Showing papers in "Applied Spectroscopy in 1991"

Polarization Modulation FT-IR Spectroscopy of Surfaces and Ultra-thin Films: Experimental Procedure and Quantitative Analysis

Abstract: Polarization modulation of the incident electromagnetic field is used to increase the sensitivity and the in situ experiment ability of the well-known method of reflexion absorption FT-IR spectroscopy, for the characterization of surfaces and ultra-thin films. The experimental procedure and signal processing of the detected intensity are described and illustrated with the use of results obtained with Langmuir-Blodgett monolayers. The quantitative analysis of the spectra is then developed, and a linear behavior of the band intensities is found for ultra-thin films exhibiting no strong absorptions. This result is checked with the use of organic and inorganic ultra-thin films of increasing thicknesses.

Time-Resolved FT-IR Absorption Spectroscopy Using a Step-Scan Interferometer

Abstract: The implementation of time-resolved step-scan FT-IR spectroscopy with a commercial interferometer is described. With the use of the photoreaction of the biological system bacteriorhodopsin as an example which exhibits infrared spectral changes smaller than 10−2 absorbance units, the quality of the method is demonstrated. A comparison with conventional flash-photolysis experiments with a monochromatic infrared monitoring beam clearly demonstrates the multiplex advantage. The advantage of covering the total time course of the reaction allows for a variety of data analysis, such as forming difference spectra between intermediates of the reaction and the deduction of time courses of absorbance changes at selected wavenumbers. The mirror stability is better than ±1.5 nm, which is sufficient for the reliable measurement of small absorbance changes.

Reheating of a Laser-Produced Plasma by a Second Pulse Laser

Abstract: Focused radiation of a Nd:YAG laser was used for ablation and production of free sample atoms from electrically conducting and nonconducting solids for analytical purposes The microplasmas were generated in an argon buffer gas atmosphere at reduced pressure In order to increase the intensities of analyte lines the microplasmas were reheated by a second Nd:YAG laser after the process of atomization was completed It is demonstrated for aluminum and manganese in glass and steel samples and for magnesium and manganese in glass, copper, and aluminum that by internal standardization a common calibration curve can be obtained

A two-dimensional fluorescence lifetime imaging system using a gated image intensifier

Abstract: A simple fluorescence lifetime imaging system using a gated microchannel plate (MCP) image intensifier coupled to a CCD camera has been developed. Nanosecond-level time-resolved fluorescence images of a sample under a pulsed light excitation can be detected directly. With a rapid lifetime determination method for multigate detection, fluorescence lifetime imaging can be promptly performed. In the present system, laser excitation of sample and shutter action of an image intensifier are fully synchronized by means of an optical fiber delay line. In order to compensate for fluctuations in the excitation source, a simple intensity monitor circuit was developed. Details of the instrumental system and verification measurements on two component samples are presented.

Infrared Studies of Wood Weathering. Part II: Hardwoods

Abstract: Infrared spectra, in the diffuse reflectance mode, are presented for three common softwoods (Western redcedar, southern pine, and Douglas fir) that have been subjected to a variety of artificial weathering conditions. The surface spectra of the three unweathered woods have distinctly different characteristic features, but after 2400 hours of full artificial weathering the surface features are virtually identical and correspond closely with those of the cellulosic polymer components. Weathering with light alone has a less pronounced effect on the wood surfaces, whereas weathering with water alone has virtually no effect in comparison to the result of both light and water used in conjunction. A photochemically induced reaction pathway for the weathering process, consistent with the experimental findings, is discussed.

Quantitative Elemental Analysis of Iron Ore by Laser-Induced Breakdown Spectroscopy

Abstract: Results are presented of the elemental analysis of iron ore using laser-induced breakdown spectroscopy (LIBS). Calibration curves for calcium, silicon, magnesium, aluminium, and titanium were produced. The precision ranges from ≈2 to ≈25%. The detection limits are element-dependent, but are of the order of 0.01%. The extension of LIBS from the laboratory to a field-based analytical technique is discussed.

