Atomic spectra spectroscopy

Atomic absorption spectroscopy involves atomising the specimen, often by spraying a solution of the sample into a flame, and then studying the absorption of radiation from an electric lamp producing the spectrum of the element to be determined. 

Hi) Line Spectra Line spectra are usually encountered when the light emitting substance i.e., the radiating species are separate atomic entities (particles) which are distinctly separated from one another, as in gas. Therefore, it is invariably known as atomic spectrum . As the line spectrum depends solely upon the type of an atom, hence it enjoys the status of a predominant type of emission spectroscopy. 

Atomic emission spectroscopy is one of the oldest instrumental techniques used for chemical analysis. It is used to study the transitions between electronic energy levels in atoms or ions. These energy differences are usually in the visible region (400-700 nm) of the electromagnetic spectrum, but if the energy difference is larger, then the transitions may lie in the ultraviolet region. 

Investigation of atomic spectra yields atomic energy levels. An important chemical application of atomic spectroscopy is in elemental analysis. Atomic absorption spectroscopy and emission spectroscopy are used for rapid, accurate quantitative analysis of most metals and some nonmetals, and have replaced the older, wet methods of analysis in many applications. One compares the intensity of a spectral line of the element being analyzed with a standard line of known intensity. In atomic absorption spectroscopy, a flame is used to vaporize the sample in emission spectroscopy, one passes a powerful electric discharge through the sample or uses a flame to produce the spectrum. Atomic spectroscopy is used clinically in the determination of Ca, Mg, K, Na, and Pb in blood samples. For details, see Robinson. 

The fact that excited atoms give off specific colors and not a rainbow of colors suggested to Niels Bohr, a Danish physicist, that electrons are permitted in only certain locations within the atom. These locations are called energy levels. Each element behaves in its own unique way when excited by heat or electricity and produces a very specific pattern of lines of color called the atomic spectrum of that element (Figure 8.5). This unique chemical fingerprint is the foundation of atomic spectroscopy, a method of analysis used by forensic and medical laboratories to identify elements... 

During the 20-plus years that mass spectrometrists lost interest in glow discharges, optical spectroscopists were pursuing these devices both as line sources for atomic absorption spectroscopy and as direct analytical emission sources [6-10]. Traditionally, inorganic elemental analysis has been dominated by atomic spectroscopy. Since an optical spectrum is composed of lines corre-... 

The use of the words term and state is not so clear cut. The word term was originally used in the early days of spectroscopy in the sense of Equation (1.4), where the frequency of a line in an atomic spectrum is expressed as the difference between two terms which are simply terms in an equation. 

In 1955, A. Walsh recognized this and showed how the absorption from the great preponderance of unexcited molecules could be exploited analytically.Thus, in atomic absorption spectroscopy (AAS) the light from a (usually modulated) somce emitting the spectrum of the desired analyte element is passed through a sample atomization cell (such as a flame or graphite tube furnace), a monochromator (to isolate the desired somce emission line) and finally into a detector to allow measmement of the change in somce line... 

Atomic absoiption spectroscopy (AAS) is probably still the most widely employed of all the atomic methods because of its simplicity, effectiveness and relatively low cost. A Tine source of radiation is required for AAS (they do not employ a continuous source of radiation) hence a complete spectrum is not obtained. The sources (which are changed depending on the element of interest) emit certain lines of radiation that have the same wavelength as that of the absorption peak of the analyte of interest. 

Excitation of the outer ns electron of the M atom occurs easily and emission spectra are readily observed. We have aheady described the use of the sodium D-line in the emission spectrum of atomic Na for specific rotation measurements (see Section 3.8). When the salt of an alkali metal is treated with concentrated HCl (giving a volatile metal chloride) and is heated strongly in the non-luminous Bunsen flame, a characteristic flame colour is observed (Li, crimson Na, yellow K, lilac Rb, red-violet Cs, blue) and this flame test is used in qualitative analysis to identify the M ion. In quantitative analysis, use is made of the characteristic atomic spectrum in flame photometry or atomic absorption spectroscopy. 

AAS Atomic Absorption Spectroscopy Atomize (flame, electro, thermal, etc.) Light e.g., glow discharge Absorption spectrum - - Concentralion ol atomic species (quantitative, using standards) 1,2... 

The most common type pf mass spectrometer used in atomic mass spectroscopy is the quadrupole mass analyzer shown in Figure 11-6, This instrument is more compact, less expensive, and more rugged than most other types of mass spectrometers, it also has ihe advantage of high scan rales so lhat an entire mass spectrum can be obtained in less than I fX) ms, ... 

Lithium metabolism and transport cannot be studied directly, because the lack of useful radioisotopes has limited the metabolic information available. Lithium has five isotopes, three of which have extremely short half lives (0.8,0.2, 10 s). Lithium occurs naturally as a mixture of the two stable isotopes Li (95.58%) and Li (7.42%), which may be determined using Atomic Absorption Spectroscopy, Nuclear Magnetic Resonance Spectroscopy, or Neutron Activation analysis. Under normal circumstances it is impossible to identify isotopes by using AAS, because the spectral resolution of the spectrometer is inadequate. We have previously reported the use of ISAAS in the determination of lithium pharmacokinetics. Briefly, the shift in the spectrum from Li to Li is 0.015 nm which is identical to the separation of the two lines of the spectrum. Thus, the spectrum of natural lithium is a triplet. By measuring the light absorbed from hollow cathode lamps of each lithium isotope, a series of calibration curves is constructed, and the proportion of each isotope in the sample is determined by solution of the appropriate exponential equation. By using a dual-channel atomic absorption spectrometer, the two isotopes may be determined simultaneously. - ... 

Flame atomic emission spectroscopy, also called flame photometry, is based on the measurement of the emission spectrum produced when a solution containing metals or some nonmetals such as halides, sulfur, or phosphorus is introduced into a flame. In early experiments, the detector used was the analyst s eye. Those elements that emitted visible light could be identified qualitatively, and these flame tests were used to confirm the presence of certain elements in the sample, particularly alkali metals and alkaline-earth metals. A list of visible colors emitted by elements in a flame is given in Table 7.1. 

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