The present paper shows how the FTIR measurements in the combustion chamber of a commercial fluidized bed boiler was performed and evaluated. Problems with interfering compounds are discussed. It is concluded that the present instrument is not suitable for measurement of hydrogen cyanide. The influence of instrument resolution and the removal of the main interfering component, carbon dioxide are demonstrated. However, the problem with interfering species is much less severe for ammonia, and the present instrument can be used for the determination of this species
