Chemical optical atomic emission

F.K. Fong, Nonradiative processes of rare-earth ions in crystals 317 J.W. O Laughlin, Chemical spectrophotometric and polarographic methods 341 S.R. Taylor, Trace element analysis cf rare earth elements by spark source mass spectroscopy RJ. Conzemius, Analysis of rare earth matrices by spark source mass spectrometry 377 37D. E.L. DeKalb and V.A. FasseL Optical atomic emission and absorption methods 405 37E. A.P. D Silva and V.A. Fassel, X-ray excited optical luminescence of the rare earths 441 F.W.V. Boynton, Neutron activation analysis 457... 

The analytical chemistry of rare earths has been reviewed by Banks and Klingman (1961), Loriers (1964), Ryabchikov (1959), and Ryabchikov and Ryabukhin (1964). Fassel (1961) reviewed the analytical spectroscopy of rare earth elements. In volume 4 of this Handbook chapters can be found on the chemical spectrophotometric and polarographic methods (O Laughlin 1979), spark source mass spectrometry (Conzemius 1979, Taylor 1979), optical atomic emission and absorption (DeKalb and Fassel 1979), X-ray excited optical luminescence (D Silva and Fassel 1979), neutron activation (Boynton 1979), mass spectrometric stable isotope dilution analysis (Schuhmaim and Philpotts 1979), and shift reagents and NMR (Reuben and Elgavish 1979). 

Compared with the sensors for atoms and radicals, the calibration of EEP sensors is also somewhat specific. To calibrate detectors of atomic particles, it will be generally enough to determine (on the basis of sensor measurements) one of the literature-known constants, say, tiie energy of parent gas dissociation on a hot Hlament. For the detection of EEPs when nonselective excitation of gas is taking place, in order to calibrate a sensor use should be made of some other selective methods detecting EEPs. The calibration method may be optical spectroscopy, chemical and optic titration, emission measurements, etc. 

The basic processes in optical atomic spectrometry involve the outer electrons of the atomic species and therefore its possibilities and limitations can be well understood from the theory of atomic structure itself. On the other hand, the availability of optical spectra was decisive in the development of the theory of atomic structure and even for the discovery of a series of elements. With the study of the relationship between the wavelengths of the chemical elements in the mid-19th century a fundament was obtained for the relationship between the atomic structure and the optical line emission spectra of the elements. 

Today, analyses of bulk fossil chemistry are largely conducted by inductively coupled plasma (ICP) atomic emission spectrometry (AES), ICP mass spectrometry (MS) or ICP optical emission spectrometry (OES) techniques (e.g. Rosenthal et al. 1999 DeVilliers et al. 2002 Green et al. 2003). These techniques permit rapid and precise (c. 1% for many elements) measurement of a number of chemical constituents simultaneously. ICP-MS offers higher sensitivities than AES and OES, enabling measurement of more elements and smaller sample sizes. 

Emission spectrometry using chemical flames (flame atomic emission spectrometry, FAES) as excitation sources is the earlier counterpart to flame atomic absorption spectrometry. In this context emission techniques involving arc/spark and direct or inductively coupled plasma for excitation are omitted and treated separately. Other terms used for this technique include optical emission, flame emission, flame photometry, atomic emission, and this technique could encompass molecular emission, graphite furnace atomic emission and molecular emission cavity analysis (MEGA). 

ESCA electron spectroscopy for chemical analysis (X-ray photoelectron spectroscopy) ESI electrospray ionization ET-AAS (Also denoted GFAAS, EAAS, EA-AAS, ETAAS, ETA-AAS) electrothermal atomization atomic absorption spectrometry ETA-CFS electrothermal atomization -coherent forward scattering (atomic magneto-optic rotation) spectrometry ETAES electrothermal atomization atomic emission spectrometry ETAES electrothermal atomization atomic fluorescence spectrometry ETA-LEI electrothermal atomization -laser enhanced ionization spectrometry... 

