In atomic mass spectrometry

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. 

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. 

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. 

A mass spectrometer is an instrument that produces ions and separates them according to their mass-lo-charge ratios, m/z. Most of the ions we will discuss are singly charged so that the ratio is simply equal to the mass pumber of the ion. Several types of mass spectrometers are currently available from instrument manufacturers. In this chapter, we describe the three types that are used in atomic mass spectrometry the quadra-pole mass spearomeier. the lime-of-ftighl mass spectrometer. and the doubk-foctising mass spectrometer. Other types of mass spectrometers are considered in Chapter 20. which is devoted to molecular mass spectrometry. I he first column in Table I l-l indicates the types of atomic mass spectrometry in which each of the three types of mass spectrometer is usually applied. 

Describe how the isotope dilution technique is used in atomic mass spectrometry. 

There are three primary instrumental approaches to eliminating or reducing interferences in atomic mass spectrometry (1) use of high mass resolution ICP-MS (HR-ICP-MS) (2) use of a collision cell to break apart polyatomic interferences (3) use of gas phase chemical reactions in a reaction cell to eliminate polyatomic interferences. The approach of changing the instrument operating conditions to form a cool or cold plasma has been discussed. 

Other Mass Spectrometers. Spectrometers such as ion traps and ion cyclotron resonance have also been used in atomic mass spectrometry, but have not yet been incorporated into a commercial instrument. The former instrument has the advantage of ion storage and ion-molecule reaction capability, while the latter instrument is capable of extremely high resolution. 

Spectra such as that in Figure Il-I5b led early workers in the field of ICPMS to have hopes of an interference-free method. Unfortunately, this hope was not realized in further studies, and serious interference problems are sometimes encountered in atomic mass spectrometry just as in optical atomic spectroscopy. 

What types of interferences are encountered in atomic mass spectrometry ... 

Gerhch D. (2004) Applications of rf Helds and collision dynamics in atomic mass spectrometry. J. Anal. At. Spectrom. 19 581 590. 

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