Typically, lignins are characterized by IR spectroscopy in the solid state. The examination of lignins in solution has long been a domain of UV and NMR spectroscopy. However, with the advent of the FTIR technique, the IR spectra of liquid samples now can be readily obtained. The need to measure IR spectra in solution exists when there is not enough time to isolate lignin from solution as, for example, is the case when spent pulping liquors have to be analyzed rapidly during a pulping process for process control. This section describes briefly the common liquid sampling accessories and applications of solution state FTIR spectroscopy to lignins. For more details on FTIR spectroscopy, the reader is referred to Chapter 4.1.

Fourier Transform Infrared Spectroscopy

The problems associated with the application of FT-IR to the characterization of coal structure are critically discussed. The controversies concerning band assignments are considered and it is concluded that the strong 1600 cm−1 band can be assigned to an aromatic ring stretching mode that in most coals is intensity enhanced by the presence of phenolic groups. The application of computer routines to the determination of OH and CH groups is considered. Established criteria for curve fitting are applied to the problem. Qualitative identification of functional groups is achieved, but consistent quantitative measurements will require a determination of the relationship between the extinction coefficients of resolved bands.

Concerning the Application of FT-IR to the Study of Coal: A Critical Assessment of Band Assignments and the Application of Spectral Analysis Programs

Publisher Summary This chapter describes the various aspects of the vibrational spectra of carbohydrates. Vibrational spectroscopy is one of the techniques most adapted techniques for the study of hydrogen bonding, which is the indicator of molecular interaction in the aqueous solutions of sugars. A polyatomic molecule, such as sugar, may be regarded as a system of masses joined by bonds having spring-like properties. The vibration of each of the masses (atoms) can be resolved into components parallel to the x, y, and z axis of a Cartesian system of coordinates. The harmonic approximation is applied in which any motion of the molecule is resolved in a sum of displacements parallel to the Cartesian coordinates and these are called “fundamental, normal modes of vibration.” The analysis of crystallographic results shows the important role played by anomeric center in the structure of sugars. Infrared dichroism in polysaccharides was applied to obtain information on the orientation of chemical groups in the crystalline structure. The computational calculation of the frequencies of carbohydrates' vibration is also elaborated in the chapter.

Vibrational spectra of carbohydrates.

Algorithms for the computation of bandwidths, and center of gravity and least-squares frequencies are developed. The sources of error are discussed, and it is shown that the above parameters can be determined with maximum uncertainties of hundredths or thousandths of a wave number.

Precision in Condensed Phase Vibrational Spectroscopy

The near-infrared (NIR) region (defined by the ASTM Working Group on NIR as 180 to 2526 nm, October 1985) was the first nonvisible portion of the spectrum to be found, in 1800, by Herschel [1]. The vibrational absorptions in the near-infrared are overtone and combination frequencies of absorption bands that occur in the mid-infrared. These overtones and combinations cause overlapping absorption bands, which make it more difficult to visually identify chemical groupings of a molecule from their near-infrared spectra than from the “fingerprint” region of the mid-infrared spectrum. The overtone and combination bands are one to three orders of magnitude weaker than the fundamental bands. This provides singularly useful sampling advantages.

Near-Infrared Analysis (NIRA): A Technology for Quantitative and Qualitative Analysis

The feasibility of applying the methods of factor analysis to Fourier transform infrared spectra is examined. The method is designed to determine the number of components contributing to a spectral region. The technique has been applied to a model system consisting of solutions of p-, o-, and m-xylenes. The method has also been used for calculating the number of independently absorbing species in several polymer systems. Spectral requirements and the general applicability of factor analysis are also discussed.

Louis D'Esposito

Papers

Factor Analysis Applied to Fourier Transform Infrared Spectra