Spectral Effects of Water in the 10,000 to 8000 cm−1 (1000 to 1250 nm) near Infrared Spectral Region. And, Can They Explain Previously Seen Effects of Water in the Spectral Region from 14,000 to 11,500 cm−1 (714 to 870 nm)?

Abstract

The spectral region from 10,000 to 8000 cm−1 (1000 to 1250 nm) is often used for high moisture samples and fibre optic systems. The first objective of this work was to determine the effects of water on the spectra of various types of materials in this spectral region. The second objective was to determine the origin/nature of spectral effects/artifacts seen in the spectral region from 14,000 to 11,500 cm−1 (714 to 870 nm) when water was added to gums and proteins (increases in peak intensities and shifts in position due to the presence of water). Spectra were obtained by diffuse reflectance and transmission using a Fourier transform spectrometer. The results showed that the effects seen in the mid-infrared and near infrared from 8000 to 4000 cm−1 (1250 to 2500 nm) were also common in this part of the near infrared (i.e. peak shifts, loss of spectral features etc). Thus, the spectra of crystalline glucose and sucrose, while distinctively different as crystalline solids, were very similar when in solution and changes in the spectra of materials, such as acetone, pyridine and ethanol, were very similar in nature to those previously found in the near infrared from 8000 to 4000 cm−1 (1250 to 2500 nm). Finally, detailed examination of spectra in the region from 10,000 to 8000 or 6000 cm−1 (1000 to 1250 or 1667 nm) did not show any spectral effects similar to those seen in gums and proteins in the 14,000 to 11,500 cm−1 (714 to 870 nm) region. Thus, the nature of these effects is still unknown.