RELIABILITY OF SEMIQUANTITATIVE DATA EXTRACTED FROM TRANSMISSION MICROSCOPY - FOURIER-TRANSFORM INFRARED-SPECTRA OF COAL

Micro-FTIR is a very promising technique for microscale characterization of organic matter, but semiquantitative aspects must be approached and Beer’s law has to be verified. The present work has been carried out on a Bruker IFS 88 FTIR microspectrometer equipped with a × 15 objective. Semiquantitative calculations on spectra of thin (7–19 μm) and ultrathin (0.5–1.5 μm) sections of a homogeneous humic coal are discussed in the current paper. The thickness of the sections has been deduced from the frequency of interference fringes and from the refractive index of the coal. Good correlations between the thickness and the absorbance or band area (0.73 < r < 0.99) has been calculated for the main IR bands. Nevertheless, in ultrathin-section spectra, wide interference fringes prevent accurate measurement of the band areas. Emphasis is placed on the advantages of such a new technique in the determination of semiquantitative parameters of organic matter functionality. © 1990, American Chemical Society. All rights reserved.