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

     

Structural analysis of photodegraded wood by means of FTIR spectroscopy

We report on the detailed analysis of chemical modifications and structural changes in the cellulose and lignin of Populus tremula (a hardwood) and Buxus sempervirens (a softwood), as a result of photodegradation in a Xenon test chamber. The results obtained by means of FTIR spectroscopy indicate that lignin is the most sensitive component to the degradation process for both woods examined. On a structural level, the virtual elimination of the amorphous cellulose was observed for both types of wood. The crystallised cellulose I component, which accounts for the whole crystalline phase, undergoes minor structural changes, this effect being more important in the case of Populus tremula that was less degraded than Buxus Sempervirens.     

Fourier transform infrared spectroscopy and the analytical study of works of art for purposes of diagnosis and conservation

This paper is a study of the analytical capacity of Fourier transform infrared spectroscopy (FT-IR) for any type of samples from works of art. The analytical information obtained with this technique on organic and inorganic compounds is extremely useful in the preliminary studies necessary for diagnosis and to decide on the conservation process. This paper reports the analysis and study with FT-IR on samples extracted from the microlayers in several works of art from different periods (16th to 18th century) comprising wall paintings and canvas. The most outstanding of these being the frescoes by A. Palomino from two ceilings in the Santos Juanes church. The analytical procedures for the different components of the works studied such as

1. (a) varnish applied to wood panels and canvas paintings,

2. (b) binding media and pigments used by the artists,

3. (c) inerts, mortars, stuccos and grounds have been optimized. The FT-IR technique offers a quick analysis of microsamples (less than 0.5 mg) and is able to characterise the different molecular groups which provide information on the nature of the different materials of organic and inorganic origin used by the artist and thus permits the diagnosis of pathologies requiring conservation treatment.

In-situ FTIR spectroscopy of iron electrodes

The reactions of an iron electrode in alkaline electrolytes of different concentrations are studiedin-situ using internal reflection and external reflection FTIR spectroscopy. Fe(OH)₂ is formed during the reaction Fe(O) Fe(II) at all investigated concentrations. The product of the reaction Fe(II) Fe(III) is-FeOOH in concentrated and-FeOOH in diluted alkaline solutions.     

Set-up for time-resolved step-scan FTIR spectroscopy of noncyclic reactions

We have established a novel technique, which allows the application of time-resolved step-scan FTIR difference spectroscopy on noncyclic reactions. Cyclic reactions are ideally suited for the step-scan technique. However, it is difficult to apply the step-scan technique to noncyclic reactions, because the investigated process has to be repeated at about 1000 sampling positions of the interferogram. Consequently, to investigate noncyclic systems the sample has to be renewed at every sampling position. In the presented novel approach the IR-beam and the excitation laser-beam are focused to a very small diameter of 200 μm. Thereby, only a small segment of the sample, which has an overall diameter of 15 mm, is excited and probed. By moving the sample, which is mounted on an x-y-stage, to different nonexcited segments the reaction can be repeated until a complete interferogram data set is recorded. In so far as the typically used flow cells are concerned their optical pathlength is too large to perform difference spectroscopy. We use 4 μm thin films to depress the water background absorption of biological samples. As test, the well known photo-cyclic reactions of bacteriorhodopsin are measured. No systematic errors appear in the difference spectra. Because of intensity loss by the IR-microscope the signal-to-noise ratio is about 5 times less as compared to conventional step-scan measurements. For the first time, the technique is then applied to a noncyclic reaction, the photolysis of caged ATP. The successful performance with 10 μs time-resolution now opens the door for many new applications of step-scan FTIR measurements to noncyclic reactions.     

FTIR spectroscopy of biodegraded historical textiles

Fungal attack is a common and severe problem in the storage rooms of museums. Fungi can damage different materials; organic materials are especially sensitive. In this work two different FTIR spectroscopy methods (micro-spectroscopy with diamond anvil cell and ATR) were used to investigate structural changes on biodeteriorated and non-affected textile fibres obtained from different Slovene museums and sacred objects. Several structural changes were observed in spectra of biodeteriorated as well as of non-affected cellulosic fibres, whereas no changes were observed in proteinaceous fibres. In the scope of spectral analysis crystallinity index has also been calculated by comparing two different band ratios. The research showed that the crystallinity index, calculated from the band intensity ratio I₁₃₇₂/I₂₉₀₀ groups fibres into two groups; biodeteriorated fibres predominantly have lower crystallinity index.     

