Supplemental material for Smooth Factor Analysis (SFA) to Effectively Remove High Levels of Noise from Spectral Data Sets

<p>Supplemental Material for Smooth Factor Analysis (SFA) to Effectively Remove High Levels of Noise from Spectral Data Sets by Yeonju Park, Isao Noda and Young Mee Jung in Applied Spectroscopy</p

In Situ and Ex Situ 2D Infrared/Fluorescence Correlation Monitoring of Surface Functionality and Electron Density of Biochars

Carboxyl, hydroxyl, and other oxygen-containing functional groups play key roles in the interfacial reactions of soil surfaces including biochar (solid-phase slow pyrolysis product) soil amendment. Intensity and directionality in both real (synchronous) and imaginary (asynchronous) coordinates of 2D infrared correlation spectra were confirmed by the time courses of pyrolysis reaction (temperature × wavenumber × absorbance; 10 °C min^–1, 1 h residence time at 500 °C) utilizing high-density (74 total spectra) in situ diffuse reflectance Fourier transform (DRIFTs) monitoring. Similar primary trends were observed for four different lignocellulosic biomass feedstocks: cottonseed hull, cotton ginning waste, flax shive, and pecan shell. In the OH stretch region (3100–3750 cm^–1), free OH was most sensitive to pyrolysis temperature and reacted before H-bonded OH indicating the evaporation of water, followed by the cleavage of interchain H-bonds. Aromatic CH (R=CH_<i>n</i>) was the primary CH functionality (within 2700–3100 cm^–1) impacted by the pyrolysis temperature perturbation and formed as the aliphatic CH_<i>x</i> was removed. Of C=O/C=C groups, electron-deficient C=O (1740 cm^–1) was most sensitive to pyrolysis, reacted synchronously (in the same direction) with the aromatic C=C (1510 cm^–1), and was formed after the most electron-rich C=O (1620 cm^–1). This electron-density trend in the C=O/C=C (1400–1800 cm^–1) region of infrared coincided with the formation of aromatic extractable carbon before aliphatic structures in 2D fluorescence emission–emission correlation spectra using 340 nm excitation wavelength. Results could be used to drive biomass pyrolysis toward desirable solid- (carboxyl-enriched biochar) and liquid-phase (less hydrophilic bio-oil) products

Investigation on the Behavior of Noise in Asynchronous Spectra in Generalized Two-Dimensional (2D) Correlation Spectroscopy and Application of Butterworth Filter in the Improvement of Signal-to-Noise Ratio of 2D Asynchronous Spectra

The behavior of noise in asynchronous spectrum in generalized two-dimensional (2D) correlation spectroscopy is investigated. Mathematical analysis on the noise of 2D spectra and computer simulation on a model system show that the fluctuation of noise in a 2D asynchronous spectrum can be characterized by the standard deviation of noise in 1D spectra. Furthermore, a new approach to improve a signal-to-noise ratio of 2D asynchronous spectrum by a Butterworth filter is developed. A strategy to determine the optimal conditions is proposed. Computer simulation on a model system indicates that the noise of 2D asynchronous spectrum can be significantly suppressed using the Butterworth filtering. In addition, we have tested the approach to a real chemical system where interaction between berberine and β-cyclodextrin is investigated using 2D UV–vis asynchronous spectra. When artificial noise is added, cross peaks that reflect intermolecular interaction between berberine and β-cyclodextrin are completely masked by noise. After the method described in this article is utilized, noise is effectively suppressed, and cross peaks are faithfully recovered. The above result demonstrates that the approach described in this article is applicable in real chemical systems

Novel Method of Constructing Two-Dimensional Correlation Spectroscopy without Subtracting a Reference Spectrum

In this study, we propose a new approach to generate two-dimension spectra to enhance the intensity of cross peaks relevant to intermolecular interaction. We investigate intermolecular interaction between two solutes (denoted as P and Q, where P has a characteristic peak at <i>X</i>_P) dissolved in the same solvent via the near diagonal cross peaks around the coordinate (<i>X</i>_P, <i>X</i>_P) in a two-dimensional (2D) asynchronous spectrum of generalized spectroscopy. Because of physical constrains in many cases, the variation ranges of the initial concentrations of P or Q must be kept very narrow, leading to very weak cross peak intensities. The weak cross peaks vulnerable to noise bring about difficulty in the investigation of subtle intermolecular interaction. Herein, we propose a new of way constructing a 2D asynchronous spectrum without the subtraction of the average spectrum often used as a reference spectrum. Mathematical analysis and computer simulation demonstrate that the near diagonal cross peaks around the coordinate (<i>X</i>_P, <i>X</i>_P) in the 2D asynchronous spectrum using the new approach possess two characteristics: (1) they can still reflect an intermolecular interaction reliably; 2) the absolute intensities of the cross peaks are significantly stronger than those generated by the conventional method. We incorporate the novel method with the DAOSD (double asynchronous orthogonal sample design scheme) approach and applied the modified DAOSD approach to study hydrogen bonding behavior in diethyl either/methanol/THF system. The new approach made the weak cross peaks, which are not observable in 2D asynchronous spectrum generated using conventional approach, become observable. The appearance of the cross peak demonstrate that When a small amount of THF is introduced into diethyl solution containing low amount of methanol, THF breaks the methanol–diethyl ether complex and forms methanol-THF complex via new hydrogen bond. This process takes place in spite of the fact that the content of diethyl ether is overwhelmingly larger than that of THF. The above result demonstrates that the new approach described in this article is applicable to enhance intensity of cross peaks in real chemical systems

Double Asynchronous Orthogonal Sample Design Scheme for Probing Intermolecular Interactions

This paper introduces a new approach called double asynchronous orthogonal sample design (DAOSD) to probe intermolecular interactions. A specifically designed concentration series is selected according to the mathematical analysis to generate useful 2D correlated spectra. As a result, the interfering portions are completely removed and a pair of complementary sub-2D asynchronous spectra can be obtained. A computer simulation is applied on a model system with two solutes to study the spectral behavior of cross peaks in 2D asynchronous spectra generated by using the DAOSD approach. Variations on different spectral parameters, such as peak position, bandwidth, and absorptivity, caused by intermolecular interactions can be estimated by the characteristic spectral patterns of cross peaks in the pair of complementary sub-2D asynchronous spectra. Intermolecular interactions between benzene and iodine in CCl₄ solutions were investigated using the DAOSD approach to prove the applicability of the DAOSD method in real chemical system