Emission and Absorption Spectrometry

When matter is excited to high energy levels, by flame, electric arc or spark, it generally decomposes into atomic ions. The dissociation of electrons is reversed as the ion leaves the high-energy zone and results in emission which is characteristic of each ion present. Transitions include those in which electrons drop from outer to inner orbits as well. These phenomena are responsible for the application of emission spectrometry to elemental analysis over wide concentration ranges in the steel, aluminum, and other industries as well as a popular technique fw environmental and forensic problems. 

In or near the high energy zones, ions will trap electrons in reducing zones to form neutral atoms. When light of frequencies corresponding to electronic transitions of the atoms is passed through the atomic cloud, such frequency light will be absorbed by the atoms and excite them. The extent of such absorption is a measure of what is present and in what quantity. This phenomenon was first observed on solar radiation by Fraunhofer, who noticed precisely defined black lines in the solar spectrum. This led to the identification of the then- as-yet undiscovered new element, helium. Since then, atomic absorption spectrometry (AAS) has become one of the trace elemental, particularly metal, analytical chemists favorite techniques. 

Molecular Absorption Spectrometry, like AAS, exploits the nature and the amount of light absorbed by a sample. Analytical methodology based on these phenomena are very widely used. 

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Trace element analysis was carried out on the ash by fusing with lithium metaborate, followed by dissolution in 10 % hydrochloric acid. The resulting solution was analysed using atomic emission and absorption spectrometry (AA). The method has been described previously (9). 

Besides a number of special techniques, in principle, the following analytical methods are applicable for the qualitative and quantitative determination of isotopes emission and absorption spectrometry, NMR and ESR spectrometry, mass spectrometry and radioanalysis. 

Because the development of most spectrometric techniques is based on the flame, it is important to mention the contribution of Teclu for studying and understanding of the oldest "reagent," the flame.203 Without a good understanding of the phenomena that occur in the flame as a reagent, it is impossible to construct a reliable apparatus for atomic emission and absorption spectrometry. The invention of the spectroscope was followed by application of spectroscopic methods to analytical devices. The instruments became more sophisticated because of developments in physics, the science that determines apparatus requirements. 

F. J. Feldman, Internal Standardization in Atomic Emission and Absorption Spectrometry, Anal. Chem., 42 (1970) 719. 

Thienpont LM, Van Nuwenboeg JE, Reinauee H and Stockl D (1996) Validation of candidate reference methods based on ion chromatography for determination of total sodium, potassium, calcium and magnesium in serum through comparison with flame atomic emission and absorption spectrometry. Clin Biochem 29 501-508. 

Another important difference between flame emission and atomic absorption is the difference in their signals. The analytical signal in flame emission is the sum of all energies emitted as excited atoms drop to the ground state. The signal comes entirely from the emitting atoms. In atomic absorption the signal is the difference between the intensity of the source in the absence of analyte atoms and the decreased intensity obtained when analyte atoms are present in the optical path. This basic difference in the two techniques also contributes to the fact that detection limits of many elements are quite similar in emission and absorption spectrometry. 

A method based on designation of the wavelengths within a particular portion of a range of radiation or absorption, for example, ultraviolet (UV), emission, and absorption spectrometry. 

The symbols used are as follows / = angle of incidence, 0 = angle of diffraction (or reflectance), p = blaze angle of the grating, d = grating spacing. (Modified from Dean, J.A. and Rains, T.C., eds.. Flame Emission and Absorption Spectrometry, Vol. 2, Marcel Dekker, Inc., New York, 1971. Used with permission.)... 

A comparison of the detection limits for the rare earth elements in flame atomic emission and absorption spectrometry (table 37D.3 in section 2.2.5) allows certain conclusions to be made. The fuel-rich oxyacetylene and nitrous oxide-acetylene flames are very effective in producing free atoms of these elements and are the flames of choice for both atomic emission and absorption analysis. The emission detection limits are equal to or better than those obtained by absorption techniques, and thus flame atomic emission methods are generally superior. Future improvements in hollow cathode discharge tubes (or development of other primary sources) may lower the atomic absorption detection limits and thereby make the two techniques more complementary. However, Kinnunen and Lindsjo (1967) have emphasized that locating the proper rare earth ab-... 

