Internal standard fused glass beads for high silicon content sample analysis by laser-induced breakdown spectrometry

Abstract

The direct analysis of high silicon content samples by Laser-Induced Breakdown Spectrometry (LIBS) is a good alternative, since the decomposition of samples with refractory characteristics is not an easy task. However, poor precision and difficulty in performing quantitative analysis due to particle size effects, heterogeneity and matrix effects are challenges which need to be overcome. An interesting approach to overcome these issues enabling quantitative measurements of Al, Ca, Fe, Mg, Si and Ti in a variety of samples by LIBS is the use of the borate fusion process for sample preparation. Results for fused glass beads were compared to those obtained for samples pressed into pellets, which is the most common sample preparation procedure for analysis by LIBS. The linearity of calibration curves (R²) using different certified reference materials (CRM) pressed into pellets was worse (R² = 0.2105–0.9276) than that observed for those fused into glass beads (R² = 0.5640–0.9778), but this still shows a lack of linearity. To minimize strong absorption effects caused by the matrix composition and improve the linearity, accuracy and precision of results for fused glass beads, B and Li, present in the flux, were used as internal standards. Better results were achieved for Fe, Mg and Si when the B emission line was used as an internal standard, while the Li emission line worked better for the measurement of Al, Ca and Ti. The accuracy of the method was evaluated by analyzing a CRM of soil (NIST SRM 2711) and relative errors of around 8% were found, indicating that internal standardization enables quantitative measurement by LIBS in those matrices.