Quantitative detection method of semiquinone free radicals on particulate matters using electron spin resonance spectroscopy

[Display omitted] •Proposed a quantitative detection method for semiquinone free radicals on particles using electron spin resonance spectroscopy.•The proposed quantitative detection method is validated by testing linearity, repeatability and accuracy precision.•The proposed method is applied to determinate semiquinone free radicals on particles in two northern China cities. Semiquinone free radicals (SFRs) exist significantly in ambient particulate matters and threaten human health due to their genotoxicity and stability compared to other radicals. Efficient quantitative detection methods for SFRs on particles are in great need. In this study, we proposed a quantitative detection method for semiquinone free radicals on particles using electron spin resonance spectroscopy (ESR). We established the relationship between free electron number (which is equal to the number of SFRs as one mole SFRs contain one mol free electron) and corresponding ESR signal intensity, thus SFRs can be quantified by obtaining the ESR signal intensity. The calibration curve was obtained using 2,2-diphenyl-1-picrylhydrazyl (DPPH) solution and has good linearity with r2 of 0.9998. The proposed quantitative detection method reaches repeatability precisions of 2.69% ˜ 4.80% in three concentration levels and recovery ratios of 75.42% ˜ 86.99% for four kinds of SFRs. We successfully used the method to determinate semiquinone free radicals on particles in two northern China cities, Beijing and Jinzhong. The proposed quantitative detection method provides basis for further monitoring of semiquinone free radicals that are existed on ambient particles as well as epidemiologic researches on human exposure risk.