Molar extinction coefficient values

Determination of the Calcofluor White Molar Extinction Coefficient Value in the Absence and Presence of -Acid Glycoprotein... 

Determination ofCalcofluor White Molar Extinction Coefficient Value... 

UV-Vis absorption and fluorescence emission of Troger base analogue 51 and its precursor 2-(4-amino-2-hydro-xyphenyl)benzothiazole were measured. In the UV-Vis spectra, all molar extinction coefficient values were in the order of 104lmol 1 cm as expected for 71-71 transitions. 

The color of pyranoanthocyanins is more orange than that of anthocyanins, which leads one to suppose that they can contribute to the red tile and orange hues characteristics of aged wines. Similar molar extinction coefficients values for malvidin 3-glucoside (1.6 x 10" L/mol/cm) and its corresponding carboxypyra-noanthocyanin (i.e., vitisin A 1.3 x lO L/mol/cm) were determined by Mateus and... 

The surface concentration of Bronsted and Lewis sites was evaluated by integration of the absorption bands at 1545 and 1455 cm due to adsorbed pyridinium ion and pyridine, with integrated molar extinction coefficients values 813 = 1-67 and Sij, = 2.22 cm pmol" [15]. Although absolute concentration of surface acid sites obtained by this method is affected by a 10 - 15% error [12], reliable and valuable information can usually be obtained on a relative scale. Moreover, in the present case pyridine is an ideal probe molecule. Indeed, being very similar in structure to the reactant involved in the present reaction, it is able to titrate exactly those acidic sites which can be reached also by HEP. 

Figure 2.17 Correlation between calculated oscillator strength values and experimental molar extinction coefficient values for a series of monoazo and disazo pigments.

This is the fundamental equation of colorimetry and spectrophotometry, and is often spoken of as the Beer-Lambert Law. The value of a will clearly depend upon the method of expression of the concentration. If c is expressed in mole h 1 and / in centimetres then a is given the symbol and is called the molar absorption coefficient or molar absorptivity (formerly the molar extinction coefficient). 

Most often, quantification has been carried out by exclusively assessing the absorption at the maximum wavelength and selection of the appropriate molar extinction coefficient. " Reasonable values will be obtained if the absorption at 600 to 650 nm is subtracted. 

A useful measure of the strength or intensity of the colour of a dye is given by the molar extinction coefficient (e) at its 2max value. This quantity may be obtained from the UV/visible absorption spectrum of the dye by using the Beer-Lambert law, i.e. 

The UV absorption spectra of niclosamide in methanol, methanolic 0.1 N HC1 and methanolic 0.1 N NaOH are shown in Fig. 3. The figures were recorded using a Perkin-Elmer double beam model 550s UV-Vis spectrophotometer. The values of the log emax (log molar extinction coefficient) at their corresponding wavelength maximum in nanometers (2max) are shown in the following table. 

The intensity of absorption gives the product G , where G is the observed yield and is the molar extinction coefficient. The absolute value of was determined by Fielden and Hart (1967) using an H2-saturated alkaline solution and an alkaline permanganate-formate solution, where all radicals are converted into Mn042. They thus obtained = 1.09 x 104 M- cm1 at 578 nm, which is almost identical with that obtained by Rabani et al. (1965), who converted the hydrated electron into the nitroform anion in a neutral solution of tetrani-tromethane. From the shape of the absorption spectrum and the absolute value of at 578 nm, one can then find the absolute extinction coefficient at all wavelengths. In particular, at the peak of absorption, (720)/ (578) = 1.7 gives at 720 nm as 1.85 X 104 M 1cm 1. 

The fluorescent properties of NHS-rhodamine are similar to TRITC. The wavelength of maximal absorbance or excitation for the reagent is 544 nm and its emission maximum is 576 nm, exhibiting a visual color of orange-red. Its molar extinction coefficient at 546 nm in a methanol environment is 63,000M 1cm 1. Other components in solution as well as the pH (in aqueous buffers) can change this value. 

AMCA-hydrazide has a maximal excitation wavelength of 345 nm and a maximum emission wavelength in the range of 440-460 nm. A solution of AMCA in PBS at a concentration of 16.7ng/ml (71.61 nmoles/ml) gives an absorbance at 345 nm of about 1.28. This translates into a molar extinction coefficient at this wavelength of about 13,900M em-1. Different solvents and conditions may alter this value somewhat. 

Table 9.3 Typical values of molar extinction coefficient e...

The vacuum ultraviolet photolysis of HI has been studied by Martin and Willard16 using the 1849 A mercury lines as the exciting radiation. They estimated the molar extinction coefficient at 1849 A to be between 110 and 150 in fair agreement with Romand s3 experimental value of 125. The hydrogen atoms produced have sufficient energy to cause the reaction... 

The resulting extinction coefficient remained constant within the accuracy of the measurements. In the transition from monoazo to disazo pigment, however, the value of the maximum molar extinction coefficient is more than doubled, because the effect of the two azo linkages is enhanced by additional interaction via the diphenyl moiety. This, however, does not improve the conjugation the shade does not shift remarkably ... 

Electronic spectra (Table 1.1, Fig. 1.2) have been measnred for the orange soln-tions of (RuO ] in aqueous base from 250-600 nm. [212-215, 222], and reproduced [215, 222]. There are two at 460 and 385 nm. [212, 213, 222] or three bands in the visible-UV region, at 460, 385 and 317 nm [214, 215]. These appear to be at the same positions as those for [RuO ] but the intensities and hence the general outline of the two spectra are very different. Woodhead and Fletcher reviewed the published molar extinction coefficients and their optimum values / dm (mol" cm" ) are 1710 for the 460 nm. band, 831 for the 385 nm. band and 301 for the 317 nm. band - the latter band was not observed by some workers [214]. The distinctive electronic spectrum of ruthenate in solution is useful for distinguishing between it, [RuO ]" and RuO [212, 222]. Measurements of the electronic spectra of potassium ruthenate doped in K CrO and K SeO and of barium ruthenate doped into BaSO, BaCrO, and BaSeO (in all cases the anions of these host materials are tetrahedral) indicate that in that these environments at least the Ru is tetrahedrally coordinated. Based on this evidence it has been suggested that [RuO ] in aqueous solution is tetrahedral [RuO ] rather than franx-[Ru(0H)3(0)3] [533, 535]. Potential modulated reflectance spectroscopy (PMRS) was used to identify [RuO ] and [RuO ] " in alkaline aqueous solutions during anodic oxidation of Ru electrodeposited on platinum from [Ru3(N)Clg(H30)3] [228]. 

A totally allowed transition has oscillator strength /=1 and molar extinction coefficient 105. Different factors may reduce the / values to different extents. Oscillator strengths / are related to integrated absorption intensities by the expression... 

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