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 transform infrared (IR) spectrometry (DRIFTS), has been studied. The particle 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 2 mum and 6 mum, respectively. 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 results. 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 demonstrated that using 2 mm deep sample cups, the criteria of infinite sample thickness is practically fulfilled. It has been also shown that band intensities of reflectance spectra were strongly influenced by the change of the reflectance of the reference material and the less the sample concentration (c) the greater the effect. If c < 0.1 w/w%, that often occurs in practice, the RSD of band intensities can vary upto +/- 10-60%. Therefore, in quantitative analysis all spectra should be measured against one and same sample of reference material.
Krivácsy
Z
Z
Hungarian Academy of Sciences, Research Group of Analytical Chemistry, University of Veszprém, H-8201 Veszprém P.O. Box 158, Hungary.
Hlavay
J
J