Simplifying quantitative measurement of free radical species using an X-band EPR spectrometer

Yusuke Makino, Megumi Ueno, Yoshimi Shoji, Minako Nyui, Ikuo Nakanishi, Koji Fukui, Ken Ichiro Matsumoto

Research output: Contribution to journalArticlepeer-review


The quantitative measurement of free radicals in liquid using an X-band electron paramagnetic resonance (EPR) was systematized. Quantification of free radicals by EPR requires a standard sample that contains a known spin amount/concentration. When satisfactory reproducibility of the sample material, volume, shape, and positioning in the cavity for EPR measurements can be guaranteed, a sample tested and a standard can be directly compared and the process of quantification can be simplified. The purpose of this study was to simplify manual quantitative EPR measurement. A suitable sample volume for achieving a stable EPR intensity was estimated. The effects of different solvents on the EPR sensitivity were compared. The stability and reproducibility of the EPR intensity of standard nitroxyl radical solutions were compared among different types of sample tubes. When the sample tubes, sample volumes, and/or solvents were the same, the EPR intensity was reproduced with an error of 2% or less for μM samples. The quantified sample and the standard sample in the same solvent and the same volume drawn into the same sample tube was able to be directly compared. The standard sample for quantification should be measured just before or after every daily experiment.

Original languageEnglish
Pages (from-to)213-221
Number of pages9
JournalJournal of Clinical Biochemistry and Nutrition
Issue number3
Publication statusPublished - 2022


  • electron paramagnetic resonance
  • quantitative measurement
  • reproducibility
  • sample tube
  • sensitivity

ASJC Scopus subject areas

  • Medicine (miscellaneous)
  • Nutrition and Dietetics
  • Clinical Biochemistry


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