Spectroscopy atomic

Atomic spectroscopy in various forms, is used for the qualitative and quantitative analysis of about 70 elements. First, we revise the principles behind the technique. 

The energy difference between the two energy levels, AE is related to the frequency of the light that is emitted, v, by the Einstein relation 

The absorption of energy and subsequent emission of radiation by an atom. 

At some point in the near future you should study An Introduction to Spectroscopy on the Spectroscopy CD-ROM that accompanies this book. The principles of atomic spectroscopy are revised in this sequence. This activity should take approximately 1.5 hours to complete. 

The emission spectra of hydrogen, helium, mercury, cadmium and zinc in the visible region of the electromagnetic spectrum. 

Electronic spectroscopy is the study of transitions, in absorption or emission, between electronic states of an atom or molecule. Atoms are unique in this respect as they have only electronic degrees of freedom, apart from translation and nuclear spin, whereas molecules have, in addition, vibrational and rotational degrees of freedom. One result is that electronic spectra of atoms are very much simpler in appearance than those of molecules. 

In atomic spectroscopy, a substance is decomposed into atoms in a flame, furnace, or plasma. (A plasma is a gas that is hot enough to contain ions and free electrons.) Each element is measured by absorption or emission of ultraviolet or visible radiation by the gaseous atoms. To measure trace elements in a tooth, tiny portions of the tooth are vaporized (ablated) by a laser pulse1 and swept into a plasma. The plasma ionizes some of the atoms, which pass into a mass spectrometer that separates ions by their mass and measures their quantity. 

Elements are incorporated into teeth from the diet or by inhalation. The figure shows trace element profiles measured by laser ablation—plasma ionization-mass spectrometry of the dentine of teeth from a modem person and one who lived in Scandinavia about a.d. 1800. The contrast is striking. The old tooth contains significant amounts of tin and bismuth, which are nearly absent in the modern tooth. The old tooth contains more lead and antimony than the modem tooth. Tin and lead are constituents of pewter, which was used for cooking vessels and utensils. Bismuth and antimony also might come from pewter. 

Even more striking in the old tooth is the abundance of rare earths (dysprosium, holmium, erbium, thulium, ytterbium, and lutetium) and the elements tantalum, tungsten, gold, thorium, and uranium. Rare earth minerals are found in Scandinavia (in fact, many rare earth elements were discovered there), but what were they used for Did people prepare food with them Did they somehow get into the food chain  

Trace element profile of a tooth from a modem man and from a person who lived in Scandinavia 200 years ago. /From a. cox. 

R Keenan, M. Cooke, and J. Appleton, Trace Element Profiting of Dental Tissues Using Laser Ablation Inductively Coupled Plasma-Mass Spectrometry Fresenius J. Anal. Chem. 1996, 354.254.] 

Trace element analyses are often required for the determination of toxic metals such as chromium, mercury and lead in environmental samples and for monitoring the workplace environment. Conventional methods requiring extraction and separation procedures are time consuming. However, recent developments in GC and HPLC interfaced to atomic absorption and plasma emission spectrometers have enabled on-line analyses to be carried out. Ideally, the GC or HPLC column should be connected directly to the spectrometer sample cell or sample area to avoid dilution and loss of resolution. In practice a short heated transfer line of stainless steel or silica is used which has an internal diameter smaller than the column i.d. 

GC may be interfaced to an atomic absorption spectrometer (AAS) via a heated stainless-steel tube (2 mm o.d.). The column effluent is introduced into the fuel mixture of the air-acetylene flame either via the nebuliser or just below the burner rail [21-24]. The nebuliser method presents a problem if the sample contains volatile analytes such as the alkyl lead 

Spectra recorded at points indicated on the peak this may be repeated for all peaks in the chromatogram 

The interfacing of the eluant from an HPLC column to a flame AAS has been achieved by matching the eluant flow-rate of approximately 1 ml min to the intake rate of the nebuliser. Five tetra alkyl lead compounds were analysed on a reverse phase Cjg column using acetonitrile/water mobile phase directly connected to the inlet capillary of the AAS nebuliser [29]. Each compound was detected at the 10 ng level. 

