References
- Official Methods of Analysis, Association of Official Analytical Chemists , 12th edition , Washington, D.C. : AOAC . section 43.121
- Official Methods of Analysis, Association of Official Analytical Chemists , 12th edition section 43.044
- 1966 . Freed, Myer, Methods of Vitamin Assay, Association of Vitamin Chemists , 3rd edition , New York : Interscience .