Dry ashing or wet digestion ? A comparative study for estimation of zinc and calcium in freshwater fish samples by atomic absorption spectrometry

Different sample treatment procedures such as dry ashing and wet digestion are commonly used to decompose biological materials and to bring the elements of interest into the measurable form. A number of reagents such as aqua regia, HNO3 / H2O2, HNO3 / HClO4 etc. are used to solubilize metals from biological matrix. In this study, performance of dry ashing and wet digestion methods has been compared for the estimation of zinc and calcium levels in the whole body freshwater fish samples. Flame atomic absorption spectrometry has been used as an analytical tool to quantify the metals. Results based on dry ashing and wet digestion methods for zinc differ significantly. Wet digestion method gives mostly higher zinc values compared to dry ashing method which indicates the possible losses of zinc during the ashing of fish samples at elevated temperature, i.e. 500 degrees C. Higher recoveries of calcium in the whole body freshwater fish samples have been obtained following wet digestion procedure using strontium as releasing agent compared to calcium determination following dry ashing method (with and without strontium) and wet digestion method without strontium which suggests the use of a releasing agent (strontium) minimizes the chemical interferences of phosphate while determining calcium by flame atomic absorption spectrometry.