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Desideri et al. [63, 64] determined Mg, Al, P, S, K, Cl, Ca, Cr, Mn, Fe, Co, Cu, Ni, Zn, As, Br, Rb, Sr, Cd, Sn, I, Hg, Pb in samples of several kinds of tea and chamomile from Italy. The sample material was pre‐dried and then ground and mixed with wax. The study was carried out using Spectro‐X‐LAB2000 energy dispersion spectrometer with a polarizer. The authors determined the contents of essential, non‐essential (micro and trace) and toxic elements Pb, Cd, Hg, and As, according to the results of the analysis of toxic element content, were lower than is deemed permissible by the World Health Organization, so the use of these tea and herbal beverages is safe for human health.

In a study by Mbaye et al. [65], a portable Niton XL3t900s spectrometer with Ag‐anode was applied for determination the contents of Mg, Al, P, S, K, Ca, Mn, Fe, Cu, Zn, As,Rb, Sr and Pb in tea samples for classification purposes for classification purposes. Commercially available tea samples purchased in China, Cameroon, and Luxembourg were investigated. Dried, milled tea was mixed with wax at a ratio of 10 : 1 and the tablets were pressed. The measurement time of the tablet was two hundred seconds. The precision of the method was tested by CRM INCT‐Tea Leaves‐1. To improve spectrum of contrast in the range of Cd Lα (3.317 keV) and K Kα lines (3.314 keV), the authors proposed the use of a combination of three filters: Al, Ti and Mo. Revenko et al. [66] provided a brief overview of the applications of filters installed between the window of the X‐ray tube and the radiator, and a theoretical and experimental assessment of the possibility of using Al‐filters of different thickness to increase the contrast of the detected Cs Lα₁ radiation has been made. Mbaye et al. [65] has found that K, Ca, Mn, and Fe concentrations are indicators of the geographical origin of tea. For tea from Luxembourg, K and Zn (<300 ppm) were two times higher than tea from China. Mn content in Chinese tea ranged from 0.7 to 1.2%, compared to Cameroonian tea and Luxembourg tea – 0.14 and 0.18%, respectively. The Fe content for Luxembourg tea is 1.2% compared to 0.16–0.45% for Chinese tea and 0.63% for Cameroonian tea. Note that the content of Pb for Luxembourg tea (100 ppm) is five times higher than for Chinese tea and two times higher for Cameroonian tea.

De La Calle et al. [12] developed a procedure for the simultaneous determination of P, K, Ca, Mn, Fe, Cu, and Zn for plant and spice samples by a TXRF spectrometer S2 PICOFOX (Bruker AXS, Germany) equipped with a 50 W X‐ray tube with a Mo‐anode. Lyophilization followed by grinding and the addition of an internal standard was used to prepare the material for analysis. After the centrifugation procedure, the suspension was deposited on the reflector. The measurement time was five hundred seconds. The accuracy of the procedure, characterized by the repeatability of the determination results, was better than 9%. The correctness of the results of the determination, evaluated by t‐test, showed a good match between certified and experimental values for CRM plants. The proposed procedure was tested to analyze 19 plants. For this aim leaves (black, green and red tea, mate, birch, lime blossom, acacia, mint, thyme, cinnamon, oregon, basil, rosemary, sage), flowers (camomile), and fruits (black and white pepper, hot and sweet paprika) were used. It has been observed that Fe and Cu contents are an indicator in the analysis of different parts of the plant: leaves, flowers, and fruits. The lowest concentrations in the studied plants were obtained for Cu and Zn: from 7 ppm (birch), 10 ppm (mate) to 37 ppm (black tea) and from 15 ppm (white pepper) to 89 ppm (birch), respectively. For samples with tea, Fe content ranged from 210 ppm (matte) to 583 ppm (red tea). The maximum Fe content obtained for camomile colors is 3125 ppm. Tea mate showed a maximum Mn content of 2722 ppm compared to green tea of 1304 ppm, black and red of 631 and 787 ppm.

