Abstract: A method for the detection and measurement of a minor element in a molten metal, the minor element being selected from the group of phosphorous, silicon, arsenic, antimony and sulfur, includes providing a first electrical lead (5) and immersing it in the molten metal (6), disposing a solid electrolyte matrix (2) in the molten metal in spaced relationship to the first electrical lead, providing a second electrical lead (3) connected to the solid electrolyte matrix (2) so that the matrix is between and separates the leads when the matrix is disposed in the molten metal, and connecting a voltmeter (7) between the other ends of the electrical leads and measuring the EMF between the leads as an indication of the concentration of the minor element in the molten metal. The solid electrolyte is a matrix (2) of alumina selected from the group consisting of .beta.-alumina and .alpha.+.beta.