Fourier-transform infrared photoacoustic spectroscopy of zeolites

Photoacoustic detection is shown to be very valuable for obtaining infrared-spectroscopic data for samples with characteristics that involve very difficult sampling. The modification reactions on the zeolite mordenite, a highly scattering material, are investigated by this technique and by gas-adsorption experiments. The mechanism of the reactions between borane groups inside the channels of the mordenite and amines at different reaction temperatures is described. At low temperatures, amine- and amino-boranes are formed that polymerize at elevated temperatures if steric hindrance is absent. The implantation of boron-nitrogen compounds inside the channels of the mordenite allow a continuous and controlled variation of the accessibility of the mordenite for gas molecules such as krypton and xenon at 273 K.     

Fluorescence and Fourier-transform infrared spectroscopy for the analysis of iconic Italian design lamps made of polymeric materials

The preservation of design object collections requires an understanding of their constituent materials which are often polymeric blends. Challenges associated with aging of complex polymers from objects with an unknown physical history may compromise the interpretation of data from analytical techniques, and therefore complicate the assessment of the condition of polymers in indoor museum environments. This study focuses on the analysis of polymeric materials from three well-known Italian design lamps from the 1960s. To assess the degree of chemical modifications in the polymers, non-destructive molecular spectroscopic techniques, Fourier-transform infrared (FTIR) and fluorescence spectroscopy, have been applied directly on the object surfaces using an optical fiber probe and through examination of micro samples. FTIR spectra of the different polymers, polyvinylacetate (PVAc) for the lamps Taraxacum and Fantasma, and both acrylonitrile–butadiene–styrene polymer (ABS) and cellulose acetate (CA) for the lamp Nesso, allowed the detection of ongoing deterioration processes. Fluorescence spectroscopy proved particularly sensitive for the detection of molecular changes in the polymeric objects, as the spectra obtained from the examined lamps differ significantly from those of the unaged reference materials. Differences in fluorescence spectra are also detected between different points on the same object further indicating the presence of different chemical species on the surfaces. With the aid of complementary data from FTIR spectroscopy, an interpretation of the emission spectra of the studied polymeric objects is here proposed, further suggesting that fluorescence spectroscopy may be useful for following the degradation of historical polymeric objects.     

Applications of photoacoustic step-scan FT-IR spectroscopy to polymeric materials

Thin coatings technology demands that characterization tools are readily available to distinguish between the composition and physical state of the coated layers versus the substrate. In principle, infrared photoacoustic spectroscopy (PAS) possesses all the appropriate features to become a mainstream technique for these types of characterizations. These features include the ability to characterize coatings of a variety of thickness (monolayers to tens of microns) and the fact that the technique requires virtually no sample preparation. One category of such samples involves systems having few micron thin layered structures coated on relatively thick polyester substrates. The phase delay of the photoacoustic signal can be used in conjunction with the knowledge of the thermal properties of the coated fluids in the calculation of the relative as well as the absolute depths of these multi-layered coatings. The phase delay is calculated at wavelengths that are characteristic of the various components of the different layers in the system. The technique is applied to the characterization of a coated system having a submicron layer as the top layer. Step-scan FT-IR photoacoustic data are presented that prove the ability of the technique to successfully isolate the infrared signature of the top layer from the infrared spectrum of the bulk material, proving the sub-micron resolution capability of the method. In addition, results will be shown that underline the fact that the most serious problem in PAS is saturation at high absorptivities.     

Industrial problem solving using infrared photoacoustic spectroscopy

Until recently photoacoustic detectors coupled to infrared spectrophotometers were low signal-to-noise devices. Often long acquisition times and low resolution were used in order to obtain any spectrum at all.However, newer designs of photoacoustic detectors which are optimized for use in the infrared have become available. Nearly theoretical signal-to-noise values of 2000/l for a single 8 cm^–1 scan have been observed using the MTEC photoacoustic detector on the Perkin-Elmer Model 1800 FT-IR. Using this combination of photoacoustic detector and the Model 1800, it is feasible to conduct quantitative measurements and so it becomes very important to understand the parameters of the measurements which determine the precision.This paper will discuss the various types of analysis that can be performed on industrial samples by using a photoacoustic detector. Aspects of sample handling and the effect of mirror velocity in the interferometer on quantitative analysis will be discussed. Not only will quantitative results be reported, but also the results of spectral difference calculations, which require the same precision as quantitative measurements, will be presented. Depth profiling and sample identification will also be discussed.     