Ca and K are present in fresh green tea and treated black tea in significant amounts. They are extracted during brewing. K, Ca, and Mn, Fe in 138 samples of black and green tea from Turkey were determined by EDXRF with radioisotope sources ⁵⁵Fe and ²³⁸Pu [67, 68]. Tea was selected three times as the bush grew on plantations located at different heights (0–240 m) above sea level. The tea material was subjected to known raw material treatment methods (twisting, crushing, grinding and pressing). For analysis, tea samples were ground in a vibration mill for 10 minutes to a particle size of 150 μm. Then, 200 mg tea was compressed into 24 mm diameter tablets and reinforced with Mylar film. The resulting thickness of the tablet for determining said elements in the plant material was 44.2 mg/cm². Since the peaks of the characteristic emission of the detected elements have overlays, the spectra obtained for specially prepared samples with known analyte content from the tea sample spectra were subtracted to determine K, Ca and Mn, Fe contents. Kα line intensities were normalized to the intensity of coherent and non‐coherent scattered radiation of sample atoms. In order to obtain a calibration function, the intensity of the Kα‐lines of the tea sample analytes was compared with the intensity of the lines of the samples prepared by the authors. The detection limits of K, Ca and Mn, Fe were 21, 40 and 116, and 157 ppm, respectively. The authors have found that tea collected for the first time from the bush contains the highest concentration of K (2.54%) and Fe (469 ppm) compared to late collection tea – K (2.38%) and Fe (358 ppm), respectively. For Ca and Mn, the reverse pattern is noticed: old leaves contain more Ca (0.47%) and Mn (0.24%) than young leaves – 0.39 and 0.2%, respectively. It is noted that the K and Ca contents in stems and leaves differ, so depending on the parts of the plant used, there is a difference in the contents for different tea versions througout the treatment. In the case of Fe, different contents have also been obtained depending on the tea treatment used; this may be due to contamination from the equipment.

Xie et al. [69] used an EXTRA II TXRF spectrometer from Seifert, Germany (Mo‐anode, 50 kV, 10–38 mA) for simultaneous determination of 15 elements in 39 samples of tea grown in the main provinces of tea production in China. For analysis, dried tea material was digested in nitric and hydrochloric acids under high pressure, and an internal standard Ga was added to the solution after cooling. In addition, tea infusions were prepared according to a standard Chinese brew procedure, the resulting solution was filtered, cooled, adjusted to PH < 2, and then Ga was added. Suspensions were prepared by diluting the resulting solutions (1 : 5) with distilled water, aliquots were applied to quartz substrates and dried under an infrared lamp. The CRM tea GBW 08505 (China) was used to control the accuracy of the results. The range of P, S, K, Ca obtained was 0.15–3.1%, Mn, Fe – 50–1800 ppm, Ti, Ni, Cu, Zn, Rb, Sr, Ba, and Pb – 0.3–150 ppm. Solubility in tea was determined: for Ca, Ti, Fe, Ba, and Pb it was up to 17%, for other elements – from 7 to 86%. The influence of the origin, type and quality of tea samples has been studied. The content of elements in tea depends on the chemical and mineral composition of the soil in which it grows. For Oolong tea, P, Ni, Cu, and Zn contents were lower and Mn and Rb were higher compared to similar values in black and green tea. Oolong tea is a semi‐fermented tea that by Chinese classification occupies an intermediate position between green and black tea. Better quality black tea corresponds to higher P, Ni, and Zn content; the opposite trend is seen for K, Ca, Ti, Mn, Sr, and Ba. In addition, the solubility of K, Ca, Mn, Zn, Rb, and Sr increases with improved black tea quality. It is obtained that the solubility of all elements is directly proportional to the time of brewing. However, as the brew time was increased, the solubility for Ca and Fe changed slightly.

Salvador et al. [70] used a spectrometer EDXRF (Mo‐anode, Zr‐filter, 25 kV, 10 mА) for determination of content of elements (22 ≤ Z ≤ 30) in five types of tea (camomile, mint, with a melissa, apple, black) from six producers. Preparation of the samples for analysis was brewing of tea, lyophilization and leaching. The resulting solution was then filtered on a special membrane and analyzed in a spectrometer (spectrum measurement for three hundred seconds). In order to control the accuracy of the results, the procedure was applied with an exposition of one hundred seconds for similarly prepared standards, each containing one element, Fe, Co, Ni, Cu, or Zn. According to the analysis results, the presence of Fe, Ni and Cu was found in all tea samples analyzed. Ti, Cr, Co, and Zn are present in chamomile tea samples and in apple tea; Ti, Co, and Zn in mint tea and Ti, Mn, Co, and Zn in melissa tea. The maximum content of Ti and Fe was obtained for tea from melissa – 10 and 100 ppm, respectively. The content of the remaining elements did not exceed 5 ppm. Brytov et al. [71] used a portable X‐ray scanning spectrometer СПАРК‐1‐2М (X‐ray tube БХ‐1, Ag anode) to identify tea samples. The authors compared 10 types of tea purchased in the commercial network of St. Petersburg. The material of the samples (2–3 g) was previously abraded for five minutes in an agate mortar. The ground samples were placed in a cuvette, and the surface was smoothed with quartz glass. Intensities of Kα‐lines Mn, Fe, Ni, Zn and scattered bremsstrahlung (background) with wavelength of 0.102 nm were measured. The measurement time for each line is 10 seconds. In the identification algorithm, the ratio of the emission intensities of the selected lines to the background intensity was used. Authors have shown that information on the content of four elements (Mn, Fe, Ni, and Zn) in tea samples is sufficient to identify the tea samples studied.

