Laser-induced breakdown spectroscopy: a unique analytical tool for the geosciences

Abstract

Introduction Knowledge about the chemical composition of minerals, rocks and soils is of fundamental importance in the earth and environmental sciences (i.e. geosciences). Historically, during the late-19 and mid-20 centuries classical wet chemical analytical methods were the means of determining the elemental composition of such geological materials. Since then, intensive research in analytical inorganic chemistry has led to the development of a multiplicity of rapid and accurate instrumental analytical techniques for use in the laboratory that can be applied to elemental analysis across the periodic table. This has been of particular benefit to research in the geosciences, where the need for chemical data has continuously expanded with regard not only to the type of elements and their concentration levels, but also application to a wide variety of geological materials across the solid–liquid–gas spectrum. One of the enduring needs within the geoscience community has been the availability of analytical instrumentation capable of routine use outside the laboratory setting. Laser-induced breakdown spectroscopy (LIBS) is one of the very few current analytical technologies suitable for routine use outside the laboratory and has a persuasive set of advantages that makes it ideally suited for chemical analysis in the field. These include rapid analysis with a compact and lightweight instrument by a single individual of most types of natural materials under ambient environmental conditions in real time, and with little to no sample preparation. Although such a field analytical technique does not provide the level of elemental detection and analytical precision possible with laboratory instruments, it nevertheless provides an efficient and invaluable capability to the field investigator. To date, LIBS has been applied widely across the geosciences in sub-fields as diverse as mineralogy and petrology, volcanology, sedimentology, natural resources exploration and exploitation, pedology, and geoarchaeology. The most common applications of LIBS in the analysis of geological materials include: (i) elemental detection and identification; (ii) quantitative elemental analysis; (iii) microscale geochemical mapping; (iv) discrimination and classification of minerals and rocks of similar character via spectral matching against an assembled spectral library; and (v) determination of sample geographical origin and provenance. Although LIBS is not able to address all questions arising in geochemical research and practice due to some inherent limitations in sensitivity, it can excel for specific geoscience applications.