Near- versus Mid-Infrared Spectroscopy: Relationships between Spectral Changes Induced by Water and Relative Information Content of the Two Spectral Regions in Regard to High-Moisture Samples

Abstract

The objectives of this work were to examine similarities and differences in the near-infrared and mid-infrared spectral regions when one is working with high-moisture materials and to study spectral changes in these regions as a method to identify the relationship of spectral information in the near-IR to fundamental absorptions in the mid-IR. Near- and mid-infrared spectra were taken with a Digilab FTS-65 Fourier transform spectrometer. Liquids were examined by transmission and solids by reflectance. Results with solutions showed that less spectral distortion arises when one is subtracting water from mid- rather than from near-infrared spectra. It was also easier to produce high-quality spectra in the mid-infrared by using attenuated total reflectance than by using transmission in the near-infrared. While mid-infrared spectra showed changes (induced by water, pH, physical state, and ionic strength) similar to those found in the near-infrared, there appeared to be more information available in the mid-infrared, even in the presence of water.