1. ; In The Condensed Chemical Dictionary Chapman and Hall Ltd, London, 6th edn, formerly by Francis M. Turner 1889–1952 p. 1177.
2. In Preliminary Study of Consumer Preferences for Cowpea Varieties in the Volta Region of Ghana Food Research Institute, Accra, Ghana, 1975, p. 49.
3. Perkin Elmer Analytical Methods for Atomic Absorption Spectrophotometer 1973
4. The Chemical Analysis of Foods J. and A. Churchill, London, 6th edn, 1970, p. 23.