Transferable calibration coefficients for semi-quantitative analysis by Laser Induced Breakdown Spectroscopy (LIBS) in samples containing calcium

This work establishes a framework for testing and developing calibration coefficients for multi-elemental analysis by LIBS, that are transferrable to various instruments under specific experimental conditions: measurements in air, full optical collection of the plasma plume, apparent plasma temperature and electron density within 6500-7500 K and 1-2 × 1017 cm-3, respectively. Here, the plasma was produced by ns laser pulses at 1064 nm, with energy of 30 mJ while for its detection we used high resolution compact spectrometers. Calibration coefficients for 14 elements were derived respect to one Ca I line (443.50 nm) considering that Ca is a common element in natural samples. The calibration coefficients were obtained from: (i) extrapolated linear peak growths, produced by changing the sample mass on a solid support (Si wafer or Al); (ii) peaks normalized on the Ca line. Their validity interval is specified while the inherent variations with the element abundance and plasma parameters are explained. The initial calibration involved nine different samples, including a multi-element standard, rock, soils ash, coal, and carbonate's mixture, while the validation was applied on two soil samples, both in form of particles on wafer and pressed into pellets. Calibration coefficients based on the linear slope produced quantification of 13 elements within accuracy of ±30% while the use of the line ratios increased the error for some considered elements. To facilitate transfer of the coefficients to other experiments, we provide practical instructions and limits of applicability. The transition from relative to absolute element concentration measurements is also explained in the text.