ИСТИНА

A number of chemical elements (so-called bio-elements, e. g. Na or K) are involved in physiological processes and are necessary for the normal development of living organisms. Other elements (mainly heavy metals like Cu, Zn) are known to provoke diseases if present at elevated levels. Thus, environmental monitoring should pursue the determination of both essential elements and pollutants. In the present study, we used LIBS and X-ray fluorescence (XRF) to study the elemental composition of aquatic organisms (fish, plants, and zooplankton). The goal was to develop an analytical protocol suitable for the monitoring of anthropogenic pollution of fluvial ecosystems. Regarding the analytical capabilities, LIBS and XRF can be considered mutually complementary techniques. Therefore, their combination offers advantages such as increasing the number of measurable elements and providing more reliable results. We used a laboratory setup based on a Nd:YAG laser (λ = 266 or 532 nm) and an ICCD detector to obtain emission spectra, and X-ray measurements were done with the Elvax CEP-01 desktop energy dispersive spectrometer with golden anode. The samples were cut, dried, ground, and pelletized. Certified reference materials of animal and plant tissues were also analyzed. Analytes of interest included Zn, Sr, B and Cl. LIBS data were used not only for conventional calibration-based measurements, but also for calibration-free analysis. To this end, plasma diagnostics and studies of spatiotemporal plasma evolution were carried out, whereafter candidate analytical lines were selected based on modeling that involved the solving of radiative transfer equations under the assumption of LTE1. A short list of analytical lines was then compiled taking into consideration the uncertainties of element ratios produced by uncertainties of temperature and signal intensity. Since these contributions depend on transition energies and probabilities, the element ratio uncertainties can be minimized by choosing appropriate temporal signal acquisition parameters that give suitable combinations of temperature and electron number density. The results were compared with XRF where possible. The reported study was funded by RFBR and BRFBR, project numbers 20-53-04036 and Б21РМ-085, respectively. [1] S.M. Zaytsev, A.M. Popov, T.A. Labutin. Stationary model of laser-induced plasma: Critical evaluation and applications, Spectrochim. Acta Part B (2019) 158:105632. DOI: 10.1016/j.sab.2019.06.002.