Phosphodiester Stretching Bands in the Infrared Spectra of Human Tissues and Cultured Cells

Abstract: Methodology has been developed recently in our Ottawa laboratory to obtain infrared spectra of intact biological tissues and whole cells with extremely high signal-to-noise ratio. This development has allowed us to evaluate the structural properties of biomolecules in tissue sections and exfoliated cells of human neoplasms by monitoring their infrared spectra (Refs. 2 and 3 and research submitted for publication). During this work we found that several changes in the infrared spectra of malignant tissues and cells are common to all cancers which we studied, including those of the colon, stomach, esophagus, skin, liver, cervix, and vagina (Refs. 2 and 3 and research submitted for publication). It is important to know the structural origin of these spectral changes, since they may reflect a step of a shared pathway in carcinogenesis. The most striking changes in the spectra that are common to various malignant tissues and cells are observed in the symmetric (νsPO2−) and asymmetric (νasPO2−) stretching bands of phosphodiester groups. These results suggest that in all cancerous tissues and cells studied to date most PO2− groups become hydrogen bonded and that the intermolecular packing among neighboring PO2− groups becomes closer. (Refs. 2 and 3 and research submitted for publication). Indirect evidence, discussed later, pointed to nucleic acids as the molecules mainly responsible for the observed changes in the νsPO2− and νasPO2− bands. Since any information concerning structural changes in nucleic acids associated with malignancy is potentially significant for our understanding of cancer, we sought to confirm the molecular origin of the phosphodiester stretching modes in the infrared spectra of tissues and whole cells. We therefore investigated the infrared spectra of human malignant colon tissues, cultured human colon adenocarcinoma cells, and the nuclei, DNA, RNA, and lipids isolated from the cultured adenocarcinoma cells. Moreover, the correlation of the intensities of the νas,PO2− and ,νsPO2− bands in the infrared spectra of human thymus and muscle tissues with their relative concentrations of nucleic acids in the cells has been studied.

Application of Step-Scan Interferometry to Two-Dimensional Fourier Transform Infrared (2D FT-IR) Correlation Spectroscopy

Abstract: The application of step-scan interferometry to two-dimensional infrared (2D IR) spectroscopy is described. In this 2D FT-IR experiment, a step-scan interferometer is used to study a system undergoing dynamic changes induced by an external perturbation. Because step-scanning removes the spectral multiplexing from the temporal domain, the time dependence of the sample response to the perturbation can be retrieved more conveniently, in comparison to conventional rapid-scan techniques. Time-resolved IR data are then converted to 2D IR correlation spectra. Peaks located on a 2D spectral plane provide information about interactions among various functional groups associated with the IR bands. In the step-scan mode, the FT-IR multiplex advantage is retained; thus, spectral regions far removed from each other can be correlated with the use of 2D analysis from a single scan. 2D FT-IR spectra for a composite film of isotactic polypropylene and poly(γ-benzyl-L-glutamate) subjected to a small-amplitude sinusoidal strain are presented. The 2D FT-IR spectra clearly differentiate bands arising from the polyolefin and polypeptide. Overlapped bands are deconvoluted into individual components on the 2D spectral plane due to their different dynamic behavior. The applicability of step-scan 2D FT-IR to a variety of dynamic experiments is discussed.

Holographic Notch Filter for Low-Wavenumber Stokes and Anti-Stokes Raman Spectroscopy

Abstract: A holographic notch filter with a 15-nm rejection band is used as a Rayleigh line filter for Raman spectroscopy with a single-stage grating spectrograph. The filter is shown to allow acquisition of Stokes and anti-Stokes spectra as close as 72 cm−1 from the exciting line.

Photoacoustic Depth Profiling of Polymer Laminates by Step-Scan Fourier Transform Infrared Spectroscopy

Abstract: The use of step-scan Fourier transform infrared (FT-IR) spectroscopy with photoacoustic (PA) detection for depth profiling studies of polymer laminates is demonstrated. Step-scan FT-IR simplifies the extraction of dept; profile information due to the single modulation frequency that can be applied over the entire spectral range. Because a single modulation frequency is generally used in step-scan FT-IR, the thermal diffusion length, μ, is constant for all wavelengths in a single scan. In addition, lock-in detection allows for easy extraction of the signal phase. Two methods of depth profiling are discussed and illustrated. The first is the conventional method of varying the probe depth by changing the modulation frequency. The other method depends on the direct use of the signal phase. The phase analysis technique is particularly useful for cleanly separating the signal due to a thin (<5 μm) surface layer from that of the bulk or substrate.

