1. WHO Technical Report Series, No. 645. 1980, Annex 2.
2. WHO Technical Report Series. No. 614, 1977, Annex 1.
3. WHO Technical Report Series, No. 681, 1982, Annex 1.
4. The international pharmacopoeia, third edition, volume 1: General methods of analysis. Geneva, World Health Organization, 1979.