Method of spectral subtraction of gas-phase Fourier transform infrared (FT-IR) spectra by minimizing the spectrum length

A new method of spectral subtraction for gas-phase Fourier transform infrared (FT-IR) spectra was developed for long-path gas measurements. The method is based on minimization of the length of the spectrum that results from subtracting the spectrum of an individual component of a gas mixture (water, CO(2), etc.) from the experimental spectrum of the mixture. For this purpose a subtraction coefficient (k(min)) is found for which the length of the resulting spectrum is minimized. A mathematical simulation with two Lorentzian absorption bands was conducted and the limits of application for the proposed method were determined. Two experimental examples demonstrate that a successful result could be achieved in the case when the subtrahend spectrum contains a number of narrow absorption bands (such as the spectrum of water vapor).     

Sm@C_(3v)(134)-C_(94)的原位高压红外吸收光谱及结构研究

对Sm@C_(3v)(134)-C_(94)的原位高压红外吸收光谱的测试,可以用来研究碳笼在高压下的形变过程和金属对碳笼形变的影响.理论计算模拟结果和常压下Sm@C_(3v)(134)-C_(94)的中红外波段的振动模式大致相符.Sm@C_(3v)(134)-C_(94)碳笼的形变随着压力升高而愈加剧烈,且在高压下的形变是各向异性的,远离Sm原子的部分比靠近Sm原子的部分形变更加明显,这是由于Sm原子对附近碳笼起到支撑作用.Sm@C_(3v)(134)-C_(94)的HOMO-LUMO带隙值随压力变化而变化:压力小于8GPa时,该值缓慢减小;压力在8~14GPa之间,碳笼形变剧烈,分子间相互作用增强,带隙值迅速减小;当压力超过14GPa,分子间排斥力增大,从而阻碍分子靠近,带隙值变化缓慢.这一结果将对金属富勒烯及其相关材料的高压下结构研究提供帮助.     

In situ real-time diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) study of hydrogen adsorption and desorption on Ir/SiO2 catalyst

The adsorption and desorption of hydrogen on Ir/SiO(2) catalyst were studied by using in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) combined with curve-fitting analysis. The results indicate that there are three different surface species formed on the catalyst that correspond to the peaks at 1950, 2010, and 2035 cm(-1), respectively, when exposed in H(2) flow at 130 °C. These surface species display different adsorption and desorption trends. Surface hydride forms after the catalyst is cooled to 80 °C and it disappears after the catalyst is heated to 130 °C again. This study may help us understand the interaction between hydrogen and noble metals and thus give more insights to heterogeneous catalytic mechanism involving hydrogen and hydrogen storage using metal materials.     

Fourier transform infrared spectral analysis of degenerative cartilage: an infrared fiber optic probe and imaging study

A preliminary investigation into the diagnostic potential of an infrared fiber optic probe (IFOP) for evaluating degenerative human articular cartilage is described. Twelve arthritic human tibial plateaus obtained during arthroplasty were analyzed using the IFOP. Infrared spectra were obtained from IFOP contact with articular surface sites visually graded normal or degraded (Collins Scale grade 1 and grade 3, respectively). Comparisons of infrared spectral parameters (peak heights and areas) were made to elucidate spectral indicators of surface degeneration. IFOP spectral analysis revealed subtle but consistent changes between grades 1 and 3 sites. Infrared absorbance bands arising from type II collagen were observed to change with degradation. More degraded tissues exhibited increased amide II (1590-1480 cm(-1))/1338 cm(-1) area ratio (p=0.034) and decreased 1238/1227 cm(-1) peak ratio (p = 0.017); similar changes were seen with Fourier transform infrared imaging spectroscopy (FT-IRIS) analysis. Grades 1 and 3 cartilage showed consistent spectral differences in the amide II, III, and 1338 cm(-1) regions that are likely related to type II collagen degradation that accompanies cartilage degeneration. These results suggest that it may be possible to monitor subtle changes related to early cartilage degeneration, allowing for IFOP use during arthroscopy for in situ determination of cartilage integrity.     

