ИСТИНА

According to recent research, copepod crustaceans belonging to the Calanoida taxon accumulate lithium. The relation between atomic composition and molecular structure of tissues can reveal the mechanism of this behaviour. We carried out combined studies of zooplankton organisms by Raman spectroscopy and LIBS. Raman spectra were recorded with a 780 nm red laser, and a 20 mJ 266 nm Nd:YAG laser was used in LIBS. Signals were collected separately from dark, light, and medium-coloured spots on the surface of pelletized samples (29 samples of zooplankton, 14 of them from the Calanus taxon). The obtained data were subjected to different matrix decomposition techniques, viz., common principal component analysis (PCA), non-negative matrix factorization (NMF), and common components and specific weights analysis (ComDim) in its PCA-based realization. Bulk composition, obtained by ICP-AES and ICP-MS after digestion, was also available. For PCA and NMF, the influence of data fusion on the results of decomposition was studied. When applied either to Raman or LIBS data separately, the both techniques allowed classification of samples in terms of Li enrichment. Lithium in Calanus appears to be associated with carotenoid compounds and amino acids. Both datasets and the result of their concatenation are described with 3 PCs. The most easy-to-interpret results were obtained using ComDim which weights data of different origin to provide meaningful contribution of all sources. ComDim suggests the existence of just 2 common components. Besides the interrelation of Li with carotenoids and amino acids, ComDim revealed its link to potassium. Interestingly, this holds true only for dark and medium-coloured spots, but not for light spots. There is always a part of Li signal not separated from other elements. This might indicate the existence of different mechanisms of Li uptake by crustaceans. ICP-AES and ICP-MS elemental analyses of zooplankton samples were funded by the Russian Science Foundation (project No. 18-77-00064). The MATLAB code for performing ComDim was kindly provided by Prof. D.N. Rutledge (AgroParisTech, France). The authors are grateful to Á. Bélteki, A. Kéri, P. Janovszky, D. Palásti, Dr. K. Fintor (University of Szeged) and Dr. R. Rajkó (Universtity of Pécs, Hungary) for their valuable assistance.