Two-dimensional Near-infrared Correlation Spectroscopy Research Articles

Determination of Methanol in Alcoholic Beverages by Two-Dimensional Near-Infrared Correlation Spectroscopy

ABSTRACTAn innovative method for the determination of concentration of methanol in white spirit was proposed using two-dimensional near-infrared (NIR) correlation spectroscopy in combination with multivariate calibration. A total of 38 white spirit samples were adulterated with level of methanol varying from 0.1 to 10%. A one-dimensional NIR spectra of all samples were collected. Spectral characteristics of white spirit adulterated with methanol were studied based on one-dimensional NIR spectra and two-dimensional NIR correlation spectra. The origin of 4396 cm−1 peak of methanol was verified in terms of the existence or absence of cross-peaks in synchronous and asynchronous two-dimensional NIR correlation spectra. For comparison, the quantitative analysis models were constructed to determine content of methanol in white spirit using synchronous two-dimensional NIR correlation spectra and traditional one-dimensional NIR spectra, respectively. The prediction statistics criteria for synchronous two-dimensional NIR correlation spectra using N-way partial least squares, average relative error and root mean square error, were 2.97 and 0.064%, respectively. For traditional one-dimensional NIR spectra using partial least squares method, average relative error and root mean square error of prediction were 5.3 and 0.079%, respectively. Comparison results show that the proposed new method has stronger predictive ability and can provide better results than traditional one-dimensional NIR spectra using partial least squares.

Spectroscopic and Quantitative Chemometric Analysis of the Epoxidised Oil/Amine System

The competitiveness between the oxirane functional group and the ester functional group present in a derivative epoxidised oil was studied by monitoring a model system which involved epoxidised oleic oil and aniline (1:1). The reaction was carried out under isothermal conditions at 95°C and monitored in situ by near infrared (NIR) spectroscopy. This system is taken as a model of the curing process in the manufacture of epoxy resins from triglycerides and diamines. Conventional spectroscopic analysis and generalised two-dimensional NIR correlation spectroscopy analysis have led to the conclusion that, even though the formation of secondary amines by ring-opening of the oxirane group as a consequence of the nucleophilic attack of the aniline is prior, the formation of amides as a consequence of the ester group reactivity is a competitive reaction. The presence of the two aforementioned reactions is also in accordance with the significant number of factors found when the spectra data matrix was analysed by evolving factor analysis. By applying multivariate curve resolution–alternating least squares to the NIR spectra obtained during the reaction, it has been possible to obtain the concentration and the spectra profiles of each chemical species involved in the reaction. The performance of the model was assessed by two parameters: alternating least squares lack of fit (lof = 1.67 %) and explained variance ( R2 = 99.68%). The recovered spectra of the generated products have the characteristic bands associated with the two postulated reactions.

Two-dimensional near-infrared correlation spectroscopy study the methanol in acidic pH region

The effect of pH on the structure of methanol was investigated by FT-NIR (Fourier transform near-infrared) spectroscopy and generalized two-dimensional (2D) correlation spectroscopy. pH perturbed 2D correlation spectra are calculated for the spectra in the 5500–4000, 7500–5500 cm −1 regions at different pH values. We observed that the stretching of CH 3 was shifted because of the direct interaction of the CH 3 group of methanol with the OH group of water, the change of free OH is more sensitive to pH than the cyclic dimmer and CH·O.

Physico-chemical description of bread dough mixing using two-dimensional near-infrared correlation spectroscopy and moving-window two-dimensional correlation spectroscopy

NIR spectroscopy presents a huge interest in exploring chemical changes during dough mixing. The aim of the present study is to investigate the potential of 2D correlation spectroscopy (2D COS) and moving-window 2D (MW2D) correlation spectroscopy to explore the time dependence of NIR spectral responses during wheat flour dough mixing. NIR spectra were continuously recorded (between 1400 and 2325 nm) during mixing of bread type-dough (based on flour, water and yeast), using an FT-NIR spectrometer with a deported probe. The probe was positioned inside the mixer in contact with the dough. The 2D spectra calculated using raw and second derivative NIR spectra were interpreted in terms of physico-chemical events. Nine different industrial flours were used as raw material to validate the analysis. The results obtained using the 2D COS and the MW2D methods give the possibility to ascribe chemical vibrations (starch, water and gluten) to NIR absorbance changes occurring during dough mixing. The analysis of the NIR spectra identified wavelength shift associated to both dough “free water” and protein secondary structure modifications. During this study, only the MW2D method allowed to identify clearly the time dependence of physico-chemical mechanisms from NIR variation bands.