Atomic Emission and Absorption Spectrometry of the Rare Earth Elements, in Mavrodineanu, R. ed.. Analytical Flame Spectroscopy (Philips GleoOampen-fabrieken, Eindhoven, Netherlands) pp. 379-410. 

Spectral overlap of emission and absorption wavelengths Is a potential cause of Interference In atomic absorption spectrometry (57) Thus, (a) the emission line of Fe at 352.424 nm Is close to the resonance line of N1 at 352.454, (b) the emission line of Sb at 217.023 nm Is close to the resonance line of Pb at 216.999 nm, and (c) the emission line of As at 228.812 nm Is close to the resonance line of Cd at 228.802 (57). To date, these practically coincident spectral lines have not been reported to be of practical Importance as sources of analytical Interference In atomic absorption analyses of biological materials. 

Both emission and absorption spectra are affected in a complex way by variations in atomisation temperature. The means of excitation contributes to the complexity of the spectra. Thermal excitation by flames (1500-3000 K) only results in a limited number of lines and simple spectra. Higher temperatures increase the total atom population of the flame, and thus the sensitivity. With certain elements, however, the increase in atom population is more than offset by the loss of atoms as a result of ionisation. Temperature also determines the relative number of excited and unexcited atoms in a source. The number of unexcited atoms in a typical flame exceeds the number of excited ones by a factor of 103 to 1010 or more. At higher temperatures (up to 10 000 K), in plasmas and electrical discharges, more complex spectra result, owing to the excitation to more and higher levels, and contributions of ionised species. On the other hand, atomic absorption and atomic fluorescence spectrometry, which require excitation by absorption of UV/VIS radiation, mainly involve resonance transitions, and result in very simple spectra. 

The general principle of detection of free radicals is based on the spectroscopy (absorption and emission) and mass spectrometry (ionization) or combination of both. An early review has summarized various techniques to detect small free radicals, particularly diatomic and triatomic species.68 Essentially, the spectroscopy of free radicals provides basic knowledge for the detection of radicals, and the spectroscopy of numerous free radicals has been well characterized (see recent reviews2-4). Two experimental techniques are most popular for spectroscopy studies and thus for detection of radicals laser-induced fluorescence (LIF) and resonance-enhanced multiphoton ionization (REMPI). In the photochemistry studies of free radicals, the intense, tunable and narrow-bandwidth lasers are essential for both the detection (via spectroscopy and photoionization) and the photodissociation of free radicals. 

The basic instrumentation used for spectrometric measurements has already been described in the previous chapter (p. 277). Methods of excitation, monochromators and detectors used in atomic emission and absorption techniques are included in Table 8.1. Sources of radiation physically separated from the sample are required for atomic absorption, atomic fluorescence and X-ray fluorescence spectrometry (cf. molecular absorption spectrometry), whereas in flame photometry, arc/spark and plasma emission techniques, the sample is excited directly by thermal means. Diffraction gratings or prism monochromators are used for dispersion in all the techniques including X-ray fluorescence where a single crystal of appropriate lattice dimensions acts as a grating. Atomic fluorescence spectra are sufficiently simple to allow the use of an interference filter in many instances. Photomultiplier detectors are used in every technique except X-ray fluorescence where proportional counting or scintillation devices are employed. Photographic recording of a complete spectrum facilitates qualitative analysis by optical emission spectrometry, but is now rarely used. 

