1. ISO Guide 35 (1989) Certification of reference materials ? general and statistical principles, 2nd edn
2. NBS Handbook;MG Natrella,1966
3. Ingamells CO, Switzer P (1973) Talanta 20:547?568
4. Lievens F, Ingelbrecht C, Pauwels J (1992) EUR-14645 EN
5. Pauwels J, G�tz A, Lamberty A, Grobecker KH, De Bi�vre P (1991) Certification report VDA-RM's 001 to 004 for Cd in plastics, CBNM Geel (Belgium)