ИСТИНА

The object of this study is zooplankton, and more specifically, several taxa of crustaceans, some of which show an unusual enrichment of trace elements (mainly Li) in their tissues. A rapid and sensitive method for elemental analysis of zooplankton is required, which would be easy for on-site implementation (i.e., on board during cruises). The LIBS is well suited for this purpose. Due to a lack of certified reference materials, it seems reasonable to use calibration-free (CF) LIBS in this case. We also present a comparison of the CF-LIBS results with those obtained by a conventional (calibration-based) technique. Pelletized samples of zooplankton were ablated by the 4th harmonic of Q-switched Nd:YAG laser (266 nm). Emission spectra were recorded using a Czerny-Turner spectrograph (resolution of 0.05 nm at 589 nm) with a gated ICCD camera within the range of 201—681 nm. Line selection for reliable plasma diagnostics as well as for analytical measurements was guided by modeling which involved solving radiative transfer equations under the assumption of LTE. In general, the obtained element ratios in CF-measurements are consistent with ICP-MS and ICP-AES data. Due to the nature of the samples, analysis involved mainly alkaline and alkaline earth elements (Li, Na, Mg, Si, P, K, Ca, Sr). As for the calibration-based approach, its straightforward use was hampered by differences in colours and reflection coefficients of samples, so that we had to use normalization to obtain valid calibration curves. Differences in sample densities also made contributions to signal uncertainties. Acknowledgement The reported study was funded by the Russian Foundation for Basic Research according to the research project № 18-33-01297. ICP-AES and ICP-MS elemental analyses of zooplankton samples were funded by the Russian Science Foundation (research project №18-77-00064).