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.