Near‐infrared multivariate model transfer for quantification of different hydrogen bonding species in aqueous systems

Abstract

It is challenging to achieve consistent quantification of hydrogen‐bonded water species by fitting Gaussian bands on spectra collected from different instruments, especially when the spectral resolution is low. Therefore, this work aims to propose a near‐infrared (NIR) multivariate calibration model transfer method to obtain reliable, consistent, and reproducible results from different spectroscopic instruments. A composite method of Gaussian deconvolution, multivariate curve resolution‐alternating least squares (MCR‐ALS), and partial least squares (PLS) was developed to quantify five water species (labeled as C1, C2, C3, C4, and C5), respectively, assigned to non‐hydrogen‐bonded, singly hydrogen‐bonded, doubly and triply hydrogen‐bonded species, distorted ice‐like structures in the liquid phase, and fully hydrogen‐bonded species showing ice‐like structure. Primary instrument (iS50) was selected due to the highest spectral resolution and spectra (7500–5845 cm−1 with spectral resolution of 0.5 cm−1) were acquired from four types of salt solutions. The developed PLS model yielded a high prediction performance when applied on two independent prediction sets with R2P higher than 0.95 and RMSEP less than 0.009 for prediction of C1‐5. Model built with primary spectra was successfully transferred to spectra of secondary instrument (iN10), producing RMSEP less than 0.010. Transferred model applied on secondary instruments (NIRECO and MPA) showed that fully H‐bonded species in deionized water decreased as temperature increased, while non‐hydrogen‐bonded and singly hydrogen‐bonded demonstrated an opposite temperature dependence. Our results confirmed that it is promising to transfer the calibration model from a sophisticated spectrometer to a simple spectroscopic instrument in terms of quantification of hydrogen‐bonded water species.

Chemometrics: An Excavator in Temperature-Dependent Near-Infrared Spectroscopy

“…The structure of water has been an interesting subject in chemistry and biology for decades due to the complex and flexible patterns of hydrogen bonding [18][19][20][21]. The effect of the temperature on the NIR spectrum of liquid water was studied as early as in 1925 [22], and over the past few decades, a number of works reported the temperature dependency of the NIR spectra of water [23][24][25][26][27][28]. Most of the researches focused on the absorption band around 6900 cm −1 measured at different temperatures, where an isosbestic point can be observed, implying the variation of the overlapped spectral components with the change of the temperature.…”

“…Most of the researches focused on the absorption band around 6900 cm −1 measured at different temperatures, where an isosbestic point can be observed, implying the variation of the overlapped spectral components with the change of the temperature. With the help of chemometric methods, the spectral features of water structures with different hydrogen bonds were obtained, and the relative abundances of different water structures that change with the temperature were found [27,28]. Thus, the temperature-dependent NIR spectroscopy combined with chemometrics provides an efficient way to explore the structure of water in aqueous systems.…”

Seeking the structure of water from the combination of bending and stretching vibrations in near infrared spectra

“…5,9 The peak can only be observed below 20°C due to the dissociation of the tetrahedral ice-like structure at high temperatures. 38,39…”