Of ultraviolet/visible spectroscopy

For an introduction to thin layer and gravity column chromatography, we separate the pigments from frozen spinach. This is one green experiment that is literally green. A number of variations of this classic procedure have been reported (P). We have made only minor changes in the procedure of Pavia and co-authors 9d). However, since we obtain the UVA is spectrum of the carotene isolated from the spinach, implementation of this experiment facilitates a discussion of ultraviolet/visible spectroscopy. 

The ultraviolet-visible method is useful for the study of electronic transitions in molecules and atoms. Although various forms of ultraviolet-visible spectroscopy can be used to study a myriad of important chemical and physical properties, we will be most concerned with its use in quantitative analysis. It is probably the single most frequently used analytical method, with the possible exception of the analytical balance. For example, a single clinical analysis laboratory in a major hospital may perform a million chemical analyses a year, primarily on serum and urine, and about 707o of these tests are done by ultraviolet-visible absorption spectroscopy. Atomic absorption and emission spectroscopy (Chaps. 10 and 11) is used primarily to analyze for metallic elements in a variety of matrices—serum, natural waters, tissues, and so forth. 

Horn, K., Applications of Ultraviolet/Visible Spectroscopy, Laboratory Report UV 31, Bodenseewerk Perkin-Elmer, Uberlingen, 5 Aug. 1986 25 p. 

Van der Waals complexes can be observed spectroscopically by a variety of different teclmiques, including microwave, infrared and ultraviolet/visible spectroscopy. Their existence is perhaps the simplest and most direct demonstration that there are attractive forces between stable molecules. Indeed the spectroscopic properties of Van der Waals complexes provide one of the most detailed sources of infonnation available on intennolecular forces, especially in the region around the potential minimum. The measured rotational constants of Van der Waals complexes provide infonnation on intennolecular distances and orientations, and the frequencies of bending and stretching vibrations provide infonnation on how easily the complex can be distorted from its equilibrium confonnation. In favourable cases, the whole of the potential well can be mapped out from spectroscopic data. 

Chromophore (Section 13 21) The structural unit of a mole cule principally responsible for absorption of radiation of a particular frequency a term usually applied to ultraviolet visible spectroscopy... 

Table 7.9 Electronic Absorption Bands for Representative Chromophores Table 7.10 Ultraviolet Cutoffs of Spectrograde Solvents Table 7.11 Absorption Wavelength of Dienes Table 7.12 Absorption Wavelength of Enones and Dienones Table 7.13 Solvent Correction for Ultraviolet-Visible Spectroscopy Table 7.14 Primary Bands of Substituted Benzene and Heteroaromatics Table 7.15 Wavelength Calculation of the Principal Band of Substituted Benzene Derivatives...

The section on Spectroscopy has been retained but with some revisions and expansion. The section includes ultraviolet-visible spectroscopy, fluorescence, infrared and Raman spectroscopy, and X-ray spectrometry. Detection limits are listed for the elements when using flame emission, flame atomic absorption, electrothermal atomic absorption, argon induction coupled plasma, and flame atomic fluorescence. Nuclear magnetic resonance embraces tables for the nuclear properties of the elements, proton chemical shifts and coupling constants, and similar material for carbon-13, boron-11, nitrogen-15, fluorine-19, silicon-19, and phosphoms-31. 

Ultraviolet-visible spectroscopy (UV = 200 - 400 nm, visible = 400 - 800 nm) corresponds to electronic excitations between the energy levels that correspond to the molecular orbital of the systems. In particular, transitions involving n orbital and ion pairs (n = non-bonding) are important and so UV/VIS spectroscopy is of most use for identifying conjugated systems which tend to have stronger absorptions... 

With the exception of single-crystal transmission work, most solids are too opaque to permit the conventional use of ultraviolet/visible (UV/VIS) electronic spectroscopy. As a result, such work must be performed through the use of diffuse reflection techniques [8-10]. Important work has been conducted in which UV/VIS spectroscopy has been used to study the reaction pathways of various solid state reactions. Other applications have been made in the fields of color measurement and color matching, areas which can be of considerable importance when applied to the coloring agents used in formulations. 

