Novel Laser Sampling Technique for Inductively Coupled Plasma Atomic Emission Spectrometry

Abstract

A novel laser sampling technique, back-surface ablation, has been developed for ICP-AES. Samples are coated onto a transparent substrate and a laser beam is irradiated onto the sample through the substrate instead of sampling directly from the sample surface. As part of the sample is vaporized by the laser beam, a high pressure develops at the sample–substrate interface. The sample at the laser spot is explosively and completely removed by the expanding vapour. Sampling efficiency is up to ten times higher than conventional ‘front-surface’ laser sampling. Also, preferential vaporization is minimized because of complete removal of the sample at the laser spot. The risk of inaccurate chemical analysis associated with non-stoichiometric thermal vaporization in front surface laser sampling is reduced. Two methods of calibration,viz., standard additions and calibration with standards in a poly(vinyl alcohol) matrix, were used for quantitative elemental analysis of household paints using front- and back-surface ablation–ICP-AES. Internal standards were used to compensate for pulse-to-pulse laser energy fluctuation and sample thickness variation across a sample. Ten elements with different thermal properties and at concentrations ranging from 10 to 1000 ppm were determined and the elemental concentrations were compared with those of microwave digestion/solution nebulization–ICP-AES. Back-surface ablation appears to be more accurate than conventional front-surface ablation.

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