Elimination of interference from water in KBr disk FT-IR spectra of solid biomaterials by chemometrics solved with kinetic modeling

Authors: Gordon, Sherald; Harry O Kuru, Rogers; MOHAMED, ABDELLATIF - King Saud University

Submitted to: Talanta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2017
Publication Date: 6/23/2017
Publication URL: http://handle.nal.usda.gov/10113/5701497
Citation: Gordon, S.H., Harry-O'kuru, R.E., Mohamed, A.A. 2017. Elimination of interference from water in KBr disk FT-IR spectra of solid biomaterials by chemometrics solved with kinetic modeling. Talanta. 174:587-598.

Interpretive Summary: A computer method was devised to correct infrared spectra of solid biomaterials for interference from water absorbed in the widely-used potassium bromide (KBr) disk technique. Our new method employs advanced matrix mathematics in combination with time-dependent water desorption kinetics to free the spectra of biomaterials such as proteins from water interference in the important amide and hydroxyl regions. The method provides accurate quantitative infrared measurement of components in solid biomaterials in KBr that were previously thought to be impossible to analyze. Its innovative treatment of absorbance peaks as a matrix of ratios solves a previously unsolvable system of mathematical equations. As a result, the interference from water contained in the KBr, which has frustrated and defeated research chemists and infrared spectroscopists for almost 70 years, is no longer a problem. Now this problem is finally solved once and for all. When used to correlate x-ray analyses and infrared spectra, our mathematical method makes analysis of complex three-dimensional structures in solid proteins and other biomaterials possible for the first time. Consequently, the correction method represents a significant advance toward practical infrared spectrometric analyses of solid biomaterials in nature. This advance is considered an important breakthrough that removes a major long-standing barrier to quantitative analyses of solid biomaterials. It uncovers and measures structural features of natural materials that are crucial to success in agriculture and many other fields of scientific research.

Technical Abstract: Infrared analysis of proteins and polysaccharides by the well known KBr disk technique is notoriously frustrated and defeated by absorbed water interference in the important amide and hydroxyl regions of spectra. This interference has too often been overlooked or ignored even when the resulting distortion is critical or even fatal, as in quantitative analyses of protein secondary structure, because the water has been impossible to measure or eliminate. Therefore, a new chemometric method was devised that corrects spectra of materials in KBr disks by mathematically eliminating the water interference. A new concept termed the Beer-Lambert law absorbance ratio (R-matrix) model was augmented with water concentration ratios computed via an exponential decay kinetic model of the water absorption process in KBr, which rendered the otherwise indeterminate system of linear equations determinate and thus possible to solve in a formal analytic manner. Consequently, the heretofore baffling KBr water elimination problem is now solved once and for all. Using the new formal solution, efforts to eliminate water interference from KBr disks in research will be defeated no longer. Resulting spectra of protein were much more accurate than attenuated total reflection (ATR) spectra corrected using the wellaccepted Advanced ATR Correction Algorithm.