LITHIUM ANALYSIS: THE POTENTIAL APPLICATION OF LASER INDUCED BREAKDOWN SPECTROSCOPY (LIBS)

To analyze major and trace elements, there are a number of instruments that can be used including XRF, electron microprobe, ICP, and AA. Some of these, however, cannot accurately determine the element Li. Li-borate fluxes are commonly used to homogenize samples for XRF beads and to dissolve samples for ICP and AA, overwhelming the Li signal from the sample. Li analysis by electron microprobe is limited because the non-energetic Li X-rays are absorbed by the vacuum chamber window, greatly reducing Li intensities at the detector. Laser Induced Breakdown Spectroscopy (LIBS) provides a method for Li analysis to complement LA-ICP-MS. LIBS is a rapid and less expensive technique that has the potential to analyze samples in the field.

A LIBS system consists of a high-energy pulsed laser that ablates the sample, creating a short-lived, high-temperature plasma. As excited ions and atoms in the plasma cool and lose energy, electrons drop to lower energy levels and emit energy in the form of photons. This light is carried by fiber optic to a spectrometer, producing a spectrum of the intensities of wavelengths between 200 and 1000 nm.

Li analysis is only possible if one can produce a calibration curve. By analyzing standard glass beads from 0 to 15% Li with LIBS, a calibration curve will be created using the multivariate technique PLS-1. The bead recipe was 2.05 g Na tetraborate (used as a flux), 0.001224 to 0.109613 g Li tetraborate (source of Li), and 0.165 g QLO-1. QLO-1 is a quartz latite USGS rock reference powder used to provide a matrix similar to igneous rocks. The curve will be tested by comparing LIBS analyses to Li analyses of spodumene and lepidolite minerals determined by AA analysis.