Methods for Analysis of Free Radicals in Cigarette Smoke

Free radicals in the particulate phase of cigarette smoke were first measured by direct electron paramagnetic resonance (EPR) spectroscopy over 60 years ago. Early efforts to measure free radicals in cigarette smoke were prompted by the theory that radicals could be involved in carcinogenesis. It was thought that free radicals could be either direct acting or produced by other components of cigarette smoke such as polycyclic aromatic hydrocarbons. Even today, it is uncertain which of these routes of action is the most important. Ultimately, the development of a strategy to minimize potential biological damage from free radicals is dependent on the extent to which free radicals delivered in cigarette smoke are directly involved in disease processes. In recent years, the primary instrumental means for identifying and studying free radicals in smoke have been both EPR and mass spectrometry (MS) techniques using spin trapping. The spin trapping technique allows stabilization of short-lived species. When coupled with MS, spin trapping allows complete structural characterization of free radicals. When coupled with EPR, spin trapping allows structural characterization by comparison to EPR spectra of known chemical species. Advances in the development of spin traps and spin trapping techniques, along with EPR and MS methods used for the study of cigarette smoke free radicals are presented in this review.