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Radicals and Transition Metals: Playground for Electron Spin Resonance Spectroscopy The EMXmicro ESR/EPR Spectrometer: the new compact class

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When challenged with the task of uniquely detecting and characterizing (free) radicals or paramagnetic transition metal complexes, Electron Spin Resonance (ESR, sometimes also called EPR for Electron Paramagnetic Resonance) is the method of choice. The newly developed EMXmicro ESR Spectrometer is the first instrument in the compact class to combine the highest possible sensitivity with a novel user interface. The simultaneous use of proven magnet technology and innovative digital electronics makes ESR accessible to users, who want to use the method routinely, without having to know much about how the instrument works.

ESR/EPR-Application Fields: Everywhere but specialized
Regardless of whether it is in (bio-)metallo-organic chemistry, bio- or polymer chemistry or in medical/pharmaceutical research, or even in industrial quality control, ESR Spectroscopy provides specific contributions. ESR can be applied to any aggregate state of the sample (solid, liquid, powder, single crystal, liquid crystal, membrane etc.) and it is often the temperature dependant studies (e.g. solid-liquid transition) that allow investigating specific structural-functional relationships. Key applications are, for example, in-situ tracking of radical polymerisation, the analysis of the coordination geometry of central ions in complex chemistry and the unique detection and quantification of free radicals, reactive oxygen species (ROS) or NO in tissues and cell cultures.

Method Diversity: Basics and Extensions
The EMXmicro ESR-Spectrometer makes use of the so called CW-ESR (i.e. Continuous Wave-ESR) technique. Microwaves in the frequency range around 10 GHz are used to excite the magnetic transitions of electron spins in the sample while they are subjected to a variable magnetic field. Unlike in the related NMR spectroscopy method, here the spectrum is obtained at a constant microwave frequency while the magnetic field sweeps through the resonance. The high detection sensitivity of the EMXmicro is the result of many years of innovation and numerous technical achievements. The main components responsible for this are microwave sources of extreme spectral purity and stability, an optimized probe for detection, as well as the use of recent advances in digital electronics.

EMXmicro
The basic configuration already offers numerous 1D- and 2D-measuring methods allowing, for example, the fully automatic monitoring of the temporal evolution of the ESR Spectrum (kinetics) , or the investigation of a sample’s saturation behaviour. The experiments are defined via a graphical user interface which is an innovative evolution of Xepr, the well known and comprehensive software of the ELEXSYS research platform of ESR spectrometers. This makes the enormous potential of ESR spectroscopy easily accessible to a wider group of users than ever before.

Furthermore, the EMXmicro offers a diverse range of extensions and accessories, for example sample temperature control from liquid Helium to 1000 °C or a motorized goniometer for single crystal studies. Special sample tubes such as multi-capillaries (AquaX) or flat cells are available in order to extend the range of capabilities and optimize performance with aqueous samples.