Most chemical and biological samples of interest for ESR spectroscopy lack an inherent stable unpaired electron, the majority of ESR methods rely on the usage of spin-labeling reagents. Commonly, nitroxides such as derivates of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) are used as they offer high stability of the unpaired electron and exceptional ESR sensitivity combined with facile and versatile moieties for binding to the sample through chemical reactions. Sigma-Aldrich offers a comprehensive array of spin labels suitable for ESR spectroscopy in high purities to allow for easy interpretation of the analytical results.