Detection of ClSO with time-resolved Fourier-transform infrared absorption spectroscopy

ClSO was produced as an intermediate upon irradiating a flowing mixture of Cl2SO and Ar with a KrF excimer laser at 248 nm. A step-scan Fourier-transform infrared spectrometer coupled with a small multipass absorption cell was employed to detect time-resolved absorption spectrum of ClSO. A transient spectrum in the region 1120-1200 cm(-1), which diminished on prolonged reaction, is assigned to the S-O stretching (nu1) mode of ClSO. A spectrum with a resolution of 0.3 cm(-1) partially reveals rotational structure with the Q-branch at 1162.9 cm(-1). Calculations with density-functional theory (B3LYP/aug-cc-pVTZ) predict the geometry, vibrational, and rotational parameters of ClSO. An IR absorption spectrum of ClSO simulated based on predicted rotational parameters agrees satisfactorily with experimental results. ClSO produced from photolysis of Cl2SO at 248 nm is internally hot.     

Fourier transform infrared photoacoustic spectroscopy of dental calculus

The mid and far FTIR spectra of supragingival and subgingival calculus were measured, respectively. From the subtraction spectra of the two types of calculus, the protein components of calculus have been obtained. The results of photoacoustic spectroscopy indicated the presence of protein layer on the surface of early calculus.     

Quantitative applications of photoacoustic spectroscopy in the infrared

Quantitative photoacoustic and transmission infrared spectroscopy have been compared for a highly overlapped three component mixture with concentrations varying from 0 to 60%. A partial leastsquares model has been employed for the quantitative analysis. High correlation coefficients were obtained for both the transmission and photoacoustic model.     

Rheo-optical Fourier-transform infrared (FTIR) spectroscopy of polymers

Rheo-optical FTIR spectroscopy has been applied to monitor the onset, progress and decay of strain-induced crystallization in loading-unloading cycles of sulfur-crosslinked natural rubber at 300 K and 343 K. From the short-time spectroscopic data conclusions were also drawn with respect to the orientation of the average polymer and the polymer chains in the strain-induced crystal phase.     

Applying Fourier-transform infrared spectroscopy and chemometrics to the characterization and identification of lactic acid bacteria

The infrared absorption spectra of 55 lactic acid bacteria belonging to the genera Lactobacillus, Weissella and Carnobacterium were obtained and mathematically analyzed. Sixteen reference strains and 39 food strains isolated from meat and meat products and belonging to the genera Lactobacillus (6 species), Weissella (3 species) and Carnobacterium (2 species) were processed under standardized conditions and their medium infrared spectra obtained using Fourier-transform infrared (FT-IR) spectroscopy. Reproducibility indexes and similarities between FT-IR spectra were calculated using modified correlation coefficients to detect the ranges with the best reproducibility and discrimination properties. Hierarchical cluster analysis and stepwise discriminant analysis (SDA) were subsequently carried out to detect classes and create library groups. Reference strains could be distinguished on the basis of their spectral data and their clustering was in agreement with differences in chemical composition of the cell wall. For the 39 food isolates, the capability of two identification systems was compared. Unknown strains were identified (a) using the linear functions obtained from SDA (canonical variables) of the variables that provide the best discrimination of spectra, and (b) by calculating a differentiation index when a range of the unknown's transformed IR spectrum was compared to all spectra included in a reference library. The system based on the differentiation index obtained a higher rate of identification, allowing for detection of outliers. FT-IR spectroscopy is shown to afford additional information to phenotypic and genotypic data which may help to establish a more robust taxonomic classification.     

