Abstract: A system is provided for measuring the concentration of an element in molten metal such as silicon, chromium, manganese or aluminum. The system includes a probe with a sensor having a solid electrolyte, a reference electrode in contact with a first surface of the electrolyte and an auxiliary electrode at a second surface thereof. The auxiliary electrode includes an oxide of the element to be measured and a metal-silicate selected from the group consisting of alkali metal-silicates, alkaline earth metal-silicates and mixtures thereof. The metal-silicate has a working point at about the temperature of the molten metal so as to form a viscous semi-molten mass adjacent the second surface of the electrolyte. The metal-silicate is capable of diffusing oxygen in the semi-molten state. Preferably the metal-silicate is in the form of a fibrous material so that it can be easily applied to the surface of the electrolyte.