Quality control of X-ray fluorescence determination of microelements in natural materials applying GeoPT program

Complete text of publication follows. Participation of routine analytical laboratories in the GeoPT program allows it to estimate the quality of obtained analysis results. In GeoPT program, the Analytical Center of Institute of Geochemistry (Irkutsk, Russia) performs an intralaboratory quality control based on analysis of GeoPT samples by different analytical methods, such as atomic absorption spectrometry (AAS), atomic emission spectrometry (AES), inductively coupled plasma mass spectrometry (ICP-MS), and x-ray fluorescence analysis (XRF). The results of X-ray fluorescence determination of Sr, Zr, Nb, Y, Rb, V, Cr, Ni, Co, Cu, Zn, Pb, Ba in GeoPT samples obtained in the Laboratory of X-ray Analysis Methods at Institute of Geochemistry are presented in this report. The analyses were performed using X-ray fluorescent spectrometers VRA-30 (Carl Zeiss, Germany) and S4 Pioneer (Bruker AXS, Germany). The techniques to determine the microelements provide the determination limits (ppm) Ba-50, Sr-5, Zr-10, Nb-5, Y-10, Rb-5, V-10, Cr-20, Ni-10, Co-10, Cu-10, Zn-10, and Pb-10. The estimation for the reliability of X-ray fluorescence analytical results was based on a comparison with the data obtained using other methods and Z' criterion. Z' criterion is applied to for an estimation of analysis results of II category used in applied geochemical researches. Most of the XRF results and the results obtained from AAS, AES and ICP-MS are found to correlate well with each other and with the certified data for all elements determinable, with the exception of Sr, Pb, and Cr. The estimation of XRF reliability using Z' criterion were obtained through the data on each of the six rounds. The uncertainties have been found in XRF testing for Nb, Ni and Pb contents close to the determination limit. Besides, Z' criterion was compared with the admissible relative standard deviations taken in domestic normative documents. It is shown that 50% of GeoPT program uncertainties do not exceed admissible values. Thus, participating in GeoPT program provides analytical laboratories with an objective means of estimating their analytical capabilities and the quality control of obtained data and finding unexpected deviations in during analysis.