Typical absorption

Figure 2.5 shows, for a sample in the gas phase, a typical absorption line with a HWHM (half-width at half-maximum) of Av and a characteristic line shape. The line is not infinitely narrow even if we assume that the instmment used for observation has not imposed any broadening of its own. We shall consider three important factors that may contribute to the line width and shape. 

In solution, lignin is most conveniendy analyzed quaUtatively and quantitatively by uv spectroscopy. Typical absorptivity values, D, at 280 nm for milled wood (MW) lignins and other types of lignins are Hsted ia Table 4. These values are used for quantitative determination of the lignins ia suitable solvents. 

A typical absorption curve for vitreous siUca containing metallic impurities after x-ray irradiation is shown in Eigure 12. As shown, the primary absorption centers are at 550, 300, and between 220 and 215 nm. The 550-nm band results from a center consisting of an interstitial alkah cation associated with a network substituent of lower valency than siUcon, eg, aluminum (205). Only alkaUes contribute to the coloration at 550 nm. Lithium is more effective than sodium, and sodium more effective than potassium. Pure siUca doped with aluminum alone shows virtually no coloration after irradiation. The intensity of the band is deterrnined by the component that is present in lower concentration. The presence of hydrogen does not appear to contribute to the 550-nm color-center production (209). 

A typical absorption curve obtained for a metal-free vitreous sihca after a large dose of y-rays is shown in Eigure 13. The main band is at 215 nm three smaller bands occur at 230, 260, and 280 nm. The 230-nm band may result from an electron trapped at a sihcon atom having an incomplete oxygen bond (205). 

Many 3-substituted thiophenes have a characteristic absorption at 760-780 Typical absorption bands exist for the different... 

Visible and ultraviolet absorption spectra are measured in an absorption spectrometer. The source gives out intense visible light or ultraviolet radiation. The wavelengths can be selected with a glass prism for visible light and with a quartz prism or a diffraction grating for ultraviolet radiation (which is absorbed by glass). A typical absorption spectrum, that of... 

Figure 2-1. Typical absorption spectra of transition-metal complexes.

The total anthocyanin content can often be determined in crude extracts containing other phenolic materials by measuring absorptivity of the solution at a single wavelength (Table 6.3.1). This is possible because anthocyanins have typical absorption bands in the 490 to 550 nm region of the visible spectra — far from the absorption bands of other phenolics with spectral maxima in the UV range. ... 

The absorption band of the colored form of spironaphthooxazine has been measured in thermal equilibrium with the spiro form, particularly in a polar solvent at low temperature. Typical absorption spectra of the colorless and the colored form in polymer fdms are shown in Figure 1.8. 

Figure 8.2 illustrates the format of a typical absorption costing exercise. This exercise can easily be used to calculate the overall profit or loss of each enterprise and its profit margin. See for example Fig. 8.3. One of the difficulties of this exercise is allocating the fixed costs between the various enterprises. Take housing for example if the shed is shared between beef cattle and sheep, then the allocation of the cost could be made on a space and time basis. On a large-scale farm with several workers there will probably be a shepherd, a stockman, and a tractor driver for the arable crops. However, on a smaller farm where the farmer and his family do all the work then division of time between...

Table 5.5 shows the main characteristics of UV spectrophotometry as applied to polymer/additive analysis. Growing interest in automatic sample processing looks upon spectrophotometry as a convenient detection technique due to the relatively low cost of the equipment and easy and cheap maintenance. The main advantage of UV/VIS spectroscopy is its extreme sensitivity, which permits typical absorption detection limits in solution of 10-5 M (conventional transmission) to 10 7 M (photoacoustic). The use of low concentrations of substrates gives relatively ideal solutions [20]. As UV/VIS spectra of analytes in solution show little fine structure, the technique is of relatively low diagnostic value on the other hand, it is one of the most widely used for quantitative analysis. Absorption of UV/VIS light is quantitatively highly accurate. The simple linear relationship between... 

The intensity ratio between typical absorption bands and the least changing band was used to illustrate the changes in the spectra. The change (m) in the absorption bands is mainly observed at the initial irradiation stage (30-40 min). The most marked decrease in the band intensity was found for the carbonyl group in the anhydride unit (1770 cm-1). 

