Process for selectively measuring sodium ions in solution

in the process for selectively measuring sodium ion concentration in an aqueous solution containing sodium and other monovalent cations which process includes the steps of providing an electrode with an ion selective glass sensing membrane which is selectively sensitive to sodium ions in the presence of other cations, immersing said sensing membrane and a standard reference electrode in said solution while said glass electrode and said reference electrode are electrically connected to a potentiometer, the improvement wherein said ion selective glass sensing membrane has a composition consisting essentially of:

• ______________________________________ Component Mole % ______________________________________ Na.sub.2 O 10-20 Al.sub.2 O.sub.3 2-15 Ta.sub.2 O.sub.5 2-8 SiO.sub.2 65-80 ##STR7## ______________________________________

in the process for selectively measuring sodium ions in an aqueous solution containing sodium and other monovalent cations including the step of immersing a sodium ion selective glass electrode in said solution and obtaining a resulting potentiometric response as a measure of the sodium ion concentration of said solution, the improvement wherein said sodium ion selective glass electrode is formed from a sodium aluminosilicate glass composition containing Na.sub.2 O, Al.sub.2 O.sub.3, SiO.sub.2 and one other essential glass forming component together comprising not less than about 97 mole percent of said composition, and wherein said other essential glass forming component is Ta.sub.2 O.sub.5 constituting from about 1-10 mole percent of the total mole percent amounts of Na.sub.2 O, AL.sub.2 O.sub.3, SiO.sub.2 and Ta.sub.2 O.sub.5 and wherein said glass composition optionally includes up to about 3 mole percent of other compatible glass forming, modifying or refining components.