Comparative study of the matrix effect in Cl analysis with laser-induced breakdown spectroscopy in a pellet or in a dried solution layer on a metallic target

Chlorine content brought by salt in a composite powder was determined when the sample was prepared in pellet or first dissolved into solution and then dropped on the surface of a pure metallic target. The purpose is to address the matrix effect when the mixture powders of different kinds of mineral salt are used, and to compare the influence of the matrix effect for two kinds of sample preparation. Three types of powder mixture, NaCl + KBr, NaCl + MgSO₄, and NaCl + Na₂CO₃, were then first prepared with well controlled proportion of salt (NaCl) and mineral salt powder. On one hand, pellets were prepared for laser ablation. On the other hand, mixture powder was dissolved in deionized water for analysis with surface-assisted laser-induced breakdown spectroscopy (LIBS) of solution by dropping it on the surface of a pure aluminum target. Calibration curves were established for the pellets and the solutions, respectively. The slopes of these curves provided an assessment of the matrix effect related to the different mineral salt matrix and different forms of the sample preparation. The similar responses from chlorine for the solution samples showed absence of matrix effect for analysis with the surface-assisted solution analysis configuration. This result was further confirmed by the consistence of the measured temperatures and the electron densities of the produced plasmas. In contrast, the slopes of the chlorine calibration curves exhibited significant variation for different pellet samples corresponding to different powder mixtures, which is an indication of matrix effect in the LIBS analysis of the pellet samples.