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 well-accepted Advanced ATR Correction Algorithm.
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•Absorbed water interference in KBr is finally eliminated from important regions of FTIR spectra.•A novel chemometric method corrects spectra in KBr disks by eliminating water interference.•An R-matrix model was solved via exponential decay kinetic modeling of the KBr water absorption.•The baffling KBr water problem that has frustrated spectroscopists for over 70 years is now solved.•Corrected spectra of solid protein were much more accurate compared to corrected ATR spectra.