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.
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