VIS range

Molecular absorption, particularly in the UV/Vis range, has been used for a variety of different characterization studies, including determining the stoichiometry of metal-ligand complexes and determining equilibrium constants. Both of these examples are examined in this section. 

A UV/Vis absorbance detector can also be used if the solute ions absorb ultraviolet or visible radiation. Alternatively, solutions that do not absorb in the UV/Vis range can be detected indirectly if the mobile phase contains a UV/Vis-absorbing species. In this case, when a solute band passes through the detector, a decrease in absorbance is measured at the detector. 

Figure 9. Comparison between a simulation based on the Mie theory of OD in the UV-Vis range for 3 nm clusters of pure Au, Ag, and Auo.4Ago.6 alloy in silica (a), with the experimental OD of the same systems in ion-implanted silica (b). (Reprinted from Ref [1], 2005, with permission from Italian Physical Society).

Applications Applications of UV/VIS spectrophotometry can be found in the areas of extraction monitoring and control, migration and blooming, polymer impregnation, in-polymer analysis, polymer melts, polymer-bound additives, purity determinations, colour body analysis and microscopy. Most samples measured with UV/VIS spectroscopy are in solution. However, in comparison to IR spectroscopy additive analysis in the UV/VIS range plays only a minor role as only a limited class of compounds exhibits specific absorption bands in the UV range with an intensity proportional to the additive concentration. Characteristic UV absorption bands of various common polymer additives are given in Scheirs [24],... 

The oldest application of solvent extraction in spectrophotometric determinations uses extraction from the original aqueous solution and subsequent back-extraction into a second aqueous phase. Here the extractant provides only separation or concentration, as in the case of Np(IV) and Pu(IV) determination [16]. However, as only a few element species (e.g., Mn04, Cr04 ) are capable of absorbing light in the UV-VIS range, usually all spectrophotometric methods are based on reactions of analytes with... 

There are numerous excitation sources available for LIF instruments. A xenon arc lamp is the most common light source within commercial LIF analyzers. While they offer uniform broad spectral coverage across the UV-vis range and sufficient uniform power output, they are low precision sources and do not offer sufficient real-time or dynamic optical power control. The white output also necessitates an excitation... 

Similarly, fused silica windows are not required except for the most demanding applications in UV spectroscopy, so fitting the vacuum shroud with a pair of well-polished KBr windows is usually appropriate, unless one needs IR transparency at 500-200 cm when one has to use Csl windows. If one needs to probe the far-lR range (<200 cm ) one has to use polyethylene windows (the covers that come with KF flanges have proven adequate), but this makes it of course impossible to probe the same samples in the mid-IR or UV-vis range. 

The intensity of radiation coming from the light source varies over the entire UV-Vis range. Most UV-Vis spectrophotometers have dual light sources. A... 

UV-Vis range. Newer spectrometers are usually computer controlled and allow the user greater flexibility, e.g. in overlaying spectra of a reaction mixture over time, or constructing a calibration graph to determine the concentration of an unknown. 

What happens if an organic compound absorbs light in the uv/vis range ... 

Shown below are some data concerning light absorption in the uv/vis range by pentachlorophenol (PCP). Absorption values for the neutral species are given in ethanol, those for the dissociated species at pH 10 in aqueous solution. 

Table VI. Range of Relative Errors for Three Particle Sizes of Whole Coal (%)...

Halogenated purines. 8BrdAdo has been used to study some of the steps in the cyclization reaction that yields the purine cyclonucleosides/tides (Flyunt et al. 2000 Chatgilialoglu et al. 2003). Upon the reaction of eaq, the very reactive vinylic radical at C(8) is formed [reaction (238) k= 1.6 x 10 dm3 mol-1 s 1] which undergoes rapid H-abstraction from the hydroxymethyl group at C(5 ) [reaction (239)]. In neither of these reactions are radicals formed which strongly absorb in the accessible UV/Vis range. Upon addition of the C(5 ) radical to C(8) [reaction (239) k = 1.6 x 105 s-1], an aminyl radical is formed whose UV/Vis spectrum is... 

TABLE VI. - Range of properties of distillate burner fuels produced in the United States during 1974... 

All compounds with UV or visible (VIS) range absorbance Ultraviolet/visible photometer PAHs (EPA 8310) Nitroaromatics, nitramines (EPA 8330) Nitroglycerine (EPA 8332) —Detection based on a single wavelength is prone to interferences. —Does not have the selectivity for positive compound identification. 

This article shows how the evanescent wave can be used with advantage for spectroscopic purposes in the field of biomedical engineering. Three types of spectroscopy can be done with the evanescent wave in the UV-VIS range of the spectrum (a) attenuated total reflection (ATR) spectroscopy, which is well known in the infrared (b) the excitation of Raman scattering with the evanescent wave and (c) the excitation of fluorescence with the evanescent wave. The first two types will be discussed in this article the third is discussed for example by Hirschfeld U) and more recently by Watkins and Robertson (2). But before going into details a historical review may be of some interest. 

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