Determination of 17 trace elements in coal and ash reference materials by ICP-MS applied to milligram sample sizes

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