Elemental analyses, spectroscopic methods

Instruments known as spectroscopes or spectrometers are generally used for elemental analyses. Spectroscopic methods examine the interaction between atoms and light and are defined primarily by the portion of the electromagnetic spectrum that they use. Instead of the spectrum, more powerful mass spectrometers use electromagnetic fields to sort atoms according to their weight. Specific atomic weights, or masses, correspond to specific elements and isotopes. 

In order to calculate a copolymerization reactivity ratio, it is first necessary to determine the composition of the copolymer or of the unconverted monomer mixture (or both). Elemental analysis, spectroscopic methods (IR, UV, NMR), refractive index determination, or turbidimetric titration can be suitable for determining the copolymer composition. 

Haver, T.C. In Trace Analysis Spectroscopic Methods for Elements Wlneforndner, J.D., Ed. Wiley-Interscience New York, 1976 pp 41-42. 

D ace Analysis Spectroscopic Methods for Elements. Edited by J. D. Winefordner... 

Trace Analysis Spectroscopic Methods for Elements. Edited by J. D.Winefordner Contamination Control in Trace Element Analysis. By Morris Zief and James W. Mitchell Analytical Applications of NMR. By D. E. Leyden and R. H. Cox Measurement of Dissolved Oxygen. By Michael L. Hitchman Analytical Laser Spectroscopy. Edited by Nicolo Omenetto... 

Winefordner, J. D. (ed.) Trace Analysis. Spectroscopic Methods for Elements, New York, Wiley-Interscience, 1976... 

H. G. J. Moseley, Phil. Mag. [6], 26, 1024 (1913). The following remarkable quotation from this paper (p. 1030) supports Moseley as the founder of x-ray emission spectrography The prevalence of lines due to impurities suggests that this may prove a powerful method of chemical analysis. Its advantage over ordinary spectroscopic methods lies in the simplicity of the spectra and the impossibility of one substance masking the radiation from another. It may even lead to the discovery of missing elements, as it will be possible to predict the position of their characteristic lines. ... 

EXAFS analysis is a powerful spectroscopic method for structural analysis which has been extensively applied to the problem of structure determination in nanoparticles, and especially bimetallic nanoparticles [170-172]. The X-ray absorption spectrum of an element contains absorption edges corresponding to the excitation of electrons from various electronic states at energies characteristic of that element, i.e., K edges arise from the excitation of electrons from Is states, and LI, II, III edges from excitations from 2s, 2p 1/2, and 2p3/2 states. When the X-ray energy is increased above an edge, oscillations (fine... 

Non-reacted vinyl groups of these crosslinked polymers may be expressed by the residual unsaturation (RU). The RU is a measure for both the reactivity of the monomer and the structure of the crosslinked polymer. The RU may be determined by spectroscopic or chemical methods. For the spectroscopic determination a model compound of low molar mass is required as a reference for the standardization [217, 231, 254]. For the chemical determination a reagent of low molar mass is added to the pendant vinyl groups. Then the RU is obtained either by elemental analysis or by back-titration of the non-reacted reagent [231, 283-285]. 

Owing to their superior fluorescent yield, heavy elements ordinarily yield considerably more intense XRF bands than the light elements. This feature can be exploited to determine the concentration of inorganic species in a sample, or the concentration of a compound that contains a heavy element in some matrix. Many potential XRF applications have never been developed owing to the rise of atomic spectroscopic methods, particularly inductively coupled plasma atomic emission spectrometry [74]. Nevertheless, under the right set of circumstances, XRF analysis can be profitably employed. 

Atomic spectroscopy is an excellent method of analysis for trace or ultratrace levels of many elements in the periodic table. The major disadvantage of all atomic spectroscopic methods is that they provide no information on the oxidation state of the element or its speciation. This disadvantage can be redressed by the use of selective reagents coupled... 

In essence, NAA involves converting some atoms of the elements within a sample into artificial radioactive isotopes by irradiation with neutrons. The radioactive isotopes so formed then decay to form stable isotopes at a rate which depends on their half-life. Measurement of the decay allows the identification of the nature and concentration of the original elements in the sample. If analysis is to be quantitative, a series of standard specimens which resemble the composition of the archaeological artifact as closely as possible are required. NAA differs from other spectroscopic methods considered in earlier chapters because it involves reorganization of the nucleus, and subsequent changes between energy levels within the nucleus, rather than between the electronic energy levels. 

Widening interest in the quaHty of the environment has led to increased demand for information on a wide range of trace-metal contents of foodstuffs. Trace metals in foodstuffs are normally determined by spectroscopic techniques after complete destruction of the organic matrix. Destruction is achieved either by wet oxidation or by dry ashing additional treatment is normally required in order to obtain the metals of interest in a form suitable for analysis. Both methods of destruction are time consuming and tedious this is particularly true of the wet-oxidation procedure, which has the additional disadvantage of being potentially hazardous the methods require considerable analytical skill and experience. Both methods are prone to produce erroneous results either by the loss of an element of interest or by adventitious contamination from the component parts... 

Quantitative analysis of copolymers is relatively simple if one of the comonomers contains a readily determinable element or functional group. However, C,H elemental analyses are only of value when the difference between the carbon or hydrogen content of the two comonomers is sufficiently large. If the composition cannot be determined by elemental analysis or chemical means, the problem can be solved usually either by spectroscopic methods, for example, by UV measurements (e.g., styrene copolymers), by IR measurements (e.g., olefin copolymers), and by NMR measurements, or by gas chromatographic methods combined with mass spectroscopy after thermal or chemical decomposition of the samples. 

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