Polarization fourier transform infrared spectroscopy

Some Fourier transform infrared spectroscopic studies with linearly and circularly polarized radiation are reported. They were all carried out by means of the differential technique, consisting in the comparison of two single-channel spectra of opposite polarization. Thus, linear dichroic or circular dichroic spectra with positive and negative bands were recorded. Typical application examples of both techniques are presented.     

The destruction-free analysis of polymers by fourier transform infrared photoacoustic and fourier transform Raman spectroscopy: A comparison

With the introduction of rapid–scanning Fourier transform infrared (FTIR) and recently Raman (FT–Raman) spectroscopy, vibrational spectroscopy has been launched into a new era of applications in polymer chemistry and physics. Thus, the increase in sensitivity provided by multiple scanning has led to the breakthrough of new, destruction–free sampling techniques, such as photoacoustic and Raman spectroscopy. This paper provides a comparison between data produced by FTIR photoacoustic and FT–Raman analysis of a range of polymers, and structural information available from both techniques is discussed.     

Far infrared fourier transform spectroscopy of semiconductors

Fourier transform spectroscopy (FTS) is one of the most important tools in the study of shallow level donors and acceptors in semiconductors. When combined with a two-step photothermal ionization process detected photoconductively, FTS allows measurement of optical transitions of donor-bound electrons (and acceptor-bound holes) in ultra-pure germanium samples with impurity concentrations <10⁹ cm^–3 (i.e. one electrically active impurity in 4×10¹³ host atoms). The experimental high resolution study of the hydrogen-like excited state series of shallow levels has yielded as many as 19 lines of width as small as 10eV for some centers. These results have stimulated theoretical work which has led to the unambiguous assignment of quantum states to many bound excited states. Extensive studies of ultra-pure Ge crystals grown under different well-controlled conditions have led to the discovery of a large number of novel shallow impurity complexes. Study of the multiplicities and symmetries of the associated electronic states has led to a detailed understanding of the unusual static and dynamic structures of these novel centers. The chemical composition has been deduced from correlations between the concentration of a particular center and the materials involved in crystal gowth. Isotopic substitution of hydrogen with deuterium has led to the unambiguous proof of the presence of hydrogen in several of the novel centers. In addition to the high resolution spectra of shallow electronic levels, vibrational spectra of bond-centered interstitial oxygen in ultra-pure Ge are noteworthy for their extraordinarily sharp lines.     

Fourier transform raman spectroscopy using a bench-top fourier transform infrared spectrometer

The use of a bench top FTIR spectrometer for near infrared Fourier transform Raman spectroscopy is demonstrated. The use of near infrared excitation results in fluorescence free Raman spectra allowing previously difficult samples to be measured.     

Mammalian cell growth studiedin situ by fourier transform infrared spectroscopy

Fourier transform infrared techniques were used to monitor mammalian cell growth plated on attenuated total reflection (ATR) crystals. Consistently, the growth kinetics plots generated from the obtained spectra demonstrated a sigmoidal curve representing a sequence of slow, rapid, then tapering cell growth which correlated well with non-spectral cell growth determinations. Significant advantages over traditional methods of measuring cell growth kinetics are demonstrated. The technique has promising potential to be used to study events in areas such as toxicology and cell biology.     

Near infrared Raman spectra of human brain lipids

Human brain tissue, in particular white matter, contains high lipid content. These brain lipids can be divided into three principal classes: neutral lipids including the steroid cholesterol, phospholipids and sphingolipids. Major lipids in normal human brain tissue are phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, phosphatidic acid, sphingomyelin, galactocerebrosides, gangliosides, sulfatides and cholesterol. Minor lipids are cholesterolester and triacylglycerides. During transformation from normal brain tissue to tumors, composition and concentration of lipids change in a specific way. Therefore, analysis of lipids might be used as a diagnostic parameter to distinguish normal tissue from tumors and to determine the tumor type and tumor grade. Raman spectroscopy has been suggested as an analytical tool to detect these changes even under intra-operative conditions. We recorded Raman spectra of the 12 major and minor brain lipids with 785 nm excitation in order to identify their spectral fingerprints for qualitative and quantitative analyses.     

涂石蜡大米傅立叶变换红外吸收光谱识别分析

针对11种未涂石蜡大米和18个涂不同量石蜡的大米样品,以石油醚提取的油脂为试样,采用傅立叶变换红外光谱仪,扫描样品的傅立叶变换红外吸收光谱,并对光谱进行预处理,提取红外特征信息,将2855与1746、1462与1163 cm-1处特征峰的面积比值为坐标,采用Origín 6.0软件作识别分类图.结果表明:特征峰的面积比值与所涂石蜡量成线性变化,大米油脂的特征峰面积比值在一定的区域分布,涂以0.05%以上石蜡的大米,其油脂特征峰面积比值与未涂石蜡米油脂的值有一定区别.     

Polychlorobiphenyls differentiation and identification by gas chromatography/fourier transform infrared spectroscopy

Reference infrared vapour phase spectra of 20 polychlorobiphenyls (PCBs) have been obtained by gas chromatography/Fourier transform infrared spectroscopy (GC/FTIR). These spectra are consistent with those of PCB obtained by diffuse reflectance IR spectroscopy (DRIFT) and with those of more simple molecular structures (iodochlorobenzenes, 1-bromodichlorobenzenes). The IR frequencies of the GC/FTIR spectra of PCB are assigned in terms of substitution patterns. This work shows that GC/FTIR can be a good approach for differentiation and identification of PCB in complex mixtures.     

