Quantitative analysis of niobium in electropolishing solution by laser-induced breakdown spectroscopy using porous silicon†

For the construction of the international linear collider, mass production of niobium (Nb) superconducting cavities is essential. In the surface treatment of the Nb cavities, on-site analysis of electropolishing solution composed of hydrofluoric acid and sulfuric acid is desired. In this work, we analyzed the electropolishing solutions containing from 1.0 g L⁻¹ to 10.0 g L⁻¹ Nb by surface-enhanced laser-induced breakdown spectroscopy (surface-enhanced LIBS) that needs only a microvolume sample and simple operations. The sample solution was trapped on porous silicon (Si) fabricated by metal-assisted etching (metal-assisted chemical etching) through a wiping process. Nb emission lines were detected with low laser energy irradiation (2.0 mJ per pulse) onto the substrate. A regression model was built by partial least squares regression, and the Nb concentrations of test samples were predicted with a mean absolute error of approximately 0.4 g L⁻¹. To the best of our knowledge, this is the first report that applied LIBS to the analysis of the highly toxic electropolishing solution. The proposed method would be helpful for the quality control of surface treatment and the efficient use of solution.