Modified Glass and Solid State Membrane Electrodes:

Glass electrode can be made selective for ions other than hydrogen ion through some modifications. This modification is probable through changing the composition of the glass and the internal solution of glass electrode. By adding aluminum oxide to sodium oxide and silicon oxide glass and changing internal filling solution from hydrochloric acid to sodium chloride like electrode becomes selective to Na⁺ ions. There are other types of glass electrode with composition of Li₂O, Al₂O₃ and SiO₂   is also used as sodium electrode. The Sodium electrode has several applications within measurement of sodium in water analysis and in biological fluid analysis. For measuring potassium and ammonium ions, modified glass containing 27 % of Na₂O, 4 % Al₂O₃ and 69 % SiO₂. Potassium/ammonium electrode is now replaced by other ion selective electrodes using more selective membrane.