1. AOAC (1990a) Manganese, iodine, bromine, arsenic and boric acid in water. Preparation of sample. Official method of analysis (15th edn, AOAC 920.202). Association of Official Analytical Chemistry. Washington DC, USA
2. AOAC (1990b) Meat and meat product. Preparation of sample. Official method of analysis (15th edn, AOAC 983.18). Association of Official Analytical Chemistry. Washington DC, USA
3. AOAC (1990c) Plants. Preparation of sample. Official method of analysis (15th edn, AOAC 922.02). Association of Official Analytical Chemistry. Washington DC, USA
4. AOAC (1990d) Sampling of eggs and egg product. Official method of analysis (15th edn, AOAC 939.14). Association of Official Analytical Chemistry. Washington DC, USA
5. AOAC (1990e) Sampling of plants. Official method of analysis (15th edn, AOAC 922.01). Association of Official Analytical Chemistry. Washington DC, USA