1. European Standard 45 001;CEN/CENELEC;General criteria for the operation of testing laboratories,1989
2. General requirements for the technical competence of testing laboratories,1990
3. Proper sampling: a precondition for accurate analyses;Wegscheider,1994
4. International Vocabulary of Basic and General Terms in Metrology;ISO,1993
5. Survey of reference materials, Volume 1: Biological and environmental reference materials for trace elements, nuclides and micro-contaminants;IAEA-TECDOC-854;A report prepared by the IAEA and UNEP,1995