Information retrieval from the inductively coupled plasma

Abstract

This paper describes various means by which information can be derived from the signals obtained from inductively coupled plasmas. The first part describes how Bayesian analysis may be used to infer the species contributing to observed spectra and to estimate the contributions of those species to the intensity in each spectral channel. An example is given in which a synthetic mixture of rare earths (Nd, Sm, Eu and Gd), in the presence of a high level of Ba, is analysed and an inferred spectrum synthesized that fits the observed data to within three standard deviations at all spectral positions. The second part deals with the use of correlated measurements as a means of reducing noise and improving the precision of analytical measurements. The use of rapid peak jumping in quadrupole MS to emulate simultaneous measurement is shown to offer significant improvements in the determination of lead isotope ratios with precisions of the order of 0.04% being achieved. Optical detection of ICP spectra has been revolutionized by the introduction of array detectors. It has been reported that simultaneously measured line and near background signals have a degree of mutual correlation and this results in noise reduction on their subtraction. Under ideal conditions the removal of correlated noise yields improvements in detection limits of about one order of magnitude. The final part describes how the ICP and other atomic spectrometric sources can be employed to obtain molecular information. The two basic approaches are to employ prior separation of the molecular species or to use tunable ionization sources whose conditions can be varied so as to provide both atomic and molecular information. A specific example of prior separation given here is the coupling of capillary electrophoresis to ICP-MS and its use for the speciation of Cr ^III and Cr ^VI and Ni-humic acid complexes.