Plasma AES has several advantages (possibility for the qualitative and simultaneous multi-element analysis, measurements in the vacuum UV region, high sensitivity, low detection limits, less chemical interferences, low running costs) and it has become more and more important for the determination of traces in a great variety of samples. On the other hand, it does not compensate totally for any other instrumental method of analysis, but it compensates for those faults which might exist in other techniques. The complementary nature of plasma AES and AAS capabilities for trace elemental analysis is an important feature of these techniques. Plasma AES exhibits excellent power of detection for a number of elements which cannot be determined or are difficult to determine at trace levels by flame AAS e.g. B, P, S, W, U, Zr, La, V, Ti) or by electrothermal AAS (B, S, W, U). Thus, optical plasma emission and atomic absorption are not actually alternatives, but in an ideal way complement one another. 

Various techniques can be used for quantitative analysis of chemical composition, including (i) optical atomic spectroscopy (atomic absorption, atomic emission, and atomic fluorescence), (ii) X-ray fluorescence spectroscopy, (iii) mass spectrometry, (iv) electrochemistry, and (v) nuclear and radioisotope analysis [41]. Among these, optical atomic spectroscopy, involving atomic absorption (AA) or atomic emission (AE), has been the most widely used for chemical analysis of ceramic powders. It can be used to determine the contents of both major and minor elements, as well as trace elements, because of its high precision and low detection limits. 

Many methods used for qualitative analysis are destructive either the sample is consumed during the analysis or must be chemically altered in order to be analyzed. The most sensitive and comprehensive elemental analysis methods for inorganic analysis are ICP atomic emission spectrometry (ICP-AES or ICP optical emission spectrometry [ICP-OES]), discussed in Chapter 7, and ICP-MS, discussed in Chapters 9 and 10. These techniques can identify almost all the elanents in the periodic table, even when only trace amounts are present, but often require that the sample be in the form of a solution. If the sample is a rock or a piece of glass or a piece of biological tissue, the sample usually must be dissolved in some way to provide a solution for analysis. We will see how this is done later in this chapter. The analyst can determine accurately what elements are present, but information about the molecules in the sample is often lost in the sample preparation process. The advantage of ICP-OES and ICP-MS is that they are very sensitive concentrations at or below 1 ppb of most elements can be detected using these methods. 

Several techniques are currently available for the quantitative analysis of chemical composition, including (1) optical atomic spectroscopy (atomic absorption, atomic emission, and atomic fluorescence), (2) x-ray fluorescence spectros-... 

Fundamental quantities, such as wavelengths and transition probabilities, determined using spectroscopy, for atoms and molecules are of direct importance in several disciplines such as astro-physics, plasma and laser physics. Here, as in many fields of applied spectroscopy, the spectroscopic information can be used in various kinds of analysis. For instance, optical atomic absorption or emission spectroscopy is used for both qualitative and quantitative chemical analysis. Other types of spectroscopy, e.g. electron spectroscopy methods or nuclear magnetic resonance, also provide information on the chemical environment in which a studied atom is situated. Tunable lasers have had a major impact on both fundamental and applied spectroscopy. New fields of applied laser spectroscopy include remote sensing of the environment, medical applications, combustion diagnostics, laser-induced chemistry and isotope separation. 

Tungsten is usually identified by atomic spectroscopy. Using optical emission spectroscopy, tungsten in ores can be detected at concentrations of 0.05—0.1%, whereas x-ray spectroscopy detects 0.5—1.0%. ScheeHte in rock formations can be identified by its luminescence under ultraviolet excitation. In a wet-chemical identification method, the ore is fired with sodium carbonate and then treated with hydrochloric acid addition of 2inc, aluminum, or tin produces a beautiful blue color if tungsten is present. 

For intermediate temperatures from 400-1000°C (Fig. 11), the volatilization of carbon atoms by energetic plasma ions becomes important. As seen in the upper curve of Fig. 11, helium does not have a chemical erosion component of its sputter yield. In currently operating machines the two major contributors to chemical erosion are the ions of hydrogen and oxygen. The typical chemical species which evolve from the surface, as measured by residual gas analysis [37] and optical emission [38], are hydrocarbons, carbon monoxide, and carbon dioxide. 

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