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.     

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.     

A fourier transform infrared spectroscopic study of the molecular interaction in synthetic bilayer membrane

Fourier transform infrared spectroscopy is used to study the molecular interaction between gramicidin D and bilayer membranes, dioctadecadimethylammonium bromide (2C₁₈N⁺2C₁Br⁻), and 1,2-di-palmytoyl- -α-phosphatidylcholine (DPPC). Frequencies and bandwidths of the symmetric CH₂ stretching band measured as a function of temperature are used to study variation of packing of alkyl chains. The bilayer membrane prepared from 2C₁₈N⁺2C₁Br⁻ is found to have a gel to liquid crystal phase transition at 42°C. The presence of gramicidin in the membrane causes an increase in the mobility of the alkyl chain and also a decrease in the abruptness of the transition.The frequencies of amide I and II bands of gramicidin reflecting secondary structures of polypeptides are used to identify its conformation in membranes and to study the interaction between gramicidin and the matrices. Gramicidin is found to have hydrophobic interaction with 2C₁₈N⁺2C₁Br⁻, whereas it has both hydrophobic and hydrophilic interactions with DPPC.     

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.     

Fiber-optic evanescent wave fourier transform infrared (FEW-FTIR) spectroscopy of polymer surfaces and living tissue

The new method of fiber-optic evanescent wave Fourier transform infrared (FEW-FTIR) spectroscopy has been applied to studies of polymer surfaces and the diagnostics of normal, precancerous and cancerous tissue. This technique using optical fibers and fiber-optic sensors operating in the attenuated total reflection (ATR) mode in the mid-infrared (IR) region of the spectrum (850 – 1850 cm⁻¹) has found recently application in the area of tissue diagnostics. The method is suitable for noninvasive and rapid (seconds) direct measurements of the spectra of normal and pathological tissues in vitro, ex vivo, and in vivo. The FEW-FTIR technique is an ideal diagnostic tool for different types of soft, porous, foam, and rough polymer surfaces. Inhomogeneous coatings and defects on polymer surfaces as well as layer structures have also been detected by this method. It is convenient to apply this method to analyze large pieces of soft plastics and/or surfaces covered by plastics, since these types of surfaces are comparatively hard to analyze by traditional absorption spectroscopy. The FEW-FTIR technique is non-destructive, fast (15 seconds), and remote (up to a fiber length of 3m). In addition, it is sensitive enough to detect any changes in the vibrational spectra of a polymer surface, without heating and damaging it. The surfaces of polyethylene crumpled bags and rumpled films have been investigated in the range of 2000 – 1000 cm⁻¹. The distinct spectra of these surfaces as well as spectra of polytetrafluoroethylene have been recorded. The spectra of white and colored foams and different plastics have also been studied. Weak but distinct spectra have been recorded for carbon fibers (black, narrow fibers with a diameter of about 10 μm). Using the FEW-FTIR technique, measurements can be taken without preparing the sample. High quality spectra have also been obtained for the bulk and surfaces of apple, banana, grapefruit, and other food products. The method is expected to be further developed for geological and microelectronic applications.     

Near infrared fourier transform Raman spectroscopy of human artery

We report the first near IR FT-Raman spectroscopy of normal diseased human artery. In normal human aorta, two bands at 1669 cm⁻¹ and 1452 cm⁻¹ dominate the spectrum and can be assigned to protein amide I and C-H in-plane bending vibrations, respectively. Weaker bands are also observed between 1250 and 1350 cm⁻¹. Non-calcified atherosclerotic lesions with a large amount of necrotic debris below the tissue surface show a relative increase in the intensity of the 1452 cm⁻¹ band. In atherosclerotic aortas which contain calcified deposits several hundred microns below the tissue surface, a strong 961 cm⁻¹ band is observed due to the symmetric stretch of phosphate groups in the calcified salts. The results show that this method provides the capability to probe biological substituents several hundred microns below the tissue surface.     

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.     

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.     

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.     

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.     

