Comparative study of calibration-free laser-induced breakdown spectroscopy methods for quantitative elemental analysis of quartz-bearing limestone.

Laser-induced breakdown spectroscopy (LIBS) has been employed for the qualitative and quantitative analysis of quartz-bearing limestone using two different calibration-free LIBS methods, that is, one-line calibration-free LIBS (OLCF-LIBS) and self-calibration LIBS (SC-LIBS) methods in conjunction with energy-dispersive x-ray spectroscopy (EDS) and x-ray fluorescence spectroscopy (XRF). The plasma is generated by focusing a Q-switched Nd:YAG laser (1064 nm, 134 mJ pulse energy, 9 ns pulse duration) in air under atmospheric pressure. Spectral analysis revealed the presence of Ca, Si, and Mg. Plasma temperature is deduced using the neutral spectral lines of pertinent elements using the Boltzmann plot method, and an average value of 3462 K is used for the quantitative analysis. An average value for electron number density is calculated as (1.3±0.3)×10  cm from the Stark broadening of isolated neutral Ca, Si, and Mg lines and a singly ionized Ca line. The elemental composition determined by different LIBS methods and other traditional analytical techniques are OLCF-LIBS (Ca, 71.82%; Si, 28.12%; Mg, 0.048%), SC-LIBS (Ca, 69.19%; Si, 28.92%; Mg, 1.87%), EDS (Ca, 68.86%; Si, 30.12%; Mg, 0.32%), and XRF (Ca, 68.62%; Si, 27.18%; Mg, 1.56%). By comparing the results of both CF-LIBS methods along with EDS and XRF, it is demonstrated that the SC-LIBS method is more appropriate than the OLCF-LIBS and gives compositions comparable with that determined by EDS and XRF and, hence, displays its ability as a powerful tool for the compositional analysis of complex minerals.