CARBON-BASED STANDARDS FOR ELECTRON-PARAMAGNETIC-RESONANCE SPECTROSCOPY

In order to meet the need for a good new EPR intensity and g-value sta ndard whose paramagnetic species are carbon-based radicals, several ma terials 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 becaus e of its chemical stability, spin density, EPR signal line shape and l ine width, microwave power saturation characteristics, availability, a nd homogeneity. Effects of dilution with KBr, KCl, and polymer are neg ligible, although the line width is broadened in the presence of param agnetic gases. Several model standard compounds have been prepared in a polymer matrix to minimize changes in packing density over time.