Quantitative Study of Spodumene by Time-of-Flight Secondary Ion Mass Spectrometry (tof-SIMS)

In this paper, the quantitative feasibility of time-of-flight secondary ion mass spectrometry (tof-SIMS) for major and minor elements in spodumene was evaluated in terms of calibration method with a matrix-matched or non-matrix-matched standard and an internal standard element using Al or Si. The matrix-matched standard calibration method was studied using spodumene 503R as the external standard and unknown sample, with signal intensities collected under positive ion mode using 100 µm of raster size. The sensitivities of Li, Na, Al, Si, Mn, and Fe were obtained by applying the sample-standard bracketing method, and the corresponding concentrations were given as the division of signal intensities by sensitivities. It was found that there were no significant differences between concentration results using Al and Si as the internal standard element. After 100% normalization, the concentrations at a 95% confidence level of matrix Li₂O, Al₂O₃, and SiO₂ in oxide form were found to be 7.62 ± 0.27%, 27.68 ± 0.10%, and 64.32 ± 0.29%, respectively, which agreed with those from LA-ICPMS measurements and/or EPMA analyses. The comparison of the minor components including Na₂O, MnO, and FeO showed that the contents from tof-SIMS were consistent with references from LA-ICPMS, giving ratios within 0.98-1.02. Furthermore, the element behavior investigation of NIST SRM 610 showed that the ionization efficiencies differentiated among the studied elements, resulting in far lower sensitivities of Li, Na, Mn, and Fe in spodumene than the values from the proposed matrix-matched standard calibration method. Thus, the matrix-matched standard calibration method for element determination of spodumene by tof-SIMS was recommended. The successful determination of major and minor elements in spodumene also promises the future application of tof-SIMS to trace element quantification.