Quantification of ZnSO₄ in aqueous solution by liquid-solid matrix transfer and double-pulse laser-induced breakdown spectroscopy

The concentration of zinc sulfate in aqueous solution was measured by double-pulse (DP) laser-induced breakdown spectroscopy (LIBS). ZnSO₄ is an essential chemical in the spin bath liquid used for industrial production of viscose fibers from cellulose. For DP-LIBS the ZnSO₄ analyte was transferred from the water matrix to a solid cellulose matrix (commercial filtration paper). Various emission lines of Zn in the UV/VIS range were measured at 560 different positions on the dried paper sample. The line intensities were strongly varying across the sample as observed by LIBS imaging. Signal analysis revealed broad and bimodal distributions of intensities. Normalization of analyte intensities to emission lines from the matrix reduced the apparent inhomogeneity of samples and achieved monomodal signal histograms and good analytical figures of merit. The mean error of predicted concentration of ZnSO₄ in aqueous solutions was 0.19 g/L (samples with concentration C_ZnSO4 = 0–11 g/L). Applications of DP-LIBS in viscose fiber production is envisaged.