Fluorescence detection of carbon-centered radicals in aqueous solution

A simple, highly sensitive method for the simultaneous determination of arrays of carbon-centered radicals in aqueous systems is described. Radicals are efficiently trapped by an amino-nitroxide to form stable products which are then reacted with fluorescamine to produce highly fluorescent adducts. The adducts are easily separated by reversed-phase high performance liquid chromatography. The detection limit for individual radical adducts (0.5 to 2 nM) is two to three orders of magnitude lower than those of current methods employing electron paramagnetic resonance detection. Results on the photolysis of ketones and alpha-keto acids demonstrate the potential of this technique. This approach should be widely applicable to the study of radical processes in biological and chemical systems.