Multielemental analysis of Antarctic soils using calibration free laser-induced breakdown spectroscopy

Abstract

Laser-induced breakdown spectroscopy (LIBS) is a quick technique that allows the analysis of all types of samples without destroying them and with much reduced sample treatment. One of its many applications is the study of geological samples such as soils. Because of the complexity of the matrix, it is very difficult to find or manufacture standards for these types of samples. Therefore, a good alternative is to make use of a methodology, called Calibration Free (CF), where instead of using standards, the physical parameters of the plasma created by the interaction of the laser with the sample are studied and related to the elements and species that compose it. This methodology is followed to perform a multielemental quantitative analysis of soil samples from Antarctica. Two studies were made, differing in the optimization of the instrumental parameters in order to obtain the best possible spectra in the chosen spectral lines. In both cases, the signal to noise ratio (SNR) was used to evaluate the quality of the spectra, but in the second study a full factorial design 23 with center and axial points was developed to get better results. The choice of spectral lines was based on a series of criteria, being stricter in the second study. The samples were mainly composed of the following oxides: SiO2, Al2O3, Fe2O3, CaO, MgO, Na2O, TiO and K2O. In the second study, it was also possible to determine the species present in lower concentrations: Mn, Cr, V, Sr, Zr, BA and Li. The results were compared with those provided by ICP-OES analysis, obtaining close values for most oxides, especially in the second study. For minority elements, the CF-LIBS and the ICP-OES results were within the same order of magnitude in all cases except the Cr case. These results show that CF-LIBS can be very useful in the characterization of complex samples from remote regions, such as Antarctic soils.