Analysis of Cuban nickeliferous minerals by laser-induced breakdown spectroscopy (LIBS): non-conventional sample preparation of powder samples

Abstract

In the present study, a new method to quantify Al, Cr, Fe, Mg, Mn, and Ni in nickeliferous minerals by laser-induced breakdown spectroscopy (LIBS) is proposed. Thirty-three mineral powder solid samples, previously analyzed by inductively coupled plasma optical emission spectroscopy (ICP OES), and two certified reference materials were used as reference samples for the calibration, and an innovative sample preparation was implemented and described. The use of Bi, Sc and Y as internal standards and the usefulness of other normalization modes were assessed in the normalization of the LIBS emission signals from the analytes. A slurry was made by mixing the solid mineral samples, grinding them into a fine powder, and using water in different proportions. Then, the mixture was homogenized and instantly weighed with a constant mass of a standard liquid solution of Y, which was preliminarily chosen as the internal standard among the three elements assessed, and a 10% (w v⁻¹)-polyvinyl-alcohol solution. After 2 h in an oven at 50 °C, the samples, which were immobilized in the polymer film, were subjected to LIBS analysis. The best sample dilution, emission line and normalization of the emission signal were selected for each analyte. The concentrations of the assessed analytes varied from 0.49 to 26.82% for Al, 0.40 to 2.21% for Cr, 6.8 to 52.93% for Fe, 0.41 to 20.53% for Mg, 0.11 to 1.50% for Mn and 0.23 to 3.02% for Ni. The standard error of validation (SEV) for the newly developed method was 1.34, 0.16, 6.08, 0.88, 0.09, and 0.35% for Al, Cr, Fe, Mg, Mn, and Ni, respectively.