Detection and characterisation of radicals using electron paramagnetic resonance (EPR) spin trapping and related methods

Methods ◽  
2016 ◽  
Vol 109 ◽  
pp. 21-30 ◽  
Author(s):  
Michael J. Davies
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Spin Trapping ◽  
Paramagnetic Resonance ◽  
Epr Spin Trapping ◽  
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.

Photodegradation of 4-chloronitrobenzene in the presence of aqueous titania suspensions in different gas atmospheres

2011 ◽  
Vol 64 (7) ◽  
pp. 1466-1472 ◽  
Author(s):  
Miaomiao Ye ◽  
Tuqiao Zhang ◽  
Zhiwei Zhu ◽  
Yan Zhang ◽  
Yiping Zhang
Keyword(s):  
Spin Trapping ◽  
Photocatalytic Efficiency ◽  
Liquid Chromatography Mass Spectrometry ◽  
Paramagnetic Resonance ◽  
Mineralization Processes ◽  
Degussa P25 ◽  
Epr Spin Trapping ◽  
Electron Paramagnetic ◽  
Nitrate Anions ◽  
Spin Trapping Technique

The photocatalytic degradation of 4-chloronitrobenzene (4-CNB) was carried out using Degussa P25 TiO2 as photocatalyst in three different gas atmospheres: nitrogen, oxygen, and ozone. The total organic carbon (TOC) and inorganic anions including chloride, nitrite, and nitrate anions were measured to monitor the mineralization processes, while the degradation of 4-CNB and the formation of intermediates were followed by liquid chromatography–mass spectrometry (LC/MS). Results showed that the photocatalytic efficiency followed the order of TiO2/UV/N2 < TiO2/UV/O2 < TiO2/UV/O3, which was further proved by evaluating the reaction activities using electron paramagnetic resonance (EPR) spin trapping technique. Chlorine atom, nitro group and hydrogen atom of the benzene ring could be displaced by hydroxyl radical (•OH) leading to the formation of chloride, nitrite (III) anions and a variety of phenols, then the nitrite (III) anions were further oxidized to nitrate (V) anions. 4-Nitrophenol and 5-chloro-2-nitrophenol were identified and quantified in both of the TiO2/UV/N2 and TiO2/UV/O2 processes while no aromatic intermediates were monitored in the process of TiO2/UV/O3.

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