It is shown that reduction of particle size for ground durum wheat does not cause a concomitant decrease in the amount of specular reflection observed in the mid-infrared spectrum of the neat sample. Specular reflection can be reduced, but not completely eliminated, by dilution of the wheat in a nonabsorbing matrix such as KCl. The lack of dependence of mid-infrared diffuse reflection spectra of neat ground durum wheat on particle size is explained by the morphology of the surface of each particle and the low effective depth of penetration of mid-infrared radiation into particles of very high absorptivity. It is concluded that mid-infrared diffuse reflection spectra of wheats do not provide information characteristic of the overall composition of the wheat when the particle size exceeds a few micrometers, but that near-infrared diffuse reflection spectra will provide representative analytical data even when the particle size is large.
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