Electron paramagnetic resonance (EPR) is a spectroscopic technique sensitive to unpaired electrons present in paramagnetic species such as free radicals and organometallic complexes.

Electrochemistry (EC) is an interfacial science, where reduction and oxidation processes are studied. A single electron reduction or oxidation generates a paramagnetic species with an unpaired electron, thus making EPR a valuable tool in the study of electrochemical systems.

In this work a novel electrochemical cell was designed and developed to be used with a specific type of EPR resonator, called loop gap resonator (LGR). After building and characterising the performance of the EC-EPR setup, it was adapted for quantitative measurements in electrochemical EPR (QEC-EPR).

Thus, for the first time, the technique of EC-EPR has been fully characterised for analytical work, opening possibilities to study electrode reactions quantitatively with accuracy and precision not obtained before, as demonstrated in Chapter 8 of this thesis.