Extinction coefficient which is called as molar extinction coefficient helps you in measuring the strength of absorbance of light at a given wavelength. This article will help you know how to calculate extinction coefficient which is also known as molar absorption coefficient or molar absorptivity. Extinction coefficient is usually calculated for the chemical compound or the chemical species.
Formula for calculating the extinction coefficient of the chemical compound is given as follows:
A = є c l
In the above formula,
- “є” is the extinction coefficient of the sample
- “l” is the pathlength or the wavelength of the sample
- “c” is the concentration of the species
- “A” is a absorbance value
This formula is stated according to the Beer-Lambert law which relates the absorption of light by the chemical species by the properties of the material through which the light is travelling. Different conventions are used in case of different disciplines i.e. depending upon whether the absorbance is defined with respect to the transmission via natural or common algorithm.
Estimate the values of the wavelength of the species whose extinction coefficient is to be calculated, concentration of the species and absorbance of the species.
When there are more than one absorbing species in a solution then the absorbance of the species is the sum of the overall absorbances in the species.
Therefore,
A = A1+A2+….An
Where, A1, A2, … An is the absorbance of the individual components in the chemical species.
Examples:
Coefficient of extinction for proteins whose value can’t be determined
If you have the protein mixtures or the mixtures with unknown extinction coefficient then you can roughly estimate the coefficient of extinction for these compounds. For such substances coefficient of extinction in percent is assumed as 10.
Most of the values of extinction coefficient for the proteins fall in the range of 4.0 to 24.03. Therefore the above value is considered as an arbitrary value.
Immunoglobulins
In case of most of the antibodies in mammals the extinction coefficient falls in the range of 13-15. In this case the rough estimation of the coefficient of extinction is assumed to be 14. This value is assumed when you don’t know the value or are unable to estimate the value of extinction coefficient.
Using online calculators to calculate the extinction coefficient
You can also use the online calculators for calculating the coefficient of extinction. For using these online calculators, you need to know the compound used in your experiment. Insert the values of the required fields in the text boxes provided and click on the calculate button to calculate the extinction coefficient.
These calculators can be used to calculate the extinction coefficient of the individual species as well as chemical compounds.
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