Ultraviolet and Visible Regions

Table 1 Hsts several of the chemical deterrninations and the corresponding reactions uti1i2ed, which are available on automated clinical analy2ers. With the exception of assays for various electrolytes, eg, Na", K", Cl , and CO2, deterrnination is normally done by photometric means at wavelengths in the ultraviolet and visible regions. Other means of assay include fluorescence, radioisotopic assay, electrochemistry, etc. However, such detection methods are normally required only for the more difficult assays, particularly those of semm or urine constituents at concentrations below )Tg/L. These latter assays are discussed more fully in the Hterature (3,4).

Approximately 70 different elements are routinely determined using ICP-OES. Detection limits are typically in the sub-part-per-billion (sub-ppb) to 0.1 part-per-million (ppm) range. ICP-OES is most commonly used for bulk analysis of liquid samples or solids dissolved in liquids. Special sample introduction techniques, such as spark discharge or laser ablation, allow the analysis of surfaces or thin films. Each element emits a characteristic spectrum in the ultraviolet and visible region. The light intensity at one of the characteristic wavelengths is proportional to the concentration of that element in the sample. 

Usually, the ultraviolet and visible regions of the spectrum are recorded. Many of the most intense emission lines lie between 200 nm and 400 nm. Some elements (the halogens, B, C, P, S, Se, As, Sn, N, and O) emit strong lines in the vacuum ultraviolet region (170-200 nm), requiring vacuum or purged spectrometers for optimum detection. 

Electrochemically generated products can be readily characterized by in situ measurement of their absorption spectra in the ultraviolet and visible regions. Optically transparent electrodes (OTEs) prepared from thin layers... 

Reflectance spectroscopy in the infrared and visible ultraviolet regions provides information on electronic states in the interphase. The external reflectance spectroscopy of the pure metal electrode at a variable potential (in the region of the minimal faradaic current) is also termed electroreflectance . Its importance at present is decreased by the fact that no satisfactory theory has so far been developed. The application of reflectance spectroscopy in the ultraviolet and visible regions is based on a study of the electronic spectra of adsorbed substances and oxide films on electrodes. 

The discovery of polyhedral boranes and polyhedral heteroboranes, which contain at least one atom other than in the cage, initiated a new era in boron chemistry.1-4 Most commonly, of the three commercially available isomeric dicarba-closo-dodecaborane carboranes(l,2-, 1,7-, and 1,12-), the 1,2-isomer 1 has been used for functionalization and connection to organic molecules. The highly delocalized three-dimensional cage bonding that characterizes these carboranes provides extensive thermal and kinetic stabilization as well as photochemical stability in the ultraviolet and visible regions. The unusual icosahedral geometry of these species provides precise directional control of all exopolyhedral bonds. 

Conjugated molecules absorb energy in the ultraviolet and visible regions of the electromagnetic spectrum. 

Most cells used in infrared spectrometry have sodium chloride windows and the path length is likely to vary with use because of corrosion. For quantitative work, therefore, the same cell should be used for samples and standards. In general, quantitative analysis in the infrared region of the spectrum is not practised as widely as in the ultraviolet and visible regions, partly because of the additional care necessary to obtain reliable results and partly because the technique is generally considered to be less sensitive and less precise a precision of 3-8% can be expected. 

In ultraviolet and visible region, electronic transition of atoms and molecules are observed. This is why it is called electronic spectroscopy. In infrared region the absorption of radiation by an organic compound causes molecular vibrations and so it is called vibrational spectroscopy. 

Analysis of organic compounds. Large number of organic molecules absorb radiation in ultraviolet and visible region. So molecules having high molecular absorptivities can be determined directly. 

The resulting, synthetic melanin were black powder and absorbed light over the ultraviolet and visible regions (Tab. IV). They contained very stable free radical, being of interest to physiology. 

L. N. M. Duysens and J. Amesz, Fluorescence spectrophotometry of reduced phosphopyridine nucleotide in intact cells in the near-ultraviolet and visible region, Biochem. Biophys. Acta 24, 19-26 (1957). 

Since polymers are often used as clear plastics or coatings and have many applications in which transparency is an important property, a knowledge of the optical properties of specific polymers is essential. The radiation scale, of course, includes microwave, infrared, ultraviolet, and visible regions, but the emphasis in this chapter is on the latter. 

Only the n— it, ir-. ir, and more rarely the n— a excitations occur in the near ultraviolet and visible regions, which are the available regions for ordinary spectrophotometers. Species which absorb in the visible region are colored, and black is observed when all visible light is absorbed. 

L. L ng, Absorption Spectra in the Ultraviolet and Visible Region, Part II. Akad5miai Kiado, Budapest, 1961. 

The absorption in the ultraviolet and visible regions consists of the Hartley bands (2000 to 3200 A), the Huggins bands (3000 to 3600 A), and the Chappuis bands (4400 to 8500 A). The absorption coefficients of these bands arc given in Figs. VI I2 andVI 12b. Figure VI 12c shows the absorption coefficients in the vacuum ultraviolet region. 

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