CARBON-BASED STANDARDS FOR ELECTRON-PARAMAGNETIC-RESONANCE SPECTROSCOPY

In order to meet the need for a good new EPR intensity and g-value standard whose paramagnetic species are carbon-based radicals, several materials were investigated, including coal, fusinite (a coal maceral), and several carbohydrate chars. Of the prototypical standards prepared, a chemically-treated fusinite is recommended as most suitable because of its chemical stability, spin density, EPR signal line shape and line width, microwave power saturation characteristics, availability, and homogeneity. Effects of dilution with KBr, KCl, and polymer are negligible, although the line width is broadened in the presence of paramagnetic gases. Several model standard compounds have been prepared in a polymer matrix to minimize changes in packing density over time.