[22] Spin trapping

The method of detecting reactive short-lived free radicals by the spin-trapping technique was first demonstrated in the late 1960s. At this time, the spin-trapping method involves the addition of an organic compound (spin trap) to the solution under investigation. The spin trap is capable of rapidly trapping free radicals to form more persistent radicals (spin adducts) detectable by electron spin resonance (ESR). The most commonly used spin traps are nitrones and nitroso compounds that usually give nitroxide spin adducts. An immediate requirement of the technique is that the spin trap and spin adducts are soluble in the medium of interest and that free diffusion of the spin trap to the location of the free radical event is allowed. The environment should permit high mobility of the spin adduct so that the ESR spectrum consists of a pattern of sharp lines. The detection of the ESR spectrum of a nitroxide spin adduct is proof that a radical has been trapped in the solution under investigation. Spin trapping is a kinetic method––that is, the success of the spin trapping experiment depends critically on the rate conditions that exist in the system.