Angular Dependence of Diffuse Reflectance Infrared Spectra. Part III: Linearity of Kubelka-Munk Plots

Abstract

The linearity of plots of the Kubelka-Munk function against concentration is investigated for weak and strong absorption bands in the spectrum of a typical organic analyte, caffeine. The linear region is extended when measurements are made with an off-axis optical geometry, in comparison to an in-line configuration. For the latter configuration, the linearity is improved when crossed polarizers are placed before and after the sample.

Vibrational Spectroscopy

“…Because of its relative simplicity and wide applicability, infrared transmission-absorption spectroscopy [13-18a] and diffuse reflectance spectroscopy [13,[17][18][19][20][21] are most frequently used today in catalysis research. A wide variety of techniques has been developed for photon vibrational spectroscopies, which have to be selected according to the surface and optical properties of the system to be studied.…”

“…Diffuse reflectance techniques have been reviewed by Kortüm [19] and by Wendlandt and Hecht [45] and their application in the infrared region has been discussed by Griffiths and coworkers [20,21]. These techniques can be used with materials in the form of powders or pellets, which are usually terminated by two parallel surfaces.…”

Analysis of wood surfaces and ground wood by diffuse reflectance (DRIFT) and photoacoustic (PAS) Fourier transform infrared spectroscopic techniques

“…The intensity of absorbed radiation, in diffuse reflectance, in general is expressed by Kubelka-Munk function, F(Ro~), by the following equation (Brimmer and Griffiths 1988): Faserrichtung des Radialschnitts, (C) senkrecht zur Faserrichtung des Radialschnitts und (D) diagonal zur Faserrichtung des Radialschnitts pellet method have limitations because of sample preparation. Specular reflectance requires mirror-like surfaces.…”

“…K-M plot usually deviate negatively from linearity at high concentration (Brimmer and Griffiths 1988). "Infinite depth" is defined as thickness at which any further increase in thickness causes no change in infrared spectrum.…”

Analysis of wood vacuum pyrolysis solid residues by diffuse reflectance infrared Fourier transform spectrometry

“…Due to the assumptions made, Kubelka-Munk equation for diffuse reflectance measurements has been reported to be valid for dilute dispersion of an analyte in non-absorbing matrices (16,17). Its linearity could be further improved by improving sample preparation technique (18,19) and optical geometry of the system (20 This work contributes to the knowledge of thermal conversion solid residue characteristics and extends the previously reported semiquantitative infrared approach to wood charcoals produced under vacuum pyrolysis (VP) conditions within a higher range of temperatures. Emphasis has been made on usefulness of DRIFT technique in fast determination of constituents of many lignocellulosic solid residues obtained by various liquefaction techniques.…”