ИСТИНА

Ferromanganese nodules (FMNs) are rich in rare-earth and rare-metal elements and, therefore, they are considered as a promising source for them. The main spectroscopic challenge to analyze FMNs by emission spectroscopic techniques, such as LIBS, is spectral interferences from iron and manganese which have rich emission spectra. As a result, the strongest Nb I line at 405.85 nm is completely merged by Mn I and Fe I lines. Therefore, a task to search for appropriate analytical lines should be solved for analytical application of LIBS to FMNs. In this work, we have demonstrated how spectra modeling by our algorithm described in [1] can provide us an information about possible analytical lines of niobium. As samples we have used the certified reference samples of FMNs produced in Russia (OOPE series, Nb content 20-90 ppm). After spectra building, we selected several spectral ranges to experimentally measure emission spectra of plasma in these ranges for different plasma conditions: “soft” conditions (long delay, cold plasma) and “severe” conditions (short delay, hot and dense plasma). After inspection of 5 spectral ranges where strong Nb lines can be observed we have obtained that only two lines (as predicted by the algorithm) Nb I 509.53 nm and Nb I 410.09 nm are appropriate for analytical usage because of absence of spectral interference. Although the intensity of Nb I 410.09 nm is larger than one of Nb I 509.53 nm, the latter provided smaller detection limit (5 ppm) due to high efficiency of spectrometric system in the range near 500 nm. So, the work has clearly demonstrated the efficiency of spectra modeling to search for analytical lines in complex matrix, such as FMNs. 1. Zaytsev S.M., Popov A.M., Labutin T.A. Stationary model of laser-induced plasma: Critical evaluation and applications, Spectrochimica Acta Part B, 2019, V.158, Article number 105632.