A New Line-Narrowing Procedure Based on Fourier Self-Deconvolution, Maximum Entropy, and Linear Prediction

Abstract: We propose a new methodology to reduce the widths of spectral lines. This procedure, which is performed entirely in the time domain, combines elements of the methods of Fourier Self-Deconvolution (FSD), Maximum Entropy (MEM), and Linear Prediction (LP) in such a way as to take advantage of the efficacies of each of these procedures. The procedure is illustrated with examples.

A color analysis of the brancacci chapel frescoes

Abstract: About one hundred significant spots (area = 0.5 cm2) that were homogeneously colored were selected on the frescoes "Resurrection of the son of Teofilo," "Saint Peter in pulpit," and "Saint Peter heals invalids by his shadow" in the Brancacci Chapel (Chiesa del Carmine, Florence). The reflectance spectra of these spots were recorded before and after restoration with the use of an external integrating sphere, which was connected through optical fibers to a UV/visible spectrophotometer, and the data were stored in a personal computer. Spectrophotometric investigations were also performed on small samples of frescoes, which were appropriately prepared, in a laboratory, with pure pigments. The results we obtained are discussed in the light of our main purposes: (1) to achieve nondestructive identification of pigments; (2) to help create time-unalterable color archives; (3) to establish a method for monitoring eventual color changes; and finally (4) to obtain useful information for the fields of art restoration and art history.

Application of ATR-IR to the Analysis of Surface Structure and Orientation in Uniaxially Drawn Poly(ethyleneterephthalate)

Abstract: A critical examination of the use of ATR-IR for the examination of surface composition and orientation in uniaxially drawn poly(ethyleneterephthalate) (PET) films has been performed. This work has identified the band at 1410 cm−1 as a satisfactory reference band in ATR-IR analyses for surface composition and orientation analyses in oriented PET films. Other commonly used reference bands at 790 and 1510 cm−1 have been shown to be influenced by both incident infrared polarization and orientation within the polymer films. Control of sample clamping pressure in a conventional ATR-IR clamp has been shown to afford optimized sample contact, needed in conjunction with the use of valid reference bands to obtain reproducible in-plane surface dichroism measurements of films with varying degrees of orientation.

Practical and convenient 355-nm and 337-nm sharp-cut filters for multichannel Raman spectroscopy

Abstract: The interference from Rayleigh and other elastic scattering is a serious problem for multichannel Raman spectroscopy. This problem becomes more serious if the surface subjected to the excitation reflects stray light, particularly in front-face excitation and in systems using rotating samples or applying the flow technique to avoid local heating and accumulation of the photoproduct. In order to eliminate this problem the conventional multichannel Raman spectrometer uses a specially designed triple polychromator equipped with a subtractive double-grating filter stage. However, due to the complicated optical arrangements, including three gratings and at least six mirrors, the throughput of the instrument is usually low. This is a severe disadvantage if one needs to detect extremely weak Raman signals. This is particularly true when time-resolved resonance Raman (TRR) spectroscopy is performed. In order to have an optimum TRR signal, the ideal method is to apply a single spectrograph equipped with a sharp line elimination filter tuned to the wavelength of the exciting line. Several filters such as chevron filters and colloid filters have been designed for this purpose. Unfortunately, most of these filters are only applicable in the visible region. In addition, the requirement of a high degree of collimation also reduces the throughput of the signal. Several commercially available sharp-cut long-wavelength bandpass filters and a recently developed J-aggregate filter applying organic dye molecules are also useful for the elimination of exciting lines in the visible region.

Infrared Emission Spectroscopy: A Theoretical and Experimental Review:

Abstract: Thermal-induced infrared emission spectroscopy is reviewed, with emphasis on developments in theory and experiment. The theory associated with obtaining thermal-induced infrared emittance spectra as a function of sampling optics is discussed. The FT-IR configuration and data reduction methods needed to properly obtain high-quality spectra, close to room temperature, are also considered. Optical and experimental parameters which affect the spectrum are demonstrated by example, with a discussion of methods which optimize the signal-to-noise ratio. The applications shown range from polymer films on both metal and semiconductor surfaces to a single filament analyzed by micro-emission spectroscopy.

