A simple,rapid and reliable gas-diffusion flow injection(GDFI)method for ammonium determination in building materials has been developed.It is based on leaching ammonium froma ground solid sample into an alkaline solution with subsequent ammonia gas generation. Ammonia is then transported in a nitrogen stream to the GD cell of the FI system where it is absorbed into it sacceptor solution containing a mixture of the acid–base indicators cresol red and thymolblue.