Multi-frequency S2FTIR PA spectral depth profiling by use of sinusoidal phase modulation and harmonic demodulation up to 2250 Hz (10th harmonic)

Multi-frequency phase modulation for step-scan Fourier transform infrared photoacoustic spectroscopy (S²FTIR PAS) is demonstrated using a single frequency sinusoidal modulation of the interferometer movable mirror with modulation amplitude 5.2 λ_He-Ne. A digital signal processing (DSP) lock-in amplifier is used to demodulate the photoacoustic response at the fundamental phase modulation frequency and its harmonic frequencies. Because the phase modulation is sinusoidal and of the appropriate amplitude, all the even and odd harmonics (up to the 10th harmonic) can be detected with good signal-to-noise ratio (SNR). Applications of this multi-frequency phase modulation approach for photoacoustic depth profiling are demonstrated by the study of a simple two-layered polymer sample. The sampling depth multiplexing advantage (as compared to that obtained with other types of phase modulation) is clearly demonstrated with the analysis of the phase and magnitude of signals at the fundamental frequency and all the harmonic frequencies. This is the first report of using the sinusoidal phase modulation method to easily obtain multi-frequency and high-frequency light modulation for FTIR PAS depth profiling. Although these data have been obtained sequentially, it would be possible (with considerable economy of time) to obtain them simultaneously by use of the internal digital signal processing capability of the instrument.     

Multi-frequency S2FTIR PA spectral depth profiling by use of sinusoidal phase modulation and harmonic demodulation up to 2250 Hz (10th harmonic)

Multi-frequency phase modulation for step-scan Fourier transform infrared photoacoustic spectroscopy (S²FTIR PAS) is demonstrated using a single frequency sinusoidal modulation of the interferometer movable mirror with modulation amplitude 5.2 λ_He-Ne. A digital signal processing (DSP) lock-in amplifier is used to demodulate the photoacoustic response at the fundamental phase modulation frequency and its harmonic frequencies. Because the phase modulation is sinusoidal and of the appropriate amplitude, all the even and odd harmonics (up to the 10th harmonic) can be detected with good signal-to-noise ratio (SNR). Applications of this multi-frequency phase modulation approach for photoacoustic depth profiling are demonstrated by the study of a simple two-layered polymer sample. The sampling depth multiplexing advantage (as compared to that obtained with other types of phase modulation) is clearly demonstrated with the analysis of the phase and magnitude of signals at the fundamental frequency and all the harmonic frequencies. This is the first report of using the sinusoidal phase modulation method to easily obtain multi-frequency and high-frequency light modulation for FTIR PAS depth profiling. Although these data have been obtained sequentially, it would be possible (with considerable economy of time) to obtain them simultaneously by use of the internal digital signal processing capability of the instrument. Received: 8 January 1998 / Accepted: 22 February 1998     

Advanced pulse calibration techniques for the quantitative analysis of TG–FTIR data

Two different pulse calibration techniques to estimate the total quantities of evolved gaseous substances formed in thermogravimetric (TG)–FTIR runs were compared and assessed. A gas-pulse calibration method was based on the use of a specific device able of sending a known quantity of a gaseous compound of interest to the FTIR analyzer. A second calibration method was based on the vaporization in the TG analyzer of liquid solutions of the compound of interest. Data obtained by these techniques were compared to those from conventional concentration-based calibration. The results confirmed the reliability of pulse calibration techniques to obtain quantitative data on evolved gaseous products in TG–FTIR applications. Moreover, both the gas-pulse and the vaporization-based calibration techniques proved to have several advantages with respect to conventional techniques. Among these are the need of a more limited number of standards and no need for online gas dilution systems.     

Application of temperature modulation to FTIR spectroscopy: an analysis of equilibrium and non-equilibrium conformational transitions of poly(ethylene terephthalate) in glassy and liquid states

Journal of Thermal Analysis and Calorimetry - In this paper, the application of a temperature modulation to the temperature-resolved FTIR analysis is reported. The advantage offered by the...     

Biaxial orientation characterization on-line and off-line and structure properties correlations in films

In this paper, biaxial orientation characterization techniques are briefly reviewed. Results obtained using birefringence and Fourier Transform Infrared Spectroscopy (FTIR) techniques are presented for different applications: On-line monitoring of birefringence for an amorphous polymer (polystyrene); On-line and off-line determination of orientation (birefringence) of polyethylene terephthalate (PET) and finally off-line measurement of orientation on polyethylene (LDPE) films using FTIR. Some typical morphologies of blown LDPE films are reported and discussed. Finally, correlations between orientation on one hand and shrinkage and tear strength on the other are attempted.     

