Rapid analysis of wheat flour by different handheld near-infrared spectrometers: A discussion of calibration model maintenance and performance comparison.

With the commercial availability of handheld near-infrared (NIR) spectrometers at significantly reduced costs, novel applications for qualitative and quantitative in-the-field and on-site analysis of such instruments for new user communities are currently reported. In the present study, the feasibility of rapid quantitative analysis of the essential quality parameters protein, wet gluten, moisture, ash, and sedimentation of wheat flour samples with three handheld NIR spectrometers based on different monochromator principles (Linear Variable Filter, Fourier-Transform Technique and Fabry-Perot Tunable Filter) has been investigated. In view of the long-term (two years) measurement and calibration schedule with reference sample batches of significantly varying parameter values, the necessary countermeasures for the important issue of calibration maintenance have been addressed and discussed in detail. Due to the variation of available reference values for the different flour parameters, the total number of reference samples varied between 124 (for sedimentation) and 235 (for moisture). These samples were then split up in a 3/1 calibration/test set ratio. Based on the detailed analysis of the statistical calibration parameters and the prediction accuracy for the test sample sets of the different flour parameters, the performance of the spectrometers under investigation has been compared. Despite instrumental and sampling deficiencies, such as hardware changes and significantly varying sample batches, respectively, during the long-term measurement schedule, the results proved the general suitability of the different handheld NIR spectrometers for the rapid quantitative on-site determination of the essential wheat flour parameters.

Molecular structure and vibrational spectroscopic investigation of secnidazole using density functional theory.

Secnidazole (alpha,2-dimethyl-5-nitro-1H-imidazole-1-ethanol) is an antimicrobical drug, and it is particularly effective in the treatment of amebiasis, giardiasis, trichomoniasis, and bacterial vaginosis. Secnidazole crystallizes as a hemihydrate, which belongs to a monoclinic system having space group P2(1)/c, with a = 12.424 A, b = 12.187 A, c = 6.662 A, and beta = 100.9 degrees. The optimized geometries and total energies of different conformers of the secnidazole molecule have been determined by the method of density functional theory (DFT). For both geometry and total energy, it has been combined with B3LYP functionals having extended basis sets 4-31G, 6-31G, and 6-311++G(d,p) for each of the three stable conformers of secnidazole. Using this optimized structure, we have calculated the infrared and Raman wavenumbers and compared them with the experimental data. The calculated wavenumbers are in an excellent agreement with the experimental values. Based on these results, we have discussed the correlation between the vibrational modes and the crystalline structure of the most stable conformer of secnidazole. A complete assignment is provided for the observed Raman and IR spectra.

Simultaneous determination of the micro-, meso-, and macropore size fractions of porous polymers by a combined use of Fourier transform near-infrared diffuse reflection spectroscopy and multivariate techniques.

Fourier transform near-infrared (FT-NIR) diffuse reflection spectroscopy was used in combination with principal component analysis and partial least-squares regression to simultaneously determine the physical and the chemical parameters of a porous poly(p-methylstyrene-co-1,2-bis(p-vinylphenyl)ethane) (MS/BVPE) monolithic polymer. Chemical variations during the synthesis of the polymer material can alter the pore volume and pore area distributions within the polymer scaffold. Furthermore, mid-infrared and near-infrared (NIR) spectroscopic chemical imaging was implemented as a tool to assess the uniformity of the samples. The presented study summarizes the comparative results derived from the spectral FT-NIR data combined with chemometric techniques. The relevance of the interrelation of physical and chemical parameters is highlighted whereas the amount of MS/BVPE (%, v/v) and the quantity (%) of micropores (diameter, d < 6 nm), mesopores (6 nm < d < 50 nm), and macropores (50 nm < d < 200 nm) could be determined with one measurement. For comparison of the quantitative data, the standard error of prediction (SEP) was used. The SEP for determining the MS/BVPE amount in the samples showed 0.35%, for pore volume quantiles 1.42-8.44%, and for pore area quantiles 0.38-1.45%, respectively. The implication of these results is that FT-NIR spectroscopy is a suitable technique for the screening of samples with varying physicochemical properties and to quantitatively determine the parameters simultaneously within a few seconds.

In situ study of diffusion and interaction of water and mono- or divalent anions in a positively charged membrane using two-dimensional correlation FT-IR/attenuated total reflection spectroscopy.

