Lateritic weathering kaolinites have been characterized in situ and differentiated for the first time by means of infrared microspectroscopy (IRMS). Four classical OH-stretching bands have been observed in the Fourier transform infrared (FTIR) spectra, at 3695, 3668, 3650 and 3620 cm−1, denoted ν1, ν2, ν3 and ν4, respectively, plus a band at 3595 cm−1 associated with the octahedral substitution of Fe3+ for Al3+. Infrared microspectroscopy of thin-sections of lateritic weathering profiles provides useful information on the types of kaolinite present in different horizons of the profile. The spectra obtained from large well-ordered kaolinite crystals look like those obtained by diffuse reflectance in that, compared with the KBr disk spectra of <2 µm powders, bands at 3668 and 3650 cm−1 are enhanced, and the strong absorption of KBr disks at 3695 cm−1 is replaced by a broad weaker band from 3700–3680 cm−1. In laterites, these large well-ordered kaolinites often exhibit a band at 3595 cm−1 indicative of significant Fe3+ substitution for Al3+ in the structure. The IR microspectra obtained from regions of small, more poorly-ordered kaolinites do not differ so markedly from that of KBr disks. All show enhanced absorption around 3650 cm−1 compared with well-ordered kaolinites, indicating that the disorder is due, at least in part, to domains of dickite-like and/or nacrite-like stacking in their structure. The 3595 cm−1 band is always weaker than that of the well-ordered kaolinite in the same profile. The IRMS data from well-characterized reference kaolinites show that the ratio Aν2/Aν3 is a pertinent IR order index for kaolinites. The larger this index, the larger is the area of the 3595 cm−1 band, and the larger and the more ordered is the kaolinite sample. It is suggested that the diversity of FTIR spectra observed reflects intergrowths of kaolinite-dickite polymorphs, or at least mixtures of high- and low-defect kaolinites which are frequently encountered in the lateritic geosphere rather than pure kaolinitic phases. The largest kaolinites having secondary crystallized in voids are the most ordered and the most ferruginous and have been considered as useful mineralogical tracers of the recent evolution of old lateritic terrains.

A low-cost infrared microscope is evaluated in both transmission and attenuated total internal reflection (ATR) sampling modes. Transmission spectra of 60 to 250 micrometer samples exhibited an excellent signal-to-noise ratio. Signal-to-noise in transmission mode also correlated well with theoretical predictions. The quantitative capability of the microscope was demonstrated by measuring the colorant concentration of red, yellow, and blue polypropylene fibers. These latter measurements were conducted using the ATR sampling mode of the microscope. Colorant concentrations could be measured to 1% by weight, and calibration curves with excellent R2 values were obtained over the dye concentration range of 1 to 10% by weight colorant.

Synchrotron radiation-based Fourier transform IR (SR-FTIR) microspectroscopy has been developed as a rapid, direct, non-destructive and bioanalytical technique. This technique, taking advantage of synchrotron light brightness and a small effective source size, is capable of exploring the molecular chemistry within the microstructures of a biological tissue without the destruction of inherent structures at ultraspatial resolutions within cellular dimensions. This is in contrast to traditional ‘wet’ chemical methods, which, during processing for analysis, often result in the destruction of the intrinsic structures of feeds. To date there has been very little application of this technique to the study of feed materials in relation to animal nutrient utilisation. The present article reviews four applications of the SR-FTIR bioanalytical technique as a novel approach in animal nutrition and feed science research. Application 1 showed that using the SR-FTIR technique, intensities and the distribution of the biological components (such as lignin, protein, lipid, structural and non-structural carbohydrates and their ratios) in the microstructure of plant tissue within cellular dimensions could be imaged. The implication from this study is that we can chemically define the intrinsic feed structure and compare feed tissues according to spectroscopic characteristics, functional groups, spatial distribution and chemical intensity. Application 2 showed that the ultrastructural–chemical makeup and density of yellow- and brown-seeded Brassica rape could be explored. This structural–chemical information could be used for the prediction of rapeseed quality and nutritive value for man and animals and for rapeseed breeding programmes for selecting superior varieties for special purposes. More research is required to define the extent of differences that exist between the yellow- and brown-seeded Brassica rape. Application 3 showed with the SR-FTIR technique that chemical differences in the ultrastructural matrix of endosperm tissue between Harrington (malting-type) and Valier (feed-type) barley in relation to rumen degradation characteristics could be identified. The results indicated that the greater association of the protein matrix with the starch granules in the endosperm tissue of Valier barley may limit the access of ruminal micro-organisms to the starch granules and thus reduce the rate and extent of rumen degradation relative to that of Harrington barley. It is the first time that the microstructural matrix in the endosperm of barley has been revealed by using the SR-FTIR technique, which makes it possible to link feed intrinsic structures to nutrient utilisation and digestive behaviour in ruminants. Application 4 showed with the SR-FTIR technique that the chemical features of various feed protein (amide I) secondary structures (such as feather, wheat, oats and barley) could be quantified. With a multi-component fitting program (Lorentz function), the results showed feather containing about 88% β-sheet and 4% α-helix, barley containing about 17% β-sheet and 71% α-helix; oats containing about 2% β-sheet and 92% α-helix; and wheat containing about 42% β-sheet and 50% α-helix. The relative percentage of the two may influence protein value. A high percentage of β-sheet may reduce the access of gastrointestinal digestive enzymes to the protein structure. Further study is required on feed protein secondary structures in relation to enzyme accessibility and digestibility. In conclusion, the SR-FTIR technique can be used for feed science and animal nutrition research. However, the main disadvantage of this technique is the requirement for a special light source; a synchrotron beam.