Chapter 16 - LIBS study of geological samples coupled with chemometric methods

Abstract

Laser-induced breakdown spectroscopy (LIBS) offers an alternative tool for rapid and cost-effective in situ elemental analysis of all Earth materials, including rocks and minerals, in terrestrial and extraterrestrial environments. In addition, this technique addresses two nagging issues: (1) cumbersome sample preparation procedures prior to analysis and (2) sample loss during analysis. This chapter deals with three case studies involving characterization of important Earth materials to resolve fundamental issues faced by geoscientists. Elemental analysis based on LIBS data has led to rapid classification and in situ discrimination of rock samples (igneous, sedimentary, and metamorphic). The spectral signatures of heavy as well as light elements in rock samples helped in their discrimination, and the change in diameter of laser-ablated spots could be attributed to rheological variations. The chemical characterization of moldavite, an impact ejecta glass (expected to occur on Mars), showed the presence of various siderophile elements (chromium, iron, cobalt, and nickel), including iridium, a geochemical fingerprint of the chondrite meteorite impactor. LIBS data on moldavites are in good agreement with results obtained from electron probe microanalysis and other previous reports. The study of topsoil samples, a terrestrial analog, constitutes the third subject of investigation using the LIBS technique. The variable presence of magnetic phases in topsoil samples observed in mass magnetic susceptibility measurements is in agreement with LIBS data. The concentration of toxic elements predicted by the partial least squares regression approach concurs with magnetic measurements.