Two-dimensional (2D) correlation analysis based on time-resolved FT-IR/attenuated total reflection (ATR) spectroscopy has been used to study the diffusion behavior of water and mono- or divalent anions in the positively charged membranes of different charge density. In 2D FT-IR/ATR spectra, the splitting of the water delta(OH) bending band in the spectral range 1700-1500 cm-1 indicates that there are three different states of water in the positively charged membrane, that is, the water molecules forming strong or weak hydrogen bonds with hydrophilic groups of the membrane and water molecularly dispersed with weaker hydrogen bonds. The wavenumber difference of the delta(OH) band in the low- and high-charge-density membrane indicates that water molecules form much stronger hydrogen bonds with hydrophilic groups in the high-charge-density membrane. The sequential order of the three water bands intensity changes shows that, in the process of water diffusion into the high-charge-density membrane, the hydrogen-bonding interaction between hydrophilic groups of the membrane and water molecules takes place gradually due to the highly cross-linked network structure of the membrane; in the process of water diffusion into the low-charge-density membrane, the strong hydrogen-bonding interaction between hydrophilic groups of the membrane and water molecules takes place instantaneously and this type of water easily diffuses due to the weak interactions between the water molecules and the membrane polymer. Furthermore, the diffusion processes of the electrolyte solution such as NaAc and Na2SO4 aqueous solutions in the positively charged membrane have also been examined.

Quantitative determination of pharmaceutical drug formulations by near-infrared spectroscopic imaging.

Over the last decade Fourier transform infrared (FT-IR) and near-infrared (NIR) spectroscopic imaging with focal plane array (FPA) detectors have proved powerful techniques for the rapid visualization of samples by a combination of spectroscopic and spatial information. Using these methods, selected sample areas can be analyzed with reference to the identification and localization of chemical species by FT-IR spectroscopy in the transmission or attenuated total reflection (ATR) mode and by NIR spectroscopy in diffuse reflection with a lateral resolution in the micrometer range. The present communication focuses on the quantitative determination of the active ingredient composition of a solid drug formulation by NIR spectroscopic imaging with a focal plane array detector and the results obtained are compared to the quantitative data obtained by conservative light-fiber NIR spectroscopic diffuse reflection measurements with a single-element detector. The communication also addresses the issue of penetration depth of NIR radiation into the investigated solid material.

Solid state characterization of olanzapine polymorphs using vibrational spectroscopy.

FT-Raman, infrared and near infrared investigations of two polymorphs of olanzapine are presented, establishing the main features that allow the discrimination of these crystalline forms using vibrational spectroscopic methods. Ab initio calculations on the basis of the density functional theory were used to determine the stable conformations. The calculated vibrational spectra were compared to the experimental ones in order to identify the conformers corresponding to each polymorph and to assign the vibrational bands to the internal vibrations of the olanzapine molecule. Our results support the hydrogen bonding pattern proposed by the reported crystalline structure and provide valuable information on the structural and thermodynamical relationship between the investigated polymorphs.

Fourier transform infrared spectroscopic investigation of the electric-field-induced reorientation of the nematic 7CPB with different prealignment.

Time-resolved Fourier transform infrared (FT-IR) polarization spectroscopy was employed to study the electric-field-induced reorientation of nematic p-cyanophenyl-p-n-heptylbenzoate (7CPB) in the bulk of the cell and near (within 1 microm) the surface of the electrodes. The initial orientation of 7CPB on the germanium electrodes was varied in order to obtain information concerning the behavior of the liquid crystalline molecules in the boundary region. Model systems containing the 7CPB on rubbed polyimide and poly(vinyl alcohol), non-rubbed polyimide and poly(vinyl alcohol), and blank germanium were prepared and investigated.

Near-infrared spectroscopic monitoring of the diffusion process of deuterium-labeled molecules in wood. Part I: softwood.

The diffusion process of several molecules (D2O, n-butanol (OD) and t-butanol (OD)) in softwood (Sitka spruce) was investigated by means of a deuterium exchange method and Fourier transform near-infrared (FT-NIR) polarization spectroscopy. The location of OH groups in different states of order of cellulose in wood was clarified by analyzing the FT-NIR transmission spectra ranging from 7200 to 6000 cm(-1). Four absorption bands were assigned to 2 x v(OH) absorptions of the amorphous regions, OH groups in semi-crystalline regions, and two types of intramolecular hydrogen-bonded OH groups in the crystalline regions, respectively. The saturation level of accessibility was very different for these absorption bands (i.e., 70-80, 60, and 40-50% for the amorphous, semi-crystalline, and crystalline regions, respectively). However, the saturation accessibilities for each absorption band varied little with molecular structure and geometry of the diffusants. The diffusion rate of D2O was much faster than that of n-butanol (OD) and t-butanol (OD) for all states of orders. The size effect of the butanols led to slight differences in the diffusive transport in the crystalline regions.

Near-infrared spectroscopic monitoring of the diffusion process of deuterium-labeled molecules in wood. Part II: hardwood.

