Multi-energy calibration and sample fusion as alternatives for quantitative analysis of high silicon content samples by laser-induced breakdown spectrometry

Abstract

Calibration aiming at quantitative analysis of complex samples is one of the most difficult issues in laser-induced breakdown spectroscopy (LIBS) due to matrix interferences, heterogeneity, and sample particle size effects. The multi-energy calibration (MEC) method was proposed aiming at simplifying the calibration process in atomic spectrometric techniques and making matrix matching feasible. MEC requires preparation of standards by mixing sample aliquots with either a blank or a reference solution, which is not easy to perform for solid samples, especially when complex matrices are involved. In particular for LIBS, this strategy can be hindered by sample heterogeneity and differences in particle size distribution. In turn, sample preparation by fusion is an interesting approach to minimize these drawbacks. In this context, this work proposed MEC and borate fusion as alternatives for quantitative analysis of high silicon content samples by LIBS. Boron and lithium, constituents of the flux, were used as internal standards (ISs) aiming at minimizing strong absorption effects caused by matrix components and improving the accuracy of the results. The accuracy and precision of MEC-LIBS was demonstrated by determining Al₂O₃, Fe₂O₃, and TiO₂ in SRM 2703 (sediment for solid sampling) and SRM 679 (brick clay); relative errors from −4 to 15% and relative standard deviations (RSD) between 4.0 and 7.0% were attained, showing that the approach is feasible for quantitative analysis of complex samples. The limits of detection were between 0.4 and 0.6% for all analytes.