Mass spectrometry atomic

One of the more recent branches of atomic spectrometry, although perhaps the most exciting one, is atomic mass spectrometry, which has had a very important impact on science and technology. At present, atomic mass spectrometry is ordinarily performed using inductively coupled plasma ion sources and either a quadrupole or a scanning sector-field mass spectrometer as an analyser. The remarkable attributes of such a combination, being an indispensable tool for elemental analysis, include  

The success of inductively coupled plasma mass spectrometry (ICP-MS) has resulted in a broad availability of sophisticated instrumentation packages with user-friendly software and sample-analysis cookbooks at reasonable cost [10]. 

Despite these strengths, ICP-MS has also some important drawbacks, many of them related to the spectral isotopic and/or chemical interferences, which affect analyte signal intensities and, therefore, the applicability of the technique. The complexity of the optimisation of the methodological and operating conditions, the differences in the ionisation rates of the various elements, the sequential isotopic measurements and the limited speed of signal acquisition (a serious drawback in multielemental analysis of fast transient signals) are some other problems to be considered. 

In order to overcome, or at least minimise, such drawbacks we can resort to the use of chemometric techniques (which will be presented in the following chapters of this book), such as multivariate experimental design and optimisation and multivariate regression methods, that offer great possibilities for simplifying the sometimes complex calibrations, enhancing the precision and accuracy of isotope ratio measurements and/or reducing problems due to spectral overlaps. 

1 Fundamentals and Basic Instrumentation of Inductively Coupled Plasma Mass Spectrometry 

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Mass analysis is a relatively simple technique, with the number of ions detected being directly proportional to the number of ions introduced into the mass spectrometer from the ion source. In atomic mass spectrometry the ion source produces atomic ions (rather than the molecular ions formed for qualitative organic analysis) which are proportional to the concentration of the element in the original sample. It was Gray who first recognized that the inductively coupled plasma would make an ideal ion source for atomic mass spectrometry and, in parallel with Fassel and Honk, and Douglas and French developed the ion sampling interface necessary to couple an atmospheric pressure plasma with a mass spectrometer under vacuum. 

Figure 1.2 shows the basic instrumentation for atomic mass spectrometry. The component where the ions are produced and sampled from is the ion source. Unlike optical spectroscopy, the ion sampling interface is in intimate contact with the ion source because the ions must be extracted into the vacuum conditions of the mass spectrometer. The ions are separated with respect to mass by the mass analyser, usually a quadrupole, and literally counted by means of an electron multiplier detector. The ion signal for each... 

In atomic mass spectrometry, the rate of production of ions is measured directly. This is proportional to the concentration of ions, and hence atoms. A plot of ion count rate against atom concentration will therefore yield a straight line. 

D. W. Roppenall, G. C. Eiden, C. J. Barinaga, Collision and reaction cells in atomic mass spectrometry development status and applications, J. Anal. Atom. Spectrom., 19 (2004), 561-570. 

P. C. Uden, S. M. Bird, M. Kotrebai, P. Nolibos, J. F. Tyson, E. Block, E. Denoyer, Analytical selenoamino acid studies by chromatography with interfaced atomic mass spectrometry and atomic emission spectral detection, Fresenius J. Anal. Chem., 362 (1998), 447-456. 

Koppenaal, D.W., Atomic mass spectrometry. Anal. Chem., 64 (1992) 320R. 

Two other types of analytical methods are based on mass. In gravimetric titrimetry, which is described in Section 13D, the mass of a reagent, of known concentration, required to react completely with the analyte provides the information needed to determine the analyte concentration. Atomic mass spectrometry uses a ma.ss. spectrometer to separate the gaseous ions formed from the elements making up a sample of matter. The concentration of the resulting ions is then determined by measuring the electrical current produced when they fall on the suiface of an ion detector. This technique is described briefly in Chapter 28. 

Atomic spectroscopic methods are used for the qualitative and quantitative determination of more than 70 elements. Typically, these methods can detect parts-per-million to parts-per-billion amounts, and, in some cases, even smaller concentrations. Atomic spectroscopic methods are, in addition, rapid, convenient, and usually of high selectivity. They can be divided into two groups optical atomic spectrometry and atomic mass spectrometry. ... 

As shown in Table 28-1, several methods are used to atomize samples for atomic spectroscopic studies. Inductively coupled plasmas, flames, and electrothermal atomizers are the most widely used atomization methods we consider these three methods as well as direct current plasmas in this chapter. Flames and electrothermal atomizers are widely used in atomic absorption spectrometry, while the inductively coupled plasma is employed in optical emission and in atomic mass spectrometry. 

Plasma atomizers, which became available commercially in the mid-1970s, offer several advantages for analytical atomic spectroscopy. Plasma atomization has been used for atomic emission, atomic fluorescence, and atomic mass spectrometry. 

Atomic mass spectrometry has been around for many years, but the introduction of the inductively coupled plasma in the 1970s and its subsequent development for mass spectrometry led to its successful commercialization by several instrument companies. Today inductively coupled plasma mass spectrometry (ICP-MS) is a widely used technique for the simultaneous determination of more than 70 elements in a few minutes. Some other sources, such as the glow discharge, are also used for atomic mass spectrometry. Because the ICP predominates, however, the discussion here focuses on ICP-MS. 

Name four characteristics of inductively coupled plasmas that make them suitable for atomic emission and atomic mass spectrometry. 

Part V covers spectroscopic methods of analysis. Basic material on the nature of light and its interaction with matter is presented in Chapter 24. Spectroscopic instruments and their components are described in Chapter 25. The various applications of molecular absorption spectrometric methods are covered in some detail in Chapter 26, while Chapter 27 is concerned with molecular fluorescence spectroscopy. Chapter 28 discusses various atomic spectrometric methods, including atomic mass spectrometry, plasma emission spectrometry, and atomic absorption spectroscopy. 

Chapter 28 in this edition covers atomic mass spectrometry, including inductively coupled plasma mass spectrometry. Flame photometry has been deemphasized. 

In their reviews in the Journal of Analytical Atomic Spectrometry series. Atomic Spectrometry Update and Atomic Mass Spectrometry and X-Ray Fluorescence Spectrometry, Bacon etal. (1991, 1993) include various variants of X-ray fluorescence spectrometric techniques such as synchrotron radiation XRF microprobe (SRXRF-microprobe), X-ray microfluorescence (XRMF), total reflection XRF (TXRF), and synchrotron radiation XRF (SRXRF). This tradition continues in reviews in this journal dedicated to X-ray fluorescence spectrometry (Potts et al. 2001,... 

Reviews are also plentiful. Articles (Kop-penaal 1990, 1992) on atomic mass spectrometry in the fundamental review series in Analytical Chemistry include substantial coverage of ICP-MS, as do those in the reviews published in the Journal of Analytical Atomic Spectrometry (Bacon etal. 1991,... 

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