Flame Atomic Absorption Spectrometric Determination of Cadmium, Cobalt, and Nickel in Biological Samples Using a Flow Injection System with On-Line Preconcentration by Co-precipitation without Filtration

Abstract: Cadmium, cobalt, and nickel at ng/g to μg/g levels in plant and animal tissue reference materials and at μg/L levels in blood and urine were determined by flame atomic absorption spectrometry. The analyte elements were preconcentrated and separated from the bulk of the matrix by on-line co-precipitation with the hexamethylene ammonium hexamethylene dithiocarbamate iron(II) chelate complex in a flow injection system. The precipitate was collected in a knotted reactor made from 150-cm-long, 0.5-mm-i.d. Microline tubing without using a filter. The precipitate was dissolved in methyl isobutyl ketone and introduced directly into the nebulizer-burner system of an atomic absorption spectrometer. Ascorbic acid in an HC1/KC1 buffer was added on-line in order to reduce iron(III) to iron(II) because of its much better efficiency as a collector for trace elements. Reagent concentrations were optimized so that at least 200 mg/L of iron and 15 mg/L of copper could be tolerated in the sample solution without causing significant interferences. The portion of the analyte retained in the collector was about 70% for cadmium and 50% for cobalt and nickel. Enrichment factors of 24, 19, and 20 were obtained for cadmium, cobalt, and nickel, respectively, with the use of a 40-s co-precipitation time, resulting in enhancement factors, including the effect of the organic solvent, of 52, 43, and 52, respectively. The detection limits (3σ) for cadmium, cobalt and nickel were 0.15, 1.3, and 1.5 μg/L, respectively, and the precision was 1.5% RSD for 10 μg/L, Cd, 2.7% RSD for 50 μg/L Co, and 1.8% RSD for 50 μg/L Ni. The analytical results obtained for a number of standard reference materials and control samples were in good agreement with the certified or recommended values.

Quantitative determination of sugar cane sucrose by multidimensional statistical analysis of their mid-infrared attenuated total reflectance spectra

Abstract: A fast and accurate method for determining the sucrose content of sugar cane juice has been developed. The application of principal component regression (PCR) has been proposed for the development of a prediction equation of sucrose content by mid-infrared spectroscopy. An attenuated total reflectance (ATR) cell is used in place of the more familiar transmission cell. PCR involves two steps: (1) the creation of new synthetic variables by principal component analysis (PCA) of spectral data, and (2) multiple linear regression (MLR) with these new variables. Results obtained by this procedure have been compared with those obtained by the conventional application of polarization.

Infrared Study of β-Propiolactone in Various Solvent Systems and Other Lactones

Abstract: Many lactones exhibit two significant bands in the carbonyl stretching region which result from Fermi resonance interaction between νC=O and a combination or overtone of a lower-lying fundamental (or fundamentals). However, for β-propiolactone, three significant bands in the carbonyl stretching region of the spectrum are observed. These bands result from νC=O in Fermi resonance between the combination tone ν6 + ν13,A' and 2ν10,A'. The extent of Fermi resonance interaction between νC=O and the combination and/or overtone is dependent upon the solvent system. Approximate unperturbed νC=O frequencies have been calculated, and these νC=O frequencies decrease in frequency in the solvent order n-hexane, carbon tetrachloride, and chloroform. The unpertrbed νC=O frequencies were also calculated with the use of reported frequencies and band intensities for many other lactones, and the unpertubed νC=O frequencies decrease significantly as the amount of ring strain is reduced in the lactone structures. An equation, based on perturbation theory for obtaining approximate unperturbed νC=O frequencies for situations where three modes are in Fermi resonance, was developed and used to assign the unperturbed νC=O frequencies for β-propiolactone in various solvent systems. This method assumes that all or nearly all of the intensity in the three bands in Fermi resonance arises from the νC=O mode.

