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.
Research Center for Analytical Sciences, College of Chemistry, Nankai University. Tianjin 300071, China.
Spectrochim Acta A Mol Biomol Spectrosc. 2019 Apr 15;213:83-89. doi: 10.1016/j.saa.2019.01.059. Epub 2019 Jan 17.
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.
导数计算是一种在光谱分析中提高分辨率的有力方法。本文讨论了基于连续小波变换（CWT）的高次导数方法在近红外（NIR）光谱分析中的应用。比较了模拟光谱的常规数值微分（NM）、傅里叶变换（FT）、Savitzky-Golay（SG）和 CWT 方法的结果。结果表明，CWT 方法与 FT 和 SG 一样有效，但更易于进行高次导数计算，并且第四阶导数被证明是提高分辨率、降低噪声和旁瓣效应的良好选择。对于水-乙醇混合物的 NIR 光谱，可以从第四阶导数中观察到光谱的复杂性，包括具有各种分子间相互作用的 OH 和 CH 的光谱特征。通过对混合物的导数光谱进行拟合，可以得到乙醇的系数与含量呈线性关系，而水的系数则呈非线性关系，这表明乙醇对混合物中水分子结构的影响。此外，在拟合后残差光谱中发现了水-乙醇簇的信息。因此，高次导数可以是提高 NIR 光谱分辨率以理解水溶液相互作用的有效方法。