Infrared detection in flow analysis - developments and trends (review)

Flow analysis offers an inexpensive and versatile means for the automation of analytical procedures and hence it has been incorporated in many different techniques. However, the use of infrared detection in flow analysis systems is not common. Whereas Fourier transform infrared (FTIR) spectroscopic detection has been routinely used in gas chromatography (GC), its use for liquid chromatography, and now for flow analysis, flow injection analysis, or sequential injection analysis, is not frequent. The most prominent reasons are probably: (i) the strong absorption of most of the common solvents, specially water, (ii) the relative poor sensibility compared to UV–vis, fluorescence, etc. (iii) FTIR is normally not even considered a valuable detection technique, (iv) problems arising from obtaining adequate information from transient IR signals from the injected samples, and (v) only a few analytical chemist uses routinely the FTIR technique. This practice neglects that IR spectroscopy offers some unique features that now, using modern FTIR instrumentation, can be exploited in an advantageous manner. It is important to realize that each sample (analyte/matrix) represents a special and unique analytical problem; which defines the mode of operation and implementation of the IR technique. Flow analysis–IR techniques – as well as all techniques – has a number of shortcomings to solve these problems. In this article, most of these strategies such as the use of: baseline correction, derivative spectroscopy, stopped flow systems, reverse flow systems, multiparametric calibrations, etc., will be discussed. Additionally, recent developments in on-line gas phase generation–FTIR and hydride generation–FTIR spectrometry, as well as the principles of the HPLC–FTIR and capillary electrophoresis–FTIR hyphenation are also discussed. This review aims to provide an account of the state of the art, of these relatively new techniques. Its beginning, developments, applications and new trends, basically in the MID–IR, and by using transmission cells.     

Optical and spectroscopic characteristics of oleate adsorption as revealed by FTIR analysis

Fourier transform infrared transmission (FTIR/TS), external reflection (FTIR/ERS), and internal reflection (FTIR/IRS) spectroscopies are three important sampling techniques for the study of adsorbed surfactants. The optical and spectral characteristics of a three-phase system were calculated using theoretical simulation and discussed based on experimental results for oleate adsorption at the air/water interface and at the water/fluorite interface. It is shown that a thorough understanding of the optical properties and spectral characteristics from FTIR analysis helps to improve the experimental design and explanation of experimental results and is important to properly quantify surfactant interfacial adsorption phenomena.     

聚氨酯动态拉伸红外光谱分析

聚氨酯薄膜在5Hz拉伸频率作用下,测得其同相和正交的动态偏振红外光谱.由此可知,薄膜拉伸初期的粘弹性在分子水平上主要由代表软硬段界面游离的氨酯键1719 cm^-1和有强相互作用的酯键1732 cm^-1界面有相互作用的氨酯键1709 cm^-1和游离的酯键1748 cm^-1,四种官能团代表的链段来表现:前者主要提供弹性变化,后者主要提供粘性变化.     

一种新颖的基于FTIR-CWT及ANN分类法的同科属中药材菟丝子与金灯藤的识别研究

采用水平衰减全反射傅里叶变换红外光谱法（HATR-FTIR）测定了同属种子植物中药材菟丝子及金灯藤的FTIR,运用基于连续小波多分辨率分析法对吸收较为相似的菟丝子及金灯藤的FTIR进行特征提取。选择第7、10、13分解层数的特征向量,进行人工神经网络（ANN）训练,再用训练出来的网络对不同产地的植物种子菟丝子和金灯藤所得FTIR小波提取的特征向量进行分类。通过对32个不同样本的验证,说明能够采用基于FTIR-连续小波特征提取及人工神经网络分类法对同科属中药材菟丝子与金灯藤进行识别。     

A critical comparison of solid sample preparation techniques in infrared spectroscopy

The growing capabilities of FTIR spectrometers and computers have opened the use of new sample preparation techniques in infrared spectroscopy. In addition to the established KBr pellet technique and ATR spectroscopy, diffuse reflectance and photoacoustic spectroscopy are increasing in importance. A systematic experimental comparison of these techniques has been made in order to make proper use of their mutual advantages.     

