EFFECT OF SAMPLE PACKING ON THE SCATTERING PROPERTIES OF THE REFERENCE MATERIAL IN DIFFUSE-REFLECTANCE INFRARED SPECTROMETRY

Effect of the sample packing on the scattering properties of KBr, one of the most conventional matrix used in diffuse reflectance Fourier tr ansform infrared (IR) spectrometry (DRIFTS), has been studied. The par ticle size of KBr ranged between 2 and 15 mum with a mean of 9.9 mum. The average particle size of quartz and calcite used as analytes were less-than-or-equal-to 2 mum and less-than-or-equal-to 6 mum, respectiv ely. The scattering coefficient of KBr has been found to increase with increasing pressure applied during sample packing. 1 MPa pressure was necessary for reproducible scattering properties and quantitative res ults. The scattering coefficient of KBr using 1 MPa pressure for 1 min during sample packing has been determined from calibration curves and found to be as s = 107 +/- 11 cm-1. It has been experimentally demons trated that using 2 mm deep sample cups, the criteria of infinite samp le thickness is practically fulfilled. It has been also shown that ban d intensities of reflectance spectra were strongly influenced by the c hange of the reflectance of the reference material and the less the sa mple concentration (c) the greater the effect. If c < 0.1 w/w%, that o ften occurs in practice, the RSD of band intensities can vary upto +/- 10-60%. Therefore, in quantitative analysis all spectra should be mea sured against one and same sample of reference material.