Читать книгу X-Ray Fluorescence in Biological Sciences - Группа авторов - Страница 50

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 (P, S, and K) are explained by the differences in effects of absorption by the tea matrix, confirmed by studies of samples of biological origin [13, 89]. In addition, for P, S, and K, the effect of inhomogeneity in the sample distribution on the carrier was more significant when the suspension was used. It should also be noted that the determination of Cl and Br using the acid decomposition method is difficult due to the volatility of these elements, and therefore the use of suspension is recommended for them. The best measurement results for most elements are obtained by analyzing solutions after acid decomposition of tea leaves, whereby this sample preparation method is used to analyze samples of Krasnodar tea. To determine Cl and Br, samples were prepared as suspensions. The average value of the relative standard deviation of the analysis results from the certified values of the CRM for the method used in the verification was not more than 6% for Mg, P, S, Mn, Ni, Cu, Zn, Br, Rb; for K, Ca, Sr, Ba, and Pb – not more than 16%. The largest discrepancies were obtained by determining Ti and Fe. The total uncertainty of TXRF results, considering all stages of analysis (sample preparation and measurement), for all elements except for Ti was on average no more than 16% (n = 3). The uncertainty of applying a sample onto the carrier averaged 7% (n = 7).

Table 3.5 shows the ranges of element concentrations, average concentrations, and standard deviations from the average (n = 3) obtained from the analysis of 19 samples of tea leaves of Krasnodar tea.

The Student's test was used to evaluate the two quantitative data sets obtained by TXRF and wavelength dispersive X‐ray fluorescence (WDXRF). Good results convergence was obtained for Cl, K, Ca, Mn, Fe, Cu, Zn, Rb, Sr, and Ba. However, the concentrations of P, S, Ni observed in the data had relatively low convergence (74% on average), which is explained by the possible influence of unconsidered factors, which demands further research. Advantages of TXRF over WDXRF include using fewer CRM to quantify data, reducing detection limits for most elements by about an order of magnitude, and not having matrix effects when emitters meet the thin layer criterion.