A method has been developed to accurately determine total particulate-phase free radicals in mainstream cigarette smoke. Cambridge filter pad (CFP) was usually employed to collect particulate-phase free radicals in mainstream cigarette smoke, but it was found that it was not suitable for the accurate determination of total particulate-phase free radicals in mainstream cigarette smoke. More than 20% of particulate-phase free radicals in the mainstream cigarette smoke were observed breaking through Cambridge filter pads in our experiments. A special filter pad with tiny electron paramagnetic resonance (EPR) signal was found out that was suitable for the quantitative analysis of total particulate-phase free radicals in the mainstream cigarette smoke. To reduce the difference between test results brought about by using different EPR spectrometers, a new calibration method was developed by using the ratios of EPR signal intensities of DPPH (1,1-diphenyl-2-picryl-hydrazyl) standard samples to those of high pitch and the spin number of the DPPH standard samples to make calibration curve. This method has been validated through intra- and inter-laboratory studies and has shown excellent repeatability and reproducibility.

Key words: quantitative analysis, mainstream cigarette smoke, particulate-phase free radical, electron paramagnetic resonance