Optical Spectrometry Coupled with Laser Ablation for Analytical Applications on Solids

Abstract

The possibilities of localised analysis, analysis of both conducting and nonconducting samples, absence of sample preparation and operation at atmospheric pressure inherent to the laser ablation (LA) techniques are of great interest for industrial applications, as they have the premises for becoming general, all-round and robust direct solid-sample analytical techniques. A general description of the laser ablation process, under conditions relevant to analysis, is presented, with special importance given to the choice of the laser source, as recently published results show that the black-box approach, that was previously adopted, is insufficient. The use of sources in the UV (excimer lasers or frequency-tripled or quadrupled Nd: YAG lasers) is shown to be essential for reproducibility. To illustrate the possibilities and limitations of laser ablation, three different analytical techniques are discussed, each making use of a particular phase of the laser ablation process: in LA-OES, that is Optical Emission Spectroscopy, the direct emission of the produced plasma is analysed; in LA-LIF, transitions of the cooled atomic vapour are resonantly excited by a dye-laser; in LA-ICP-OES, the laser is only used as a sampling technique, and the analysis is done on the subsequently formed aggregates by vaporising them in a plasma torch. In each case, the set-up is described and the results obtained on the detection limits and the reproducibility are discussed to show the possibilities of the techniques and ways of further improvement.