[Alberto_Kravina]

Hi all

Has anyone of you ever performed Raman spectroscopy on solutions with different concentrations? I was just wondering if there is some sort of empirical relationship between scattering intensity and concentration of scattering molecules. In the experiment I did I used a linear relationship and the results are pretty good. However, I don't think that you can call it Lambert-Beer's law since L.B. is, strictly speaking, only valid when talking about absorbtion. My intuition would tell me that the dependence could look something like the dependence of fluorescence intensity with increasing concentration, which rises linearly and then falls off exponentially at higher concentrations (see attached picture, concentration dependence of Pyrenebutyric acid). It looks intuitively pleasing as the scattering intensity rises when the concentration becomes higher, but then if there are too many scattering centres the intensity could go down again, I think.

Does anyone have an idea or some experience with this kind of problem?

[TTAGGGn]

If your talking about fluorescence spectroscopy then the emission of fluorescence increases when concentration increases, that's assuming you are using very dilute amounts


There is a point where the concentration of the analyte can self absorb therefore decreasing the emission of fluorescence because the molecules are closer together that the electromagnetic radiation will be absorbed by another molecule rather than passing through the solvent into the detector. So there is a cut off point in how concentrated a solution you are using before you start to see a decrease in emission.

[Mitch]

I know you can't quantitate with IR, I'm not sure about RAMAN.

[Alberto_Kravina]

There is a point where the concentration of the analyte can self absorb therefore decreasing the emission of fluorescence because the molecules are closer together that the electromagnetic radiation will be absorbed by another molecule rather than passing through the solvent into the detector. So there is a cut off point in how concentrated a solution you are using before you start to see a decrease in emission.

Yeah, That is what I thought could also happen with Raman scattering, the concentration dependence would look pretty much like the one I posted on the picture, which shows quantitatively what you described. I was not able to find any reference to this topic up to now, maybe the best thing one can do is just measure it by him/herself and then try the function which fits best

[TTAGGGn]

look up self-absorption or self-absorber or excimer or quencher