An ion activity or concentration analyzer including an ion selective electrode, a reference electrode and a flow-through electrolytic cell. A sample liquid enclosure conducts a flow of an aqueous sample past the anode and cathode electrodes of an electrolytic cell that is polarized to generate hydrogen and hydroxyl ions. The ion selective and reference electrodes are so positioned, with respect to the cathode electrode, that the hydroxyl ion concentration is increased in the vicinity thereof. This increased hydroxyl ion concentration causes a reduction in the hydrogen ion concentration and thereby substantially eliminates the interfering effect of hydrogen ions on the operation of the ion selective and reference electrodes.