## 2 Materials and Methods
### Procedure for Measuring the Total Ion Content of Dried Tea  
Micro and macro elements from solid material (tea leaves) were analyzed using ICP-EOS method (Thermo iCAP Dual 6500 with horizontal plasma, Schaumburg, IL, USA). Samples of 0.5 g of each of the 9 teas were mineralized in 65% HNO\({}_{3}\) under high pressure, in 3 lab replicates. Samples were weighed and placed in Teflon dishes, then topped up with 8 mL of nitric acid and sealed. One blank sample--pure HNO\({}_{3}\)--was used for each group of nine samples. The samples were mineralized using the temperature rise algorithm specified for biological samples, never exceeding 220 \({}^{\circ}\)C. The procedure was carried out in an Ethos One microwave digestion system (Milestone, Bologna, Italy). The vessels were opened after the digestion process and the acid samples were brought to room temperature. They were then topped up with water to a volume of 50 mL. The detection threshold obtained for each element was no lower than 0.1 mg kg\({}^{-1}\) (assuming a detection capacity of the measuring apparatus of more than 10 ppb). Measurements were carried out on an  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Numbering** & & & & & \\
**Used in Further** & **Tea** & **Origin** & **Moisture Content, \%** & **Ash Content, \%** & **Protein Content, \%** \\ \hline
1 & Nepal Everest (black tea) & Nepal & 3.98 \(\pm\) 0.33 & 6.21 \(\pm\) 0.27 & 20.31 \(\pm\) 0.35 \\
2 & Ceylon Kenilworth (black tea) & Sri Lanka & 7.17 \(\pm\) 0.29 & 6.04 \(\pm\) 0.19 & 15.30 \(\pm\) 0.13 \\
3 & Black Vietnam (black tea) & Vietnam & 6.58 \(\pm\) 0.27 & 6.15 \(\pm\) 0.18 & 29.65 \(\pm\) 0.34 \\
4 & Fog Green Tea (green tea) & Taiwan & 5.13 \(\pm\) 0.31 & 7.28 \(\pm\) 0.26 & 23.20 \(\pm\) 0.37 \\
5 & Sencha Kyoto Organic (green tea) & Japan & 4.91 \(\pm\) 0.33 & 7.27 \(\pm\) 0.32 & 24.00 \(\pm\) 0.17 \\
6 & Yunnan Green (green tea) & China & 5.18 \(\pm\) 0.25 & 7.34 \(\pm\) 0.32 & 23.67 \(\pm\) 0.31 \\
7 & White Monkey (white tea) & China & 4.56 \(\pm\) 0.14 & 5.68 \(\pm\) 0.22 & 16.31 \(\pm\) 0.22 \\
8 & Yin Zhen Hunan (white tea) & China & 4.89 \(\pm\) 0.18 & 5.77 \(\pm\) 0.21 & 15.23 \(\pm\) 0.33 \\
9 & Pai Mu Tan Rose (white tea) & China & 5.01 \(\pm\) 0.10 & 5.31 \(\pm\) 0.37 & 15.44 \(\pm\) 0.24 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Overview of analyzed teas by region of origin and basic analytical parameters.  
ICP-OES spectrometer (Thermo Fisher Scientific, Schaumburg, IL, USA) and the detection capability was determined both along and across the plasma flame (radially and axially). Before measuring each batch of samples, the equipment was calibrated using certified Merck models at concentrations of 10,000 mg l\({}^{-1}\) (for macronutrients) and 1000 mg l\({}^{-1}\) (for trace elements and metals). The measurement result for each element was corrected to account for the measurement of elements in the blank sample. In each case, a 3-point calibration curve was used for each element, with optical correction using the internal model method, in the form of yttrium and ytterbium ions, at concentrations of 2 mg l\({}^{-1}\) and 5 mg l\({}^{-1}\), respectively. The analytical methods were validated using two independent tests. A certified reference material (NIEST CRM 7: Tea Leaves) was used. A model addition method of known concentration was used to identify appropriate measurement lines and avoid possible interferences. The recoveries obtained for each element are shown in Table 2 below.