Absorption element characteristics

I n atomic spectroscopy, samples are vaporized at 2 000-8 000 K and decompose into atoms. Concentrations of atoms in the vapor are measured by emission or absorption of characteristic wavelengths of radiation. Because of its high sensitivity, its ability to distinguish one element... 

Analysis of FTIR spectra of the ionomer(Figures 3 and 4) was also informative about the structure. It was reported previously that IR absorption bands at 1893 cm" and 1905 cm"l were characteristics of 4-methylstyrene (of > 50) and 4-bromomethyl styrene (of Exxpro elastomer, Figure 5). Such absorption bands were not found in the FTIR spectra of the above ionomers. However, new absorption peaks, characteristics of the quaternary phosphonium salts, at 1580, 1100, 100, 670-730 cm" were observed. The presence of both phosphorous and boron in the above ionomers was also confirmed in terms of the elemental analysis data, collected from the inductively coupled plasma/atomic emission spectroscopy(ICP/AES) technique. These results were in good agreement with the expected convertion of the respective phosphonium salts. 

Atomic absorption spectrometry A method for elemental analysis of solutions based on the photoelectric absorption of characteristic light (produced by a special lamp) by thermally excited of atoms. 

Spectrophotometric techniques have been the basis of many coal analysis methods. One of the most widely used techniques for analysis of trace elements is atomic absorption spectrometry, in which the standards and samples are aspirated into a flame. A hollow cathode lamp provides a source of radiation that is characteristic of the element of interest and the absorption of characteristic energy by the atoms of a particular element. X-ray fluorescence is also employed as a quantitative technique for trace element determination and depends on election of orbital electrons from atoms of the element when the sample is irradiated by an x-ray source. 

To conclude this article, it is important to state that, in general, commercial oenological laboratories are equipped with automated instrumentation that carry out the above analyses (and others besides) in a single step. The most widely used instrumental technique is based on FTIR analysis. The infrared spectrum of an organic solution such as wine presents complex absorption spectra characteristic of the different wine components. The Michelson interferometer, which is at heart of the FTIR method, is based on the division of a polychromatic band of infrared radiation into two beams which then follow different optical pathways one beam traverses the sample cell directly, while the other is reflected on a mobile mirror before arriving at the sample cell. For each elemental wavelength arriving at the detector cell there will be a phase difference, which is continuously varied... 

In the conversion of net line intensity to analyte concentration, it may be necessary to correct for absorption and/or enhancement effects. Absorption effects include both primary and secondary absorption. Primary absorption occurs because all atoms of the spiecimen matrix absorb photons from the primary source. Since there is competition for these primary photons by the atoms making up the specimen, the intensity — wavelength distribution of the photons available for excitation of a given analyte element may be modified by other matrix elements. Secondary absorption refers to the absorption of characteristic analyte radiation by the specimen matrix. As characteristic... 

The method of IR spectroscopy is little informative in the case of indenyl derivatives of rare earth elements. From the data given in [4] only absorption bands characteristic of a functional group may be distinguished. They are 2155 (CN), 2225 and 1370 (NCO), 2045 and 965 (NCS), 2110 and 1280 cm (N3). Evidently, it is groundless to draw conclusions on the nature of metal-indenyl and metal-pseudohalogen bonds on the basis of the IR spectra frequencies as it was done in works [1-6, 11, 13, 14, 20]. 

Nuclear magnetic resonance (NMR) spectrometry is based on the net absorption of energy in the radiofrequency region of the electromagnetic spectrum by the nuclei of those elements that have spin angular momentum and a magnetic moment. For the nuclei of a particular element, characteristic absorption, or resonance frequencies, and other spectral features provide useful information on identity and molecular structure. 

Noltes, J. G., Henry, M. C., Janssen, M. J., An Infrared Absorption Band Characteristic for Aromatic Compounds of Fourth Main Group Elements, Chem. Ind. [London] 1959 298/9. 

