Determination of metal concentration in the same fraction of fish tissues in which metallothioneins (MTs) are measured (heat-treated cytosol, S50) is of great importance for correlating the MT level with levels of metals that induce it (Zn, Cu, Cd). Separation of MTs from other proteins comprises ten-fold dilution of S50 cytosol with 0.9% NaCl solution, and subsequent heat-treatment. The presence of salt interferes with Cd measurement by graphite furnace AAS. EDTA was, thus, used as a modifier which allows atomisation of Cd at lower temperatures, and consequently efficiently separates the Cd signal from the NaCl background signal. A method employing an atomisation temperature of 900 °C, and the addition of EDTA solution adjusted to pH ∼ 7.0, was validated, showing that reliable Cd measurements are performed in both Cd standard solutions containing 0.9% NaCl, and in the heat-treated cytosol of red mullet tissues, despite the fact that these samples contain a substantial amount of MTs.
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