[Jen]

I need to find the extinction coefficient of a-tocopherol in a solution of THF (tetrahydrofuran).  Where can I find this information?  Are there charts of extinction coefficients listed somewhere?

I also need the extinction coefficients for b-carotene in THF and xanthophyll in THF.

Please help.

Jen

[ARGOS++]

Dear Jen,

Sorry!, I don’t know either source.

But do you know the precision you need, and that you can find such a precision, except as a rule of thumb, in Literature?

Usually only for Professors or “Qualitative Analysis” you can use literature values you may find.
For Quantitative Analysis it is much more common/precise to determine its value from a reference sample in your particular environmental, as: 

ε = f(λ, solv, %, Sw, pH, etc.)

(I know, it’s not all time an easy task/way!)

If you are interested in more information about, you may visit:

Corrected Beer-Lambert Bouguer Law

Or also:

Spectroscopy FAQ / Beer-Lambert Bouguer Law FAQ

So I don’t know that you really will find valid values for.
Sorry!

Good Luck!
                    ARGOS⁺⁺

[Jen]

hmm, so you are saying I can determine the value of E myself?  Please explain more on how to do that, I am a biologist not a chemist so this is very confusing to me.  Do you have any links in english?

Jen

[ARGOS++]

Dear Jen,

On the FAQ-Page above, in the seventh block, you will find an answer for the question:
“How to determine/find … extinction coefficients?”
This answer contains also a recipe for how to do – if to do!
If we make several (allowed) assumptions we can significantly reduce the required effort to get a result.

On the other hand, if the assumptions hold, we can use the “Special Beer-Lambert Law” and set:

A_{λ, solv.} = ε_{λ, solv.} * c * d

With other words: ε_{λ, solv.} is the conditions (c and d) for only a special Absorbance value.
So the only things you have to do (if assumptions hold) is:
A.)   Measure a spectrum of your known pure reference.
B.)   Measure an Absorption value of your reference at the given λ for a known Concentration c and the known Pathlength d inside the linear range of your Spectrometer.
C.)   Do a small calculation, - and that’s it.

But before we start, you will have to answer a number of questions to test the assumptions and a few other things:
1.)   Will you ever measure two or all compounds simultaneous in the same particular Sample and determine all three concentrations at once? (I suppose: Yes)
(Then you have a hard job, if you not use the MCA-Method instead!!)
2.)   From “where” you got the problem? – From a professor, or his/her assistant?
3.)   Do you know which β-Carotene and which Xanthophyll you will have to measure, or you know at least the source of them?

To give you an imagination for my last question I have scanned the following picture for you:
You may see, β-Carotene is not like β-Carotene, and NIST knows others too.
As for Xanthophyll, the Dihydroxy-β-Carotene exact similar will be true, you would run into several troubles, if you use literature values without any exact knowledge!!
(How many times different are already measured as the SAME in literature?)

As soon as I know your answers we may start.

Good Luck!
                    ARGOS⁺⁺

P.S.: I’m doing UV/Vis- and other Spectroscopy, and MCA since a lot of years.
.

[ARGOS++]

Dear ALL,

I BEG Your pardon!, I just realized, that my given Links/References above were NOT WORKING!
SORRY! I did a typing mistake!

I have now corrected both Links/References and tested too.
Sorry once again.

Good Luck!
                    ARGOS⁺⁺

P.S.: Why did nobody tell me the broken Links/References?!?
.