Mechanism of the photochemistry of p-benzoquinone in aqueous solutions. 1. Spin trapping and flash photolysis electron paramagnetic resonance studies

1986 ◽  
Vol 90 (23) ◽  
pp. 6266-6270 ◽  
Author(s):  
A. Ike Ononye ◽  
Alan R. McIntosh ◽  
James R. Bolton
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Aqueous Solutions ◽  
Flash Photolysis ◽  
Spin Trapping ◽  
Paramagnetic Resonance ◽  
Electron Paramagnetic

Quantitative Electron Paramagnetic Resonance: The Importance of Matching the Q-Factor of Standards and Samples

2001 ◽  
Vol 55 (10) ◽  
pp. 1375-1381 ◽  
Author(s):  
Richard L. Blakley ◽  
Dwight D. Henry ◽  
Walter T. Morgan ◽  
William L. Clapp ◽  
Carr J. Smith ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Free Radicals ◽  
Free Radical ◽  
Spin Trapping ◽  
Microwave Energy ◽  
Q Factor ◽  
Paramagnetic Resonance ◽  
Tert Butyl ◽  
Electron Paramagnetic ◽  
Stable Free Radicals

Electron paramagnetic resonance (EPR) quantification of free radicals from different samples facilitates comparison of free radical concentrations. Stable free radicals, such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), in a suitable solvent (e.g., benzene) can be used as a quantification standard. Free radicals found in samples can be shorter lived than radicals in prepared standards and require stabilizing spin-trapping agents such as N-tert-butyl-α-phenylnitrone (PBN) in an appropriate solvent (e.g., benzene). Analysis in our laboratory showed that free radicals from spin-trapped samples quantified against a standard of TEMPO in benzene displayed large differences among identical samples measured on either a Micro-Now 8300, Micro-Now 8400, or Bruker EMX EPR instrument. The Bruker instrument reported that the typical TEMPO in benzene standard had a Q-factor of ∼4400 while the Q-factor of our PBN-containing samples was ∼2500. (The Q-factor is inversely proportional to the amount of dissipated microwave energy in an EPR cavity.) By placing the TEMPO standard in a PBN/benzene solvent matrix we were able to match the Q-factor of our standards and samples, resulting in each of the three EPR instruments giving the same quantified free radical yields for the samples. This result points out the importance of matching the Q-factor between samples and standards for any quantitative EPR measurement.

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