The use of ultraviolet (UV) spectroscopy for on-line analysis is a relatively recent development. Previously, on-line analysis in the UV-visible (UV-vis) region of the electromagnetic spectrum was limited to visible light applications such as color measurement, or chemical concentration measurements made with filter photometers. Three advances of the past two decades have propelled UV spectroscopy into the realm of on-line measurement and opened up a variety of new applications for both on-line UV and visible spectroscopy. These advances are high-quality UV-grade optical fiber, sensitive and affordable array detectors, and chemometrics. 

J.A. Schmidt, Ultraviolet/visible spectroscopy of chromophores in mechanical pnlps, in Encyclopedia of Analytical Chemistry, John Wiley Sons Ltd, Chichester, 8388-8406 (2000). 

B.M. Weckhuysen, Ultraviolet-visible spectroscopy, in B.M. Weckhuysen (ed.). In situ Spectroscopy of Catalysts, American Scientific Pnblishers, Stevenson Ranch, 255-270 (2004). 

T.J. Thurston, R.G. Brererton, D.J. Foord, R.E.A. Escott, Principal components plots for exploratory investigation of reactions using ultraviolet-visible spectroscopy application to the formation of benzophenone phenylhydrazone, Talanta, 63, 757-769 (2004). 

Optical Spectroscopy General principles and overview, 246, 13 absorption and circular dichroism spectroscopy of nucleic acid duplexes and triplexes, 246, 19 circular dichroism, 246, 34 bioinorganic spectroscopy, 246, 71 magnetic circular dichroism, 246, 110 low-temperature spectroscopy, 246, 131 rapid-scanning ultraviolet/visible spectroscopy applied in stopped-flow studies, 246, 168 transient absorption spectroscopy in the study of processes and dynamics in biology, 246, 201 hole burning spectroscopy and physics of proteins, 246, 226 ultraviolet/visible spectroelectrochemistry of redox proteins, 246, 701 diode array detection in liquid chromatography, 246, 749. 

We have found a direct calorimetric determination of both K and AH° to be capable of producing much more reliable thermodynamic data than infrared or ultraviolet-visible spectroscopy. Furthermore, things that react extensively have enthalpies but may not have convenient changes in absorption bands. The procedure for the simultaneous determination of K and AH° from calorimetric measurements has been described (20—22). 

Difference ultraviolet/visible spectroscopy, photosystem 11, 33 225-228 Diffusion, conversion of radial to linear, 36 352-353... 

Ultraviolet-visible spectroscopy has played only a minor role in the investigation of the thietanes and its counterparts. As expected, the colorless compounds absorb in the UV region below 300 nm. For photolysis experiments, many phenylated and alkylated thietanes and thietane oxides have been measured in methyl cyanide or methanol by Langendries and de Schryver. The spectra exhibit a maximum in the vicinity of 250-265 nm ( 12,000-25,000). 

Hostettmann, K. et al., On-line high-performance liquid chromatography ultraviolet-visible spectroscopy of phenolic compounds in plant extracts using post-column derivatization, J. Chromatogr., 283, 137, 1984. 

Biermann, H. W E. C. Tuazon, A. M. Winer, T. J. Wallington, and J. N. Pitts, Jr., Simultaneous Absolute Measurements of Gaseous Nitrogen Species in Urban Ambient Air by Long Pathlength Infrared and Ultraviolet-Visible Spectroscopy, Atmos. Environ., 22, 1545-1554 (1988). 

The tautomerism of 4 (Figure 1) was also studied by UV-Vis (ultraviolet-visible) spectroscopy in polar aprotic solvents the effect of added water, darkness, and indirect sunlight were also evaluated. The experimental spectroscopic results are discussed in Section 13.14.3.1.1 (i). Theoretical calculations using ZINDO/S were performed to state the allowed absorption transitions <2005SAA875>. The five tautomeric structures of 4 as well as the calculated energies for each are depicted in Figure 2. 

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