Line spectra were first observed by J. von Fraunhofer, D. Brewster, and J. F. W. Herschel in the 1820s.180 In the ensuing decades a considerable amount of work was done on spectral phenomena prior to the demonstration by Bunsen and Kirchhoff in 1859 that line spectra could be used for qualitative chemical analysis. Accounts have appeared of the development of the spectroscope both prior and post Bunsen and Kirchhoff.181-183 Significant observations were undoubtedly made prior to 1860 by Stokes, Stewart, Fox Talbot, and others. The priority claims of Stokes, who recorded his ideas in some private letters to William Thomson, have been examined.184 The work of Bunsen and Kirchhoff did not owe a great deal to that of their predecessors, with the exception of the demonstration by W. Swan in 1856 that the almost omnipresent yellow line that coincided with Fraunhofer s dark solar D line was due to contamination by minute quantities of sodium salts.185 186 Platinum played an important role in the early development of spectroscopy. The metal was widely used to support the material in the flame, since it did not colour the flame itself. Bunsen ensured the purity of all his samples for spectrum analysis by recrystallization (sometimes up to fourteen times) in platinum vessels, thereby preventing contamination by minute quantities of salts that could be leached from glass vessels.187 Sharply contrasting views have been expressed about the failure of chemists prior to Bunsen to exploit spectroscopy.188-190 

After Bunsen had detected and isolated caesium, spectroscopy was taken up with great enthusiasm by William Crookes, and this led to his detection and isolation of thallium in 1861.191 Crookes letters to Charles Hanson Greville Williams, who was also working with the spectroscope, and who felt he deserved some of the credit for the discovery of thallium, have been published.192 The use of spectrochemistry in the search for hitherto unknown chemical elements in Britain over the period 1860-1869 has been described. It was perceived that, like Crookes, a scientist could make his reputation by discovering a new element. This resulted in several claims for the existence of new elements that later proved to be unfounded.193 Once Kirchhoff had established beyond doubt that the dark Fraunhofer lines were caused by the same element that caused emission lines of identical wavelengths, the way was open for the chemical analysis of the atmosphere of the sun and stars. This was a process which had been declared to be an impossibility by Auguste Comte less than 30 years previously.194 

In 1952, Walsh in Australia realized the inherent advantages of atomic absorption spectroscopy over methods based on flame emission for quantitative analysis, and he has given a personal account of the development of the technique.197 Walsh s death in 1998 resulted in a memorial issue of the journal Spectrochimica Acta (B). As well as a brief biography of Walsh and a list of his publications, this contained 22 papers on all aspects of the history of atomic absorption spectroscopy. Together they constitute a valuable record of the birth of this important technique, the difficulties of bringing satisfactory instruments to market, and the history of the application of the method to quantify metals in a wide variety of materials and environments.198 

Atomic absorption remained the technique of choice until relatively recently. However, with the introduction of plasma sources, atomic emission, in the form of inductively coupled plasma spectroscopy, has made a comeback. This development is now receiving historical attention, and was the subject of a symposium held in 1999. Papers discussed atomic emission analysis prior to 1950,206 the fact that emission techniques developed continuously, even in the period when absorption methods were dominant,207 and the development of the plasma sources on which the new techniques depend.208 Also discussed was the powerful hyphenated technique of ICP-MS,209 and the history of one of the leading manufacturers of atomic emission instruments.210 

Water pollution remains a serious problem in the United States and in other industrial countries. The photo shows land left over after strip mining in Belmont County, Ohio. The various water pools shown are contaminated with waste chemicals. The large pool to the right of center contains sulfuric acid. The smaller pools contain manganese and cadmium. Trace metals in contaminated water samples are often determined by a multielement technique such as inductively coupled plasma rnassj spectrometry or inductively coupled plasma atomic emission spectroscopy. Botft these methods are discussed in this chapter. 

