1. Feinendegen LE, Kasparek K (1980) In: Brätter P, Schramel P (eds) Trace element analytical chemistry in medicine and biology. W de Gruyter, Berlin, p 1
2. Fell GS, Shenkin A, Halls DJ (1980) In: Brätter P, Schramel P(eds) Trace element analytical chemistry in medicine and biology. W de Gruyter, Berlin, p 217
3. Iyengar GV (1982) Anal Chem 54:554
4. Mertz W (1981) Science 213:1332
5. Thorn JM, Aggett PJ, Delves HT, Clayton BE (1978) Arch Dis Child 53:931