Abstract: SO.sub.2 concentration is measurable by a gas sensor having a solid electrolyte of beta-alumina. A beta-alumina pellet may be laminated with Na.sub.2 SO.sub.4 pellets on the both sides.

Abstract: An electrochemical oxygen pump utilizing a solid electrolyte is provided on a closed gas flow path in which a carrier gas is circulated. By applying a constant direct current voltage to the oxygen pump, the oxygen in the carrier gas is pumped-out and discharged from the path to the atmosphere so that the oxygen partial pressure in the closed gas flow path is held at a sufficiently low and constant value. Under this state, a sample containing oxygen is charged into the closed gas flow path. Then, the oxygen content in the sample can be determined by measuring the quantity of electricity which passes through the oxygen pump during pumping of the oxygen released from the sample. Under this arrangement, the oxygen content in samples of metals, alloys, metal compounds, metalloids or gases can be determined as absolute values rapidly and accurately.