Fourier transform near-infrared (FT-NIR) transmission spectroscopy was applied to monitor the diffusion process of deuterium-labeled molecules in hardwood (Beech). The results are compared with previous data obtained on softwood (Sitka spruce) in order to consistently understand the state of order in cellulose of wood. The saturation accessibility and diffusion rate varied characteristically with the OH groups in different states of order in the wood substance, the diffusants, and the wood species, respectively. The variation of saturation accessibility should be associated with the fundamental difference of the fine structure such as the microfibrils in the wood substance. The effect of the anatomical cellular structure on the accessibility was reflected in the variation of the diffusion rate with the wood species. The size effect of the diffusants also played an important role for the diffusion process in wood. Since the volumetric percentage of wood fibers and wood rays is relatively similar, the dichroic effects due to the anisotropy of the cellulose chains were apparently diminished. Finally, we proposed a new interpretation of the fine structure of the microfibrils in the cell wall by comparing a series of results from hardwood and softwood. Each elementary fibril in the hardwood has a more homogeneous arrangement in the microfibrils compared to that in the softwood.

Electric-field-induced reorientation of liquid crystalline p-cyanophenyl-p-n-alkylbenzoates: a time-resolved study by fourier transform infrared transmission and attenuated total reflection spectroscopy.

Time-resolved polarization Fourier transform infrared (FT-IR) transmission and attenuated total reflection (ATR) spectroscopy were applied to investigate the reorientation phenomena of the three members of the homologous series of nematic liquid crystalline p-cyanophenyl-p-n-alkylbenzoates 6CPB, 7CPB, and 10CPB under the external perturbation of an electric field. In conjunction with a newly constructed measurement cell, this method allowed us to differentiate the response of the LC system in the surface layer and in the bulk of the cell at different temperatures and voltages. The relaxation time of the LC molecules close to the wall of the cell was found to be shorter than in the bulk. However, at a field strength of 7 V, the initial orientation in the bulk preceeds the analogous process in the surface region.

Polarized infrared spectroscopic study on the orientation of the molecules in the smectic-C* phase of a ferroelectric liquid crystal with a naphthalene ring: alternative theory for the analysis of polarization-angle-dependent intensity changes.

A theory to explain the polarization-angle dependence of polarized infrared spectra of a ferroelectric liquid crystal in the surface-stabilized ferroelectric liquid crystal state is proposed. It describes the relationship between the intensity of the absorption bands and the polarization angle of the infrared radiation. Using this theory the polarization-angle dependence of the infrared band intensities was analyzed for a ferroelectric liquid crystal with a naphthalene ring and two phenyl rings with a stacked layer structure in the smectic-C* phase. The polarization-angle-dependent spectra were measured at 137 degrees C under external dc electric fields of +40 and -40 V to investigate the orientation of the molecules. Plots of the infrared absorbance versus polarization angle for representative bands were subjected to a curve fitting procedure by a least squares method. From the curves obtained the orientation of the transition dipole moments with respect to the molecular long axis and the orientation of the molecular long axis with respect to the rubbing direction of the cell were estimated based upon the suggested theory. The polarization-angle-dependent infrared spectra obtained were also analyzed by two-dimensional (2D) correlation spectroscopy. The 2D correlation analysis clearly detects a slight phase difference in the polarization-angle dependence which is hardly recognized in ordinary plots of the intensity changes in the infrared bands. The 2D correlation analysis allows us to separate asymmetric and symmetric stretching bands due to the chiral methyl group from those arising from other methyl groups in the alkyl chains.

Time-resolved infrared spectroscopic study of the switching dynamics of a surface-stabilized ferroelectric liquid crystal.

The orientation dynamics of a ferroelectric liquid crystal with a naphthalene ring (FLC-3) during the electric-field-induced switching between two surface-stabilized states was investigated by means of time-resolved Fourier-transform infrared spectroscopy. Time-resolved infrared spectra of the planar-aligned cell of FLC-3 were measured as a function of the polarization angle ranging from 0 degree to 180 degrees under a rectangular electric field +/-40 V with a 5-kHz repetition rate in the smectic-C* (Sm-C*) phase at 137 degrees C. From these spectra details about the mutual arrangement of different molecular segments at all the delay times in the Sm-C* phase were derived. It was found that the C=O group in the core moiety exhibits a dynamical behavior different from that in the chiral moiety during the electric-field-induced switching between the two surface-stabilized states. The most important finding in the present study is that during the electric-field-induced switching the FLC molecule not only rotates around the layer normal, but also revolves around its own long axis. Furthermore, time-resolved infrared spectroscopy revealed that each group in the core moiety passes almost simultaneously through the projection of the layer normal in the cell window during the dynamic switching.

