Submitted to: Applied Spectroscopy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2010
Publication Date: 4/5/2010
Citation: Gordon, S.H., Mohamed, A., Harry O Kuru, R.E., Imam, S.H. 2010. A chemometric method for correcting FTIR spectra of biomaterials for interference from water in KBr discs. Applied Spectroscopy. 64(4):448-457. Interpretive Summary: A new method was devised to correct infrared spectra of solid biomaterials for interference from water absorbed in the well known potassium bromide (KBr) disc preparation technique. The correction method uses a new mathematical curve-fitting technology to free the spectra of proteins and polysaccharides from water bands in the important amide and hydroxyl regions. The method gives more accurate quantitative infrared analyses of components in solid biomaterials in KBr than was previously possible. Its innovative treatment of absorbance peaks as a matrix of ratios not only solves a previously unsolvable system of multivariate mathematical equations, but also gives the unknown absorbance coefficients of the solid biomaterial. When used to correlate x-ray analyses and infrared spectra, the mathematical curve-fitting method makes analysis of complex three-dimensional structures in solid proteins and polysaccharides possible for the first time. Water contained in the KBr is no longer a problem. Consequently, the correction method represents a significant advance toward practical infrared spectrometric analyses of solid biomaterials in nature. This breakthrough removes a long-standing barrier to valid quantitative analyses of biochemical structures and will enable scientists to obtain knowledge crucial to progress in many areas of agricultural research.
Technical Abstract: FTIR analysis of solid biomaterials by the familiar KBr disc technique is very often frustrated by water interference in the important protein (amide I) and carbohydrate (hydroxyl) regions of their spectra. A method was therefore devised that overcomes the difficulty and measures FTIR spectra of solid biomaterials in KBr discs by mathematically eliminating the interference which arises from absorbed water vapor and water molecules bound in the KBr crystal lattice. The derivation of a linear system of chemometric equations that solves the water interference problem in a rigorous objective way is presented. Infrared spectra that result after correction by the method can be used reliably for quantitation as well as identification. A major advantage is realized in quantitation as the technique permits cryogenic pulverization of the biomaterial in KBr to minimize the particle size and closely approach the condition required by the Beer-Lambert law. Extensive pulverization, which produces large water absorbance bands that obscure the amide I and hydroxyl regions of interest, is no longer problematic. The method is illustrated by removing strong water interference to extract FTIR spectra of gluten and corn starch in pressed KBr discs.