Comparison of aqua regia and HNO3-H2O2 procedures for extraction of Tl and some other elements from soils

The relationship between aqua regia (ISO 11466) and HNO(3)-H(2)O(2) (ISO/CD 20279) extraction procedures for atomic emission spectrometric (ICP/OES and ICP/MS) determinations of Tl, P, Mn, Fe, Mg, Ca, Sr, Al, K, As, Bi, Zn, Pb, Co, Cd, Ni, V, Be, Cu and Cr was investigated. Soil samples (155) representing areas with different contents of the elements were selected for the comparison. Tl was the element of the highest interest and therefore the sampling sites were chosen to achieve as wide range of Tl contents as possible. Both extraction procedures are comparable in results (differences lower than 10% for the most of the elements) for all the tested elements. Statistically non-significant differences between the two extraction procedures were found for P, Zn, V and K (the slope was very close to 1 and the intercept included zero). Statistically significant values of intercepts were found for Fe, Al, Ca, Cd, Sr and Ni. Significantly higher results for aqua regia were found for Cu (12%), Pb (17%), Mn (11%) and lower results by aqua regia were found for Mg (4%), As (13%), Co (20%), Be (11%), Cr (4%) and Bi (6%). The results for Tl, the element of the highest interest, after HNO(3)-H(2)O(2) extraction procedure, were approximately 6% higher than the results after aqua regia extraction. Content of Tl in the soil samples was from 0.08 to 2.8 mg kg(-1). A highly significant linear relationship was found (R(2)=0.97).