Application of a digital signal processor to Fourier-transform infrared spectroscopy

Summary The application of a digital signal processor (DSP) to Fourier-transform infrared spectroscopy is described, which allows for near real-time display of the transformed interferograms as spectra.     

Analysis of organic acids in wines by Fourier-transform infrared spectroscopy

Fourier-transform infrared (FTIR) spectroscopy has been a major point of development in many wine laboratories in recent years. It enables almost instant analysis of several properties of wine, usually with very good precision and accurate results. Nevertheless, validation procedures should not be forgotten and should be fully performed. Recovery experiments were performed by spiking wine samples with different amounts of organic acids (tartaric, malic, lactic, acetic and citric—the most prominent in wines). After FTIR analysis of the total acidity and of each organic acid concentration, recoveries were calculated. For total acidity recovery results were, in general, good and very close to 100% (64–111%). On the other hand, for individual organic acid concentrations, the recovery results were lower than 100% (11–73%) for all spiking additions. These results could be explained by spectroscopic interferences between the organic acids. Because they have similar infrared spectra, it is not easy to distinguish between them and, therefore, to achieve accurate calibration. When total acidity, with a different infrared spectrum from the other abundant compounds in the wine, was taken as a single property the recovery results were acceptable.     

Investigation of the dislocation of natural fibres by Fourier-transform infrared spectroscopy

Dislocations were thought the weakest link in natural fibres which had negative effects on the tensile strength of the fibres. This paper presents a systematic approach to examine the dislocations in hemp fibres firstly by optical microscopy (OM) and field emission scanning electron microscopy (FE-SEM) for the morphologies of the dislocations and then by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) for the crystallinity index and hydrogen bonds and main chemical compositions of the dislocation regions in hemp fibres. The results showed that (i) dislocations resulted in fibril distortion and intensified amorphous features of hemp fibres; (ii) crystallinity index reduced from 48.4% examined by FTIR and 56.0% by XRD determination for hemps without dislocations to 41.3% for the dislocation regions; (iii) the FT-IR spectra showed much higher absorbance of hemp fibres without dislocations which was two times that of dislocation regions across the whole range of wavenumbers; (iv) deconvolving spectra in O-H stretching region showed a lower number of hydrogen bonds, weaker inter- and intra-molecular hydrogen bonding in the dislocation regions, indicating a possible decrease in the tensile strength of hemp fibres; (v) the FT-IR spectra indicated the removal of the hemicelluloses in dislocation regions and hence possible loss of lignin because of disappearing the bands at 1368 cm⁻¹, 1363 cm⁻¹ and 1506 cm⁻¹; (vi) the spectra in fingerprint region gave rise to the ratio of syringyl (S)/guaiacyl (G) of 0.9 in dislocation regions which was lower than that (1.1) of hemp without dislocation, this means a significant reduction of lignin content and a higher cellulose content in the dislocation regions.     

Fourier-transform infrared and Raman difference spectroscopy studies of the phosphorus-containing dendrimers

FT IR and Raman spectra of 12 generations of the phosphorus-containing starburst dendrimers containing P=S and P=O bonds with terminal aldehyde and P-Cl groups were compared. The influence of the encirclement on the band frequencies and intensity is studied and due to the predictable, controlled and reproducible structure of the dendrimers the information usually inaccessible is obtained. Bands in the IR difference (G2'(P=O)-G2'(P=S)) spectra have characteristic EPR-like form. The strong band at 1600 cm(-1) show marked changes of the optical density in dependence of the aldehyde (-CH=O) or azomethyne (-CH=N-) substituents in the aromatic ring. The analysis of difference spectra enables one to assign the characteristic bands nu(P=S) and nu(P=O) for the bonds in the core, in the repeating unit and in the terminal groups of the dendrimers. This assignment is supported by the calculation of the absorption curves of the different fragments of dendrimer with the force constants and electro-optical parameters. The IR and Raman spectra of dendrimers are depended on the ratio of number terminal groups to a number of repeating units, which in its turn is strictly determined by the generation number. Thus, the marked differences in the vibrational spectra of the first successive generations aspire to zero for the higher ones. The rather rigid repeated units with little conformational flexibility define the perfect microstructure of the studied phosphorus-containing dendrimers up to the eleventh generation.     

