The process suggested by Munns and Holland involves a double digestion of 5 g of sample. The first digestion uses a combination of sulphuric acid, nitric acid and sodium molybdate. The second step uses a 1:1 nitric acid/perchloric acid mixture. Sullivan and Delfino [7] used a sulphuric acid/ nitric acid mixture to digest the fish tissue at room temperature for 24 hours. Hydrogen peroxide is then added and the mixture heated to 265 °C. After cooling, potassium permanganate is added to maintain an oxidizing medium. This, eventually, being reduced with hydroxylamine solution.