Attenuated total reflectance infrared microspectroscopy of coal

The measurement of i.r. microspectra utilising an attenuated total reflection (ATR) objective is described. The ATR objective contains a small crystal about 100 μm in diameter which must contact the coal surface. This allows i.r. spectra to be measured from standard polished petrography blocks, without further preparation. The spectra obtained are similar to normal absorption spectra, unlike specular or diffuse reflection spectra. The spectra reflect the changes in coal structure with rank typically seen with macro i.r. methods. A silicon crystal gave better results than a germanium crystal because it has a greater depth of penetration into the sample.