Application of two-dimensional near-infrared correlation spectroscopy to the discrimination of Chinese herbal medicine of different geographic regions

Fructus Lycii is a traditional Chinese medicinal herb. The objective of this paper was to apply two-dimensional (2D) near-infrared (NIR) correlation spectroscopy to the discrimination of Fructus Lycii of four different geographic regions. Generalized 2D-NIR correlation spectroscopy was able to enhance spectral resolution, simplify the spectrum with overlapped bands, and provide information about temperature-induced spectral intensity variations that was hard to obtain from one-dimensional NIR spectroscopy. The 2D synchronous and asynchronous spectra showed remarkable differences within the range of 4950–5700 cm −1 between samples of different geographic regions. Using NIR instead of IR made the 2D approach more convenient and fast, and it can be applied to more area like process control. This approach can also be applied analogously to the discrimination of other Chinese herbal medicine of different geographic regions.

Studies on the structure of water using two-dimensional near-infrared correlation spectroscopy and principal component analysis.

The structure of water molecules in the pure liquid state has been subjected to extensive research for several decades. Questions still remain unanswered, however, and no single model has been found capable of explaining all the anomalies of water. In the present study, near-infrared spectra of water in the temperature region 6-80 degrees C have been analyzed by use of principal component analysis and two-dimensional correlation spectroscopy in order to study the dynamic behavior of a band centered around 1,450 nm at room temperature, which is due to the combination of symmetric and antisymmetric O-H stretching modes (first overtone) of water. It has been found that the wavelengths 1,412 and 1,491 nm account for more than 99% of the spectral variation, representing two major water species with weaker and stronger hydrogen bonds, respectively. A third species located at 1438 nm, whose concentration was relatively constant as a function of temperature, is also indicated. A somewhat distorted two-state structural model for water is suggested.

1P048二次元近赤外相関分光法による卵白アルブミンの酸変性過程の研究 : 水和状態と二次構造変化の同時観測

1P048二次元近赤外相関分光法による卵白アルブミンの酸変性過程の研究 : 水和状態と二次構造変化の同時観測

Resolution Enhancement and Band Assignments for the First Overtone of OH(D) Stretching Modes of Butanols by Two-Dimensional Near-Infrared Correlation Spectroscopy. 3. Thermal Dynamics of Hydrogen Bonding in Butan-1-(ol-d) and 2-Methylpropan-2-(ol-d) in the Pure Liquid States

Two-dimensional (2D) near-infrared (NIR) correlation spectroscopy was used to study the temperature-induced changes in the hydrogen bonding of butan-1-(ol-d) and 2-methylpropan-2-(ol-d) in the pure liquid phase. The similarity between the 2D correlation spectra of both studied butanols and their nondeuterated analogues proves that the isotopic substitution in the hydroxyl group affects little the dynamic properties of the hydrogen bonding. This conclusion also confirms the heterospectral analysis, performed for the spectra of the deuterated samples and their nondeuterated counterparts. In the asynchronous spectra of 2-methylpropan-2-ol and its deuterated analogue, we identified new bands at 7040 and 5226 cm-1, respectively, which are probably due to an intramolecular effect. Moreover, a heterospectral asynchronous plot develops a peak at (5286, 7085), not seen in the homospectral 2D plots of butan-1-(ol-d) and butan-1-ol, giving rise to an additional resolution enhancement. This new peak reveals different...

Two-Dimensional Near-Infrared Correlation Spectroscopy Studies of Compatible Polymer Blends: Composition-Dependent Spectral Variations of Blends of Atactic Polystyrene and Poly(2,6-dimethyl-1,4-phenylene ether)

Two-Dimensional Near-Infrared Correlation Spectroscopy Studies of Compatible Polymer Blends: Composition-Dependent Spectral Variations of Blends of Atactic Polystyrene and Poly(2,6-dimethyl-1,4-phenylene ether)

Application of two-dimensional near-infrared correlation spectroscopy to protein research

The purpose of the present paper is to demonstrate the potential of generalized two-dimensional (2D) near-infrared (NIR) correlation spectroscopy in studies of hydration and structure of proteins. We describe here two examples. The first example is concerned with heat denaturation process of ovalbumin in aqueous solutions and the second one deals with isomerizations with varying pH of serum albumin. New insight has been obtained into the hydration and unfolding process of secondary structures of ovalbumin and serum albumin by studying temperature- or pH-dependent correlation patterns in 2D synchronous and asynchronous spectra. Generalized 2D NIR correlation spectroscopy emphasizes spectral features not readily observable in conventional one-dimensional spectra, enabling to extract subtle but valuable structural changes concerning with the protein denaturation.

