1. Martindale,The Extra Pharmacopoeia, Pharmaceutical Press, London, 1977, p. 52.
2. British Pharmacopoeia, H. M. Stationery Office, London, 1980, p. 328.
3. Martindale,The Extra Pharmacopoeia, Pharmaceutical Press, London, 1977, p. 56.
4. K. Florey,Analytical Profiles of Drug Substances, No. 7, Academic Press, New York, 1978, p. 344.
5. M. R. F. Ashworth,The Determination of Sulphur-Containing Groups, Vol. 2: Analytical Methods for Thiol Groups, Academic Press, New York, 1976.