Ultraviolet spectra INDEX

FIG. 8.4 Determination of the microenvironment of a molecule (a) a portion of the ultraviolet spectrum of benzene in (1) heptane, (2) water, and (3) 0.4 M sodium dodecyl sulfate and (b) ratio of the intensity of the solvent-induced peak to that of the major peak for benzene versus the index of solvent polarity. The relative dielectric constant is also shown versus the index of polarity. (Redrawn, with permission, from P. Mukerjee, J. R. Cardinal, and N. R. Desai, In Micellization, Solubilization and Microemulsions, Vols. 1 and 2 (K. L. Mittal, Ed.), Plenum, New York, 1976.)... 

Figure 1 is the ultraviolet spectrum of a 10 mcg/ml solution of vitamin D3 in methanol. The spectrum was obtained using a Cary Model 219 recording spectrophotometer (Varian Instrument Co., Palo Alto, CA). Vitamin D3 and related compounds have a characteristic UV absorption maximum at 265 nm and a minimum at 228 nm. The extinction coefficient at 265 nm is about 17,500 and 15,000 at 254 nm. An index of purity of vitamin D3 is a value of 1.8 for the ratio of the absorbance at 265 to that at 228 nm. The high absorbance at 254 nm enables one to use the most common and sensitive spectrophotometric detector used in high performance liquid chromatography (HPLC) for the analysis of vitamin D3 in multivitamin preparations, fortified milk, other food products, animal feed additives etc. 

The ultraviolet spectrum of pyrazine in cyclohexane shows maxima at 260 nm (corresponding to a tt-tt transition) and 328 nm (corresponding to a n-7r transition) in each case with vibrational fine structure the coefficients of molecular extinction are 5600 and 1040, respectively.78,79 Substitution of halogen has a bathochromic effect on the ultraviolet spectrum of pyrazine.80 A useful index of the ultraviolet and visible spectra of pyrazine derivatives is available for the period from 1955 to 1963.81 The far-ultraviolet spectrum of pyrazine... 

If a laser beam produces in the outer atmosphere a spectrum spanning from the ultraviolet to at least the red, then the return light will follow different optical paths depending on the wavelength (Fig. 19). The air refraction index is a function of air temperature T and pressure P ... 

A short guard column containing the same stationary phase as the analytical column is placed before the analytical column to protect it from contamination with particles or irreversibly adsorbed solutes. A high-quality pump provides smooth solvent flow. The injection valve allows rapid, precise sample introduction. The column is best housed in an oven to maintain a reproducible temperature. Column efficiency increases at elevated temperature because the rate of mass transfer between phases is increased. Mass spectro-metric detection provides quantitative and qualitative information for each substance eluted from the column. Ultraviolet detection is most common and it can provide qualitative information if a photodiode array is used to record a full spectrum of each analyte. Refractive index detection has universal response but is not very sensitive. Evaporative light scattering responds to the mass of each... 

The Pharmacopea and the Essential Oil Association of the United States require the following analyses as an index of oil purity refractive index, optical rotation, refractive index and optical rotation of a 10% distillate, specific gravity, aldehyde content, evaporation residue and ultraviolet absorption spectrum (Kesterson et al. 157 and Sale 29). 

Since the polarizers discussed above involve light reflection combined with the real part of the refractive index tensor, they can be used effectively over a broad spectral range about a central wavelength. Calcite Glan-Thompson polarizers, for example, operate successfully over the entire visible spectrum. When fabricated of crystalline quartz, these polarizers can be used to polarize ultraviolet light as well as visible light. 

Ultraviolet Spectrophotometry A portion of tiie methanol extract is diluted with water and examined at both acid and alkaline pH by ultiaviolet spectrophotometry. The features of any resultant spectrum should be checked in the index to Ultraviolet Absorption Data in Part 3. If the identity is suspected, tiie spectrum maybe compared witii tiiat given in tiie monograph in Part 2. 

