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The SI unit of molar absorption coefficient is the square metre per mole (m 2 /mol), but in practice, quantities are usually expressed in terms of M −1 ⋅cm −1 or L⋅mol −1 ⋅cm −1 (the latter two units are both equal to 0.1 m 2 /mol).
First step is to plot the absorbance(A) values of standard solution against molar concentrations (c) of the known solution. Then the best straight line is plotted, passing through the origin. The experimental points are plotted as per Beer’s law: A= E*c*l where E= molar extinction coefficient and l= optical path length usually 1 cm.
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
The molar extinction coefficient of Hb has its highest absorption peak at 420 nm and a second peak at 580 nm. Its spectrum then gradually decreases as light wavelength increases. On the other hand, H b O 2 {\displaystyle HbO2} shows its highest absorption peak at 410 nm, and two secondary peaks at 550 nm and 600 nm.
A. R. Forouhi and I. Bloomer deduced dispersion equations for the refractive index, n, and extinction coefficient, k, which were published in 1986 [1] and 1988. [2] The 1986 publication relates to amorphous materials, while the 1988 publication relates to crystalline.
Variable pathlength absorption spectroscopy uses a determined slope to calculate concentration. As stated above this is a product of the molar absorptivity and the concentration. Since the actual absorbance value is taken at many data points at equal intervals, background subtraction is generally unnecessary.
Thus, for a fixed path length, UV-Vis spectroscopy can be used to determine the concentration of the absorber in a solution. It is necessary to know how quickly the absorbance changes with concentration. This can be taken from references (tables of molar extinction coefficients), or more accurately, determined from a calibration curve.
This quantity is called the extinction coefficient and denoted κ. In accordance with the ambiguity noted above , some authors use the complex conjugate definition, where the (still positive) extinction coefficient is minus the imaginary part of n _ {\displaystyle {\underline {n}}} .