Comparison of Acid Mixtures Using Conventional Wet Digestion Methods for Determination of Heavy Metals in Fish Tissues

Abstract

Sample preparation is an important step of any analytical procedure. Considering low budget and limited unsophisticated technology available in small laboratories, it is necessary to carefully evaluate and optimise the efficiency of the conventional wet digestion method. The study focuses on comparison of different acid mixtures for fish tissue pre-treatment. Four of the most commonly used acid mixtures: nitric/peroxide (NO), nitric/perchloric (NP), aqua regia (NH) and sulphuric/perchloric/nitric (SPN) acid mixtures were evaluated for accurate determination of Pb, Zn, Cd, Cu, Cr and Fe in tuna fish homogenate standard reference material (SRM) and fish tissues by flame atomic absorption spectroscopy. SPN mixture was found to be the most suitable for determination Pb, Cd, Cr and Fe in fish tissue. NO and NH gave good extraction for Zn and Cu while NH showed the least extraction capacity for determination of all the metals in fish tissue. Highest recovery efficiency of the methods were Zn(98%) and Cu(97%) for NP; Cr(101%) and Fe(102%) for SPN and Cd(101%) for NH. On the basis of this, the two preferred acid mixtures are NP and SPN. Application of method SPN is recommended for both extraction and recovery analysis of fish tissue. However, to avoid potential hazards with the use of perchloric acid, it should be added gradually at the later stage of the digestion process.