Solvent extinction

Solvent Extinction coefficient, a [m ] Thermal conductivity, h[Wm" K ] a/h [W K] Molecule Distance from the bottom of sample cell [pm] AT/AP [KWr j (experimental data)... 

FIGURE 8.1-2 Deeprea Ventures solvent extinction flowsheet for separation of matals in a manganese nodule lench liquor. From Ref. 11, with permission. 

T. W. Chapman, Equilibrium Stage Calculations for the Solvent Extinction of Metals, in Fun-... 

T. W. Chapman, Solvent Extinction of Metals—Metal Transfer Rales and Contactor Design, in... 

Batterham, G. J., Munksgaard, N. C., and Parry, D. L. (1997). Determination of trace metals in seawater by inductively coupled plasma mass spectrometry after off-line dithiocarba-mate solvent extinction.J. Anal. At. Spectrom. 12(11), 1277. 

The quantity e is called the absorption coefficient or extinction coefficient, more completely the molar decadic absorption coefficient it is a characteristic of the substance and the wavelength and to a lesser extent the solvent and temperature. It is coimnon to take path length in centimetres and concentration in moles per... 

The electronic transitions which produce spectra in the visible and ultraviolet are accompanied by vibrational and rotational transitions. In the condensed state, however, rotation is hindered by solvent molecules, and stray electrical fields affect the vibrational frequencies. For these reasons, electronic bands are very broad. An electronic band is characterised by the wave length and moleculai extinction coefficient at the position of maximum intensity (Xma,. and emai.). 

The former exhibits absorption tjrpical of an isolated keto group, whereas the latter shows a high intensity -band associated with the conjugated system HO—C=C—C=0. The proportions of the two forms under various conditions are readily determined from the ultraviolet spectra. The ultraviolet spectra in various solvents are shown in Fig. A, 7, 2. Since the absorption of the keto form is negligible, the percentage of enol present is 100(em/e ), where e is the observed extinction at 245 mp. and that of the pure enol. It was shown that in alcoholic solution is 1900 and the percentage of enol is 12. Thus e is ca. 16000, and use of this value permits the approximate evaluation of the enol content in different solvents. The results are collected in Table XII. 

The ultraviolet absorption spectrum of thiazole was first determined in 1955 in ethanolic solution by Leandri et al. (172), then in 1957 by Sheinker et al. (173), and in 1967 by Coltbourne et al. (174). Albert in 1957 gave the spectrum in aqueous solution at pH 5 and in acidic solution (NHCl) (175). Nonhydroxylic solvents were employed (176, 177), and the vapor-phase spectrum was also determined (123). The results summarized in Table 1-15 are homogeneous except for the first data of Leandri (172). Both bands A and B have a red shift of about 3 nm when thiazole is dissolved in hydrocarbon solvents. This red shift of band A increases when the solvent is hydroxylic and, in the case of water, especially when the solution becomes acidic and the extinction coefficient increases simultaneously. 

In view of the chromophoric character of the elemental iodine itself, many colorimetric methods have been proposed for the deterrnination of inorganic iodine (88—92). These methods use the visible portion of the spectmm in reading iodine concentrations. In the visible range the extinction coefficient for iodine is not high enough to be used for minute quantities of iodine in water and other solvents (93). Higher sensitivities have been reported for elemental iodine in potassium iodide solutions in the ultraviolet (93,94). 

The solvent used was 5 %v/v ethyl acetate in n-hexane at a flow rate of 0.5 ml/min. Each solute was dissolved in the mobile phase at a concentration appropriate to its extinction coefficient. Each determination was carried out in triplicate and, if any individual measurement differed by more than 3% from either or both replicates, then further replicate samples were injected. All peaks were symmetrical (i.e., the asymmetry ratio was less than 1.1). The efficiency of each solute peak was taken as four times the square of the ratio of the retention time in seconds to the peak width in seconds measured at 0.6065 of the peak height. The diffusivities obtained for 69 different solutes are included with other physical and chromatographic properties in table 1. The diffusivity values are included here as they can be useful in many theoretical studies and there is a dearth of such data available in the literature (particularly for the type of solutes and solvents commonly used in LC separations). 

Mercaptoquinolines of this type exist in the zwitterion or the zwitterion-extended quinone form to a greater extent than do the analogous hydroxy compounds ° (see Table V and Section II,R), and the color of 8-mercaptoquinoline has been attributed to the zwitterion structure.The concentration of the zwitterion decreases as the dielectric constant of the solvent decreases in the order H2O > MeOH > EtOH > Bu OH as indicated by the change in the molecular extinction coefficient. ... 

