Abstract
Temperature-dependent near-infrared (NIR) spectroscopy has been developed and taken as a powerful technique for analyzing the structure of water and the interactions in aqueous systems. Due to the overlapping of the peaks in NIR spectra, it is difficult to obtain the spectral features showing the structures and interactions. Chemometrics, therefore, is adopted to improve the spectral resolution and extract spectral information from the temperature-dependent NIR spectra for structural and quantitative analysis. In this review, works on chemometric studies for analyzing temperature-dependent NIR spectra were summarized. The temperature-induced spectral features of water structures can be extracted from the spectra with the help of chemometrics. Using the spectral variation of water with the temperature, the structural changes of small molecules, proteins, thermo-responsive polymers, and their interactions with water in aqueous solutions can be demonstrated. Furthermore, quantitative models between the spectra and the temperature or concentration can be established using the spectral variations of water and applied to determine the compositions in aqueous mixtures.
Highlights
Near-infrared (NIR) spectroscopy has been recognized as a powerful technique to study the structure of water [1]
Quantitative determination can be achieved using the spectral variation of water with the temperature or concentration and successfully applied to the quantification of the compositions in aqueous mixtures
The results indicate that the water species with three hydrogen bonds (S3) plays an important role in the stabilization of poly(N-isopropyl acrylamide) (PNIPAM), which may connect the NH and CO groups in the polymer
Summary
Near-infrared (NIR) spectroscopy has been recognized as a powerful technique to study the structure of water [1]. The spectral variations induced by both the temperature and the concentration were obtained The former can be used for structural analysis, and the latter can be used for building a calibration model for quantitative analysis. The spectral variation of water induced by the temperature reflects the structural changes and interactions of water and solutes in aqueous solutions. Further works on extracting structural and quantitative information from temperature-dependent NIR spectra by chemometric methods were summarized. To capture the temperature-induced spectral information of water, chemometric algorithms were proposed for improving the resolution of NIR spectra. Quantitative determination can be achieved using the spectral variation of water with the temperature or concentration and successfully applied to the quantification of the compositions in aqueous mixtures
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