Analysis of fiber blends using horizontal attenuated total reflection Fourier transform infrared and discriminant analysis

We have investigated the utility of a horizontal attenuated total reflection Fourier transform infrared spectrometer (HATR/FT-IR) for the analysis of fiber and textile blends. The identification of a blended textile can be accomplished by subtracting a reference spectrum of the textile's most abundant component, leading to a difference spectrum that infers the identity of the second constituent of the blended textile. Mathematical post-processing of the spectra employing discriminant analysis provided a useful statistical tool to confirm the fiber blend components.     

Comparative investigation of Fourier transform infrared (FT-IR) spectroscopy and X-ray diffraction (XRD) in the determination of cotton fiber crystallinity

Despite considerable efforts in developing curve-fitting protocols to evaluate the crystallinity index (CI) from X-ray diffraction (XRD) measurements, in its present state XRD can only provide a qualitative or semi-quantitative assessment of the amounts of crystalline or amorphous fraction in a sample. The greatest barrier to establishing quantitative XRD is the lack of appropriate cellulose standards, which are needed to calibrate the XRD measurements. In practice, samples with known CI are very difficult to prepare or determine. In a previous study, we reported the development of a simple algorithm for determining fiber crystallinity information from Fourier transform infrared (FT-IR) spectroscopy. Hence, in this study we not only compared the fiber crystallinity information between FT-IR and XRD measurements, by developing a simple XRD algorithm in place of a time-consuming and subjective curve-fitting process, but we also suggested a direct way of determining cotton cellulose CI by calibrating XRD with the use of CI(IR) as references.     

Quantitative analysis of hemoglobin content in polymeric nanoparticles as blood substitutes using Fourier transform infrared spectroscopy

Based on the penetrability of IR within the polymeric nanoparticles, a novel Fourier transform infrared spectroscopy (FTIR) method, with polyacrylonitrile (PAN) as the internal reference standard, was developed to quantify the hemoglobin (Hb) content in Hb-based polymeric nanoparticles (HbPN). The HbPN was fabricated by double emulsion method from poly(ethylene glycol)–poly(lactic acid)–poly(ethylene glycol) triblock copolymers. Depending on the characteristic un-overlapped IR absorbances at 1540 cm⁻¹ of Hb (amide II) and at 2241 cm⁻¹ of PAN (–C≡N), calibration equations, presenting the peak height ratio of Hb and PAN as a function of the weight ratio of Hb and PAN, were established. This new quantification method is validated and used to the determination Hb content in HbPN. Due to the good results of this calibration strategy, the proposed simple FTIR approach with minimal sample-needed and solvent-free makes it useful for routine analysis of protein content and could be also applied to any other drug/protein encapsulated particles.     

Synthesis, growth and thermal and Fourier transform infrared spectral characterization of tetraethylammonium tetrachloro manganate (II) monohydrate crystals

Single crystals of a novel tetraethylammonium tetrachloro manganate (II) monohydrate (TEATC-Mn) were grown by slow evaporation solution technique at room temperature. These crystals belong to a class of interesting ferroelectric materials. The grown crystals were characterized through powder X-ray diffraction (XRD), thermogravimetry, differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC) studies and Fourier transform infrared (FTIR) spectra. While the results of the elemental analysis of the compound agree with the stoichiometry, its crystallinity is confirmed by the powder X-ray diffraction pattern. The weight losses observed were suitably explained based on the formulated decomposition pattern. The differential thermal analysis of the compound conforms to the thermogravimetric study. The endothermic peak observed in the high temperature differential scanning calorimetry suggests the occurrence of a phase transition in the compound between 300 and 370 °C while the corresponding low temperature study shows thermal anomalies at −41.7, −51.7 and at −52.4 °C. This suggests the occurrence of both first and second order phase transitions. The characteristic absorptions in the FTIR spectrum further characterize the compound. Further investigations on the ferroelectric behaviour of the compound at low temperatures are in progress.     

Fourier transform infrared (FT-IR) imaging coupled with principal component analysis (PCA) for the study of photooxidation of polypropylene

Fourier transform infrared (FT-IR) imaging coupled with principal component analysis (PCA) is used to characterize the photooxidation of polypropylene (PP) and identify the photooxidative products at different oxidation times. PP slices were exposed to ultraviolet (UV) irradiation for times up to 60 hours and spatially resolved spectra were acquired with a transmission FT-IR imaging system in order to view the steric inhomogeneity of the photooxidation process of PP. The evolution of the oxidized products with irradiation time is shown through the application of PCA. Carboxylic acid is the major oxidized product in the initial period from 0 h to 8 h while ketone becomes the major product with the increase of irradiation time. Carboxylic anhydride is identified for the first time to our knowledge in oxidized PP after 16 h irradiation. Carboxylate ester is also observed in the oxidized PP after 32 h irradiation. Possible mechanisms forming these products have been discussed.     

