Inductively coupled plasma isotope examples

Since about 1990, however, inductively coupled plasma (ICP, see Section 2.1.5) has become increasingly popular at the expense of TI in this area of application [9]. Although TI can provide better results for some analyses, ICP is more versatile and requires less sample preparation effort. Moreover, the advantage of better precision for TI is often compromised by the sample, for example, sample inhomogeneity. Nevertheless, there are still many examples where TI is used, such as for isotope analysis [10-13] and geochronology [14]. 

The table below lists some common spectral interferences that are encountered in inductively coupled plasma mass spectrometry (ICP-MS), as well as the resolution that is necessary to analyze them.1 The resolution is presented as a dimensionless ratio. As an example, the relative molecular mass (RMM) of the polyatomic ion 15N160+would be 15.000108 + 15.994915 = 30.995023. This would interfere with 31P at a mass of 30.973762. The required resolution would be RMM/8RMM, or 30.973762/0.021261 = 1457. One should bear in mind that as resolution increases, the sensitivity decreases with subsequent effects on the price of the instrument. Note that small differences exist in the published exact masses of isotopes, but for the calculation of the required resolution, these differences are trivial. Moreover, recent instrumentation has provided rapid, high-resolution mass spectra with an uncertainty of less than 0.01%. 

The technique involves the use of an inductively coupled plasma to convert trace elements to their gaseous ions followed by analysis of these ions by mass spectrometry. Examples include the quantitative analysis of trace copper by isotope dilution and the analysis of trace contaminants in boron, indium phosphide and reagent acids. 

Inductively Coupled Plasma Mass Spectrometry (ICP/MS) is a powerful technique for elemental and isotope analysis which has undergone extensive development over the last decade by a number of research groups (1,2,3). These research efforts have led to the recent development of commercially available ICP-MS systems which, by virtue of their novelty, are now just beginning to demonstrate capabilities well suited to the characterization of materials used in the semiconductor industry. This paper will outline the principles of ICP-MS and provide some examples of the instrumentation s analytical capabilities. 

Thermal ionization. Solid samples are heated to a high temperature (1000-1800 °C) in a vacuum, producing either positive or negative ions. The TIMS method has been used, for example, to obtain records of seawater Sr/ Sr and from biogenic carbonate (e.g. McArthur et al. 2001 Burton Vance 2000). This technique permits precise isotope ratio measurements (external reproducibility <5ppm for Nd/ Nd and Sr/ Sr ratios), but it is restricted to those elements with a relatively low first ionization potential. Inductively-coupled plasma. Sample solutions, or laser ablation products, are ionized in a stream of argon within a plasma torch. The advantage of this technique is that the plasma... 

The gas chromatograph may be interfaced with atomic spectroscopic instruments for specific element detection. This powerful combination is useful for speci-ation of different forms of toxic elements in the environment. For example, a helium microwave induced plasma atomic emission detector (AED) has been used to detect volatile methyl and ethyl derivatives of mercury in fish, separated by GC. Also, gas chromatographs are interfaced to inductively coupled plasma-mass spectrometers (ICP-MS) in which atomic isotopic species from the plasma are introduced into a mass spectrometer (see Section 20.10 for a description of mass spectrometry), for very sensitive simultaneous detection of species of several elements. 

It is well-known that Br can substitute for Cl in tissues (Goodwin et al., 1969). The two stable isotopes of Br could effectively be used by inductively coupled plasma mass spectrometry (ICP-MS) for studies of the dynamics of Br transport in the body, and also in the much-neglected field of Cl metabolism in human subjects (Janghorbani et al., 1988). An important example of the last possibility relates the known disturbances in electrolyte (Cl and Br) metabolism in cystic fibrosis (Theile et al., 1985 Miller etal., 1986). 

This process shows an apparent simplicity, as stated by Gunther and Hattendorf [12], which might be one of the reasons for the increasing popularity of this technique. In theory, one just needs to put a sample inside the chamber, fire a few laser pulses, and a portion of the sample will be vaporized and swept into the inductively coupled plasma mass spectrometer (ICPMS). In a few seconds, the corresponding transient signals that can provide qualitative, quantitative, and isotopic information for tens of elements appear on the screen. Examples of typical LA-ICPMS signal profiles are shown in Figure 39.3. 

Inductively Coupled Plasma Mass Spectrometry (ICPMS) is nowadays the method of choice in many stndies dne to its sensitivity, simplicity (sample preparation is rarely required), cost, throughput, and availability of isotopic composition information. Several examples of deployment of ICPMS for all kinds of assays will be presented throughout this chapter. 

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