Time-resolved optical absorption spectroscopy experiments have shown that arenesul-fonyl radicals decay with clean second-order kinetics14 the values of 2 k,/a h where s2 is the extinction coefficient at the monitoring wavelength, increased linearly with decreasing viscosity of the solvent, further indicating that reaction 16 is clearly a diffusion-controlled process. 

The extinction coefficients of carotenoids have been listed completely bnt solvent effects can shift the absorption patterns. If a colorant molecnle is transferred into a more polar environment, then the absorption will be snbjected to a bathochro-mic (red) shift. If the colorant molecnle is transferred into a more apolar enviromnent, the absorption will be subjected to a hypsochromic (blue) shift. If a carotenoid molecule is transferred from a hexane or ethanol solution into a chloroform solution, the bathochromic shift will be 10 to 20 nm. 

Amotf was the first to develop a set of equations for acetone to simultaneously calculate chlorophyll a and chlorophyll b in 1949. Several authors later proposed different new equations based on more adjusted and accurate extinction coefficients due to the development of higher resolution spectrophotometers adapted to each special condition. Moreover, besides 80% acetone, coefficients for diethyl ether and ethanol were also established and their respective equations developed, as reviewed by Schwartz and Lorenzo and Eder. Solvents chosen should be those for which specific absorbance coefficients have been published to derive equations and updates should be carefully tracked for new values. 

Porra, R.J., Thompson, W.A., and Kriedemann, P.E., Determination of accurate extinction coefficients and simultaneous equations for assaying chlorophylls a and b extracted with four different solvents verification of the concentration of chlorophyll standards by atomic absorption spectroscopy, Biochim. Biophys. Acta, 975,384, 1989. 

Due to varying solvent systems, varying purities and water contents of purified pigments, different molar extinction coefficients have been reported." - - The most reliable ones commonly applied are 60,000 L/mol cm for betanin, 56,600 L/mol cm for amaranthin, and 48,000 L/mol cm for betaxanthins. ° Pigment contents may be calculated with the following formulae." - ... 

As was discussed in the previous part, the temperature elevation in the solutions can be ascribed to the absorption of the NIR light by the solvents. In order to quantitatively explain the temperature elevation coefficient, AT/AP, for other solvents, we proposed a simple model that can parametrize the temperature elevation. As easily predicted, the AT/AP value is closely related to the extinction coefficient of light absorption, a, and the thermal conductivity, X. Heat generated at the focal point ofthe NIR beam is proportional to the extinction coefficient, a, and the incident laser power, P, as represented by Eq. (8.5). 

Figure 8.10 Plot of AT/AP as a function of a/X. The temperature elevation coefficients are proportional to the ratio ofthe extinction coefficient of the solvents, a, and the thermal conductivity of the solvents, X.

Fortunately the metallocenes are generally quite soluble in a number of organic solvents, and it is therefore relatively straightforward to use intensity criteria for distinguishing between d-d and Laporte-allowed transitions. For the neutral metallocenes the extinction coefficients of the spin-allowed d-d bands usually lie between 101 and 102 (occasionally as high as ca. 200), whilst for the metallicenium species e tends to be slightly... 

Phthalocyanine-based dyes are especially useful for CD-R, as the chromophore absorption band falls in the desirable spectral range, and they are noted for excellent photostability. Unlike cyanine dyes, phthalocyanines tend to have very poor solubility, particularly in solvents such as alcohols and aliphatic hydrocarbons (which do not attack polycarbonate and are therefore used for spin coating). Therefore, the main barrier to the wider use of these dyes is the relatively high cost of synthesizing soluble derivatives. Suitable modifications to the Pc core which have been developed, notably by Mitsui Toatsu, are shown in Scheme 7. The bulky R groups reduce undesirable molecular association (which in turn lower the extinction coefficient and hence reflectivity), whereas partial bromination allows fine-tuning of the film absorbance and reflectivity. The metal atom influences the position of the absorption band, the photostability, and the efficiency of the radiationless transition from the excited state.199 This material is marketed by Ciba as Supergreen.204... 

Table 8. n - it transition in dimethyl and cyclohepteno cyclopropenone and its solvent dependence (from Ref.143 extinctions in log e)... 

Lissamine rhodamine B sulfonyl chloride is relatively insoluble in water, but may be dissolved in DMF prior to the addition of a small aliquot to an aqueous reaction. Do not dissolve in DMSO, as sulfonyl chlorides will readily react with this solvent (Boyle, 1966). The compound has a maximal absorptivity at 556 nm with an extremely high extinction coefficient of up to 93,000M em-1 (in methanol) in highly purified form. Its emission maximum occurs at 576 nm, emitting red luminescence. 

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