In situ detection of F2 laser-induced oxidation on hydrogen-terminated Si(111) and Si(110) surfaces by Fourier transform infrared transmission spectroscopy

Although oxidation of silicon has been intensively investigated experimentally and theoretically, the composition and structure of the interface region between the bulk oxide and silicon are not very well known. In this work, we report on the vacuum UV laser-induced oxidation of well-defined atomically flat Si(111)-(1×1):H and Si(110)-(1×1):H surfaces, prepared by wet-chemical processing, using an F₂ laser (157 nm). The silicon samples were irradiated under ultra high vacuum conditions in water and oxygen atmospheres. The photo-induced partial oxidation of the first monolayer, controlled by the oxidant pressure, was monitored by in situ Fourier transform infrared transmission spectroscopy with different photon detectors. The chemical reactions occurring at the surface were monitored by the shift and decreasing strength of the stretching vibration of Si---H surface bonds. The IR absorption spectra recorded during surface processing yield detailed information on the rearrangement of chemical bonds with a sensitivity reaching monolayer resolution.     

Single-pass attenuated total reflection Fourier transform infrared spectroscopy for the analysis of proteins in H2O solution

The application of single-pass attenuated total reflection Fourier transform infrared (ATR-FT-IR) microscopy was investigated for secondary structure analysis of 15 representative proteins in H2O solution. This is the first reported application of single-pass ATR-FT-IR for protein analysis; thus, the method was validated using transmission FT-IR and multipass ATR-FT-IR as referee methods. The single-pass ATR-FT-IR technique was advantageous since the single-pass geometry permits rapid secondary structure analysis on small volumes of protein in H2O solution without the use of demountable thin path length sample cells. Moreover, the fact that H2O backgrounds were small allowed the simultaneous observation of the amide I-III, A, and B regions without having to perform H2O subtraction. A comparison of replicate protein spectra indicated that the single-pass ATR-FT-IR method yields more reproducible data than those acquired by transmission FT-IR. The observed trends for the amide I-III and A bands obtained by single-pass ATR-FT-IR agreed with those in the literature for conventional transmission FT-IR.     

Low cytotoxicity porous Nd(2)(SiO(4))(3) nanoparticles with near infrared excitation and emission

Porous Nd(2)(SiO(4))(3) nanoparticles were successfully synthesized by a controlled route. This kind of silicate nanoparticle could be excited by near-infrared (NIR) radiation (808 nm) and triggered a NIR emission (1066 nm) at room temperature. By monitoring the 1066 nm emission, the long-lived luminescent lifetime was determined to be 19.5 μs. These NIR nanoparticles with appropriate diameters (<100 nm) were suitable for cell assays. MTT assays showed that the cytotoxicity of the porous Nd(2)(SiO(4))(3) nanoparticles was very low. Therefore, these porous silicate nanoparticles are potential biosafe high-performance NIR biolabeling materials.     

In Situ Fourier transform infrared spectroscopic study of the thermal degradation of isotactic poly(propylene)

The conformational change of isotactic poly(propylene) (iPP) during the thermal degradation process has been carefully studied by in situ Fourier transform infrared (FT-IR) spectroscopy. This new method of studying thermal degradation of iPP not only shows the conventional kinetic parameter information of thermal degradation such as the degradation activation energy DeltaE and the degradation factor n, which are in accord with the results of traditional thermogravimetry experiments, but also indicates that many significant molecular structure changes occur during the thermal degradation process that come from some characteristic absorption band changes of in situ FT-IR. A multivariate approach, principal components analysis (PCA), is applied to the analysis of infrared (IR) data, and the results further confirm the multi-step processes of the thermal degradation of iPP. Above all, this is a new application to polymer thermal degradation by in situ FT-IR that connects the intermediate conformational change with final results during thermal degradation.     

In situ Fourier transform P-polarized infrared reflection absorption spectroscopic investigation of an interface properties of SiO2/Si(100) deposited using electron cyclotron resonance microwave plasma at room temperature

Amorphous SiO₂ films have been deposited onto the Si substrate, without heating, using sputtering-type electron cyclotron resonance (ECR) microwave plasma. In situ Fourier transform P-polarized infrared reflection absorption spectroscopy (ISFT-PIRRAS) has been used to study the properties of a-SiO₂/Si interface. The results from ISFT-PIRRAS monitoring indicated that the interface stress led to significant distortion in the local structure, which resulted in the broadening of a transverse optical mode (TO₃) located at 1050 cm⁻¹. The interface stress decreased with increased film thickness. In addition, the longitudinal optical phonon mode (LO₃, located at 1223 cm⁻¹) related to TO₃ mode was observed due to Berreman effect [B. Harbecke, Appl. Phys. A: Solids Surf. 38 (1985) 263]. This phonon mode is very sensitive to SiO₂ film thickness, which enables it to be used to detect and characterize ultra thin SiO₂ film. When the film thickness is over 30 nm, a non-linear dependence of the intensity of LO₃ mode on film thickness was observed. However, the TO₃ mode has a near linear dependence on film thickness. Thus, it is more accurate and suitable to detect thick film by monitoring TO₃ mode intensity.     

Stopped flow apparatus for time-resolved Fourier transform infrared difference spectroscopy of biological macromolecules in 1H2O

Stopped flow spectroscopy is an established technique for acquiring kinetic data on dynamic processes in chemical and biochemical reactions, and Fourier transform infrared (FT-IR) techniques can provide particularly rich structural information on biological macromolecules. However, it is a considerable challenge to design an FT-IR stopped flow system with an optical path length low enough for work with aqueous (1H2O) solutions. The system presented here is designed for minimal sample volumes (approximately 5 microL) and allows simultaneous FT-IR rapid-scan and VIS measurements. The system employs a micro-structured diffusional mixer to achieve effective mixing on the millisecond time scale under moderate flow and pressure conditions, allowing measurements in a cell path length of less than 10 microns. This makes it possible to record spectra in 1H2O solutions over a wide spectral range. The system layout is also designed for a combination of kinetic and static measurements, in particular to obtain detailed information on the faster spectral changes occurring during the system dead time. A detailed characterization of the FT-IR stopped flow system is presented, including a demonstration of the alkaline conformational transition of cytochrome c as an example.     

Fabrication of Cd(3)As(2) nanowires by direct vapor-solid growth, and their infrared absorption properties

In this work the authors introduce and provide details of the synthesis and spectral characterization of single-crystal nanowires in less common, high performance, group II-V semiconductors such as Cd(3)As(2). The growth mechanism critically deviates from a known vapor-liquid-solid one by being completely non-catalytic and involving only two states: vapor and solid. The resultant nanowires range from ～50 to 200?nm in diameter and reach lengths up to tens of micrometers, with their fast growth direction being normal to the (112) crystal planes. According to infrared (IR) optical absorption measurements, the nanowires have several IR active direct type light absorption transitions at 0.11, 0.28 and 0.54 eV, suggestive of their possible utility in low cost optoelectronic devices and photodetectors operating in the long wavelength range of the electromagnetic spectrum.     

Fourier transform infrared (FT-IR) spectroscopy and improved principal component regression (PCR) for quantification of solid analytes in microalgae and bacteria

