Quantitative measurements in electrochemical electron paramagnetic resonance

Abstract

The quantification of absolute number of paramagnetic centers in continuous wave (CW) Electron Paramagnetic Resonance (EPR) is a demanding measurement, where the interaction between the sample and the EPR spectrometer needs to be understood and controlled precisely. When utilizing electrochemical EPR (EC-EPR), additional challenges are introduced due to the dynamic nature of the electrochemical systems, (e.g. diffusion of radical species on the timescale of EPR experiments). Here we report a full characterization of an EC-EPR setup for quantifying the absolute number of paramagnetic species originating from EC generation. The data reported indicate that with EC-EPR it is possible to quantify intermediates or products from electrode reactions within 3% accuracy over a threefold concentration range, even in organic solvents. The set-up has high sensitivity, with the quantification of 3–4μM concentrations shown to be routine. Furthermore, sub-μM concentrations can be accessed through signal averaging. These studies provide a platform for the future use of quantitative EPR and new capability for studying and characterizing electrochemical systems.