An ab initio and DFT study of structure and vibrational spectra of gamma form of oleic acid: comparison to experimental data.

Oleic acid (cis-9-octadecenoic acid) is the most abundant cis-unsaturated fatty acid in nature; it is distributed in almost all organisms. In this work, we present a detailed vibrational spectroscopy investigation of Oleic acid by using infrared and Raman spectroscopies. These data are supported by quantum mechanical calculations, which allow us to characterize completely the vibrational spectra of this compound. The equilibrium geometry, harmonic vibrational frequencies, infrared intensities and activities of Raman scattering were calculated by ab initio Hartree-Fock (HF) and density functional theory (DFT) employing B3LYP with complete relaxation in the potential energy surface using 6-311G(d, p) basis set. After a proper scaling the calculated wavenumbers show a very good agreement with the observed values. A complete vibrational assignment is provided for the observed Raman and infrared spectra of Oleic acid. In this work, we also investigate the deviation of vibrational wavenumbers computed with two quantum chemical methods (HF and B3LYP).

Near-infrared spectroscopic observation of the ageing process in archaeological wood using a deuterium exchange method.

The ageing degradation of the fine wood structure of dry-exposed archaeological wood was investigated by Fourier transform near-infrared spectroscopy with the aid of a deuterium exchange method. The archaeological wood sample was taken from an old wooden temple in Japan (late 7th century), which has been designated as a UNESCO world heritage site. Comparing the analytical results with those of a modern wood sample of the same species, the ageing process of archaeological wood was clarified as a change in the state of order on a macromolecular structural level. It can be concluded from NIR spectra that the amorphous region, and partially semi-crystalline region, in cellulose, hemicellulose, and lignin decreased by the ageing degradation, whereas the crystalline region in cellulose was not affected by the ageing. The accessibility of the diffusant to effect H/D-exchange was monitored by an OH-related absorption band obtained from FT-NIR transmission spectroscopy and characteristically varied with the ageing process of the wood samples, the absorption bands characteristic of a specific state of order and the diffusion agent. Finally, we proposed a morphological model to describe the variation of the fine structure of the microfibrils in the cell wall with ageing degradation. The state of microfibrils changed loosely by ageing, so that elementary fibrils were arranged loosely under 5 A, whereas several elementary fibrils in the modern wood were arranged in very close proximity under 3 A to each other.

Two-dimensional/ATR infrared correlation spectroscopic study on water diffusion in a poly(epsilon-caprolactone) matrix.

In the present contribution, two-dimensional ATR-FTIR spectroscopy was used to study the diffusion of water in poly(epsilon-caprolactone) (PCL). In the spectral region of the nu(OH) stretching vibration of water, four absorption bands (3635, 3560, 3411, and 3220 cm(-1)) can be identified. The higher wavenumber band pair at 3635 and 3560 cm(-1) is assigned to the antisymmetric and symmetric OH stretching vibrations, respectively, of water which is partially hydrogen-bonded to the carbonyl groups of PCL, whereas the lower frequency band pair at 3411 (antisymmetric) and 3220 cm(-1) (symmetric) is attributed to the OH stretching vibrations of bulk water which is fully hydrogen-bonded to other water molecules. From the asynchronous map of a 2D correlation analysis of spectra recorded during the diffusion of water into PCL, it was concluded that during the diffusion process the water molecules first penetrate into the free volume (microvoids) of the PCL matrix or are molecularly dispersed in the polymer matrix and then form hydrogen bonds with the C=O groups of the polymer.

Monitoring the melt-extrusion transesterification of ethylene-vinylacetate copolymer by self-modeling curve resolution analysis of on-line near-infrared spectra.

The transesterification of molten ethylene-vinylacetate (EVA) copolymers by octanol with sodium methoxide as catalyst in an extruder has been monitored by on-line near infrared (NIR) spectroscopy. A total of 60 NIR spectra were acquired for 37 min with the last spectrum recorded 31 min after the addition of octanol and catalyst was stopped. The experimental spectra show strong baseline fluctuations which are corrected for by multiplicative scatter correction (MSC). The chemometric methods of the orthogonal projection approach (OPA) and multivariate curve resolution (MCR) were used to resolve the spectra and to derive concentration profiles of the species. The detailed analysis reveals the absence of completely pure variables which leads to small errors in the calculation of pure spectra. The initial estimation of a concentration that is necessary as an input parameter for MCR also presents a non-trivial task. We obtained results that were not ideal but applicable for practical concentration control. They enable a fast monitoring of the process in real-time and resolve the spectra of the EVA copolymer and the ethylene-vinyl alcohol (EVAL) copolymer to be very close to the reference spectra. The chemometric methods used and the decomposed spectra are discussed in detail.