Process control of apple winemaking by low-resolution gas-phase Fourier-transform infrared spectroscopy

Four apple wine fermentation processes have been observed by means of direct-inlet gas-phase FTIR spectroscopy. The apple juice concentrates were each fermented by two species of Saccharomyces cerevisiae starters, and the experiment was repeated. The development of the concentrations of 1-propanol, 4-methylpyridine, acetaldehyde, acetic acid, and ethyl acetate was monitored. Two different sampling methods were used--static headspace and direct injection of the must. The performance of the FTIR method is limited by the high ethanol concentration. It can be mathematically proven that the amount of sample can be selected so that any distortion due to ethanol is minimized. Headspace GC-MS was used for preliminary compound identification.     

Detection of structural disorders in pancreatic tumour DNA with Fourier-transform infrared spectroscopy

We have investigated the application of Fourier-transform infrared (FTIR) spectroscopy to detect structural disorders in pancreatic tumour deoxyribonucleic acid (DNA). The DNA was isolated from the tumour and the adjacent histological normal tissue from 15 pancreatic tumour patients. The first derivative and vector normalised spectra were evaluated using hierarchical cluster analysis. Structural disorders in the tumour DNA were detected in the phosphodiester–deoxyribose spectral region. Based on such data within the spectral interval of 1192–1059 cm⁻¹, classification was achieved with a sensitivity and specificity of 87 and 80%, respectively. The test with blinded samples from eight patients based on data from the same spectral region showed a sensitivity and specificity of 100 and 62.5%, respectively. Our finding constitutes a novel diagnostic approach and suggests that the infrared spectroscopic method can offer application to various clinical and laboratory studies, for which the status of the DNA structure is important.     

Two-dimensional Fourier-transform infrared correlation spectroscopy study of the high-pressure tuning of proteins

2D FTIR gives new information about the pressure effect on the structure and dynamics of macromolecular systems. Application of this analysis to proteins can unravel the relation of conformational changes and H/D exchange processes. For lipoxygenase, a pressure of 6.5 kbar induces irreversible conformational changes resulting in an increased exposure of interior parts of the protein to the solvent. At the transition pressure the spectral changes indicate a correlation between conformational changes and H/D exchange. Below and above this pressure, the effects of H/D exchange on the spectral changes are predominant.     

Complete quality analysis of commercial surface-active products by Fourier-transform near infrared spectroscopy

Using proper calibration data Fourier-transform near infrared spectroscopy is used for developing multivariate calibrations for different analytical determinations routinely used in the surfactants industry. Four products were studied: oleyl-cetyl alcohol polyethoxylated, cocamidopropyl betaine (CAPB), sodium lauryl sulfate (SLS) and nonylphenol polyethoxylated (NPEO). Calibrations for major as well as very low concentrated compounds were achieved and every model was validated through linearity, bias, accuracy and precision tests, showing good results and the viability of NIR spectroscopy as a full quality control method for this products. Duplicate and complete analysis on a single sample takes at most 3 min, requiring neither sample preparation nor the use of reagents. The analytical reference procedures involved in this work represent the typical ones used in the industry and the NIR method shows good results in the analysis of components with weight concentrations less than 1%.     

