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1.118 0.917 0.886 0.913 1.016 1.123 0.985 0.983 SBMT 02 1.034 1.012 0.847 0.819 0.841 0.934 1.030 0.913 0.942 LB1 1.011 1.028 0.984 0.923 0.929 0.972 0.979 0.984 0.989 Tr1 1.015 1.021 0.949 0.938 0.953 1.004 1.019 1.019 1.016

The CRM list includes: GBW 08505 – Tea leaves, SRM1573a – Tomato leaves, SRM1515 – Apple leaves, SBMT 02 – Herb mix, LB1 is CRM 8923‐2007 – Birch leaves, and Tr1 is CRM 8922‐2007 – Meadow herbal mix. The sample plants list includes ground coffee, instant coffee, two samples of tea leaves, cinnamon, turmeric, black pepper, pepper paprika, oatmeal, haricot, rice flour, wheat flour, rye and linen flour. The content ranges of some elements in CRMs and the sample plants are, %: Na (0.0024–1.96); Mg (0.095–1.2); Al (0.002–1.0); Si (0.009–1.1); P (0.083–0.6); S (0.097–0.96); Cl (0.023–1.92); K (0.37–4.44); Ca (0.054–5.05); Mn (0.0007–0.12); Fe (0.0056–0.26); Sr (0.0002–0.0345). The element content ranges in real plants are, %: Na (0.003–0.31); Mg (0.08–1.63); Al (0.004–2.37); Si (0.009–15.44); P (0.087–0.45); S (0.06–0.96); Cl (0.01–1.20); K (0.71–5.37); Ca (0.31–21.40); Mn (0.0020–1.2); Fe (0.0083–1.40); Sr (0.0025–0.091). For most elements, the concentration ranges are wider for real plants than comparable CRMs.

      Our estimates showed that for analytical lines from Na Kα to Cl Kα, the I_rel values were close to the I_rel values for Si Kα. The weak dependence of I_rel on the chemical composition of the samples used in this case (0.996–1.041, see Table 3.6) confirms the possibility of using an external standard method to calculate concentrations. For Kα lines in the wavelength range Ni Kα to Sr Kα I_rel were close to the I_rel values for coherently scattered radiation of the Rh Kα ‐line. It follows from the obtained data that with the same contents of the analyzing elements the relative intensities of analytical lines from Fe Kα to Sr Kα can differ by 2.2–2.5 times (for K Kα in 1.34, for Ca Kα in 1.86 and for Ti Kα in 1.97 times). It is obvious that for elements with Z from ²⁰Ca to ³⁸Sr the proximity of the values I_rel to similar values for coherently scattered radiation of the Rh Kα‐line allows one to significantly improve accuracy of the analysis when using a method of the standard of a background. It should be noted that in publications of recent years have in some examples used the method of fundamental parameters. This method is included in most software modern X‐ray spectrometers, both large spectrometers and portable. In its application, it is important to ensure the homogeneity of the material of the samples to be analyzed. This problem is relatively easy to solve for coffee samples and more difficult for tea leaves.

3.8 Conclusion

      The review showed that in recent years the XRF method has been frequently used to identify both basic and trace elements in tea and coffee, as it has some advantages over traditional analytical methods, which use pre‐treatment of sample material for analysis, which can contribute significantly to the total measurement error. The result of the determination is influenced by the utensils used to grind and prepare the material, water and brew time, and the chosen drying method. The chemical composition of the analyzed samples depends on the degree of fermentation, the grade of the material, the time of harvest, and the chemical composition of the soil in which the plant grew. It is worth noting that the limited set of standard samples makes it difficult to obtain accurate results, so additional analytical methods are desirable to monitor the accuracy of the determination results. Researchers, who used X‐ray spectrometers of different types, showed prospects for using XRF for this purpose. When analyzing the products in question with XRF, various methods were used to convert experimental intensities into the content of the elements to be determined: an external standard; background standard and fundamental parameters. Estimates of interelement effects on the intensity of analytical lines for tea, coffee and some plants are presented.

      Tea leaves and coffee grains contain most of the elements necessary for human health. Researchers will have to do a lot of work to assess the contents of various elements in certain varieties of tea and coffee, to identify the dependence of their chemical composition on the influence of natural factors and to understand the mechanisms of influence on certain factors of human life.

References

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      13 13 Borgese, L., Bilo, F., Dalipi, R. et al. (2015). Total reflection X‐ray fluorescence as a tool for food screening. Spectrochim. Acta

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