Atomic spectrometry update. Atomic mass spectrometry

Abstract

The review this year is dominated by the large number of publications on AMS, ICP-MS and SIMS. The increasing number of new AMS installations bears witness to the increasing interest in the technique now that smaller and simpler systems are becoming more widely available. Although high-energy systems still have an important role to play, each of the new systems was compact and of relatively low-energy. The development of ion sources that can accept gaseous samples has lowered the sample size requirement for radiocarbon analysis such that it is now little more than the background level. Contamination therefore has become a major issue. The numerous papers on improvements to SIMS analysis demonstrate the important role the technique plays in materials science. Unlike for most of the techniques covered, fundamental studies on SIMS analysis abound with particular attention being paid to understanding the ionization processes and the representativeness of the measured ion beam. Quantum chemistry calculations have been used to determine the fundamental processes occurring in cell ICP-MS. This approach contrasted with the empirical studies that are normally undertaken. Although many applications are still being published using collision and/or reaction cell ICP-MS, there were fewer novel or fundamental studies than in previous years. This suggests that cell ICP-MS is becoming a more routine method of analysis. The same can probably also be said of hyphenated ICP-MS methods for speciation, which continues to grow in importance but which is very much at the applied end of the spectrum. Speciation is notable in that it cuts across a number of MS techniques and conventional organic MS techniques are increasingly being investigated for structure determination of organometallic species. Each year seems to find further expansion of MC-ICP-MS into ‘non-traditional’ isotope analysis. This was the year for Ti isotope analysis.

This Update is the 21st and last annual review on atomic mass spectrometry and follows the same format as last year's.¹ Although an attempt is made to consider all relevant refereed papers, conference abstracts, reports, book chapters and patents for inclusion, the content of the review is highly selective. The selection of papers is based on criteria applied to focus sharply on the most significant developments in instrumentation and methodology or improved understanding of the fundamental phenomena involved in the MS process. The main ruling criterion for all speciation papers is that the work should involve or be intended for the study of natural systems. For example, the study of synthetic metal clusters is generally not included whereas the determination of organometallic compounds in environmental samples is.

Applications of atomic MS are not covered in this Update and readers are referred to the Updates on Industrial Analysis: Metals, Chemicals and Advanced Materials,² Environmental Analysis³ and Clinical and Biological Materials, Food and Beverages.⁴ Other, fundamental, reviews appear on X-ray fluorescence spectrometry⁵ and atomic emission, absorption and fluorescence spectrometries.⁶

Throughout this review, the term molecular ion will be restricted to denote only the positive or negative radical ion formed by removal or capture, respectively, of an electron. In contrast, addition of a proton or cation to a neutral molecule gives molecular adduct ions. Deprotonated molecules are considered as fragments.

Although reproducibility or precision is a key figure of merit in MS, there is no agreed format for quoting it. The reader can assume that values of precision given in this Update as a percentage correspond to the RSD unless otherwise specified. For isotope ratios, however, values of precision are generally given as the SD of a permil value.

It is a widespread phenomenon that analytical techniques in general and MS in particular spawn a large number of abbreviations and acronyms. A glossary of all abbreviations used in this Update appears at the end of the review. Most abbreviations are not defined in the text but those which are unlikely to be commonly known are defined in the text when used first and again in the glossary. It should be noted that throughout the text the letter C denotes the element carbon and not the unit of charge, the coulomb.

The writing team would welcome feedback from readers of this review and invite you to complete the Atomic Spectrometry Updates questionnaire on http://www.asureviews.org.