Atomic spectroscopic methods are used for the qualitative and quantitative determination of more than 70 elements. Typically, these methods can detect parts-per-million to parts-per-billion amounts, and, in some cases, even smaller concentrations. Atomic spectroscopic methods are, in addition, rapid, convenient, and usually of high selectivity. They can be divided into two groups optical atomic spectrometry and atomic mass spectrometry.  

Spectroscopic determination of atomic species can only be performed on a gaseous medium in which the individual atoms or elementary ions, such as Fe, Mg, or Al, are well separated from one another. Consequently, the first step in all atomic spectroscopic procedures is atomization, a process in which a sample is volatilized and decomposed in such a way as to produce gas-phase atoms and ions. The efficiency and reproducibility of the atomization step can have a large influence on the sensitivity, precision, and accuracy of the method. In short, atomization is a critical step in atomic spectroscopy. 

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. 

Atomization is a process in which a sample is converted into gas-phase atoms or elementary ions. 

Dispersing the radiation from the star into its component wavelengths reveals that the spectrum of a star is not the continuous spectrum of a black body but there are 

Calculate the wavelengths of the first three transitions in the Balmer series. Using the value for RH above with n = 2 and n2 = 3,4 and 5 gives the following  

The first transition is in the red at 656 nm, with the other two transitions appearing in the blue at 486 and 434 nm. The separation between the transitions is also getting closer as the term in 1 /n becomes very small, until finally the series converges on a limit with a wavelength of 364.740 nm. 

The Lyman, Balmer, Paschen, Brackett and Pfund series 

Other series are present in the spectrum of the H atom, starting from different initial levels and undergoing transitions to higher levels. There is formally no limit to the value of n in the upper state but eventually in the limit the electron is so far from the nucleus that it is no longer confined by the attraction of the proton and it leaves the atom a process called ionisation. The ionisation event can be seen in any one of the series of the H atom when the separation between the lines of the series begins to converge towards zero - the ionisation limit at a fixed wavelength. 

The use of such equipment must always be done unxJer guidance frorn a J. ifemonstrator or techniciany All equipment in this section has an inherent risk due to. its use of mains electricity.  

Safety note in atomic Spectroscopy, the use of. high-pressure gas sources, e.g. cylinders, an be particularly hazardous.. Always consult a demonstrator or technician before use.  

Atomic spectroscopy is a quantitative technique used for the determination of metals in samples. Atomic spectroscopy is characterized by two main techniques atomic absorption spectroscopy and atomic emission spectroscopy. Atomic absorption spectroscopy (AAS) is normally carried out with a flame (FAAS), although other devices can be used. Atomic emission spectroscopy (AES) is typified by the use of a flame photometer (p. 168) or an inductively coupled plasma. The flame photometer is normally used for elements in groups I and II of the Periodic Table only, i.e. alkali and alkali earth metals. 

In both AAS and AES the substance to be analysed must be in solution. In order to do quantitative analysis, i.e. determine how much of the metal is present, the preparation of analytical standard solutions is necessary. While the concentration range over which the technique can be used may be different, for various instruments, the principles associated with the preparation of analytical standard solutions are the same (Boxes 27.1 27.5). 

Sample/standard dilutions - all dilutions should.be done using approffriate glassware or plastic ware. Typically, this involves the use of grade A pipettes for the transfer of knoyvn volumes of liquids and grade A vojurhetric flasks for subsequent dilations. 

