The first total reflection X-ray fluorescence round-robin test of rat tissue samples: Preliminary results

The purpose of the study was performing a round-robin test for the element analysis of mammalian tissue samples using total reflection X-ray fluorescence (TXRF). To achieve this goal, the selected rat organs (kidney, heart, spleen and lung) were subjected to microwave digestion and, in the liquid form, were sent to four European laboratories participating in the inter-comparison investigation. There, using various commercially available TXRF spectrometers, their elemental composition was determined. The carried inter-laboratory comparisons involved macroelements with the concentration above 1000 mu g/g (P, S and K) as well as microelements (Ca) and trace elements (Fe, Cu, Zn and Se) occurring, respectively, in the concentrations of 100-1000 mu g/g and below 100 mu g/g. The validation parameters such as the detection limits of the examined elements as well as the intra-day and inter-day precision were determined. To verify the variation in the results acquired in participating laboratories, for all measured elements, the inter-laboratory precision was evaluated. The data obtained by TXRF were also compared with the ones resulting from ICP-MS (Se) and ICP-OES analysis (P, S, K, Ca, Fe, Cu and Zn). The results obtained as part of the study confirmed the high usefulness of the TXRF method in the elemental analysis of animal tissues. As expected, the best results in terms of the examined validation parameters were obtained for elements with higher atomic numbers (Fe, Cu, Zn and Se). For these analytes, the round-robin test confirmed a good accuracy (around 100% for Fe, Cu, Zn) and precision (intra-day < 6%, inter-day < 12% and inter-laboratory < 12%) what supports the use of TXRF for their determination in the mammalian tissue samples. The obtained results allowed, moreover, to indicate potential issues that require resolving in order to increase the usefulness of the method in case of the analysis of light elements such as P, S or K. It is worth mentioning here, inter alia, the improvement of the sample preparation procedures aiming at the reduction of self-absorption in its dried residue, optimization and/or unification of the sensitivity calibration and the spectra fitting procedures in particular laboratories.