1. Bowen, H.J.M.: Trace Elements in Biochemistry 1966 New York, Academic Press
2. Tompsett, S.L., Fitzpatrick, J.: Analyst (London), 75, 279 (1950)
3. Versieck, J., Cornelis, R.: Anal. Chim. Acta, 116, 111 (1980)
4. Christian, G.D., Patriarche, G.J.: Anal. Lett., 12B, 11 (1979)
5. Bentley, G.E., Markowitz, L., Meglen, R.R.: Ultratrace Metal Analysis in Biological Science and Environment, Advancements in Chemistry Series, Number 172 (Risby, T.H. ed.) 1979, Washington, D.C., Amer. Chem. Soc.