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Electron Paramagnetic Resonance (EPR)

Electron paramagnetic resonance (EPR) or electron spin resonance (ESR) spectroscopy is a technique for studying chemical species that have one or more unpaired electrons, such as organic and inorganic free radicals or inorganic complexes possessing a transition metal ion.

cogsHow does it work?

The basic physical concepts of EPR are analogous to those of nuclear magnetic resonance (NMR), but it is electron spins that are excited instead of spins of atomic nuclei. Because most stable molecules have all their electrons paired, the EPR technique is less widely used than NMR. However, this limitation to paramagnetic species also means that the EPR technique is one of great specificity, since ordinary chemical solvents and matrices do not give rise to EPR spectra.

EPR spectroscopy is used in various branches of science, such as chemistry and physics, for the detection and identification of free-radicals and paramagnetic centres such as F centres. EPR is a sensitive, specific method for studying both radicals formed in chemical reactions and the reactions themselves. Medical and biological applications of EPR also exist.

Although radicals are very reactive, and so do not normally occur in high concentrations in biology, special reagents have been developed to spin-label molecules of interest. These reagents are particularly useful in biological systems. Specially-designed nonreactive radical molecules can attach to specific sites in a biological cell, and EPR spectra can then give information on the environment of these so-called spin-label or spin-probes.


Characterisation of metallo-proteins; examining structure and electronic parameters; examining structure-function relationships; in-vivo detection of free-radical intermediates; effects of complex metal additions on biological materials; high sensitivity measurements on the effects of operating environment (pH, molecular motion, charge).

Sample Handling Requirements:

Solids, liquid, gases, metals, ceramics, polymers, biological

Complementary Techniques:


Warwick capability:

Bruker ELEXSYS-II X-Band.


Dr Ian Hancox, 024 76 150380 email i dot hancox at warwick dot ac dot uk.

EPR equipment

Typical results format, and sample:

EPR spectrum copper



Warwick collect/analyse data
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