Classification of the biological material with use of FTIR spectroscopy and statistical analysis

Rapid detection and discrimination of dangerous biological materials such as bacteria and their spores has become a security aim of considerable importance. Various analytical methods, including FTIR spectroscopy combined with statistical analysis have been used to identify vegetative bacteria, bacterial spores and background interferants. The present work discusses the application of FTIR technique performed in reflectance mode using Horizontal Attenuated Total Reflectance accessory (HATR) to the discrimination of biological materials. In comparison with transmission technique the HATR is more rapid and do not require the sample destruction, simultaneously giving similar absorbance bands. HATR-FTIR results combined with statistical analysis PCA and HCA demonstrate that this combination provides novel and accurate microbial identification technique.     

Thermogravimetric analysis of teeth for forensic purposes

Journal of Thermal Analysis and Calorimetry - The objectives of this study were to characterize the thermal decomposition of human teeth and to evaluate the decomposition of organic matter,...     

FTIR spectroscopy examination of leukemia patients plasma

In the present study, Fourier-transform infrared microspectroscopy (micro-FTIR) was applied for the analysis of human plasma samples in order to detect spectral parameters, which might serve as biomarkers for monitoring and identification of leukemia patients. Samples of plasma were obtained from healthy and patient persons suffering from chronic lymphocytic leukemia and analyzed by micro-FTIR.The results show that spectral peaks at 1056, 1270 and 1592 cm⁻¹ appearing in all examined samples obtained from healthy persons were significantly reduced in all tested patient samples. Cluster analysis of the obtained spectra at these specific regions provided excellent classification of the healthy and the patient samples which correlate completely with clinical data. These parameters could be used as a basis for developing a spectral method for the detection and identification of this type of human leukemia.     

Analysis of renal stones by FTIR spectroscopy

A study of the chemical composition of renal stones is important for understanding their etiology. And the therapy for the stone disease is usually based on the analysis of calculi, permitting a porper management of the disease and the prevention of its recurrence. FTIR spectroscopy has been used for urinary stones analysis. The routine, easy and rapid measurements give unambiguous information about the stone composition. Especially a precise wavelength scale of the Fourier method is helpful here. A relatively good spatial resolution is important as very often the stones are composed of core and various layers of different chemical composition. A quantitative determination of the proportion of various materials in calculi is also possible.     

FTIR spectroscopy studies of nucleic acid damage

Fourier transform infrared (FTIR) spectra of RNA isolated from tumour brain (glioma) and DNA isolated from low-dose gamma-irradiated epididymis cells of rats from the Chernobyl accident zone have been investigated in the 700-4000 cm(-1) region. The total absorbed radiation doses were equal to or less than 57 cGy. Observed changes in the FTIR spectra represent the damage in the primary, secondary and tertiary structure of nucleic acid, which seem to be connected with modification of bases and sugars, and redistribution of the H-bond network. FTIR data for tumour and gamma-irradiated nucleic acid show some similar features. A great amount of statistical data and good mathematical approaches are needed for the use of these data as diagnostic criteria.     

FTIR spectroscopy of buried interfaces in molecular junctions

We demonstrate that ATR-FTIR spectroscopy can be used to record high-quality vibrational spectra of molecules at buried interfaces in metal-molecule-silicon and metal-molecule-metal junctions. This provides quantitative information on the structure and conformation of molecules at buried interfaces, an issue of critical importance to molecular electronics. In the model systems of Au on octadecyltrichlorosilane self-assembled monolayer on Si or mecaptohexadecanoic acid multilayers on Au-covered Si, ATR-FTIR suggests that metal deposition leads to not only conformational disorder within the film but also the direct interaction of metal atoms/clusters with alkyl backbones.     

