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A Chemometric Method for Correcting Fourier Transform Infrared Spectra of Biomaterials for Interference from Water in KBr Discs

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Abstract:

Mid-infrared (mid-IR) analysis of solid biomaterials by the familiar KBr disc technique is all too often frustrated by water interference in the very important protein (amide) and carbohydrate (hydroxyl) regions of their spectra. A method was therefore devised that overcomes the difficulty and corrects IR spectra of solid biomaterials in KBr discs by mathematically eliminating the interference that arises from water molecules absorbed and 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 quantitative analysis as well as structure identification. A major advantage is realized in quantitative analysis as the technique permits cryogenic pulverization of the biomaterial in KBr to prevent change in chemical structure and minimize the particle size to closely approach the solid solution condition required by the Beer–Lambert law. Extensive pulverization, which produces large water absorption bands that overlap and obscure the amide and hydroxyl regions of interest, is no longer problematic. The method is illustrated by removing strong water interference to extract the spectra of corn starch and gluten in pressed KBr discs. Results of the new method are compared with attenuated total reflection (ATR) spectra of gluten corrected using the conventional advanced ATR correction algorithm.

Keywords: BIOMATERIAL; CHEMOMETRICS; INFRARED SPECTROMETRIC METHOD; KBR DISC; KBR PELLET; KBR WATER CORRECTION METHOD; R-MATRIX METHOD; WATER INTERFERENCE

Document Type: Research Article

DOI: http://dx.doi.org/10.1366/000370210791114301

Affiliations: 1: Cereal Products and Food Science Research, National Center for Agricultural Utilization Research; Agricultural Research Service, United States Department of Agriculture, 1815 N. University Street, Peoria, Illinois 61604, USA. sherald.gordon@ars.usda.gov 2: Cereal Products and Food Science Research, National Center for Agricultural Utilization Research; Agricultural Research Service, United States Department of Agriculture, 1815 N. University Street, Peoria, Illinois 61604 3: New Crops Research, National Center for Agricultural Utilization Research; Agricultural Research Service, United States Department of Agriculture, 1815 N. University Street, Peoria, Illinois 61604 4: Bioproduct Chemistry and Engineering Research, Western Regional Research Center, Agricultural Research Service, United States Department of Agriculture, 800 Buchanan Street, Albany, CA 94710

Publication date: April 1, 2010

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