Clay is used for the manufacture of roofing tiles. Quality controls during this process require the determination of halogen and sulfur content. This is ideally accomplished using Metrohm Combustion IC. With this method, the sulfur is determined as sulfate and the halogens as halogenides. Because clay often contains high contents of alkali and earth alkali metal ions that attack the pyrolysis tube, tungsten oxide is added prior to combustion.