The practice of using varios methods of sample preparation for the X-ray fluorescence determination of macroelements in geological rocks, soils and sediments

To determine the content of macronutrients in rocks, soils and sediments, three methods of sample preparation were used by the X-ray fluorescence method: pressing powder samples; fusing in gold-platinum crucibles to obtain glass discs; fusing on graphite substrates followed by melting and tablet pressing. A detailed description of each of the methods used is provided. For fusion in gold-platinum crucibles, a ready-made LITHIUM BORATE FLUX (from the company CHEMPHYS) was used, its composition: Li₂B₄O₇ (67%) + LiBO₂ (33%) + alloying additive LiBr. For fusion on graphite substrates, powders of lithium tetraborate and metaborate in a ratio of 2:1, dried at 600°C. Random errors of the analysis are estimated: errors of sample preparation and intensity measurement. It is shown that in all cases, the total errors do not exceed the permissible level when conducting mass analyses of the III category. Standard samples of rocks, sediments and soils were used to obtain the grades, The metrological characteristics of X-ray fluorescence analysis techniques using each of the three sample preparation methods are presented. The residual standard deviations of the calibration dependencies are compared. The correctness of the analysis results was verified on three standard samples. The advantages and disadvantages of each sample preparation method are noted. The use of the simplest, cheapest and express method of pressing tablets from the source material is possible only if the content of elements in the analyzed samples does not exceed the limits of the calibration dependencies of this technique. The method of fusion in gold-platinum crucibles requires preliminary information about the chemical composition of the analyzed sample. The method of fusing on graphite substrates (followed by melting and pressing the tablet) is more versatile and has no restrictions on the composition of the fused sample. It is shown that the systematic errors of the method for pressed tablets exceed the errors of the methods using the second and third techniques. The work was performed on the AXIOS Advanced wave dispersive X-ray fluorescence spectrometer (PANalytical B.V., Holland).

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