Atomic spectroscopy is a quantitative technique used for the determination of metals in samples. Atomic spectroscopy is characterized by two main techniques atomic absorption spectroscopy and atomic emission 

Representative emission spectra are shown schematically in Fig. 2.2 for hydrogen, potassium, and mercury on a common wavelength scale from the near infrared to the ultraviolet. Under the coarse wavelength resolution of this figure, the emitted light intensities are concentrated at single, well-defined emission lines. In H, the displayed emission consists of four convergent series of lines, the so-called Ritz-Paschen and Pfund series in the near infrared, the Lyman series in the vacuum ultraviolet, and the Balmer series in the visible. Johann Balmer, a schoolteacher in Basel in the late nineteenth century. 

The mercury spectrum is even less regular. The electron configuration in Hg consists of two valence electrons outside of a closed-shell core. .. (5s) (5p) (4/) (5d) . The Hg spectrum features that are not anticipated in H or K arise from electron spin multiplicity (i.e., the formation of triplet as well as singlet excited states in atoms with even numbers of valence electrons) and from spin-orbit coupling, which assumes importance in heavy atoms like Hg (Z = 80). The mercury spectrum in Fig. 2.2 has been widely used as a spectral calibration standard. 

In this chapter, we review electronic structure in hydrogenlike atoms and develop the pertinent selection rules for spectroscopic transitions. The theory of spin-orbit coupling is introduced, and the electronic structure and spectroscopy of many-electron atoms is greated. These discussions enable us to explain details of the spectra in Fig. 2.2. Finally, we deal with atomic perturbations in static external magnetic fields, which lead to the normal and anomalous Zeeman effects. The latter furnishes a useful tool for the assignment of atomic spectral lines. 

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INS Ion neutralization An inert gas hitting surface is spectroscopy [147] neutralized with the ejection of an Auger electron from a surface atom Spectroscopy of Emitted Ions or Molecules Kinetics of surface reactions chemisorption... 

Lochmuler, C. Atomic Spectroscopy—Determination of Calcium and Magnesium in Sand with a Statistical Treatment of Measurements published on the web at http //www.chem.duke.edu/ clochmul/exp4/exp4.html. 

Sneddon, J., Thiem, T. and Lee, Y.-I. (1997) Lasers in Atomic Spectroscopy, John Wiley, New York. 

Chemical Analysis. The presence of siUcones in a sample can be ascertained quaUtatively by burning a small amount of the sample on the tip of a spatula. SiUcones bum with a characteristic sparkly flame and emit a white sooty smoke on combustion. A white ashen residue is often deposited as well. If this residue dissolves and becomes volatile when heated with hydrofluoric acid, it is most likely a siUceous residue (437). Quantitative measurement of total sihcon in a sample is often accompHshed indirectly, by converting the species to siUca or siUcate, followed by deterrnination of the heteropoly blue sihcomolybdate, which absorbs at 800 nm, using atomic spectroscopy or uv spectroscopy (438—443). Pyrolysis gc followed by mass spectroscopic detection of the pyrolysate is a particularly sensitive tool for identifying siUcones (442,443). This technique rehes on the pyrolytic conversion of siUcones to cycHcs, predominantly to [541-05-9] which is readily detected and quantified (eq. 37). 

Naiiow-line uv—vis spectia of free atoms, corresponding to transitions ia the outer electron shells, have long been employed for elemental analysis usiag both atomic absorption (AAS) and emission (AES) spectroscopy (159,160). Atomic spectroscopy is sensitive but destmctive, requiring vaporization and decomposition of the sample iato its constituent elements. Some of these techniques are compared, together with mass spectrometry, ia Table 4 (161,162). 

J. W. Robinson, Atomic Spectroscopy, Marcel Dekker, Inc., New York, 1990. 

Atomic Spectroscopy and Journal of Analytical Atomic Spectromety, regular and occasional topical bibHographies. 

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. 

Analytical Atomic Spectroscopy Surface Analysis," Mnnual Book ofMSTM Standards, part 3.06, American Society for Testing and Matedals, Philadelphia, Pa., 1992. 

