1. E. J. UNDERWOOD, Trace Elements in Human and Animal Nutrition, Academic Press, New York, 3rd ed., 1977.
2. W. MERTZ, Science, 213 (1981) 1332.
3. A. S. PRASAD, Trace Elements in Human Health and Disease, Vol. 1, Zinc and Copper, Academic Press, New York, 1976.
4. K. SCHWARZ, C. M. FOLTZ, J. Am. Chem. Soc., 78 (1957) 3292.
5. H. S. DANG, D. D. JAISWAL, S. SOMASUNDARAM, Radiochem. Radioanal. Letters, 34 (1978) 99.