Atomic Spectrometry Update—Industrial Analysis: Metals, Chemicals and Advanced Materials

Abstract

This Atomic Spectrometry Update is the latest in an annual series appearing under the title ‘Industrial Analysis’. The structure of the review is broadly the same as in previous years.

Direct analysis of solid samples continues to be a prime objective for industrial atomic spectrometry and laser sampling techniques (for both MS and AES) are becoming increasingly common, especially in the field of metals analysis. More traditional approaches using glow discharge sources are, however, still undergoing development and are frequently applied to the determination of elemental depth profiles. A novel sampling system has even been described which permits elemental mapping over many tens of square centimeters of a sample surface at one time using GD-AES. The development of rf GD sources is beginning to extend the applications of GD-MS and GD-AES to non-conductive samples and may be particularly useful in the field of advanced materials. However, although seldom reflected in the volume of published literature, XRF still often remains the method of choice within industry for direct analysis of solid samples. The capabilities of the technique have recently been extended to include spatially resolved analysis, through the development of instruments with microbeam capabilities and of software packages that are capable of carrying out the analysis of small, irregularly shaped particles, and this is now beginning to be exploited. TXRF continues to become more established within the semiconductor industry for the determination of contaminants on wafer and device surfaces and the applications of the technique have recently been extended to include the analysis of light elements (e.g., Al, C, F, Mg, N, Na and O). It has been estimated that there are now over 100 TXRF instruments in use within the semiconductor industry, and the possibility of establishing an industry wide ISO standard method based around the technique has been discussed at a recent conference. XRF is also frequently the method of choice for many process control applications. In the field of catalyst analysis, however, traditional solid sampling techniques such as SIMS, XPS and electron microscopy (usually in combination with XRD) continue to dominate.

Rapid multi-element techniques, such as ICP-MS, are becoming more widely available and the capabilities are being exploited for a diverse range of ‘fingerprinting’ applications (precious metal identification, oil–source rock correlations, origin of illicit drugs, archaeological artefact correlations, etc.). The range of elements covered by ICP-MS is being extended to include ‘difficult’ elements (i.e., those which suffer from molecular ion interferences) through the use of novel sample introduction techniques and/or cool plasmas. Reports on the application of high resolution ICP-MS are starting to appear in the literature and it is clear that this technique offers very high potential, particularly for applications in the nuclear industry and for the analysis of advanced materials. At the moment, however, the number of such reports is relatively small, due to the limited availability and high cost of the instrumentation. In cases where multi-element capability is not required, it is often difficult to justify expensive instrumentation such as that described above, and so many workers are developing innovative approaches to improve sensitivity and eliminate interferences with cheaper alternatives such as FAAS and ETAAS. A large proportion of such work has to some extent been stimulated by the commercial availability of robust and automated sample preparation and sample introduction equipment (ultrasonic nebulizers, thermosprays, direct injection nebulizers, on-line matrix separation/preconcentration systems, hydride generation/desolvation systems, etc). Direct injection nebulization (DIN) appears to offer particular advantages for ICP-AES and ICP-MS analysis, since it allows direct analysis of samples containing volatile analytes (e.g., As, Hg and P in organic feedstocks), and when combined with flow injection, can allow extremely rapid analysis (up to 240 samples per hour).

Every year sees a growing awareness regarding the impact of industrial products and processes on the environment and this is the driving force for much of the research in the field of atomic spectrometry at the current time. Methods for determination of total element concentrations are fairly well established, although developments in ICP-AES (e.g., axially viewed plasma, ultrasonic nebulization) have meant that this technique may be starting to undergo something of a renaissance, as it can now be used for applications which, a few years ago, would have required the use of a more sensitive technique such as ICP-MS or ETAAS. The extension of the UV wavelength range of some newer ICP-AES instruments to allow determination of chlorine down to ppm levels also increases the attractiveness of the technique for environmental applications. In many cases, however, determination of total element concentrations in environmental samples is not sufficient, since it is well known that toxicity can vary enormously depending on the chemical form of the element. Methods for element speciation are much less well developed than those for total element concentrations and so the former is a very active field of research at the present time. Most of the work reported is concerned with development of methods for extracting, and if necessary derivatizing, chemical species prior to measurement using a chromatographic system coupled with an atomic spectrometric detector. In view of the complexity of these problems, it seems likely that this will remain an active area of research for many years to come.