The performance of microwave-assisted decomposition of most difficult samples of organic and inorganic natures in combination with the microwave-assisted solution preconcentration is illustrated by sample preparation of carbon-containing matrices followed by atomic spectroscopy determination of noble metals. Microwave-assisted extraction of most dangerous contaminants, in particular, pesticides and polycyclic aromatic hydrocarbons, from soils have been developed and successfully used in combination with polarization fluoroimmunoassay (FPIA) and fluorescence detection. 

One contemporary author has described the situation regarding atomic spectroscopy in the following manner ... 

Atomic spectroscopy, 1, 231-234 Atropisomers, 1,200 Aurintricarboxylic acid beryllium(II) complexes, 2, 482 Aurocyanides dissolution, 6,784 Autotrophic bacteria... 

Chapter 3 is devoted to pressure transformation of the unresolved isotropic Raman scattering spectrum which consists of a single Q-branch much narrower than other branches (shaded in Fig. 0.2(a)). Therefore rotational collapse of the Q-branch is accomplished much earlier than that of the IR spectrum as a whole (e.g. in the gas phase). Attention is concentrated on the isotropic Q-branch of N2, which is significantly narrowed before the broadening produced by weak vibrational dephasing becomes dominant. It is remarkable that isotropic Q-branch collapse is indifferent to orientational relaxation. It is affected solely by rotational energy relaxation. This is an exceptional case of pure frequency modulation similar to the Dicke effect in atomic spectroscopy [13]. The only difference is that the frequency in the Q-branch is quadratic in J whereas in the Doppler contour it is linear in translational velocity v. Consequently the rotational frequency modulation is not Gaussian but is still Markovian and therefore subject to the impact theory. The Keilson-... 

The quasi-classical theory of spectral shape is justified for sufficiently high pressures, when the rotational structure is not resolved. For isotropic Raman spectra the corresponding criterion is given by inequality (3.2). At lower pressures the well-resolved rotational components are related to the quantum number j of quantized angular momentum. At very low pressure each of the components may be considered separately and its broadening is qualitatively the same as of any other isolated line in molecular or atomic spectroscopy. 

Unfortunately, these rather basic errors are distressingly common, yet cause much unnecessary dissatisfaction. No printer is perfect, and relying on catalog data can result in the publication of incorrect data in a paper. This occurred, e.g. in 1994 when data was taken from an out-of-date NIST catalog, rather than the appropriate certificate. Published in the Journal of Analytical Atomic Spectroscopy, the paper by Soares et al. (1994) cited a certified value for Cr in NIST SRM 1548, when consultation of the Certificate would have shown that for several technical reasons the element value reported could not be certified. 

Practically all classical methods of atomic spectroscopy are strongly influenced by interferences and matrix effects. Actually, very few analytical techniques are completely free of interferences. However, with atomic spectroscopy techniques, most of the common interferences have been studied and documented. Interferences are classified conveniently into four categories chemical, physical, background (scattering, absorption) and spectral. There are virtually no spectral interferences in FAAS some form of background correction is required. Matrix effects are more serious. Also GFAAS shows virtually no spectral interferences, but... 

Atomic spectroscopy has been reviewed [92] a recent update is available [93]. An overview of sample introduction in atomic spectrometry is available [94]. Several recent books deal with analytical atomic spectrometry [95-100],... 

Adapted from Moenke-Blankenburg [217]. From L. Moenke-Blanken-burg, in Lasers in Analytical Atomic Spectroscopy (J. Sneddon et al., eds), VCH Publishers, New York, NY (1997), pp. 125-195. Reproduced by permission of Wiley-VCH. 

M. Cullen (ed.), Atomic Spectroscopy in Elemental Analysis, Blackwell Publishing, Oxford (2003). 

K. W. Jackson (ed.), Electrothermal Atomization for Analytical Atomic Spectroscopy, John Wiley Sons, Ltd, Chichester (1999). 

G. Schlemmer and B. Radziuk, A Laboratory Guide to Graphite Furnace Analytical Atomic Spectroscopy, Springer-Verlag, Berlin (1998). 

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