In bioanalytical chemistry, a detailed chemical understanding of biomaterials is often difficult to obtain due to the sheer number of analytes contained in a sample along with the samples' generally low reproducibility. This study presents a Fourier transform infrared (FT-IR) spectroscopic technique in conjunction with innovations in sample preparation and chemometric data preprocessing to overcome these limitations. These methodologies were applied to quantitative analyses of 31 representative compounds commonly found in biomaterial, which have been incorporated into a spectroscopic calibration database, that is, albumin (protein); D-alanine, glycine, histidine, valine, arginine, cysteine, phenylalanine, tyrosine, methionine, L-glutamine, and glutamic acid, (amino acids); glucose, fructose, galactose, mannose, sucrose, lactose, glycogen, agarose, and starch (carbohydrates); DNA (salmon sperm), sulphonoquinovosyl diglyceride ( sulpho-lipid ), and 1,2-diacyl-sn-glycero-3-phospho-L-serine ( phospho-lipid ); succinic acid and malic acid ( carboxylic acids ); glycolic acid (a -hydroxy acid), sodium pyruvate, b -carotene, frustules (microalgae silica-shells), and ammonium formate. Two proof-of-principle applications were based on calibration models incorporating these solids, i.e., characterization of E. coli and microalgae. The former aims for detection of bacterial contamination and the latter to enable investigations of changes in chemical composition of microalgae cells in response to shifting environmental conditions. Chemometric preprocessing steps have been developed for handling sample-to-sample fluctuations of absorption path lengths and baselines; the former incorporated mass normalization while the latter utilized a novel baseline correction method that requires no a priori information. Data preprocessing, chemometric calibration, and evaluation algorithms have been combined, together with an extensive spectral database of the aforementioned compounds (～1500 samples), for quantitative calibration purposes through the remotely accessible Virtual Chemometrics Lab , which can be utilized for a multitude of applications through a graphical user interface.     

Identification of natural dyes on laboratory-dyed wool and ancient wool, silk, and cotton fibers using attenuated total reflection (ATR) Fourier transform infrared (FT-IR) spectroscopy and Fourier transform Raman spectroscopy

Attenuated total reflection (ATR) infrared and Fourier transform (FT) Raman spectra were obtained from wool threads dyed in the laboratory with natural dyes used in antiquity, following a procedure similar to ancient methods for dyeing wool. The ATR spectra were primarily dominated by the signals of the wool, making it difficult to identify the dye on the fibers only by visual inspection of the infrared spectrum. However, the Raman spectra showed more significant characteristics attributable to the dyes as previously studied in the literature on modern synthetic dyes. A library-search method was thus applied to the second derivatives of both the ATR and Raman spectra to verify the possibility of identifying the dye. Two libraries were constructed, one consisting of the ATR spectra of undyed wool (raw, washed, and mordanted) and the transmission spectra of pure dyes and the other consisting of the Raman spectra of undyed wool and of pure dyes. Correlation and first-derivative correlation search algorithms were used. The results presented here suggest that the two types of spectroscopy are complementary in this kind of work, allowing the almost complete identification of historic dyes on wool. In fact, through the combined use of the two searches, most dyes were identified with a good index of similarity and within the first five hits. Only for annatto was identification totally impossible using either technique. Subsequently the same method was applied to wool, silk, and cotton threads taken from ancient Caucasian and Chinese textiles.     

Transmittance Fourier transform infrared spectra of liquid water in the whole mid-infrared region: temperature dependence and structural analysis

Transmittance Fourier transform infrared (FT-IR) spectra of liquid water in the 4-80 degrees C temperature range are reported in the whole mid-infrared (MIR) region (4000-360 cm (-1)). The spectra were recorded by using a newly developed, home-made transmittance cell, working in light vacuum conditions (pressures of the order of 3-4 millibar). This permits the elimination of the aqueous vapor bands from the liquid spectra, particularly in the bending region, and the rapid collection of data without fluxing large amounts of nitrogen through the interferometer sample chamber. The temperature evolution of the OH stretching and HOH deformation bands is discussed in terms of Gaussian components analysis and a two-state model describing the equilibrium between different H-bond structures of liquid water. From this picture, structural and thermodynamic information about the hydrogen-bonding network of water is obtained.     

Transformation and spectrum properties of partially coherent beams in the fractional Fourier transform plane

An analytical and concise formula is derived for the fractional Fourier transform (FRT) of partially coherent beams that is based on the tensorial propagation formula of the cross-spectral density of partially coherent twisted anisotropic Gaussian-Schell-model (GSM) beams. The corresponding tensor ABCD law performing the FRT is obtained. The connections between the FRT formula and the generalized diffraction integral formulas for partially coherent beams passing through aligned optical systems and misaligned optical systems are discussed. With use of the derived formula, the transformation and spectrum properties of partially coherent GSM beams in the FRT plane are studied in detail. The results show that the fractional order of the FRT has strong effects on the transformation properties and the spectrum properties of partially coherent GSM beams. Our method provides a simple and convenient way to study the FRT of twisted anisotropic GSM beams.