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Spectrochim Acta A Mol Biomol Spectrosc. 2019 Apr 15;213:83-89. doi: 10.1016/j.saa.2019.01.059. Epub 2019 Jan 17.

High order derivative to investigate the complexity of the near infrared spectra of aqueous solutions.

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Xinjiang Laboratory of Native Medicinal and Edible Plant Resources Chemistry, College of Chemistry and Environmental Science, Kashgar University, Kashgar 844006, China; Research Center for Analytical Sciences, College of Chemistry, Nankai University. Tianjin 300071, China; Tianjin Key Laboratory of Biosensing and Molecular Recognition, Tianjin 300071, China; State Key Laboratory of Medicinal Chemical Biology, Tianjin 300071, China; Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300071, China. Electronic address:
Research Center for Analytical Sciences, College of Chemistry, Nankai University. Tianjin 300071, China.


Derivative calculation is a powerful method for resolution enhancement in spectral analysis. A high order derivative method based on continuous wavelet transform (CWT) is discussed in the analysis of near infrared (NIR) spectra. The results for a simulated spectrum obtained from conventional numerical differentiation (NM), Fourier transform (FT), Savitzky-Golay (SG) and CWT method were compared. CWT method was found to be as efficient as FT and SG, but easier for high order derivative computation, and the fourth order derivative was proved to be a good choice for resolution enhancement as well as reduction of noise and sidelobe effects. For the NIR spectra of water-ethanol mixtures, the complexity of the spectra can be observed from the fourth derivative, including the spectral features of OH and CH with various intermolecular interactions. Fitting the derivative spectra of the mixtures by those of pure water and ethanol, the obtained coefficients for ethanol show a linear relation with the content but that for water exhibit a non-linear relation, which reveals the influence of ethanol on water structure in the mixture. Furthermore, the information of the water-ethanol clusters was found in the residual spectra after the fitting. Therefore, high order derivative can be an efficient way to improve the resolution of NIR spectra for understanding the interactions in aqueous solutions.


Continuous wavelet transform; High order derivative; Molecular interaction; Resolution enhancement; Water structure


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