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DIGESTION
Biological samples are characterized by mainly consisting of carbon, hydrogen and oxygen compounds. Prior to determination of e.g. metals, this main component is usually eliminated by oxidation to carbon dioxide and water. This can be achieved either by heating the dry sample in the presence of oxygen (dry ashing) or by means of so-called oxidising acids, as in analytical packages M-3 and M-4. Digestion is carried out with nitric acid/hydrogen peroxide in sealed teflon containers in a microwave system, which prevents the loss of volatile components. Samples are centrifuged before analysis..
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REPORTING OF CONTENTS
Biological samples often consist mainly of water. Variations in water content cause variations in element concentrations. These are eliminated if concentrations are expressed as dry sample content, e.g. mg/kg dry weight. It is nevertheless customary to express the contents of certain samples, especially foodstuffs, in non-dried material (wet weight).
Samples intended for determination of mercury are dried at 50°C before analysis, or analysed without prior drying, due to the volatility of mercury. If contents are to be expressed in dry weight, the dry matter content is determined separately (at 105°C) and the concentrations recalculated to dry weight.
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