Comparison of EDXRF and ICP-OES after microwave digestion for element determination in plant specimens from an abandoned mining area

In this study an energy dispersive X-ray fluorescence (EDXRF) method has been applied to the analysis of some major and minor elements (K, Ca, Mn, Fe, Cu, Sr, Pb and Zn) in four higher plants growing on the waste landfills surrounding an abandoned Pb-Zn ore concentration factory. The validation of the procedure was performed by using a certified standard reference material (NIST SRM 1571: 'Orchard leaves' from National Institute of Standards and Technology) and by comparison with data obtained from two routine microwave assisted digestion procedures commonly applied to vegetation specimens (Dig A: HNO3 + H2O2, Dig B: HNO3 + H2O2 + HF) plus ICP-OES. No statistically significant differences at the 98% confidence level were found between EDXRF and Dig A results, concerning to Ca, Pb, Sr and Zn. On the contrary, statistically significant differences were found for K, Mn, Fe and Cu due to the presence of a silica residue. The addition of HF (Dig B) neither accomplishes the solubilization of these elements. After Dig B a solid residue is formed mainly composed by Ca and F, according to the results obtained by scanning electronic microscopy (SEM). Taking into account all these facts, the EDXRF method proposed proved to be an effective tool for metal determination in vegetation specimens since it allows obviating the matrix destruction stage and the poor recoveries for some elements