Two-Dimensional Near-Infrared Correlation Spectroscopy Studies on Composition-Dependent Spectral Variations in Ethylene/Vinyl Acetate Copolymers: Assignments of Bands Due to Ethylene Units in Amorphous, Disordered, and Orthorhombic Crystalline Phases

Generalized two-dimensional (2D) correlation spectroscopy has been applied to the study of the composition-dependent near-infrared (NIR) spectral changes in 11 different ethylene/vinyl acetate (EVA) copolymers with vinyl acetate (VA) content from 6 to 42 wt %. The 2D synchronous correlation analysis of the 11 NIR spectra has separated the bands due to ethylene units from those due to the VA units. The obtained results are consistent with those reached by the calculation of the second derivative and by chemometrics analysis reported in our previous paper. However, the 2D correlation analysis has given clearer evidence for the band separation. Two-dimensional asynchronous correlation analysis has revealed out-of-phase variations between some bands due to ethylene and some bands due to VA and has determined the order of intensity change between them. On the basis of the order of intensity change, the bands of ethylene in the orthorhombic crystalline phase have been discriminated from those in the amorphous and disordered phases. This paper discusses the potentials of three powerful techniques, 2D correlation analysis, the calculation of the second derivatives, and that of regression coefficients in chemometrics, in unraveling rather complicated NIR spectra.

Resolution Enhancement and Band Assignments for the First Overtone of OH Stretching Modes of Butanols by Two-Dimensional Near-Infrared Correlation Spectroscopy. 2. Thermal Dynamics of Hydrogen Bonding in n- and tert-Butyl Alcohol in the Pure Liquid States

The temperature-dependent near-infrared (NIR) spectral variations of n- and tert-butyl alcohols in the pure liquid state have been studied by generalized two-dimensional (2D) correlation analysis. ...

Resolution Enhancement and Band Assignments for the First Overtone of OH Stretching Mode of Butanols by Two-Dimensional Near-Infrared Correlation Spectroscopy. Part I: sec-Butanol

The first paper in a series devoted to self-association in neat butanols presents the results of two-dimensional (2D) near-infrared (NIR) correlation analysis of temperature-induced spectral variations of sec-butanol. By taking advantage of resolution enhancement in the 2D correlation spectra, it was possible to identify spectral features due to vibrations of the free and associated OH groups in the first-overtone region. On the basis of a few assumptions, band assignments of the various types of OH bonds have been proposed. The monomer band (near 7100 cm−1) can be resolved into three components; two of them are due to a rotational isomerism (7089 and 7116 cm−1), and the third one is attributed to the free terminal OH groups in linear polymers (7055 cm−1). The presence of the 7055 cm−1 band implies that the intensity of the monomer peak cannot be used as a measure of the concentration of the monomer species (except in very diluted solutions). Thus, previous estimations of equilibrium constants and thermodynamic parameters associated with hydrogen-bond dissociation have been subject to unacceptable error. At higher temperatures, a new band near 6550 cm−1 becomes visible. This band originates from bended OHO bond, mostly in the cyclic polymers. In order to obtain more detailed information on the complex mechanism of the thermal dissociation of hydrogen-bonded sec-butanol in the pure liquid phase, the entire experimental temperature range was divided into narrower ranges, and then 2D correlation analysis was performed for smaller data sets. It has been shown that the variations of population of the polymeric species and the cyclic dimers are faster than the corresponding changes for the monomers. At elevated temperatures an appreciable dissociation of the cyclic species takes place.

Two-Dimensional Near-Infrared Correlation Spectroscopy Study of Premelting Behavior of Nylon 12

The premelting behavior of Nylon 12 has been investigated by two-dimensional (2D) Fourier-transform (FT) near-infrared (NIR) correlation spectroscopy. FT-NIR spectra of Nylon 12 in a cast film have been measured over a temperature range of 30−150 °C. The 2D NIR correlation analysis reveals that there are at least eight bands in the 6800−6100 cm-1 region where the first overtone of an NH stretching mode of Nylon 12 is expected to appear. They may be ascribed to free- and hydrogen-bonded NH groups in various environments. The asynchronous 2D NIR correlation spectrum in the above region indicates that the amide group with a free carbonyl oxygen (structure C) appears first and then unassociated free amide (structure A) and amide with free NH (structure B) follow as the temperature is increased. In the 6000−5500 cm-1 region of the synchronous spectrum, four dominant autopeaks corresponding to the first overtones of the CH2 stretching modes are observed at 5840, 5770, 5680, and 5640 cm-1, and negative cross peaks are found between the 5770 cm-1 band and the rest. This observation, together with the careful inspection of the dynamic NIR spectra, suggests that the band at 5770 cm-1 is due to the contribution of the CH stretching vibration of an ordered or highly associated form of Nylon 12, which decreases with temperature, while other NIR bands correspond to more disordered forms. The corresponding asynchronous spectrum indicates that the intensity variation of the bands at 5840, 5680, and 5640 cm-1 actually occurs at a lower temperature compared to the onset of the intensity decrease of the 5770 cm-1 band. A substantial amount of disordered or dissociated components corresponding to the above three bands start appearing before the disappearance of more ordered components represented by the 5700 cm-1 band. Probably, they appear as the premelting precursors (or even possibly as the indirect cause) to the precipitous decrease of the ordered components associated with the melting of Nylon 12 occurring at a much higher temperature.

二次元近赤外相関分光法の可能性

二次元近赤外相関分光法の可能性