Application of Fourier transform infrared rapid scan techniques to photochemical investigations

The technique of rapid scan FT-IR has been applied to the study of a photochemical process. Surface dependent aspects of solid state coumarin photochemistry have been elucidated by rapid scanning FT-IR spectroscopy. Reaction pathways can be controlled as a function of the surface.     

Photopatterned surfaces for site-specific and functional immobilization of proteins

Photosensitive silanes containing nitroveratryl (Nvoc)-caged amine groups and protein repellent tetraethylene glycol units were synthesized and used for modification of silica surfaces. Functional surface layers containing different densities of caged amine groups were prepared and activated by UV-irradiation of the surface. The performance of these layers for functional and site-selective immobilization of proteins was tested. For this purpose, biotin and tris-nitrilotriacetic acid (tris-NTA) were fist coupled to the activated surface, and the interaction of streptavidin and His-tagged proteins with the functionalized surfaces was monitored by real-time label-free detection. After optimizing the coupling protocols, highly selective functionalization of the deprotected amine groups was possible. Furthermore, the degree of functionalization (and therefore the amount of immobilized protein) was controlled by diluting the surface concentration of the amine-functionalized silane with a nonreactive (OMe-terminated) tetraethylene glycol silane. Immobilized proteins were highly functional on these surfaces, as demonstrated by protein-protein interaction assays with the type I interferon receptor. Protein micropatterns were successfully generated after masked irradiation and functionalization of the caged surface following the optimized coupling protocols.     

High resolution fourier transform infrared spectrum of difluoroethyne,FCCF.

Difluoroethyne, monitored by FTIR spectroscopy, has been prepared in the vapour phase by vacuum pyrolysis and photolysis of difluoromaleic anhydride and pyrolysis of 3-bromo-3,3-difluoropropanoic trifluoroacetic anhydride. The infrared spectrum of difluoroethyne has been assigned at both low and high resolution and wavenumber values for all five fundamentals estimated. Difluoropropadienone was observed as a pyrolysis product and difluorocyclopropenone as a photolysis product.     

板蓝根颗粒中蔗糖含量的红外光谱法测定

A method for rapid quantitative determination of sucrose in isatis-root granules by Fourier Transform Infrared Spectrophotometry(FTIR) was developed. Potassium ferricyanide was chosen as an inside mark material because it has only one strong absorption peak at 2117cm-1 and the peak was chosen as its quantitative peak. The peak at 1283cm-1 is the characteristic absorption of sucrose and was chosen as the quantitative peak of sucrose. The ratio of the two absorbances is I=Ai/As.K3[Fe(CN)6] and sucrose were mixed according to a certain mass ratio m=mi/ms to prepare standard samples. The curve of m versus I is the quantitative working curve. The linear range for sucrose is 5.0～23.0mg/g,the recovery is in the range of 91%～103%,the relative standard deviation is less than 5%.     

Flow injection analysis with fourier transform infrared detection for clinical and process analysis

As the analysis of glucose and urea is of special interest in the field of clinical and process analysis, an enzymatic FIA-FTIR system is presented, based on the reactions of glucose to gluconic acid using glucose oxidase as well as of urea to ammonium carbonate catalyzed by urease. The method is tested with standard solutions, with samples simulating the blood composition and with a variety of fruit juices and soft drinks. Whereas the systematic error is within few percent, as concluded from the slope of the calibration graph, the reproducibility of the method is up to now not satisfactory for routine applications in process analysis and has to be improved.     

Conditions of measurement of infrared absorption band intensities by fourier transform spectrometry

The influence of infrared spectra of some different conditions required in the use of modern FTIR spectrometers has been studied. This work has been performed in two ways: firstly, the influence of factors such as apodization function, level of zero filling, number of data points and phase correction procedure is determined from experimental data, and, secondly, numerical simulation of the whole process has been carried out in order to separate experimental error from that deu to the mathematical treatment.     

Fourier transform infrared investigations of phosphate-silicate coatings on iron

The influence of silica addition and of the annealing on the structure and properties of phosphate coatings are investigated. It has been observed that silica stabilizes phosphates and reduces the transport of iron towards the surface.     

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.