X-Ray Fluorescence in Biological Sciences. Группа авторов

been determined. Nineteen commercially available samples of Krasnodar tea have been investigated. Table 3.4 shows the name, type, shape, and quality of each tea according to producer information on the package. Krasnodar tea plantations are the northernmost of all tea plantations in the world. Tea in the Krasnodar region has been grown since the beginning of the twentieth century. The first attempts to grow tea bushes brought from China proved unsuccessful. In the harsh winter, the bushes died. Only seeds brought from Georgia managed to grow tea. The first tea plantation appeared near the city of Sochi, in a valley of mountains 220 m above the sea. The history of Russian tea breeding began with this plantation. The tea qualities “granulated”, “long leaf,” and “packed” are common in the classification of tea quality.

One of the original types of Krasnodar tea is a skull tea. It is produced by two enterprises: Dagomys Chai Group of Companies and Matcsestin Tea Factory. It includes shank, stem particles, and tea leaf. This tea does not belong to the varieties of tea, but it is not inferior to other types of Krasnodar tea. In fact, in some parameters it exceeds many granulated and packaged varieties. Skull tea can be stored longer than usual. It is necessary to note that in Japan tea is also made from shank and thin stems of tea bush. It is called kukicha. Raw materials that are used in the production of skull tea undergo the same treatment as other parts of the plant. Based on the kind of treatment and fermentation, a green or black skull tea is obtained.

Table 3.4 Description of analyzed tea samples from Krasnodar.

Code of a sample	Tea type	Name and origin
A1	Black granulated tea, first grade	Azerchai, “Kuban‐Tea”, Krasnodar region, Belorechensk
A2	Tea black long leaf “Bouquet”
A3	Tea Green Superior Grade, packed
A4	Tea black “Bouquet,” packed
A5	Tea Black Superior Class “Peko”
D1	Tea black skull (petiolar)	Dagomys Chai, Krasnodar region, Sochi
D2	Green long leaf (Bayh) Tea “Extra”
D3	Black long leaf Tea “Extra”
D4	Black long leaf tea № 36
D5	Tea black “Extra” packed
D6	Green tea packed
M1	Tea black classic “Selection” packed	Matcsesta Tea Factory, Matcsesta, Sochi, Izmailovka village
M2	Tea green classic “Selection” packed
M3	Tea black classic “Bouquet”
M4	Tea green classic “Bouquet”
M5	Tea black long leaf “Kazachok”
M6	Petiolar green tea
M7	Tea black skull (petiolar)
С1	Tea black long leaf classic	Krasnodar since 1901, Sochi, Solokhaul village

      3.6.1 Instrumentation

      The main studies were carried out with the TXRF spectrometer S2 PICOFOX (Bruker, Germany) with a 50 W X‐ray tube and Mo‐anode, multilayer monochromator (Ni/C), and silicon‐drift detector (SDD) with energy resolution ~150 eV. Measurements of analytical line intensities for all elements were performed at 50 kV X‐ray tube voltage and 500 μA current. The material prepared for analysis was applied to quartz substrates. All measurements are made in air.

      A S4 Pioneer (Bruker, Germany) WD X‐ray spectrometer with a power of up to 4 kW with a Rh anode and a 75 μm thickness Be window was used. When the atoms P, S, Cl, and K were excited, the voltage on the X‐ray tube was 30 kV, the current was 60 mA, and the measurement time was twenty seconds. In time measurement the intensity of the analytical Kα lines of Ca, Ti, Mn, Fe, Ni, Cu, Zn, Rb, Sr, and Lα for Ba, a voltage of 50 kV and a current strength of 40 mA was used. The signal recording time for Ca, Mn, Fe, and Sr was twenty seconds, for Ba ‐ fourty seconds and for the remaining elements ‐ thirty seconds. The analyzing crystals used were PET for P, S, and Cl, and LiF 200 for the remaining elements. All measurements were made in a vacuum.

      3.6.2 Suspension Preparation

      To prepare the suspension, 2.0 ml of distilled water, an internal Ga standard with a final concentration in the dry residue of 100 mg/kg, was added to 20 mg of pre‐dried (at 85 °C for four hours) and overloaded tea leaves in the agate mortar, and mixed thoroughly. Next, 10 μl of suspension was applied to a quartz substrate, dried, and measured for five hundred seconds.

      3.6.3 Infusion Preparation

      The standard tea preparation procedure indicated on the package was reproduced. When brewed, 240 mg of tea leaves were placed in special bakes, poured with 30 ml of distilled water (temperature ~90 °C). After 5–7 minutes, 1 ml of solution was taken. Then, 100 μl of 100 mg/l internal Ga standard was added and thoroughly mixed before 10 μl was applied to a siliconized quartz glass carrier and dried. The measurement time of the sample was five hundred seconds.

      3.6.4 Acid Digestion

      10 mg of ground and dried tea leaves were placed in a special glass tube. 1 ml of concentrated nitric acid and 50 μl of hydrogen peroxide were added and heated in an oven until fully evaporated. At the end of the process, 200 μl of 10% HNO₃, 20 μl of 100 mg/l internal Ga standard were added and mixed thoroughly. 10 μl of the resulting solution was placed to a quartz carrier, dried by infrared radiation and measured for five hundred seconds.

      3.6.5 Preparation of Samples for WDXRF

      Samples were pressed as a tablet on a boric acid substrate using a semiautomatic hydraulic press. For this purpose, about 1 g of tea leaf powder was crushed in an agate mortar. Next, 0.5 g of the resulting material was pressed into tablets at a force of 18 tons.

      3.6.6 Results and Discussion

      The results show that particles of the samples prepared via acid decomposition were uniformly distributed on the quartz carrier. Non‐uniform distribution of large particles of different shapes over a carrier surface is registered for sample prepared from suspension. The authors found that analysis of the sample suspension is a fast and simple procedure for the targeted determination of elements such as Ca, Mn, Cu, Zn, Br, Sr. Possible explanations for the inaccurate information on elements with small atomic numbers