A bifunctional total NO.sub.x and O.sub.2 sensor assembly with an internal reference for high temperature sensing. Two electrochemical total NO.sub.x(NO+NO.sub.2) measuring systems and method were coupled with a metal/metal oxide internal oxygen reference to detect O.sub.2 and NO.sub.x simultaneously in a combustion environment using a single sensor. A Pd/PdO-containing reference chamber was sealed within a stabilized zirconia superstructure by a high pressure/temperature bonding method. An amperometric and potentiometric NO.sub.x sensor assembly was built on the outside of the Pd/PdO chamber. Pt-loaded zeolite Y was used to obtain total NO.sub.x capacity and also to cover the Pt electrodes for detecting oxygen in the presence of NO.sub.x.
STATEMENT OF GOVERNMENT INTEREST
 The United States Government has certain rights in this invention pursuant to Contract No. W-31-109-Eng-38 between the United States Government and the University of Chicago and/or pursuant to Contract Nos. DE-ACO2-06CH11357 and DE-PS26-02NT41422 between the United States Government and UChicago Argonne, LLC representing Argonne National Laboratory and grant DE-FC 26 03NT41615 to Ohio State University.