1. 1The Edinburgh Centre for Toxicology, Edinburgh, UK
2. 2National Board of Health Copenhagen, Denmark
3. 3Laboratory for Analytical Chemistry, Universiteit Gent, Gent, Belgium
4. 4Standardisation in Laboratory Medicine, H:S Frederiksberg Hospital, Frederiksberg, Denmark
5. 5Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden
6. 6Institut fuer Klinische Chemie, Medizinische Hochschule Hannover, Hannover, Germany