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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).
absorption coefficient is essentially (but not quite always) synonymous with attenuation coefficient; see attenuation coefficient for details; molar absorption coefficient or molar extinction coefficient , also called molar absorptivity , is the attenuation coefficient divided by molarity (and usually multiplied by ln(10), i.e., decadic); see ...
Therefore, measurements at two wavelengths yields two equations in two unknowns and will suffice to determine the amount concentrations c 1 and c 2 as long as the molar attenuation coefficients of the two components, ε 1 and ε 2 are known at both wavelengths.
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.
The attenuation coefficient of a volume, denoted μ, is defined as [6] =, where Φ e is the radiant flux;; z is the path length of the beam.; Note that for an attenuation coefficient which does not vary with z, this equation is solved along a line from =0 to as:
Nevertheless, the absorbance unit or AU is commonly used in ultraviolet–visible spectroscopy and its high-performance liquid chromatography applications, often in derived units such as the milli-absorbance unit (mAU) or milli-absorbance unit-minutes (mAU×min), a unit of absorbance integrated over time. [6] Absorbance is related to optical ...
The attenuation coefficient (NB used infrequently with meaning synonymous with "absorption coefficient") [citation needed] The Molar attenuation coefficient (also called "molar absorptivity"), which is the absorption coefficient divided by molarity (see also Beer–Lambert law) The mass attenuation coefficient (also called "mass extinction ...
For a given medium at a given frequency, the opacity has a numerical value that may range between 0 and infinity, with units of length 2 /mass. Opacity in air pollution work refers to the percentage of light blocked instead of the attenuation coefficient (aka extinction coefficient) and varies from 0% light blocked to 100% light blocked: