Near infrared reflectance spectroscopy as a tool for the control of sheep leather defatting

The fat content is one of the variables to be controlled by the tanning industry with a view to obtaining leather for various commercial purposes. Ensuring the production of quality leather products frequently entails using some defatting treatment, particularly when the raw skin is rich in natural fat. The official method for determining fat in leather, IUC 4, is rather slow; also, it uses polluting reagents and involves powdering samples for Soxhlet extraction with low-polarity solvents. The combination of NIR diffuse reflectance spectroscopy as implemented with a fibre-optic probe and multivariate calibration is probably the best choice for the direct determination of fat in leather and the monitoring of leather defatting.In this work, a method for the determination of fat in leather and the control of the defatting process in an expeditious manner and with no sample treatment was developed. Defatting tests were conducted on leather specimens from lambs of various breeds and origins in order to span as wide as possible a range of variability in their properties and natural fat content. The NIR spectra used to construct the calibration matrices were recorded directly on the leather samples prior to and after defatting. Fat contents were determined by partial least-squares regression (PLSR), using the values obtained with the official method as references. Notwithstanding the complex nature of leather, the calibration models used provided good external predictions: the largest overall relative error, obtained by using a single calibration matrix for natural and defatted specimens, was 10%. The proposed method is therefore an advantageous alternative to the official method.     

Diffuse reflectance infrared Fourier transform spectroscopy as a tool to characterise water in adsorption/confinement situations

We present experimental data acquired by diffuse reflectance infrared spectroscopy in the mid-IR (4000-400 cm(-1)), on micrometric-sized mineral grain powders. The spectral evolution of the OH-stretching band is followed when the adsorbed water film is thinned under dry conditions, from high to low hydration states. The IR bands are found to be characteristic of the degree of adsorption/confinement of the liquid water. The OH-stretching band is shifted toward shorter wavenumbers than in bulk water, showing that a significant portion of adsorbed water has a higher intermolecular bonding energy. Complementary treatment of the kinetics of water desorption, varying with the surface forces in the water film, confirms the relationships of these bands with the constrained water state. We distinguish different water types obeying liquid-liquid interactions (free and capillary water) or dominated by solid-water interactions (confined and adsorbed water). Part of this study is devoted to mesoporous silica MCM-41, of interest due to the restricted geometries of its mesopores (4.7 nm) favouring the confined water state. The methodology allows us to distinguish bulk and adsorbed/confined water, using spectral analysis coupled with an understanding of the dynamic behaviour of the desorption process.     

Tethered bilayer lipid membranes studied by simultaneous attenuated total reflectance infrared spectroscopy and electrochemical impedance spectroscopy

The formation of tethered lipid bilayer membranes (tBLMs) from unilamelar vesicles of egg yolk phosphatidylcholine (EggPC) on mixed self-assembled monolayers (SAMs) from varying ratios of 6-mercaptohexanol and EO(3)Cholesteryl on gold has been monitored by simultaneous attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and electrochemical impedance spectroscopy (EIS). The influence of the lipid orientation (and hence the anisotropy) of lipids on a gold film on the dichroic ratio was studied by simulations of spectra with a matrix method for anisotropic layers. It is shown that for certain tilt angles of the dielectric tensor of the adsorbed anisotropic layer dispersive and negative absorption bands are possible. The experimental data indicate that the structure of the assemblies obtained varies with varying SAM composition. On SAMs with a high content of EO(3)Cholesteryl, tBLMs with reduced fluidity are formed. For SAMs with a high content of 6-mercaptohexanol, the results are consistent with the adsorption of flattened vesicles, and spherical vesicles have been found in a small range of surface compositions. The kinetics of the adsorption process is consistent with the assumption of spherical vesicles as long-living intermediates for surfaces of a high 6-mercaptohexanol content. No long-living spherical vesicles have been detected for surfaces with a large fraction of EO(3)Cholesteryl tethers. The observed differences between the surfaces suggest that for the formation of tBLMs (unlike supported BLMs) no critical surface coverage of vesicles is needed prior to lipid bilayer formation.     

Protein determination in serum and whole blood by attenuated total reflectance infrared spectroscopy

Attenuated total reflectance mid-infrared spectra of serum and blood samples were obtained from 4,000 to 600 cm(-1). Models for the determination of albumin, immunoglobulin, total globulin, and albumin/globulin coefficients were established for serum samples, using reference data obtained by capillary electrophoresis. Based on the use of the amide bands I and II regions, the relative root mean square error of prediction (RRMSEP) was 4.9, 14.9, 4.5, and 7.1% for albumin, immunoglobulin, total globulin, and albumin/globulin coefficients, respectively, determined in an independent validation set of 120 samples using 200 samples for calibration. Additionally, the use of Kennard-Stone method for the selection of a representative calibration subset of samples provided comparable results using only 60 samples. For whole blood analysis, hemoglobin was determined in 40 validation samples using models built from 40 calibration independent samples with RRMSEP of 8.3, 5.5, and 4.9% with models built from direct spectra in the first case and from sample spectra recorded after lysis by sodium dodecyl sulfate and freezing, respectively, for the last two ones. The developed methodologies offer green alternatives for patient diagnosis in a few minutes, minimizing the use of reagents and residues and being adaptable for its use as a point-of-care method.     

Monitoring photooxidation of the Prestige's oil spill by attenuated total reflectance infrared spectroscopy

The recent release of ca. 70,000 tonnes of a heavy fuel oil from the Prestige-Nassau carrier along the Spanish northern coast, mainly along Galicia, was monitored using attenuated total reflectance—mid IR spectrometry. The fuel was characterized and differentiated from 10 products commonly transported along the Galician coast (and their series of weathered samples) using factor analysis. The Prestige's fuel was weathered under natural conditions and under infrared radiation to study its evolution on time. A correlation was established using the 1690-1700 cm⁻¹ carbonyl peak, where from it was deduced that IR radiation weathered the product two times faster than natural conditions. The use of 10 weathering indexes was carried out to confirm the main patterns given by factor analysis and to seek out which main functional groups and structures increased or decreased during weathering. It was found that the carbonyl and sulphoxide indexes varied greatly, as well as the total aromaticity and long chains ones. The substitution-related indexes pointed out that highly substituted aromatic structures increased although the total amount of isolated CH groups in aromatic structures reached a plateau.     

Diffusion measurements with fourier transform infrared attenuated total reflectance spectroscopy: Water diffusion in polypropylene*

The diffusion of pure liquid water into a commercial polypropylene (PP) film at 278–348 K was studied with Fourier transform infrared attenuated total reflectance spectroscopy. Abnormal diffusion behavior was indicated by a significant deviation between the experimental data and a Fickian diffusion model with the conventional saturated boundary condition applied at the water/PP interface. This deviation was observed at all the temperatures studied. With a modified boundary condition that took into account a mass‐transfer resistance at the water/PP interface, the Fickian model was able to represent the experimental data satisfactorily. The average water diffusion coefficient varied between 1.41 and 7.64 × 10^?9 cm²/s, with an activation energy of diffusion of about 19.3 kJ/mol. The interfacial mass‐transfer resistance was represented by an exponential model with an empirical relaxation parameter. The relaxation parameter β increased as the temperature increased and reached an apparent plateau. The infrared spectrum indicated a positive chemical shift of 18 cm^?1 for the less strongly hydrogen‐bonded component of the broad hydroxyl stretching band with respect to pure liquid water, indicating that hydrogen‐bonding interactions were weakened or broken when water molecules diffused into the PP matrix. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 980–991, 2002     

Transient infrared spectroscopy: a new approach to investigate valence tautomerism

In this work we present, to our knowledge for the first time, the results of a transient infrared spectroscopic study of the photoinduced valence tautomerism process in cobalt-dioxolene complexes with sub-picosecond time resolution. The molecular systems investigated were [Co(tpa)(diox)]PF(6) (1) and [Co(Me(3)tpa)(diox)]PF(6) (2), where diox = 3,5-di-tert-butyl-1,2-dioxolene; tpa = tris(2-pyridylmethyl)amine and Me(3)tpa its 6-methylated analogue. Complex (1) is present in solution as ls-Co(III)(catecholate) (1-CAT), while (2) as hs-Co(II)(semiquinonate) (2-SQ). DFT calculation of the harmonic frequencies for (1) and (2) allowed us to identify the vibrational markers of catecholate and semiquinonate redox isomers. Irradiation with 405 and 810 nm pulses (~35 fs) of (1-CAT) induces the formation of an intermediate excited species from which the ground state population is recovered with a time constant of 1.5 ± 0.3 ns. Comparing the 1 ns transient infrared spectrum with the experimental difference spectrum FTIR(2-SQ)-FTIR(1-CAT) and with the calculated difference spectrum IR(c)(1-SQ)-IR(c)(1-CAT) we are able to unequivocally identify the long lived species as the semiquinonate redox isomer of (1). On the other hand, no evidence of photoconversion is observed upon irradiation of (2) with 405 nm. Temporal evolution of transient spectra was analyzed with the combined approach consisting of singular values decomposition and global fitting (global analysis). After 405 and 810 nm excitation of (1-CAT), the semiquinonate excited species is formed on an ultrafast time scale (<200 fs) and cools down within the first 50 ps. Excitation of (2-SQ) with 405 nm wavelength produces a short lived excited state in which the semiquinonate nature of dioxolene is preserved and the ground state recovery is completed within 30 ps.     

A novel vertical attenuated total reflectance photochemical flow-through reaction cell for Fourier transform infrared spectroscopy

A unique photochemical cell design and two experiments are presented, which illustrate the usefulness of flow-through attenuated total reflectance (ATR) Fourier transform infrared (FT-IR) spectroscopy as a technique for investigating photochemical reactions at the mineral-water interface. The kinetics of the photolysis reaction of potassium oxalate (K(2)C(2)O(4)) in a ferric iron solution and oxalate adsorbed onto goethite (alpha-FeOOH) were investigated to show the capabilities of the cell. Due to complicated kinetics, the adsorption experiment demonstrates not only the types of complex problems, that may exist at the mineral-water interface, but also the ability for this novel cell design to address them.     

衰减全反射傅里叶变换红外光谱法同时测定叔丁醇和二叔丁基过氧化物

分别应用914 cm-1和875 cm-1处的甲基特征峰作为叔丁醇和二叔丁基过氧化物的定量分析峰,使用峰面积作为吸光度的评估方法,得到的标准曲线的相关系数(R2)分别是0.9987和0.9952,叔丁醇的加标回收率在95％～110％之间,应用衰减全反射傅里叶变换红外光谱法测定3个样品,计算结果的F值、t值和p值,数据表明衰减全反射傅里叶变换红外光谱法与气相色谱法的测定结果一致.     

Near infrared reflectance spectroscopy as a process signature in uranium oxides

Near-infrared (NIR) reflectance spectroscopy was examined as a potential tool for the determination of forensic signatures indicative of the chemical process history of uranium oxides. The ability to determine the process history of nuclear materials is a desired, but underdeveloped, area of technical nuclear forensics. Application of the NIR technique potentially offers a quick and non-destructive tool to serve this need; however, few data have been published on the compounds of interest. The viability of NIR was investigated through the analysis of a combination of laboratory-derived and real-world uranium precipitates and oxides. A set of reference uranium materials was synthesized in the laboratory using the commonly encountered aqueous precipitation reactions for uranium ore concentration and chemical separation processes (ammonia, hydrogen peroxide, sodium hydroxide, ammonium carbonate, and magnesia). NIR spectra were taken on a range of samples heat treated in air between 85 and 750 °C. X-ray diffraction patterns were also obtained to complement the NIR analysis with crystal phase information. Similar analyses were performed using a set of real-world samples, with process information obtained from the literature, to provide a comparison between materials synthesized in the laboratory and samples representative of industrial processes.     

Optimization of sample packing in diffuse reflectance infrared spectroscopy

Parameters of sample packing in diffuse reflectance IR Fourier transform spectroscopy (DRIFTS) have been investigated and optimized. One MPa pressure applied for 1 min was found to provide simultaneously at least ±3% reproducibility and appropriate band intensity. It has been also demonstrated that this precision can be obtained if the sample mass is controlled to ±2% and the sample is dry. A simple sample packing accessory was designed and constructed for reproducible sample preparation. Quartz concentration of dust samples has been determined and good agreement has been found with the results of the conventional pellet technique.     

Quantitative aqueous attenuated total reflectance Fourier transform infrared spectroscopy : Part II. Integrated molar absorptivities of alkyl carboxylates

A quantitative attenuated total reflectance Fourier transform infrared (ATR-FT-IR) spectroscopic method is developed for the analysis of total carboxylate concentration, [COO⁻], in aqueous solution. The short (12–13 μm) and highly reproducible pathlength of the ATR cell permits quantitative subtraction of the water peak at 1640 cm⁻¹. Carboxylate quantitation is based on the area of the asymmetric stretching peak, which is nearly independent of compound structure. The molar absorptivity of alkyl carboxylates in water is 438 ± 58 l mol⁻¹ cm⁻¹, and the integrated molar absorptivity is 2.95 ± 0.08 × 10⁴ l mol⁻¹ cm⁻² (n = 15 compounds, 0.1 M ≤ [COO⁻] ≤ 1.5 M). The [COO⁻] in solutions of mixed carboxylates is measured with a root mean square error of 2.4% and a small (+1.5) positive bias. The accuracy of the method is limited by the assumption that integrated absorbance is constant for all COO⁻ groups.     

Quantitative analysis of polymers by attenuated total reflectance fourier-transform infrared spectroscopy: Vinyl acetate and methyl content of polyethylenes

A comparison was made between the transmission and attenuated total reflectance (ATR) infrared spectroscopic techniques for the determination of the vinyl acetate content of poly(ethylene–vinyl acetate) copolymers and methyl content of polyethylene. It was demonstrated that the transmission and ATR calibration curves for ratios of absorbances of bands with maxima at very similar wavelength were coincident, while those for ratios of absorbances of bands with maxima at significantly dissimilar wavelength were shifted apart. The explanation of this behavior is based on the wavelength dependence of the interaction of the IR radiation in ATR, compared to the wavelength independence of the interaction in transmission IR. The effect of polarized radiation was investigated in each type of analysis with the ATR technique. It was found that essentially the same results were obtained with the IR radiation polarized at 0° or 90°, relative to the plane of incidence, as compared to spectra obtained with unpolarized radiation. However, larger scatter was observed with polarized radiation. The effect of clamping pressure was also investigated. It was found that a minimum clamping torque of 5 in. lb is necessary to assure good physical contact in ATR work.     

Two-dimensional infrared (2D IR) spectroscopy. A new tool for interpreting infrared spectra

Two-dimensional infrared (2D IR) spectroscopy is used to study atactic polystyrene. 2D IR is a technique based on time-resolved detection of IR signals in response to an external perturbation, such as mechanical strain. Since different chemical functional groups respond to the applied perturbation at unique and often different rates, characteristic time-dependent variations of the IR-band intensities are observed. Correlation analysis of the dynamic variation of the IR signals yields a new spectrum defined by two independent wave numbers. Peaks located on a 2D IR spectral plane imply interactions and connectivities among chemical functional groups. By spreading convoluted IR bands over two dimensions, the spectral resolution is also greatly enhanced.     

Spectroscopic evaluation of living murine macrophage cells before and after activation using attenuated total reflectance infrared spectroscopy

Infection activates immune response pathways in host macrophages and lymphocytes that might be of sufficient magnitude to facilitate early diagnoses of infections through a host immune biosignature. Attenuated total reflectance (ATR) infrared spectroscopy was used to examine the spectroscopic signatures of living mouse macrophage cells before and after activation. Cells were prepared as control samples, or activated with a combination of lipopolysaccharide and interferon-gamma (IFN-γ) and analyzed 21 h after treatment. Resulting ATR/IR spectra collected from the living cells were analyzed using principal components analysis (PCA) and other classification methods. Plotting the scores from the first two principal components against one another provides good separation between activated and control samples. Interpretation of the loadings plots indicated that cellular activation was associated with changes in nucleic acid, protein and lipid infrared bands. Spectral samples were used to develop classification models based on activation status. Linear discriminant analysis (LDA) and K-nearest neighbor (K-NN) models were developed with 100% classification rates, using leave-one-out cross-validation procedures. Activated macrophages can be distinguished from macrophages in the resting state by their ATR spectroscopy biosignatures.     

Surface study of hexagonal boron nitride powder by diffuse reflectance Fourier transform infrared spectroscopy

The surface chemistry of hexagonal boron nitride powder is examined. Surface functional groups are found to consist of a mixture of primary and secondary amine groups as well as hydroxyl groups. The surface has a net basic character indicating that the amine contribution to the overall surface chemistry is greater than that of the acidic hydroxyl contribution. A chemical surface treatment also is performed to modify the surface chemistry of hexagonal boron nitride powder. Copyright © 2005 John Wiley & Sons, Ltd.     

Fourier transform infrared spectroscopy as a tool to study structural properties of cytochromes P450 (CYPs)

Cytochrome P450 proteins (CYPs) are a big class of heme proteins which are involved in various metabolic processes of living organisms. CYPs are the terminal catalytically active components of monooxygenase systems where the substrate binds and is hydroxylated. In order to be functionally competent, the protein structures of CYPs possess specific properties that must be explored in order to understand structure–function relationships and mechanistic aspects. Fourier transform infrared spectroscopy (FTIR) is one tool that is used to study these structural properties. The application of FTIR spectroscopy to the secondary structures of CYP proteins, protein unfolding, protein–protein interactions and the structure and dynamics of the CYP heme pocket is reviewed. A comparison with other thiolate heme proteins (nitric oxide synthase and chloroperoxidase) is also included. Figure The protein secondary structure, protein unfolding, redox-partner protein–protein interaction, structural changes induced by the reduction of the heme iron, and the structure and dynamics of the active site of cytochromes P450 (CYP) can be studied using Fourier transform infrared spectroscopy (FTIR). FTIR spectroscopy is a good approach for gaining a deeper insight into structure–function relationships in CYPs. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Fourier transform infrared spectroscopy as a tool for the study of rare earths carbohydrates complexes

FT-IR spectra of the mixtures of praseodymium chloride and glucose in glassy state were investigated. From the changes of relative intensity and shifts of the characteristic frequency of glucose and water, it is concluded that the coordinated water molecules of the praseodymium ions are partially substituted by glucose through O-H groups which coordinated with praseodymium ions to form chelate ions.     

Comparison of calibration methods in quantitative diffuse reflectance infrared spectroscopy

Four different calibration methods were used for quantitative analysis of quartz and calcite in atmospheric aerosols by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS): (A) conventional calibration with one measurement on each standard (single calibration); (B) calibration with an internal standard; (C) calibration with parallel (n = 4) measurements on each standard (multiple calibration); (D) multiple calibration followed by reference reflectance correction. The accuracy and the precision of the methods were compared and it was found that by using method D the reliability of the conventional pellet preparation transmission technique can be achieved.