Digestion Procedures
There are many published methods for the digestion of fish
tissue. Most involve the use of three reagents, with one
method requiring the use of no less than six reagents. Velghe
et al. [5] describe a method whereby a small piece of fish
tissue is mixed with potassium permanganate and sulphuric
acid, and then digested on a hot-plate. After digestion, the
excess permanganate is reduced with hydroxylamine
hydrochloride. The process suggested by Munns and Holland
[6] 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.