One of the most challenging aspects of atomic spectrometry is the incredibly wide variety of sample types that require elemental analysis. Samples cover the gamut of solids, liquids, and gases. By the nature of most modem spectrochemical methods, the latter two states are much more readily presented to sources that operate at atmospheric pressure. The most widely used of these techniques are flame and graphite furnace atomic absorption spectrophotometry (FAAS and GF-AAS) [1,2] and inductively coupled plasma atomic emission and mass spectrometries (ICP-AES and MS) [3-5]. As described in other chapters of this volume, ICP-MS is the workhorse technique for the trace element analysis of samples in the solution phase—either those that are native liquids or solids that are subjected to some sort of dissolution procedure. 

C. R.J. Conzemius, Analysis of rare earth matrices by spark source mass spectrometry 377 37D. E.L. DeKalb and V.A. Eassel, Optical atomic emission and absorption methods 405 37E. A.P. D Silva and V.A. Eassel, X-ray excited optical luminescence of the rare earths 441 37E. E.W.V. Boynton, Neutron activation analysis 457... 

Application of Mdssbauer spectrometry depends on the availability of suitable sources with half-lives of excited states between about 10 and 10 s. The photon energy must not exceed lOOkeV and conversion must not be too high to ensure recoilless emission and absorption. As already mentioned, Fe, the daughter of Co, is the most frequently used Mdssbauer nuclide. Co is used as Mdssbauer source and iron of natural isotopic composition (2.17% Fe) or enriched Fe as absorber. 

Various types of GD have proved highly suitable for use as atom reservoirs for AAS however, this solid sampling approach has been less frequently used in atomic absorption than in atomic emission and mass spectrometry, possibly as a result of the wider commercial availability of electrothermal devices. 

The chemical methods for detecting total strontium include spectrophotometry, fluorometry, kinetic phosphorescence, atomic absorption spectroscopy (e.g., flame and graphite furnaces), inductively coupled plasma spectroscopy atomic emission and mass spectrometry applications (i.e., ICP-AES and ICP-MS). 

The objective of this symposium and this book is to acquaint the readers with the latest advances in the field of elemental analysis and to focus on what avenues of future research to explore in this area. The subjects included are various elemental analysis techniques such as atomic absorption spectrometry, inductively coupled plasma emission and mass spectrometry, isotope dilution mass spectrometry. X-ray fluorescence, ion chromatography, gas chromatography-atomic emission detection, other hyphenated techniques, hetero-atom microanalysis, sample preparation, reference materials, and other subjects related to matrices such as petroleum products, lubricating oils and additives, crude oils, used oils, catalysts, etc. 

Atomic absorption spectrometry (AAS) was established as the most popular gas chromatography (GC) detection technique for lead speciation analysis in the first years of speciation studies. The increase of the residence time of the species in the flame using a ceramic tube inside the flame and, later, the use of electrically heated tubes, made out of graphite or quartz where electrothermal atomization was achieved, provided lower detection limits but still not sufficiently low. Later, the boom of plasma detectors, mainly microwave induced plasma atomic emission (MIP-AES) and, above all, inductively coupled plasma atomic emission and mass spectrometry (ICP-AES and ICP-MS, respectively) allowed the sensitivity requirements for reliable organolead speciation analysis in environmental and biological samples (typically subfemtogram levels) to be achieved. These sensitivity requirements makes speciation analysis of organolead compounds by molecular detection techniques such as electrospray mass spectrometry (ES-MS) a very difficult task and, therefore, the number of applications in the literature is very limited. 

Analysis of the spectrum of the H atom led to the Bohr model, the first step toward our current model of the atom. From its use by 19 -century chemists as a means of identifying elements and compounds, spectrometry has developed into a major tool of modem chemistry. The terms spectmscopy, spectrophotometry, and spectrometry refer to a large group of instrumental techniques that obtain spectra that correspond to a substance s atontic or molecular eneigy levels. (Elements produce lines, but complex molecules produce spectral peaks.) The two types of spectra most often obtained are emission and absorption spectra ... 

Spectrometry is an instrumental technique that obtains emission and absorption spectra used to identify substances and measure their concentrations. 

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