Spin trapping is a quite simple and straightforward technique. Usually you simply supplement your system under investigation with an excess of the spin trap (e.g. in the 1-10 mM range and from higher concentrated stock solutions (some spin traps are soluble only in solvents like EtOH or similar)) and the EPR spectrum can be recorded (usually at room temperature) directly or after a short incubation time - depending on the question you want to answer. The EPR spectrum contains information about the nature of the trapped species (by analysis/simulation of the hyperfine splittings and comparison with values that can be found in databases like http://tools.niehs.nih.gov/stdb/index.cfm) and its concentration (from the 2nd integral of the 1st derivative EPR spectrum and comparsion with reference samples). Also time-resolved measurements can be performed by recording EPR spectra in defined time intervals, yielding information about the kinetics of radical formation. Nevertheless, the choice of the trapping agent depends very much on the system under investigation. Some spin traps are better suited for a certain class of radicals than others. Furthermore, some spin-adducts - especially those of the commonly used DMPO and its derivatives (e.g. DEPMPO) - have a limited lifetime (~10-20 min), resulting in a limited time-window for their observation and complications in the determination of absolute concentrations of the trapped radicals. So the first questions to answer for designing the experiment are: 1. What type of radical do you expect/want to trap, and 2. are their specific needs/limitations concerning the "timing" of the experiment (e.g. is radical formation expected to take place within second, minutes or even hours)?

I totally agree!