1. American Society for Testing and Materials (ASTM), 1999a. Standard Practice for Sampling Industrial Chemicals. West Conshohocken, PA, Method D5679-95A.
2. American Society for Testing and Materials (ASTM), 1999b. Standard Practice for Sampling Industrial Chemicals. West Conshohocken, PA, Method E300-92.
3. Association of Official Analytical Chemists International (AOAC), 1997. Fertilizers. In: Kane, P.F. (Ed.), AOAC Official Methods of Analysis, Chapter 2. AOAC, Gaithersburg, MD.
4. Essentials of Quantitative Analysis, Chapter 19;Benedetti-Pichler,1956
5. Theory and principles of sampling for chemical analysis;Benedetti-Pichler,1956