X-Ray Fluorescence in Biological Sciences. Группа авторов

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СКАЧАТЬ could be considered harmful to human health.

      Li and Yu [78] evaluated optimal conditions for excitation and detection of Se Kα‐line in biological samples. For calibration five samples prepared in the laboratory and thirty CRM biological materials IGGE (China) were used: liver, huangqi, ginseng, spinach, milk powder, wheat flour, rice and corn flour, soybean powder, cabbage, tea, chicken, and apple. Specimens were prepared by pressing at high pressure. This ensured long‐term use of tablets without deteriorating the reproducibility of measurements. The experiment on the selection of optimal conditions of excitation and detection of Se Kα‐line radiation is performed on the energy‐dispersive X‐ray spectrometer Epsilon 5 (PANalytical, Holland) (combined ScW‐anode, Ge‐detector cooled with liquid nitrogen). A maximum X‐ray tube voltage of 100 kV, a current of up to 6 mA, and a variant with a Zr secondary target without a filter between the X‐ray tube window and the emitter proved to be preferable for excitation and detection of the Se Kα‐line emission for small Se contents. The limit of detection (LOD) of Se in biological samples was reduced to 0.1 μg/g (measurement time of one thousand seconds), as a result of the selection of the optimal conditions for measuring of Se.

      Rajapaksha et al. [79] studied the elemental composition of Ceylon tea when it was classified by collection area, applying the energy‐dispersion table spectrometer SPECTRO2000 (Germany), complete with an X‐ray tube with a Pd anode and secondary targets from Co, Mo and Highly Oriented Pyrolytic Graphite. Fresh tea leaves, weighing 10 g, were frozen for 6 hours at −80 °C and lyophilized for 24 h. Then, they were ground to a fine powder, weighing 0.5 g and compressed into tablets. Standard plant materials (including spinach, olive, cabbage, and tea leaves, as well as hay) were used in the construction of the calibration function to extend the concentration range in the determination of Cl, Mn, Cu, and Rb. In calculating the calibration characteristics, the linear regression equation was applied. To account for fluorescence absorption by sample atoms, normalization of the intensity of characteristic radiation of determined elements by intensity of coherent and non‐coherent scattered radiation was used. Intensities for Kα‐line Mg, P, S, Cl were normalized for total coherently and non‐coherently scattered primary radiation intensity PdLα‐line, similarly for K, Ca, Mn ‐ total scattered radiation intensity CoKα secondary target, and for Fe, Cu, Zn, Br, Rb, Sr‐non‐coherent scattered radiation intensity, and intensity Mo Kα from secondary target.

      Based on the studies carried out, the authors drew the following conclusions:

       XRF proved an effective method for measuring the concentrations of a suite of 13 elements in tea.

       The concentration of elements in tea samples could serve as a basis for determining the origin of samples even for closely spaced areas.

      Dalipi et al. [80] used a desktop spectrometer S2 PICOFOX (Bruker AXS, Germany). 40 commercially available samples of tea, herbs, and roots were analyzed. Solid samples were ground in an agate mortar. Microwave decomposition was then applied followed by treatment with a mixture of nitric acid and hydrogen peroxide (six minutes). Ga (1 mg/l in the liquid sample prepared for analysis) was used as an internal standard. The contents of 13 elements K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Sr, Ba, and Pb in the test samples were determined. Chemometry was used for classification purposes. The findings showed that TXRF is a fast and simple method of controlling the quality of tea and grass samples, and it can be used on a regular basis in addition to other traditional spectroscopy techniques.

Table 3.1 shows the results of determining the concentrations of several elements in tea samples obtained by examining tea of different origins with XRF. The ranges of their change are significant narrow than range for rocks. Nevertheless, the question of inter‐elemental effects on the results of the determination of chemical composition seems relevant and important in the study of tea and coffee samples.

Table 3.1 Contents of some elements in the samples of tea (ppm) of different origins, obtained by XRF.

References	[65]	[79]	[63, 64]	[69]	[70]	[80]
Tea	Black	Black	Black	Black	Green	Black	Black	Green
Ti	—a	–	–	–	4–70	15–52	n/db–10	3–30	2–19
Cr	–	–	<2–3.4	<2–4.7	–	–	n/d–0.26	n/d–4.6	0.8–10
Mn	–	43–724	213–1228	28–730	160–1500	548–1500	—	162–1000	174–1130
Fe	1600–12 200	14–234	99–617	144–993	50–1800	18–752	0.2–107	79–1140	63–1040
Co	—	—	<1–1.3	<1	—	—	н/о–0.12	—	—
Ni	—	—	1.2–8.1	1.4–4.3	2–23	5.1–8.9	0.06–3.2	1–5.3	2.7–13
Cu	100–250	12–27	15.4–30.2	4.6–12	8–40	13–20	0.2–2.7	10–56	10–17.6
Zn	130–280 СКАЧАТЬ В начало < 32 33 34 35 36 37 38 39 40 41 > В конец