THE INFLUENCE OF PARTICLE-SIZE AND CONCENTRATION IN TRANSMISSION AND DIFFUSE REFLECTANCE SPECTROSCOPY OF WOOD

FTIR spectra of the tropical hardwood Guibourtia sp. (Caesalpiniaceae) have been recorded using the KBr pellet technique and diffuse reflection (DRIFT) in KBr powder. It was demonstrated by variation of the wood concentration in KBr and the particle size of the milled wood that the spectroscopic data of wood - mainly those of the intense carbohydrate band around 1100 cm-1 - are strongly influenced by these parameters. The KBr pellet technique gives reproducible results for concentrations between 0.1 and 0.5% with a particle size below 25-mu-m. The DRIFT spectra of wood powders in KBr are very much influenced both by particle size and concentration. Wood spectra are also presented which were obtained by transmission spectroscopy and FTIR microscopy of 25-mu-m microtome cuts and by reflectance on solid wood surfaces. The influence of heterogeneous dispersion of wood in KBr and the roughness of wood surfaces on reflectance spectroscopy is discussed. A simple baseline correction is recommended to increase interlaboratory comparability of wood spectra.