1. AOAC official method 968.08: Minerals in animal feed and pet food—Atomic absorption spectrophotometric method.;AOAC International,1996
2. Digestion tube and digestion block, Martin Machine, Ivesdale, IL.
3. Model 61E Thermo-Jarrell Ash inductively coupled plasma-optical/atomic emission spectrometer, Thermo Scientific, Waltham, MA.
4. Method 200.7—Determination of metals and trace elements in water and wastes by inductively coupled plasma-atomic emission spectrometry. Revision 4.4. EMMC Version.;US Environmental Protection Agency,1994
5. Certified reference material AAFCO 0625, Association of American Feed Control Officials, Oxford, IN.