1. T. S. Ma and M. Gutterson, Analyt. Chemistry46, 442R (1974);44, 451R (1972).
2. E. C. Olson, in I. M. Kolthoff, and P. J. Elving (eds.), Treatise on Analytical Chemistry, Part II, Vol. 14. New York: Wiley. 1971. p. 1.
3. S. S. M. Hassan and M. B. Elsayes, Mikrochim. Acta [Wien]1972, 115.
4. Y. A. Gawargious, G. M. Habashy, and B. N. Taltaoos, Indian J. Chem. 7, 610 (1969).
5. E. C. Olson, personal communication, 1974.