The infrared probe, which resembles a specific ion electrode, contains a sensitive element that is dipped into the sample. To operate the probe, (1) the user selects the proper wavelength by rotating a calibrated, circular variable filter (2) then adjusts the gain and slits to bring the meter to 100% (3) next, the probe is lowered into the sample. The meter indicates the absorbance. This value can be converted into concentration by reference to a previously prepared calibration curve. To detect the presence or absence of a particular fimctional group, the user scans through the portion of the spectrum where absorption bands characteristic of that group appear. 

These characteristic absorption regions called group frequencies allow the analyst to detect the different elemental patterns and from them to reconstruct the molecule either by dej duct ion or by comparison with library reference spectra. The libraries contaih severaY hundred thousand spectra. 

A teclmique that employs principles similar to those of isomorphous replacement is multiple-wavelength anomalous diffraction (MAD) [27]. The expression for the atomic scattering factor in equation (B1.8.2h) is strictly accurate only if the x-ray wavelength is well away from any characteristic absorption edge of the element, in which case the atomic scattering factor is real and Filiki) = Fthkl V- Since the diffracted... 

Color Centers. Characteristics of a color center (1,3,7) include production by irradiation and destmction by heating. Exposure to light or even merely time in the dark may be sufficient to destroy these centers. Color arises from light absorption either from an electron missing from a normally occupied position, ie, a hole color center, or from an extra electron, ie, an electron color center. If the electron is a valence electron of a transition element, the term color center is not usually used. 

For quantitative analysis, the resolution of the spectral analyzer must be significantly narrower than the absorption lines, which are - 0.002 nm at 400 nm for Af = 50 amu at 2500°C (eq. 4). This is unachievable with most spectrophotometers. Instead, narrow-line sources specific for each element are employed. These are usually hoUow-cathode lamps, in which a cylindrical cathode composed of (or lined with) the element of interest is bombarded with inert gas cations produced in a discharge. Atoms sputtered from the cathode are excited by coUisions in the lamp atmosphere and then decay, emitting very narrow characteristic lines. More recendy semiconductor diode arrays have been used for AAS (168) (see Semiconductors). 

X-Ray Absorption Spectroscopy. As the excitation energy incident on a sample is increased, sharp rises in absorption occur at the K, L,..., absorption edges where the energy just matches that required for ionization by ejection of an electron from the K, L,. .., sheUs. These energies are characteristic for each element. The absorption foUows Beer s law (eq. 1), which in this region is usually written as A( A) = )px where p is the density,... 

The complex of the following destmctive and nondestmctive analytical methods was used for studying the composition of sponges inductively coupled plasma mass-spectrometry (ICP-MS), X-ray fluorescence (XRF), electron probe microanalysis (EPMA), and atomic absorption spectrometry (AAS). Techniques of sample preparation were developed for each method and their metrological characteristics were defined. Relative standard deviations for all the elements did not exceed 0.25 within detection limit. The accuracy of techniques elaborated was checked with the method of additions and control methods of analysis. 

Both inner-shell (K and L) and outer-shell (M, N, etc.) electrons can be excited by the absorption of X rays and by the inelastic scattering of electrons. In either instance, at an electron binding energy characteristic of an element in a sample. 

The detection of impurities or surface layers (e.g., oxides) on thick specimens is a special situation. Although the X-ray production and absorption assumptions used for thin specimens apply, the X-ray spectra are complicated by the background and characteristic X rays generated in the thick specimen. Consequently, the absolute detection limits are not as good as those given above for thin specimens. However, the detection limits compare very favorably with other surface analysis techniques, and the results can be quantified easily. To date there has not been any systematic study of the detection limits for elements on surfaces however, representative studies have shown that detectable surface concentrations for carbon and... 

The basis of XRE analysis is the photoelectric absorption and the subsequent emission of X-ray photons characteristic of the fingerprints of analyte atoms in the sample. Element composition can be quantified by the relative intensities of the indivi-... 

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