The wavelengths of main peaks are listed for acid, alkaline, and neutral solution in the index of Ultraviolet Absorption Maxima (p. 1128). Infra-Red Absorption. The wavenumbers of the six major peaks in the range 2000 to 650 an (5 to 15 Lim), in descending order of ampHtude, are recorded in the monographs in Pm 2. In many cases ftie infi-a-red spectrum is also reproduced. When selecting the six principal peaks, those which are in ftie region where Nujol absorbs (1490 to 1320 cmr, 6.7 to 7.6 um) have been omitted. Corrections for cahbration errors have been applied where these are known. The six principal peaks, in ascending order of ftie main peak, are listed in the index of Infra-red Peaks (p.1141). 

The solution frequently becomes warm,12 and its refractive index,1 viscosity,2 freezing point-composition curve,3 and ultraviolet absorption spectrum 36 are not those which would be expected if no reaction took place. Usually hydrates or hemiacetals of simple aldehydes are too unstable to be isolated, but a number of them are actually known and their physical properties have been determined.4 When the carbonyl group is attached to an electron-attracting group (making the carbonyl carbon atom abnormally positive), stable hydrates are frequently formed. Glyoxal, chloral, and ketomalonic acid are common examples. 

The optical properties of ceramics are useful in the ultraviolet, visible, and infrared ranges of the electromagnetic spectrum, and one key quantity used to describe the optical property of a material is the refractive index, which is a function of the frequency of the electromagnetic radiation. Other quantities used to characterize optical performance are absorption, transmission, and reflection these three properties sum to unity and are also frequency dependent. The last three properties govern many aspects of how light interacts with materials in windows, lenses, mirrors, and filters. In many consumer, decorative, and ornamental applications, the esthetic qualities of the ceramic, such as color, surface texture, gloss, opacity, and translucency, depend critically on how light interacts with the material. 

There seems to be no limitation on what kind of detectors may be used for HPLC. Even detectors designed for use in gas phase analyses have been applied to HPLC. The principles of the detectors used for routine analysis are based on absorption of light in the ultraviolet and visible spectrum, refractive index or fluorescence. Detection problems are discussed below. 

Noble gases are intrinsically difficult to detect by spectroscopy. For example, solar photospheric spectra, which form the basis for solar abundance values of most elements, do not contain lines from noble gases (except for He, but this line cannot be used for abundance determinations). Yet, ultraviolet spectroscopy is the only or the major source of information on noble gas abundances in the atmospheres of Mercury and comets. In the Extreme Ultraviolet (EUV), photon energies exceed bond energies of molecules and the first ionization potential of all elements except F, He, and Ne, so that only these elements are visible in this part of the spectrum (Krasnopolsky et al. 1997). Other techniques can be used to determine the abundance of He where this element is a major constituent. Studies of solar oscillations (helioseismology) allow a precise determination of the He abundance in the solar interior, and the interferometer on the Galileo probe yielded a precise value for the refractive index and hence the He abundance in the upper atmosphere of Jupiter (see respective sections of this chapter). 

The crystal structure of YF3 at room temperature is Pnma, with Y ions in sites of Cs symmetry (Wyckoff, 1%4). A higher temperature hexagonal form has also been observed (Sobolev and Fedorov, 1973). The index of refraction is 1.550 at the sodium D line doublet (X = 0.589 p,m) and the dielectric constant is 10.0 at / = 760 kHz (Dulepov et al., 1976). The polarized infrared spectrum of YF3 has been obtained and the lattice vibrations have been analyzed and assigned to symmetry species (Rast et al., 1969). Electron-beam and ultraviolet excitation of rare-earth doped YF3 has determined the energy separation of the configurations 4f"" 5d and 4f" for several rare earths (Yang and DeLuca, 1976). 

Umezawa (1967) has recently published an index of antibiotics from actinomycetes. This compendium includes physical and chemical data such as, crystal type, melting point, optical rotation and ultraviolet maxima, infrared spectrum, structural diagram, etc. 

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