The procedure for determining the concentrations of Mg, K, Ca, Mn, Fe, Zn in tea samples was developed by Pereira et al. [29]. When developing a technique for determination of content of Mg, K, Ca, Mn, Fe, and Zn by a X‐ray fluorescent method in different types of tea (black, green tea, tea with a magnolia vine, with chicory, with a lemon, with a camomile, with mint, with apple and cinnamon, with a melissa and a bitter orange, with a wild strawberry, with peumus) authors used a desktop spectrometer of Shimadzu EDX 700 (Japan, the Rh‐anode, 50 W). For analysis, 200 mg of sample material was placed in 5 mm diameter Teflon cells and coated with Mylar film. Measurement conditions: air in spectrometric chamber, potential up to 50 kV, thickness of mylar film of Teflon cell 3 μm, measurement time‐ one hundred seconds. Besides the analyte elements in tea samples the presence of Si, P, S, Cl, and Cu is noted. For fruit tea samples, the metal content was 2 times lower than in fruit‐free tea. The authors obtained good results of Mg, K, Ca determination, standard deviation varied from 7 to 36%. In the case of Mn, Fe, and Zn, questionable results have been obtained which can be used as semi‐quantitative analysis results.

Tanizawa et al. [72] investigated the chemical composition and structure of the precipitate from Lipton Yellow tea formed on the surface of the mugs. The authors applied a complex of methods: XRF, SEM‐EDS, FTIR, XPS, CHN, and O analyzers, infrared spectroscopy, and X‐ray phase analysis. Distilled or tap water from Tokyo was used for brewing. The dark precipitate proved stable and insoluble in water and organic solvents (chloroform, acetone, tetrahydrofuran, dimethyl sulfoxide, methyl alcohol, and ethyl alcohol). The light precipitate was easily removed by distilled water. Analysis by XRF (3270E system, Rigaku) of the five‐day precipitate showed that the concentration of Ca in the precipitate after brewing in tap water was higher (65%) than in distilled water (50%), and the K (7%) and Si (10%) were lower in tap water, compared to distilled water – 23% and 15%, respectively. It is noted that K has greater solubility in tea solution compared to other elements.

The change in the elemental composition of Turkish tea (P, K, Ca, Mg, S, Cl, Mn, Zn, Al, Fe, Si, Rb, Cu, Ni, and Sr) depending on the collection time (May, July, September) has been investigated by Erkisli et al. [73]. A Rigaku ZSX‐100e crystal diffraction spectrometer (Rh anode) was used for semi‐quantitative element evaluation. Fresh green tea leaves were dried at 50 °C for one to two hours, then pressed into tablets using a hydraulic press. The obtained data showed maximum P, Cl, K, Mn, Ni, Cu levels for young tea leaves, and Mg, Al, Si, S, Ca, Fe, Zn, Rb, and Sr levels increase in tea collected on September.

Wastowski et al. [74] determined the inorganic components of commercial teas (dry leaves) and their infusions in hot water by energy‐dispersive X‐ray spectrometry. In this study, 14 different varieties of tea were selected from the most found and consumed in Brazil. A Shimadzu EDX‐720 X‐ray spectrometer was used. The main characteristics of this spectrometer were as follows: the x‐ray tube voltage was 15 keV (from Na to Sc) and 50 keV (from Ti to U), all measurements were performed under vacuum, with an integration time of 300 seconds. This spectrometer was able to identify only seven elements in dry tea: K, S, Ca, Cu, P, Fe, and Mn. Only S, Ca and K were recorded in infusions. The method of fundamental parameters was used to calculate concentrations from measured intensities of analytical lines [36, 42,75–77]. Although the K concentration was highest in commercial dry tea samples, it was found at low concentrations in infusions. For infusions, sulfur was the element that showed the greatest migration from tea leaf samples to their infusions. In addition, heavy metals were not found in any of them in concentrations that 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	20–149	20–85	15–37	20–60	30–54	н/о‐4.5	25–450	29–61
Rb	50–190	11–129	2.6–71	2.7–38.2	25–150	82–130	—	23–95	14–73
Sr	20–90	2–18	12–38	3.9–17.6	3.5–24	8.4–15	—	9–45	2.6–35
Pb	20–100		0.5–4.3	0.4–2.3	0.3–8.3	0.9–4	—	0.5–1.8	0.8–3.1

^a ‐ Not determined.

^b ‐ n/d: not detected.

Our estimates of this factor, presented in the last section of this chapter, have shown its significance.

There is no denying the fact that tea is the most popular drink in the world, along with water, and therefore it can be recognized as an important part of a healthy diet. However, it can be seen from this literature review that tea consumption may also lead to oral consumption of various trace elements, as tea plants have the genetic potential to absorb non‐essential trace elements. The content of trace elements in all the analyzed tea samples discussed in this section as well as in the overview Karak et al. [30], was within safe limits for human consumption. The results demonstrated that tea still provides a significant share of human needs for trace elements. However, as of the present day, the adverse effects of tea on human health associated with individual trace elements have not been clarified.