Fourier-transform infrared spectroscopy discriminates a spectral signature of endometriosis independent of inter-individual variation

Endometriosis is the growth of endometrial tissue outside of the uterine cavity. Its aetiology remains obscure, and it is difficult to diagnose ranging from asymptomatic to debilitating disease. Mid-infrared (IR) spectroscopy has become recognised as a potential clinical diagnostic tool. Biomolecules absorb mid-IR (4000 cm(-1) to 400 cm(-1)) and from this, a biochemical-cell fingerprint in the form of an absorbance spectrum can be derived. We set out to determine if IR spectroscopy could be used to identify underlying biochemical differences between endometrial tissues growing outside of the uterus (ectopic) from endometrial tissue of the uterus (eutopic). For comparative purposes, endometrial tissues from endometriosis-free women were also obtained (benign eutopic). Attenuated total reflection Fourier-transform IR (ATR-FTIR) spectroscopy or transmission FTIR microspectroscopy was employed for spectral acquisition. Principal component analysis (PCA)-linear discriminant analysis (LDA) was used for chemometric analysis. A clear segregation was exhibited between the three categories independent of inter-individual confounding differences. Importantly, there was a marked difference between eutopic endometrial tissue from patients with or without endometriosis. This indicates that IR spectroscopy coupled with multivariate analysis (e.g., PCA-LDA) may provide a non-invasive diagnostic tool for endometriosis. By analysing the underlying biochemistry of these endometrial tissues, this approach may facilitate a better understanding of this pathology.     

FT-Raman and photoacoustic infrared spectroscopy of Syncrude heavy gas oil distillation fractions

FT-Raman and photoacoustic (PA) infrared spectra of six distillation fractions derived from Syncrude heavy gas oil (HGO), which has a boiling range from 343 to 524 degrees C, were analyzed in detail in this study. Most of the information on the fingerprint region (200-1,800 cm(-1)) is provided by the FT-Raman spectra, which display approximately 30 bands that are assignable to functional groups in alkanes or aromatics. Monocyclic, bicyclic and tricyclic aromatics in the six fractions were also monitored using bands in this region. The C-H stretching region in both the FT-Raman and PA infrared spectra of the HGO distillation fractions was analyzed according to a curve-fitting algorithm used in previous investigations of samples with lower boiling points. The PA spectra of the HGO fractions were also analyzed by integration. The curve-fitting results show that the frequencies of the 11 Raman and 8 infrared bands used to model the aliphatic (approximately 2,775-3,000 cm(-1)) parts of the respective spectra are approximately constant across the entire HGO boiling range. These band positions are consistent with the results obtained in earlier studies of other distillation fractions obtained from Syncrude sweet blend. Both curve-fitting and integration show that the respective proportions of CH(2) and CH(3) groups do not vary significantly within the HGO region.     

FT-Raman and photoacoustic infrared spectroscopy of syncrude light gas oil distillation fractions

FT-Raman and photoacoustic (PA) infrared spectra of 12 distillation fractions derived from Syncrude light gas oil (LGO), which has a boiling range from 195 to 343 degrees C, were analyzed in detail in this study. In the fingerprint region (200-1800 cm(-1)) most of the information is obtained from the FT-Raman spectra, which display 36 bands that are assignable to various alkyl or aryl functional groups. Monocyclic, bicyclic and tricyclic aromatics in the 12 fractions were also characterized using Raman bands in this region. The corresponding section of the infrared spectra is much simpler, displaying a relatively small number of bands due to either aromatic or aliphatic CH(n) (n=1, 2 or 3) groups. The Cz.sbnd;H stretching region in both FT-Raman and PA infrared spectra of the LGO distillation fractions was curve-fitted according to procedures established in previous investigations of Syncrude samples with various boiling ranges. The PA spectra of the LGO fractions were also analyzed using an accepted integration strategy that requires no a priori assumptions with regard to the number of constituent bands or their shapes. The curve-fitting results show that the frequencies of the 11 Raman and eight infrared bands used to model the aliphatic ( approximately 2775-3000 cm(-1)) parts of the respective spectra decrease systematically as the median boiling points of the LGO fractions increase. These band positions are consistent with those determined in earlier studies of other distillation fractions. Both curve fitting and integration show that the abundance of CH(2) groups increases at the expense of CH(3) groups as the boiling points of the fractions increase within the LGO region.