Near and mid infrared spectrometry for the qualitative and quantitative analysis of complex materials.

摘要

The goals of this dissertation were (1) to show that more qualitative and quantitative information can be derived from both the near and mid infrared spectra of a sample than by studying either region alone, and (2) to provide a better understanding of diffuse reflectance (DR) in both the near and mid infrared spectral regions.; Assignment of the fundamentals and first overtones of the C-H stretching vibration for several cycloalkanes was done via curve-fitting analysis. Determination of the full-width at half-height (FWHH) of the first overtones of the C-H stretching modes showed them to be two to four times the FWHH of their corresponding fundamental absorptions. The increase in FWHH of the overtones is greater for symmetric stretching modes than for antisymmetric stretching modes.; DR in the near infrared spectral region was first studied using a system that included carbazole as a model organic analyte, NaCl as a nonabsorbing matrix, and mixtures of ground graphite and NaCl as an absorbing matrix. For strongly absorbing materials the effective depth of penetration of radiation is decreased by the absorption of the matrix such that, for particles on the order of 20-500 {dollar}mu{dollar}m, only reflected radiation from one or two particle layers is observed. This causes deviation from Kubelka-Munk type behavior so that the log(1/R) function provides a more linear relationship between band intensity and concentration for strongly absorbing systems.; The near and mid infrared DR spectra of several carbohydrates and ground durum wheat were used to show the effect of particle size/morphology. For 10-500 {dollar}mu{dollar}m particles, the effective penetration depth of near infrared radiation is sufficient to provide a quantitative representation of the major components of a strongly absorbing sample. For the mid infrared region, however, the effective penetration depth is decreased such that the spectrum contains information only on the constituents present within {dollar}sim{dollar}5 {dollar}mu{dollar}m of the surface of the particles.; Due to differences in the penetration of radiation complementary information is available from the mid and near infrared spectra of wheat. Although mid infrared spectra of wheats cannot provide quantitative information on the major constituents present, the spectra can be used to classify the wheats according to their relative hardness when examined by a principal components analysis.