A Simple Sample Packing Accessory for Diffuse Reflectance Infrared Spectrometry

Abstract

It has long been recognized that the reflectance spectrum of a powdered sample is greatly influenced by sample packing, since the pressure applied to the sample affects the scattering coefficient. Yeboah et al. and Christy et al. have demonstrated the effect of packing on diffuse reflectance infrared Fourier transform (DRIFT) spectra and have emphasized the necessity of using the same packing procedure for all samples and references. Both the duration and the amount of pressure applied are critical. Most measurements of band intensity by DRIFT spectroscopy have simply involved measurements of peak heights, but Murthy and Leyden have also demonstrated that reproducible packing of the sample improves the precision of band area ratio measurements. More recently, the importance of packing density was shown by Chalmers and Mackenzie, who demonstrated that different sized particles loaded at their natural packing densities yield very different DRIFT spectra. When the same particles are all packed at a constant packing density, however, the spectra become significantly more similar. Despite the proven importance of reproducible packing, many researchers simply pour samples into diffuse reflectance cups and level the tops with a razor blade or similar instrument, to avoid an elaborate sample preparation procedure.