Purity data for inorganic chemicals are usually on metals basis. A high nominal purity does not guarantee that the material has the theoretical assay value. Deviations range from some tenth % (CaCO3) up to approximate to 10% (La2O3) for commercial chemicals with nominal 99.999% purity. In critical cases, ICP-OES and/or TG measurements provide good ways to obtain quantitative assay data and to define conditions that lead to the desired results of synthesis processes as crystal growth. (C) 2004 Elsevier B.V. All rights reserved.