Intercomparison of trace element determination in samples from a coal-fired power plant

The combustion of fossil fuels, e.g. coal, is one of the anthropogenic sources of hazardous trace element emissions. This interlaboratory study was arranged to test and improve the quality of trace element analysis of different types of samples from a coal-fired power plant. Samples of coal, fly ash, by-product from flue gas desulphurisation (=FGD product, consisting mainly of CaSO₃ and CaSO₄), and two different absorption media used for the sampling of vaporous metals and metalloids in flue gases were sent to be analyzed for Al. As, Be, Cd. Co, Cr, Cu, Hg, Mn, Ni. Pb. Se, Tl, V and Zn by different Finnish laboratories using mainly atomic spectroscopic methods. In addition, neutron activation analysis and X-ray fluorescence spectroscopy were employed. 12 laboratories took part in the analysis of a HNO₃ sample, 5 in the analysis of a K₂Cr₂O₇/HNO₃ sample, 15 in the analysis of a fly ash sample, 9 in the analysis of a coal sample, and 7 in the analysis of a sample of the by-product from flue gas desulphurisation. The results were evaluated both in terms of interlaboratory agreement and in comparison with different digestion and analytical methods used in the intercomparison. The magnitude of the deviations of the results clearly indicated a need to develop the quality of power plant sample analysis. Considering the methods used, it was concluded that the composition of the acid mixture used for the digestion of solid samples is more decisive than the method of heating during the digestion.