Abstract

A new, fast and cheap method for the analysis of clays using total-reflection x-ray fluorescence spectroscopy (TXRF) has been developed following a full factorial experimental design to optimize the sample preparation conditions. The optimized method consists of the dispersion of 50 mg of clay into 2.5 ml of 1% Triton X-100 solution, the deposition of 5 μl of the suspension onto a siliconized quartz reflector and drying it at 50 °C on a heating plate. By using a commercial benchtop instrument, 15 major and trace elements were correctly quantified with 1000 s live time acquisitions. Thirty minutes were sufficient for both sample preparation and analysis. Validation experiments, performed using a certified reference material, showed recoveries in the range 80–120% for the main targeted elements, whereas the within laboratory reproducibility (RSDWLR) and the repeatability (RSDr) were lower than 20%, demonstrating the good precision and reliability of the method. Only in the case of Si, the RSDWLR and RSDr were higher than 20%, due to the variable contribution of the quartz reflector. Suitable LOD and LOQ values were estimated, varying from 0.1–0.4% for Al to 1–2 mg/kg for Sr, with higher sensitivity for elements with higher fluorescence energy (and high atomic number, Z).

Finally, a good agreement was obtained between the results of the analysis of reference materials performed with the new TXRF method and a reference method, such as wavelength dispersive x-ray fluorescence spectroscopy (WDXRF).

Based on the above performances, this method may represent a valuable and reliable alternative analytical tool when only small amounts of clay samples are available such as in the case of mineral synthesis, clays extraction from soils and sorption tests.

Articolo completo: https://www.sciencedirect.com/science/article/pii/S0169131719302595