X-Ray Fluorescence in Biological Sciences. Группа авторов

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СКАЧАТЬ 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, СКАЧАТЬ