Weighed 0.5 g of replicate six sample of CRM (DORM-2) and duplicate sample of lyophilised fish muscles were taken directly in Teflon flasks. Then added 5.0 ml concentrated HClO4 and 50 mg of Fe2(SO4)3, digested in microwave oven at one stage heating program involved 80% of total power for 3 min. The resulted digest was evaporated to remove extra HClO4, and then dilute up to 25 ml with 1 M HCl and kept as stock sample solution.