Book excerpt: It is increasingly recognized that the greatest risks of error in environmental analysis lie in the sample preparation rather than the analysis stage. This book describes the precautions that must be taken from the sampling to the sample pretreatment via the storage stage to assure good quality. Typical pitfalls - and recommendations for avoiding them - are discussed. Special emphasis is given to the monitoring of trace contaminants in environmental matrices (e. g., water, sediment, plants, air). This book, based on the experience of specialists, constitutes an invaluable guide to the quality assurance relevant to environmental chemists.