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In chemistry, the molar absorption coefficient or molar attenuation coefficient (ε) [1] is a measurement of how strongly a chemical species absorbs, and thereby attenuates, light at a given wavelength. It is an intrinsic property of the species.
Extinction coefficient refers to several different measures of the absorption of light in a medium: Attenuation coefficient , sometimes called "extinction coefficient" in meteorology or climatology Mass extinction coefficient , how strongly a substance absorbs light at a given wavelength, per mass density
This reaction is rapid and stoichiometric, with the addition of one mole of thiol releasing one mole of TNB. The TNB 2− is quantified in a spectrophotometer by measuring the absorbance of visible light at 412 nm, using an extinction coefficient of 14,150 M −1 cm −1 for dilute buffer solutions, [4] [5] and a coefficient of 13,700 M −1 cm −1 for high salt concentrations, such as 6 M ...
Thus a scattering coefficient μ s and an absorption coefficient μ a can be combined into a total extinction coefficient μ = μ s + μ a. [ 6 ] Importantly, Beer also seems to have conceptualized his result in terms of a given thickness' opacity, writing "If λ is the coefficient (fraction) of diminution, then this coefficient (fraction) will ...
ε is the molar attenuation coefficient of that material, and; c(z) is the molar concentration of that material at z. If c(z) is uniform along the path, the relation becomes =. The use of the term "molar absorptivity" for molar attenuation coefficient is discouraged. [1]
In a large scale, one must compute the extinction coefficient using the Beer-Lambert Law A=εLC in which A is the measured absorbance, ε is the slope of the standard curve, L is the length of the cuvette, and C is the concentration being determined. [26]
For example, the absorption spectrum for ethane shows a σ → σ* transition at 135 nm and that of water a n → σ* transition at 167 nm with an extinction coefficient of 7,000. Benzene has three aromatic π → π* transitions; two E-bands at 180 and 200 nm and one B-band at 255 nm with extinction coefficients respectively 60,000, 8,000 and 215.
where l is the optical path length, ε is a molar absorbance at unit path length and c is a concentration. More than one of the species may contribute to the absorbance. In principle absorbance may be measured at one wavelength only, but in present-day practice it is common to record complete spectra.