Typical absorption and fluorescence spectra are shown in Figure 11.3. Since energy is lost in the activated state (S ) before fluorescence, the emission maximum always occurs at a lower wavenumber than the absorption maximum. The difference, which is termed the Stokes shift, can be calculated approximately from the absorption spectrum using the Pestemer rule [17,18]. This rule states that the Stokes shift is 2.5 times the half-bandwidth at the absorption maximum. 

Figure 11.3 Typical absorption and emission curves for an FBA (polar solvent)...

A possible method for predicting absorption bandwidths of chromogenic molecules or FBAs using PPP-MO theory (section 1.5) has been devised. It is based on the empirical linear relationship stated by the Pestemer rule. Thus theoretical Stokes shifts are computed by the PPP-MO method and related to bandwidths. The requisite MO parameters for various typical absorption bands have been developed for use in these calculations. Reasonable correlation between calculated and experimental half-bandwidth data was found, suggesting that this approach has practical potential in predicting colour tone and brightness intensity [ 19]. 

Before irradiating a compound one has therefore to know its absorption spectrum. A typical absorption spectrum is shown in Fig. 4, affording the following information ... 

Limited decomposition of the sulphate and extensive melamine condensation overlap in this second step with condensation of sulphuric acid residues to pyrosulphuric structures. This is shown by water evolution and appearance of typical absorptions of pyrosulphate... 

In the following third step (450-520 0), (Figure 10) the melam pyrosulphate is further condensed to melon with decomposition of the pyrosulphuric structure as shown by disappearance of typical absorptions of pyrosulphate or sulphate in the IR of the melon left as a residue. This last decomposes then above 520 0 (4th step). The proposed degradation scheme for the sulphate is ... 

FIGURE 2.9 Typical absorption and emission spectra of polyfluorene in thin films (shown for poly(9,9-dioctylfluorene) 196). (From Gong, X., Iyer, P.K., Moses, D., Bazan, G.C., Heeger, A.J., and Xiao, S.S., Adv. Fund. Mater., 13, 325, 2003. With permission.)... 

In Figure 29b three typical absorption isotherms are given near the saturation levels of the alkanes in the DPPC membrane. The results presented in this graph... 

Knowledge of drug properties, especially solubility in surfactants or as a function of pH, is essential. One could anticipate precipitation of the drug as the pH changes in solution, or if release from the dosage form leads to supersaturation of the test media. Be aware that preparation of a standard solution may be more difficult than expected. It is customary to use a small amount of alcohol to dissolve the standard completely. A history of the typical absorptivity range of the standard can be very useful to determine if the standard has been prepared properly. 

Fig. 15.3 A typical frequency response curve obtained due to the introduction of air into the resonant cavities. Shown above in pink is a typical absorption profile of the resonator under vacuum, and in blue is the shift of the resonant frequency to a lower value upon introducing air into the system (See Color Plates)...

We have seen that the absorption spectra of (RE) + ions (see Eignres 6.2 and 6.3) consist of several sets of lines corresponding to transitions between the Stark snblevels of 2S+1 j states within the 4f" electronic confignration. A typical absorption spectmm of a (RE) + ion in crystals is like the one sketched in Eignre 6.16. The different sets of transitions correspond to different J J transitions (/ acconnting for the gronnd state), which, in principle, are only permitted at magnetic dipole order the selection rnle is 2 / = 0, 1, with 0 -o- 0 forbidden. 

F ure 6.16 A typical absorption spectrum of a trivalent rare earth ion (not corresponding to any specific ion) in a crystal. A generic / —> / absorption transition, with an average frequency of mo, has been marked and shaded (see the text). 

As a separate issue, the ring-opening reaction of the spirooxazine and the spiropy-ran can be sensitized by triplet energy donors[73,113-115]. A typical absorption rise for a benzophenone-sensitized ring-opening reaction is compared to that of the unsensitized fast absorption rise for NOSI3 in Fig. 13 [73,113]. In this case, both solutions were optically matched at the excitation wavelength. 

Practical Considerations. Typical absorption assay methods utilize ultraviolet (UV) or visible (vis) wavelengths. With most spectrophotometers, the measured absorbance should be less than 1.2 to obtain a strictly linear relationship (/.c., to obey the Beer-Lambert Law). Nonlinear A versus c plots can result from micelle formation, sample turbidity, the presence of stray light (see below), bubble formation, stacking of aromatic chromophores, and even the presence of fine cotton strands from tissue used to clean the faces of cuvettes. One is well advised to confirm the linearity of absorbance with respect to product (or substrate) concentration under the exact assay conditions to be employed in... 

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