Combined thermogravimetry and fourier transform infrared spectroscopy techniques for gas evolution analysis

The usefulness of thermogravimetry has been amply demonstrated for a wide variety of material analysis applications. In many instances, however, additional information is required for adequate characterization of the sample and its thermal decomposition behaviour. In this respect, the analysis of evolved gases, or condensed liquids, has proven a highly useful approach. Among the various physical methods used for analysis of the thermal degradation products, infrared spectroscopy has often been found very powerful, being versatile, rapid and widely accessible. In this study, we report a simple new approach in which the evolved gases and condensed liquids from the thermal decomposition of various products are recuperated in an infrared gas cell and on a PVC membrane filter, respectively. The gaseous components were analysed by transmission FT-IR, and the condensed liquid products were examined directly on the PVC membrane by FT-IR in the internal reflexion mode. The technique was used, for example, to examine the pyrolysis products (gases and liquid) of Koberit, a proposed substitute for asbestos. The method was also applied to the study of chemically derivatized asbestos materials in an attempt to unravel the surface chemical modifications.     

Column switching applied to capillary gas chromatography/fourier transform infrared spectroscopy

A dual oven gas chromatograph incorporating a micro, mechanical switching valve has been interfaced to an FTIR spectrometer. With this system, each oven can be operated with independent temperature control. Complete choice of the columns' type and capacity gives flexibility in the separation prior to spectroscopic evaluation. An application which demonstrates some of the advantages of column switching in GC/FTIR is presented. Minor sample components have been successfully analyzed by heart-cutting the appropriate section of the separation from a high to a low capacity column. In this way, the dynamic range of the technique is effectively increased while an efficient chromatographic inlet to the FTIR is maintained.     

In-situ measurement of photochemical changes of solid samples by fourier transform infrared photoacoustic spectroscopy

Infrared spectral changes of lithographic printing plates were measuredin-situ by PAS and RAS. The advantages of PAS over RAS were discussed for the spectral measurements of organic coatings on roughened metal surface.     

Crosslinking mechanism of an anhydride-cured epoxy resin as studied by fourier transform infrared spectroscopy

Fourier transform infrared spectra, including absorbance difference spectra, are presented which indicate that the accepted mechanism of tertiary amine-catalyzed copolymerization of cyclic anhydrides and epoxy resins requires modification. Results also show that the kinetic model is complicated by the lack of steady-state concentrations of the active species. The effect of silica filler and silane coupling agents on the reaction are also examined.     

Fourier transform Raman spectroscopy

The basic experimental aspects of Fourier transform Raman Spectroscopy are reviewed with an emphasis on detector technology. The sensitivity is comparable to dispersive Raman Spectroscopy using visible lasers. The ease of spectral subtraction is demonstrated and examples are given showing the elimination of fluorescence.     

Comparative analysis of smokeless gunpowders by Fourier transform infrared and Raman spectroscopy

Fourier Transform Infrared (FTIR) and Raman spectroscopic techniques were used to perform a comparative study of the spectral profiles of single-base, double-base and triple-base smokeless gunpowders. Preliminary results based on visual comparison of the spectra point out that spectra obtained by both vibrational techniques were useful for a rapid identification of gunpowders containing dinitrotoluene as one of the major components and triple-base gunpowders. Additionally, the Raman spectra of gunpowders with diphenylamine in its primary composition showed a characteristic band, assigned to 2-nitro-diphenylamine, allowing the identification of this type of gunpowders.     

Biological applications of fourier transform infrared spectroscopy: a study of phase transitions in biomembranes

The thermal response of aqueous lipid membranes has been investigated by Fourier transform infrared spectroscopy. Changes in infrared spectral parameters are applied to the analysis of the strutural changes which occur within the lipid bilayer as the temperature is varied. Such studies provide the basis for the interpretation of phase transitions in complex biomembranes.     

Characterization by fourier transform infrared spectroscopy (FT-IR) and 2D IR correlation spectroscopy of PAMAM dendrimer

FT-IR and 2D correlation spectroscopy were employed to study the microstructural changes occurring during phase transitions of a liquid crystal poly(amidoamine) codendrimer (PAMAM (L1)16(L2)16) generation 3, functionalized on the terminal groups by one-chain promesogenic calamitic units (4-(4'-decyloxybenzoyloxy)salicylaldehyde (L1)) and two-chain promesogenic calamitic units (4-(3',4'-didecyloxybenzoyloxy)salicylaldehyde (L2)). Spectral modifications associated with molecular conformation rearrangements allowing for molecular shape change on going from a liquid-crystalline organization to another were found. The transition temperatures were calculated, and they are in good agreement with the DSC data. Spectral analysis gives evidence of the LC phase transitions and to an additional transition associated with the existence of conformers. Various types of hydrogen bonding have been established.     

Frequency-sweep fourier transform ion cyclotron resonance spectroscopy

A single ion cyclotron resonance (ICR) absorption spectrum showing both CH⁺₃ and CH⁺₄ signals has been obtained by exciting both ion cyclotron resonances with a frequency-swept rf irradiation, followed by broad-band detection, digitization of the (time-domain) response, and finally discrete Fourier transformation to produce the (frequency-domain) spectrum. Pulsed-excitation Fourier transform ICR has demonstrated the use of broad-band detection in rapid generation of ICR spectra by Fourier transform methods; this paper demonstrates that frequency-sweep excitation can provide the broad-band irradiation required to excite ion cyclotron resonances throughout any desired mass range. It will thus be possible to obtain an ICR absorption spectrum of given mass range, signal-to-noise ratio, and resolution in an observation period which is two orders of magnitude shorter than that needed to obtain the same spectrum by conventional slow-sweep detection.