Structure–Property Relationship of Thin Plasma Deposited Poly(allyl alcohol) Films

Poly(allyl alcohol) films with a thickness of about 150 nm were deposited by pulse plasma polymerization onto different substrates (inorganic and organic). The structure/property relationships of these samples were studied in dependence on the duty cycle (DC) of the plasma by a broad combination of different techniques and probes. For the first time volume sensitive methods (FTIR and dielectric spectroscopy) are combined with surface analytics by employing XPS for that system. FTIR spectroscopy gives qualitatively the same dependence of the concentration of the OH groups on DC like XPS. The observed differences are discussed considering the different analytical depths of both the methods. The dielectric measurements show that the plasma deposited films are not thermally stable but undergo a post plasma chemical reaction during heating. The results obtained by dielectric spectroscopy are discussed in detail with the data from FTIR and XPS measurements.     

Diffuse reflectance Fourier transform IR spectroscopy

Fourier transform infrared (FTIR) spectroscopy has greatly enhanced the utility and range of applications of infrared (IR) spectroscopy in chemistry. Until the development of routine FTIR instrumentation, applications of IR were essentially limited to direct transmission measurements. Newer sampling methods in FTIR spectroscopy can be successful with less than 1% throughput of the infrared radiation and yet yield a spectrum with acceptable signal-to-noise ratio. The decreasing cost of FTIR spectrometers has made a number of such sampling techniques accessible for routine applications without compromises in performance. This article will describe one of these, diffuse reflectance.     

FT-Raman,FT-infrared and NIR spectroscopic characterization of oxygen-delignified kraft pulp treated with hydrogen peroxide under acidic and alkaline conditions

The effects of bleaching treatment of oxygen-delignified softwood kraft pulp with hydrogen peroxide under acidic and alkaline conditions were studied using standard technological techniques and spectroscopic analytical methods: near-infrared (NIR), Fourier-transform infrared (FTIR) and Fourier-transform (FT) Raman spectroscopies. Among the three tested spectroscopic techniques, NIR analysis appeared to be the most appropriate in terms of possible technological applications. The use of NIR spectroscopy combined with multivariate data analysis allowed to create models for pulp bleaching monitoring based on CIE L*a*b* measurements. Near-infrared and FTIR spectroscopic studies allowed differentiating between the effects of the acidic and alkaline peroxide bleaching stages, but failed in relation to the delignification process. The most representative bands in the FTIR and FT-Raman spectra in terms of delignification and chromophore removal exhibited no correlation with standard technological measurement results.     

Oxadiazole: Synthesis,characterization and biological activities

The synthesis of novel achiral and chiral amides incorporating 1,3,4-oxadiazole ring are reported. All the synthesized amides are characterized ¹H, ¹³C, FTIR and elemental analysis techniques. Synthesized compounds are screened for microbial and cytotoxic activities.     

TiO2/聚丙烯酸丁酯纳米复合薄膜的制备及结构表征

利用微乳液原位聚合法在普通玻璃表面上制备了TiO2/聚丙烯酸丁酯纳米复合膜.采用傅立叶变换红外光谱、高分辨透射电子显微镜和X射线光电子能谱对膜的结构进行了表征.结果表明， TiO2以纳米线的形式弥散在聚丙烯酸丁酯的高分子网络中，并且所制备的TiO2纳米线具有板钛矿相结构.     

FTIR and GC as complementary tools for analysis of corrosive gases

The gas metrology laboratory of the National Metrology Institute of South Africa has developed methodology for the gravimetric preparation of corrosive gas mixtures such as nitric oxide (NO) in nitrogen, as well as sulphur dioxide (SO₂) in nitrogen or synthetic air. Fourier transform infrared (FTIR) spectroscopy has been used to analyse for trace and ultra trace levels of infrared active gaseous species, such as NO, nitrogen dioxide and SO₂ that are difficult to analyse by other means. These corrosive gas mixtures are also analysed using gas chromatography with pulsed helium ionisation detection to complement the work done using FTIR with infrared active impurities. A comparison between the techniques of FTIR, gas chromatography and non-dispersive infrared spectroscopy for corrosive gas analysis is also presented.     

Comparison of ATR–FTIR and O-PTIR Imaging Techniques for the Characterisation of Zinc-Type Degradation Products in a Paint Cross-Section

ATR–FTIR (attenuated total reflection–Fourier-transform infrared) microscopy with imaging is widely used in the heritage field to characterise complex compositions of paint cross-sections. However, some limitations include the need for ATR crystal contact with the sample and the inability to resolve particle size below the IR diffraction limit. Recently, a novel O-PTIR (optical-photothermal infrared) spectroscopy technique claimed to open a new avenue for non-invasive, efficient, and reliable analysis at sub-micron resolution. O-PTIR produces transmission-like FTIR spectra for interpretation, without the need to touch the sample, which are highly favourable attributes for analysing heritage samples. This paper reports the comparison of O-PTIR and ATR–FTIR techniques applied to a cross-section embedding a thin paint fragment that delaminated from a late 19th to early 20th-century oil portrait. The hazy paint fragment consisted of zinc soaps (both crystalline and amorphous), gordaite (NaZn₄Cl(OH)₆SO₄·6H₂O), and zinc lactate, that could not all be well-resolved with ATR–FTIR imaging. With O-PTIR analysis, the degradation compounds could be resolved at sub-micron resolution with an equivalent or better signal-to-noise ratio. This case study shows how the two techniques can be used to obtain comprehensive information at a broad level with ATR–FTIR and a detailed level with O-PTIR.     

Regular intergrowth in the AFI-type crystals: influence on the intracrystalline adsorbate distribution as observed by interference and FTIR-microscopy

Interference microscopy and FTIR microscopy are applied to study intracrystalline concentration profiles of methanol in CrAPO-5 zeolite crystals. By using both techniques, the high spatial resolution of interference microscopy is complemented by the ability of FTIR spectroscopy to pinpoint adsorbates by their characteristic IR bands. For the first time two-dimensional concentration profiles of an unprecedented quality are reported which show a nonhomogeneous distribution of adsorbate in zeolite crystal under equilibrium with the adsorbate vapor. These nonhomogeneous profiles are attributed to regular intergrowth effects in CrAPO-5. A possible internal structure of CrAPO-5 crystals is suggested.     

Review of FTIR microspectroscopy applications to investigate biochemical changes in C. elegans

Caenorhabditis elegans nematode has emerged as a model organism paving the ways for multidisciplinary research in biomedical, environmental toxicology, aging, metabolism, obesity, and drug discovery. The wide range of applications of this model organism are attributed to C. elegans’ unique features: C. elegans are inexpensive, easy to grow and maintain in a laboratory, has a short lifespan, and has a small body size. With this increased interest, the need for analytical techniques to assess the biochemical information on intact worms continues to grow. Fourier Transform Infrared (FTIR) microspectroscopy is considered as a powerful technique that can be used to determine the chemical structure and composition of various materials, including biological samples. Furthermore, the development of focal plane array detectors has made this technique attractive to study complex biological systems such as whole nematodes. This review focuses on the use of FTIR microspectroscopy to study C. elegans. The first published work on the use of FTIR microspectroscopy to study a complex whole animal was reported in 2004. Since then, very few other studies were carried out. The objective of this review is to summarize work conducted to date using FTIR microspectroscopy to study nematodes and to discuss the information that can be gained by using this technique. This could allow scientists to add this technique to the arsenal of techniques already in use for C. elegans studies.     

Surface and depth-profile analysis using FTIR spectroscopy

Summary The introduction of Fourier Transform techniques and the increasing use of computers in infrared spectroscopy has made new techniques of investigation available to the spectroscopist, such as photoacoustic spectroscopy (PAS) and IR microscopy. These methods now complement the techniques of specular reflectance and attenuated total reflectance. Thin films on metals, sometimes with a thickness of much less than a micron, can be studied by various specular reflectance methods. The physical basis of the attenuated total reflectance technique (ATR) leads to a penetration of the radiation in the order of a few microns. It is, therefore, especially suitable for the investigation of surfaces and of layers close to the surface. By changing the modulation frequency of the IR radiation, i.e. the mirror velocity of the FTIR spectrometer, photoacoustic spectroscopy (PAS) can be employed to study layers at various depths below the surface of a sample. Therefore, this technique allows depth-profile analysis, so that PAS reveals itself as a complementary method to attenuated total reflectance spectroscopy. Samples with inhomogeneous profiles, e.g. laminated polymer films, can often be prepared as microtome slices perpendicular to the layered structure. Using infrared microscopy it is now possible to investigate different regions of the cross-section easily. The size of the regions that can be studied in this way may be as small as a few microns.

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Oberflächen- und Tiefenprofilanalyse mit Hilfe der FTIR-Spektroskopie