This paper describes the evaluation of two digestion methods used to extract 17 elements (Be, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, As, Se, Mo, Cd, Sn, Sb, Ba and Pb) from coal and coal ash, obtained as standard reference materials. An acid digestion method in open vessels using sulfuric, hydrofluoric, perchloric and nitric acid was compared with a sealed microwave digestion method using nitric acid only. The microwave method cannot break down silicates, which harbour many trace elements, but can extract As and Se quantitatively. Volatile elements such as As and Se might be lost during the open vessel digestion; therefore, the closed vessel is the method of choice. The effect of reducing the sample size from several hundred milligrams to amounts as small as 5 mg on the accuracy of determinations was investigated. No significant differences were observed so long as the total dissolved solids and the dilution factors of the final solutions remained constant.
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