Fluorescence Lifetime Imaging: An Approach for Fuel Equivalence Ratio Imaging:

Abstract: This paper describes dopants, apparatus, and procedures which can be used for planar laser-induced fluorescence (PLIF) imaging of the fuel/oxygen equivalence ratio, the most important mixture parameter in combustion studies. The lifetime imaging techniques described here provide data beyond the data available from conventional intensity imaging, and should allow the equivalence ratio to be determined in real time in a two-dimensional slice of a fuel spray. Lifetime imaging methods require the sequential gating of two 2-D detectors during the fluorescence decay. Proof-of-concept experiments indicate that lifetimes ranging from 5 to 50ns can be imaged with good accuracy. The requirements for fluorescent dopants and considerations for use under flame conditions are also discussed.

Interaction of a Laser Beam with Metals. Part I: Quantitative Studies of Plasma Emission

Abstract: Quantitative plasma power emission measurements of the effect of increasing laser energy for the interaction of a 193-nm wavelength laser on four selected metals are presented. A correlation between a theoretical model for mass vaporized and increasing laser energy intensity was found for the selected metals.

Characterization of Holographic Band-Reject Filters Designed for Raman Spectroscopy

Abstract: We report the optical transmission properties of holographic band-reject filters designed for Raman spectroscopy using excitation at 514.5 nm and at 632.8 nm. We use these data to quantitatively evaluate the compromise between rejection of elastic scatter and transmission of Raman bands as a function of Raman shift. We demonstrate the use of a single filter for the rejection of elastically scattered light from the Raman spectra of a white powder and of a clear liquid.

Raman Spectroscopic Identification of Phosphate-Type Kidney Stones:

Abstract: Phosphate-type kidney stones have been examined by the Raman spectroscopic technique by merely focusing laser light on the cut surface of the stones. Before examination of the kidney stones, Raman spectra of several standard phosphate compounds—such as calcium monobasic phosphate [Ca(H2PO4)2], calcium dibasic phosphate (CaHPO4), calcium tribasic phosphate [Ca10(PO4)6(OH)2], calcium orthophosphate [Ca3(PO4)2], brushite (CaHPO4·2H2O), struvite (MgNH4PO4·6H2O), and hydroxyapatite [Ca10(PO4)6(OH)9],—were obtained. Hydroxyapatite has a distinctive line at 961 cm−1, and one kidney stone examined showed a comparable band. It was concluded that one stone is primarily hydroxyapatite and another one is brushite. The analysis of the kidney stones by Raman spectroscopy is direct, fast, and nondestructive, and does not require tedious sample preparation.

Measurements of Aerosol Particle Sizes from a Direct Injection Nebulizer

Abstract: Photographs and laser-scattering measurements showed that a direct injection nebulizer (DIN) produced a finer aerosol with a narrower drop size distribution than that for a conventional glass concentric nebulizer when both were operated at the same liquid and nebulizer gas flow rates. The droplets from the DIN were slightly larger, however, than those leaving a Scott-type spray chamber with a glass concentric nebulizer. The droplets from the DIN had a Sauter mean diameter of ∼7 μm and a 90% mass diameter of 11–16 μm. The droplet size distribution became narrower and shifted to lower diameters as the aerosol gas flow rate increased.

Diffraction-induced stray light in infrared microspectroscopy and its effect on spatial resolution

Abstract: Model experiments were conducted in an effort to quantitatively assess the extent of stray light, resulting from diffraction, in an FT-IR microscope system. The effects of stray light were studied under conditions employing different aperturing modes, aperture sizes, and wavelengths of light. Results and consequences of the findings are discussed with respect to the spatial resolution and quantitative integrity of the data obtainable in mapping analyses of multilayer polymer laminates.

Interpreting Multicomponent Infrared Spectra by Derivative Minimization

Abstract: Stripping a constituent from a multicomponent spectrum reduces the intensity of the residual, and most interpretive schemes attempt to factor out intensities associated with various known components. A useful algorithm for doing this objectively has been described by Gillette et al.

