1. N. Cheronis and T. S. Ma, Organic Functional Group Analysis by Micro and Semimicro Methods, New York: Wiley. 1964. p. 467.
2. W. Riemann and J. Benkenkomp, in: I. Kolthoff and P. Elving (ed.), Treatise on Analytical Chemistry, Part II, Vol. 5. New York: Interscience. 1961.
3. H. Chang, J. Chem. Soc. Japan, pure sect.85, 859 (1964).
4. V. Djurkin, G. Kirkbright, and T. S. West, Analyst91, 89 (1966).
5. F. Umland and G. Wunsch, Z. analyt. Chem.213, 186 (1965).