A comparison of techniques for preparing fish fillet for ICP-AES multielemental analysis and the microwave digestion of whole fish

Four catfish fillet homogenate treatments before multielemental metal analy sis by simultaneous inductively coupled plasma/atomic emission spectroscopy were compared in triplicate. These treatments were: nitric acid wet-ashing by Parr bomb digestion; nitric acid wet-ashing by microwave digestion; tet ramethylammonium hydroxide/nitric acid wet digestion; and dry-ashing. The t etramethylammonium hydroxide/nitric acid method was imprecise (coefficients of variation >20%). The dry-ashing method was fast and sensitive but had l ow recoveries of 50% for spiked Pb and Al and was not as precise as the Par r bomb or microwave treatments. The Parr bomb method was the most precise m ethod but was less sensitive than the microwave method which had nearly the same precision. The microwave method was then adapted to homogenates of sm all whole fish less than or equal to3 cm in length. The whole fish homogena te required more vigorous digestion conditions, and addition of more acid a fter the evaporative step because of the presence of less oxidizable and ac id-soluble components than fillet. The whole fish homogenate was also more heterogeneous than catfish fillet. A quality assurance protocol to demonstr ate homogenate uniformity is essential. The use of a non-specialized microw ave oven system allowed precise results for fillet and whole fish homogenat es.