I have some solid-acid catalysts whose surface consists of free radicals. I am able to visualise this by the intensity of peaks on the EPR spectrum (sample image attached), but would like to calculate their concentrations in spin/g. Is there any protocol to convert the intensity of EPR peaks into concentration of free radicals?
You must use a standard (usually - strong pitch or weak pitch depending on the intensity of the signal), which contains a known number of spins per a mass unit, and then calculate the concentration by proportion, or better calibrate the curve adding small (known) portion of the standard, use preferably the integral intensity of the signal (a double integral of the signal). It is possible to calculate the number from the Poole modified equation, but you have to know other parameters (Q factor, filling factor etc).
Dear Goutham Rangarajan this is a very interesting technical question. Actually, as a synthetic inorganic chemist I'm absolutely not a specialist in the field. Occasionally we needed EPR spectroscopy for the full characterization of some of our new compounds. In such cases we always asked expert colleagues to help us out.
However, I came across the following potentially useful article in which the calculation of the concentration of free radicals (in spins/g) on biochar is reported. I thought that as a mostly inorganic solid, biochar is not that much different from heterogeneous catalysts. So I thought the article might be of interest to you:
Characterization of free radicals by Electron Spin Resonance Spectroscopy in biochars from pyrolysis at high heating rates and at high temperatures
https://core.ac.uk/download/pdf/160500339.pdf
(see attached pdf file)
I hope this helps. Good luck with your research and best wishes, Frank Edelmann
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