Enhancing Quantitative LIBS Determination of Lithium in Pegmatite Ores by Selecting Non-Self-Absorbed Emission Lines and Compensating for Temperature-Induced Signal Variation

Laser-induced breakdown spectroscopy (LIBS) was applied for the quantitative determination of lithium in four certified reference materials (CRMs) of lithium-bearing pegmatite ores. These CRMs cover a wide range of lithium concentrations (0.47 − 2.67 wt.% Li) and were prepared as graphite-bound pellets by hydraulic pressing. Calibration curves were constructed using five Li I emission lines at 460.3, 497.2, 610.4, 670.8, and 812.6 nm. Among them, the strong emission lines at 610.4 and 670.8 nm apparently exhibited low sensitivity due to self-absorption, whereas the weaker emission line at 460.3 nm showed nearly linear sensitivity with concentration, free from self-absorption effects. In this study, self-absorption and plasma temperature fluctuation were identified as the main factors affecting calibration performances such as sensitivity and accuracy, respectively. To avoid the degradation of sensitivity caused by self-absorption, weak emission lines must be selected. Once the influence of self-absorption is eliminated, the intensity fluctuations originating from plasma temperature variation become evident and can be corrected. By compensating for temperature-induced variation in the intensity of the non-self-absorbed Li I 460.3 nm line, a parameter proportional to the number density of Li atoms was obtained for calibration, resulting in a remarkable reduction in the root mean square error of calibration from 0.0287 wt.% to 0.0035 wt.% and a substantial improvement in accuracy. Our results suggest that, in univariate LIBS determination of lithium in pegmatite ores, selecting weak, non-self-absorbed emission lines and compensating for temperature-induced signal variation can substantially improve overall analytical performance.