The geochemistry of sedimentary rocks is increasingly being used in palaeoenvironmental studies, in the identification of marine versus continental stratigraphy and in chemostratigraphic correlation. The selection of an appropriate research methodology, particularly in terms of sample digestion, can have a significant impact on the accuracy of the results obtained. Depending on the type of rock being studied and the aim of the analysis, a suitable mixture of acids should be used. The most commonly used sample digestion methods are based on a mixture of four acids (multi-acid), aqua regia and inverse aqua regia. As opposed to multi-acid whole-rock digestion, the use of aqua regia and inverse aqua regia result in only the partial digestion of sedimentary rocks. Geochemical analyses using these two different methods were carried out on Carboniferous sedimentary rocks from the Lublin Coal Basin from Poland.The elemental concentrations obtained showed essentially different results for some of the elements. A comparison of the elemental concentrations allowed the distinction of three groups of elements: - those that showed small differences between the results from the preparation methods (Co, Mn, Bi, Cu, Zn and Fe), - those where the elemental concentrations were 20–50% lower using aqua regia digestion (i.e. Ni, P, Pb, Mg, Cd, Th, Mo, Sr), - elemental concentrations that were significantly lower (by up to 80%) following aqua regia digestion (U, Cr, Ba, Na, V, Al, Rb, K, Zr).
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