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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: ubcdumbass on February 13, 2019, 03:34:38 AM

Title: Give an example of a substance for which the molar absorptivity cannot be found.
Post by: ubcdumbass on February 13, 2019, 03:34:38 AM
... but that the absorptivity can be measured.
Can anybody give me a direction for where I can find this info? Confused as I believed molar absorptivity to be directly linked to the wavelength it was absorbing photons at, and therefore would need molar absorptivity. Thank you!
Title: Re: Give an example of a substance for which the molar absorptivity cannot be found.
Post by: mjc123 on February 13, 2019, 04:48:26 AM
Something for which the molecular weight is unknown or undefined, e.g. a polymeric sample whose MW has not been accurately determined. You can measure the absorbance of a sample, and get a specific absorbance (i.e. per unit mass), but not a molar absorptivity. (At least for the polymer; if its structure is well-defined, you may be able to get a molar absorptivity for the chromophoric group.)