ИСТИНА

This study deals with the analysis of marine zooplankton. Some species of small crustaceans are known to accumulate considerable amounts of lithium, uranium and other elements. At present, the reasons and mechanisms behind this phaenomenon are unclear. Laser-based techniques make it possible to characterise the chemical composition of animals with minimal sample destruction in order to provide basis for the elucidation of biochemical mechanisms behind the element enrichment. In our previous studies, we used full-length spectra obtained by laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy to explore the correlations between elemental and molecular composition of Calanoida and Euphausiacea crustaceans, arrow worms, and sea snails. Lithium content has been found to correlate with that of pigments and amino acids. As a follow-up research, we have considered elemental signals obtained by inductively coupled plasma mass spectrometry with laser ablation (LA-ICP-MS). This technique enabled the detection of additional elements which were hard to detect with LIBS (such as S, As, U, etc.). The experiments were carried out using the Applied Spectra J200 Tandem LA-LIBS spectrometer (266 nm ablating laser) and the Agilent 7700 Series ICP-MS spectrometer. Raman measurements were done using the Thermo Scientific DXR Raman Microscope (780 nm laser) in the range of 45–3500 cm-1. In all spectra, baseline was removed, and prominent peaks were integrated. Data blocks were Frobenius-normalised. The final matrix contained around 2700 mass-spectral and Raman signals originating from 29 zooplankton samples. Conventional PCA decomposition seemed inefficient for the exploration of the data, because the information was dispersed across too many principal components. Thus, we opted for multiblock algorithms, namely, consensus PCA (CPCA) and ComDim–PCA. For the moment, ComDim–PCA results are most easy to interpret. One of the common dimensions (CDs) contains the signals of Li and pigments together, which supports the earlier findings. The same CD also contains the U signal. Zinc is partially associated with lithium, while the other studied elements (B, Na, Mg, Al, Si, P, S, Cl, K, Ca, Fe, Cu, As, Sr, and Ba) are associated with fats and definitely go to a separate CD. Thus, a special physiological role may exist for Li, U, and Zn.