Characterization of dextrin hydrogels by FTIR spectroscopy and solid state NMR spectroscopy

Fourier transform infrared (FTIR) and ¹³C solid state nuclear magnetic resonance (NMR) spectroscopy were used to study dextrin structural changes occurring upon hydrogel formation by vinyl acrylate (VA) grafting and subsequent free radical polymerization. The degrees of VA substitution (DS) and polymerization (DP) were quantified up to 40%VA by FTIR intensity measurements and partial least squares (PLS)/FTIR, the latter being a faster and less error-prone method. Above 40%VA, both parameters are underestimated by FTIR. A spin counting NMR experiment showed high carbon observabilities for hydrogels and improved PLS/NMR models were achieved for DS and DP determination. Alternative NMR integration methods are hindered by the broad VA peaks and need for area correction, due to their CP dynamics. NMR changes in C1 profile showed that a single helical conformation predominates at lower %VA, being replaced by disordered conformations as %VA increases. Furthermore, a correlation FTIR/NMR study indicated that ring conformations are significantly affected in hydrogels, compared to unpolymerized dextrin.     

FTIR spectroscopy study of CO adsorption on Pt-Na-mordenite

Different carbonyls are formed after CO adsorption at ambient temperature on a Pt-Na-mordenite (Pt-Na-MOR) sample. Pt(3+)(CO)(2) dicarbonyls (nu(s) at 2205 cm(-1) and nu(as) at 2167 cm(-1)) are decomposed without formation of monocarbonyls. The respective mixed-ligand species, Pt(3+)((12)CO)((13)CO), formed after (12)CO-(13)CO coadsorption, display bands at 2192 and 2131 cm(-1), in excellent agreement with the theoretically calculated values. Pt(2+)-CO species absorb at 2145 cm(-1) and are not able to accept a second CO molecule. Pt(+)-CO carbonyls are characterized by a band at 2111 cm(-1). Under CO equilibrium pressure, these species are converted into dicarbonyls (nu(s) at 2135 cm(-1) and nu(as) at 2101 cm(-1)). The respective mixed-ligand species, Pt(+)((12)CO)((13)CO), manifest bands at 2123 and 2069 cm(-1), in good agreement again with the theory. Different carbonyls of metallic platinum are observed below 2100 cm(-)(1). In addition, weakly adsorbed CO was registered as Na(+)-CO complexes (2177 and 2165 cm(-1)) and Na(+)-OC-Na(+) species (2138 cm(-1)). It was found that during desorption of CO platinum was reduced, ultimately to metal. However, heating in a NO + O(2) mixture leads to reoxidation of the metal particles and restoration of the initial state of the sample.     

FTIR spectroscopy and DFT studies of carbosilane dendrimers

The FTIR spectra of G(3), G(4), and G(9) generations of polybutylcarbosilane dendrimers have been recorded and analyzed. The structural optimization and normal mode analysis were performed for G(1) generation on the basis of density functional theory (DFT). This calculation gave vibrational frequencies and infrared intensities for the t,t- and g,-g-conformers of the butyl terminal groups, attached to the same silicon atom. The g,-g-conformer is 5.83 kcal/mol less stable compared to t,t-conformer. Relying on DFT calculations a complete vibrational assignment is proposed for different parts of the studied dendrimers. The dependence of band full width at half height in the IR spectra on generation number is established. The IR spectra of carbosilane dendrimers at higher temperatures at the ambient air and isolated from atmosphere air were studied. At temperature 180 degrees C all studied carbosilane dendrimers are stable when contact with atmosphere is absent, in the air they oxidize and thus CO and SiO groups appear.     

A practical high-throughput screening system for enantioselectivity by using FTIR spectroscopy

For the first time FTIR spectroscopy has been applied to the measurement of enantiomeric purity. The underlying concept is based on the use of pseudo-enantiomers that are (13)C-labeled at appropriate positions. Upon applying Lambert-Beer's law in the determination of the concentrations of both enantiomers, the ee values are accessible, accuracy to within +/-5 % of the true values being possible. The application of a commercially available high-throughput FTIR system results in a slightly decreased accuracy (+/-7% for the ee values), but this allows a throughput of up to 10000 samples per day. The method is of interest in the area of combinatorial symmetric catalysis and directed evolution of enantioselective enzymes.     

GC/FTIR Potential for Structural Analysis of Marine Origin Complex Mixtures

Abstract

In this paper, we show the GC/FTIR contribution to the structural elucidation of marine origin complex mixtures. Three examples are given concerning aromatic hydrocarbons, fatty acid methyl esters and polychlorobiphenyls. These examples show the capability of GC/FTIR to differentiate isomers of aromatic hydrocarbons and polychlorobiphenyls and to rapidly characterize the different classes of fatty acid methyl esters (ramification, insaturation, cis/trans isomerism, hydroxyl group, cyclopropane ring).