Two different analytical approaches in Laser Induced Breakdown Spectroscopy (LIBS) technique to determine elemental concentrations in soils

Laser Induced Breakdown Spectroscopy (LIBS) is an analytical technique based on the optical emission spectroscopy of the plasma generated by high energy laser pulse and solid sample. LIBS allows to perform stand-off and in situ analysis with immediate response and a limit of detection (in the range of mgkg-1), and for these peculiarities is particularly suitable for analysis in the environmental field. In this work is presented a case of study where the elemental analysis of some polluted soils are obtained either with the classical calibration curve (CC) method or with a Local Thermodinamic Equilibrium (LTE)-based Calibration-Free (CF) method, in order to demonstrate the capability of this technique. It is important to underline that the latter methodology does not require the use of preliminary experiments with standard samples and so it does not have any limitation due to the matrix effect. Several polluted soil samples were analyzed by drawing calibration lines to determine the concentration of some trace metals (e.g., Cr, Pb, Cu, Zn, Sr, Ni), as well as those of some major elements (e.g., Fe, Mn, Mg). The elemental concentration (normalized by Fe concentration) was measured with ICP-OES and LIBS techniques respectively. For what concern LIBS measurements, a comparison was done between two different data treatment: the LTE-CF based method and the classical CC method. For some elements a comparison was tried between calibration lines and calibration-free data, in order to validate the latter techniques also for complex matrices such as soils.