Infrared Micro-Imaging of Atherosclerotic Arteries:

Abstract: Micro-FT-IR spectroscopy is a versatile technique that enables the user to obtain high-quality spectra on small samples This technique is employed to probe the subcellular chemical composition of atherosclerotic arterial walls and create three-dimensional images representing changes in the composition Two different rabbit model systems that produced atherosclerosis, either due to genetic disorder or due to physical injury, are studied The FT-IR spectra are collected from a 20- × 20-μm area of 5-μm-thick arterial section, which is smaller than a single cell The presence of cholesterol esters and other ester-containing compounds is identified from the -O-C=O stretching (1735 cm−1) absorption, and the cis unsaturation in the acyl chains of these compounds is represented by C=C-H stretching (3005 cm−1) absorption The protein content is indicated by the intensities of the amide I (1650 cm−1) band The data clearly show the changes occurring in the chemical composition of an arterial wall, varying with the physiological and morphological changes within the artery and the arteries from different animal models The power of this technique is demonstrated by excellent correlation with the hot stage polarizing microscopy technique, used to characterize the arterial lipids in situ The three-dimensional images of the arterial walls, indicating the concentration of different chemical constituents, are very useful in understanding the mechanism of atherosclerosis development

Spectroscopic Studies of Oxidized Soots

Abstract: Vibrational spectroscopy, ESCA, and C-13 CP/MAS NMR provide a detailed picture of the structure, and therefore reactivity, of the products of the reactions of soot with various oxidants. Reactions such as soot-NO2/N2O4, soot-O3, and soot-SO2, at atmospheric and sub-atmospheric pressures, and at different temperatures, have been studied. The reaction between NO2/N2O4 and n-hexane soot is rapid near room temperature, yielding several surface species, including C-NO2, C-ONO, and C-N-NO2. These functionalities have been confirmed through reaction with 15NO2 and N-18O2. The oxidation of SO2 in soot-SO2 systems yields ionic sulfate, confirmed by isotopic substitution, and requires the presence of water vapor and oxygen. The presence of simulated solar radiation in the same system results in the formation of both ionic and covalent sulfate species. The spectroscopic measurements show carboxyl surface species formed during the soot-ozone reaction. The use of FT-IR, ESCA, and C-13 CP/MAS NMR has yielded consistent results for these carbonaceous particulates in each reaction, but the vibrational spectroscopy is easily the most definitive with such systems.

Three-Dimensional Space- and Time-Resolved Fluorescence Spectroscopy

Abstract: A fluorescence spectroscopic system with both picosecond time resolution and submicrometer three-dimensional space resolution has been developed for elucidating the dynamics of inhomogeneous photophysical/photochemical phenomena. This system is based on a confocal laser scanning fluorescence microscope and a time-correlated single photon counting method. Results on demonstration experiments are shown to specify the performance of the system. Characteristics and limitations of the system are discussed.

FT-IR in Combination with the Attenuated Total Reflectance Technique: A Very Sensitive Method for the Structural Analysis of Polypeptides

Abstract: We have used Fourier transform infrared spectroscopy to analyze protein structure at nanomolar concentrations and compared its sensitivity with other commonly used spectral techniques such as circular dichroism and fluorescence. Less than 10 nM concentration of protein (immunoglobin G) was required in order to obtain IR spectra with good signal-to-noise ratio that could be utilized for curve-fitting analysis to obtain individual band areas assigned to specific secondary structural features. No signals were observable on circular dichroism, and the fluorescence signals were within the noise level for the same concentration of the protein. The results suggest that FT-IR in combination with the ATR technique has high potential for protein structural analysis, and less than 15 picomole protein is sufficient for the structural analysis.

Static Secondary Ion Mass Spectrometry and X-Ray Photoelectron Spectroscopy of Deuterium- and Methyl-Substituted Polystyrene

Abstract: Deuteration in polystyrene (PS) and the differences between PS, poly(4-methyl styrene) (P4MS), and poly(α-methyl styrene) (PAMS) were examined with static secondary ion mass spectrometry (SIMS) and x-ray photoelectron spectroscopy (XPS). Only the effects of methyl substitution could be distinguished by XPS on the basis of the valence band spectra. However, it was demonstrated that both deuterium and methyl substitution effects could be clearly distinguished by static SIMS. Additionally, the effect of these substitutions could be explained in a manner analogous to that used for electron impact (EI) mass spectrometry. By the use of deuterium-labeled polymers, H scrambling was observed during secondary ion formation from PS. The validity of previously postulated secondary ion structures was confirmed on the basis of the fragmentation patterns of both the deuterium and methyl-substituted PS.