Sources for atomic spectrometry

Thus for a metal oxide (XY), from Hxy/ux = Ny/Kn the ratio of the number densities for the metal oxide and the metal atoms (nx) as well as the degree of dissociation can be calculated when the plasma temperature, the partial pressure of oxygen in the plasma f pY) and the dissociation constant are known. For refractory oxides of relevance in dc arc analysis, these data are listed, for example, in Ref. [7]. 

The rotational temperatures are relevant to all processes in which molecules, radicals and their dissociation products are involved. They can be obtained from the intensity distribution for the rotational lines in the rotation-vibration spectra, as described by Eqs. (83-90). The molecules OH, CN etc. have often been used to measure temperature (see e.g. Refs. [21-23]). 

The gas temperature is determined by the kinetic energy of the neutral atoms and the ions. It can be determined from the Doppler broadening of the spectral lines, as described by Eq. (49). However, to achieve this contributions of Doppler broadening and temperature broadening have to be separated, which involves the use of complicated deconvolution procedures as e.g. shown for the case of glow discharges in Ref. [24]. 

Whereas the rotational and the gas temperature are particularly relevant to the evaporation processes in the plasma, the electron temperature, being a measure of the kinetic energy of the electrons, is relevant to the study of excitation and ionization by collisions with electrons. This is an important process for generation of the analyte signal both in optical atomic emission and in mass spectrometry. The electron temperature can be determined from the intensity of the recombination continuum or of the Bremsstrahlung , as described by Eq. (57). 

The excitation temperature describes the population of the excited levels of atoms and ions. Therefore it is important in studies on the dependence of analyte line intensities on various plasma conditions in analytical emission spectrometry. 

In atomic spectrometry the sample material is brought into a high-temperature source (plasma, flame, etc.) with the aid of a sampling device. The sample, which 

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Fig. 5. Sources for atomic spectrometry (Reprinted with permission from Ref. [28].)...

Sources for atomic spectrometry include flames, arcs, sparks, low-pressure discharges, lasers as well as dc, high-frequency and microwave plasma discharges at reduced and atmospheric pressure (Fig. 5) [28], They can be characterized as listed in Table 2. Flames are in thermal equilibrium. Their temperatures, however, at the highest are 2800 K. As this is far below the norm temperature of most elemental lines, flames only have limited importance for atomic emission spectrometry, but they are excellent atom reservoirs for atomic absorption and atomic fluorescence spectrometry as well as for laser enhanced ionization work. Arcs and sparks are... 

One unique type of MS, ICP-MS, needs to be discussed separately because it does not deal with molecular species, but with atomic ones. The inductively coupled plasma is a common atomization source for atomic spectrometry. This sample preparation/ sample introduction mode has been coupled with an MS to yield an instrument capable of trace level elemental analysis. Each element has a unique set of isotopes in known proportions. These can be used to quantify the element. In the case of elements with overlapping isotopic mass numbers, simple deconvolution can be used to give results for each. ICPMS has very low detection limits. 

Radio-frequency glow discharges are very useful sources for atomic spectrometry. By means of a bias potential in the vicinity of the sample, insulating samples such as ceramics can be directly ablated and analyzed by AES [295]. 

A gas plasma provides a very high temperature excitation source for atomic spectrometry. Quantitative analysis for a large number of elements may be achieved rapidly. By combination with a mass spectrometer, individual isotopes may be identified and quantified. 

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