. What is the sodium concentration of this patient?