bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Orientation in Polymer-Dispersed Liquid Crystals Using Time-Resolved FT-IR
Authors: Kohri Sachiko , Kobayashi Junji , Tahata Shin , Kita Shuichi , Karino Isamu , Yokoyama Tohru
Published: June 2005

Molecular orientation of nematic microdroplets in polymer-dispersed liquid crystal (PDLC) films has been investigated by time-resolved FT-IR (TR/FT-IR) in the presence of an applied electric field. Two kinds (fast and slow) of reorientation processes are found, and these may be attributed to reorientation of liquid crystal molecules at the surface and the central region of droplets. In addition, an induction time has been observed before the onset of the actual reorientation. It is suggested that there are no essential differences between rigid and flexible molecular segments with respect to reorientation dynamics of at least 1 ms time resolution. TR and micro-FT-IR techniques have been combined in order to study the reorientation dynamics of the different regions of droplets.
Applications of Time-Resolved Step-Scan and Rapid-Scan FT-IR Spectroscopy: Dynamics from Ten Seconds to Ten Nanoseconds
Authors: Johnson T. J. , Simon A. , Weil J. M. , Harris G. W.
Published: June 2005

The step-scan technique in Fourier transform infrared (FT-IR) spectroscopy is employed in new applications of time resolved spectroscopy (TRS). Results are demonstrated on time-resolved laser emissions and photolytically generated chemical reactions using both emission and absorption modes. New achievements in FT-IR temporal resolution are demonstrated, as well as the complementary nature of step-scan and rapid-scan time-resolved spectroscopy.
Dynamic Infrared Linear Dichroism: Instrumental Characterization and Optimization
Authors: Chase Bruce , Ikeda Richard
Published: June 2005

A dynamic infrared linear dichroism (DIRLD) spectrometer similar to the one described by Noda and Marcott has been constructed. The effects of variations in chopping frequency, film stretching frequency, and film stretching amplitude have been examined. In addition, the effect of poor phase adjustment and degraded polarization purity has been probed. The experiment has been found to be quite insensitive to small changes in these operating parameters, leading to good reproducibility in the qualitative results across different instruments.
Infrared Spectroscopic Characterization of Alzheimer Plaques
Authors: Fabian Heinz , Choo Lin-P'Ing , Szendrei Gyorgyi I. , Jackson Michael , Halliday William C. , Otvos Laszlo , Mantsch Henry H.
Published: June 2005

Neuritic plaques in the brains of victims of Alzheimer's disease are primarily composed of a 42 amino acid polypeptide, the β-amyloid peptide (βA4), the neurotoxicity of which is related to its aggregation. Fourier transform infrared spectroscopy has been used to study the conformational properties of two synthetic analogues of βA4 peptides known to be involved in the formation of the neuritic plaques formed in patients with Alzheimer's disease and the influence of a single, naturally occurring point mutation upon the tendency of the peptide to aggregate. Peptides from both “normal” Alzheimer's and the more severe Dutch variant of the disease were found to form aggregated antiparallel strands. However, the replacement of a single, negatively charged amino acid (glutamic acid) with an uncharged amino acid (glutamine) in the Dutch-type peptide results in significant differences in the strength and stability of these aggregates and the microenvironment of a number of amino acids. The differences in the strength and the stability of the aggregates are attributed to the presence of varying (small) proportions of the classical secondary structures and differences in net charge. Environmental (solvent) effects were shown to significantly affect the strength of the inter-molecular hydrogen bonding in the aggregates, solvent systems mimicking the membrane/water interface resulting in more strongly hydrogen bonded aggregates. Infrared spectra of material from autopsied human Alzheimer's brains show spectral features indicative of the formation of similar aggregates, which may be related to plaque formation. This observation suggests that IR spectroscopic methods may in the future be useful in the diagnosis and monitoring of Alzheimer's disease.
FT-IR Emission Spectroscopy and its Applications
Authors: Mink János , Keresztury Gábor
Published: June 2005

The practical aspects of infrared emission spectroscopy are reviewed briefly, with emphasis on recent developments and on special problems encountered in measurements of adsorbed species on opaque substrates. A few examples are given for cases when the species of interest give rise to inverted emission bands on the background of substrate emission. The feasibility of recording IR emission spectra of adsorbates on metal powders is demonstrated.
Asynchronous Pulsed-Laser-Excited Fourier Transform Raman Spectroscopy and its Applications
Authors: Sakamoto Akira , Furukawa Yukio , Tasumi Mitsuo , Masutani Koji
Published: June 2005

An asynchronous pulsed-laser-excited Fourier transform Raman spectrophotometer based on a conventional continuous-scan interferometer has been developed. The additional assembly required for pulsed-laser-excited measurements, which consists of a pulsed Nd:YAG laser, a gate circuit, and a low-pass filter, can be attached to any conventional FT-Raman spectrophotometer. The principle of the signal-processing of this method is almost the same as that of the asynchronous time-resolved Fourier transform infrared spectroscopy reported previously. This method does not require the synchronization between the Raman excitation and the sampling of the A/D converter. As an application of this method, it is demonstrated that the use of a pulsed laser and a gate circuit can give a significant increase in signal-to-noise ratios over continuous-wave measurements with the same average laser power. It is also shown that when a constant background (for example, thermal radiation from samples at high temperatures) or a long-lived background is present, the use of pulsed excitation and a gate circuit can effectively reduce the background. Moreover, pulsed excitation can be used for recording time-resolved Raman spectra by using an FT-Raman spectrophotometer. The time resolution is governed only by the width of the probe laser pulse. The potentiality of this method is demonstrated.
Carbon Dioxide Clathrates: An IR Spectroscopic Marker for Arthritis?
Authors: Eysel Hans H. , Jackson Michael , Mantsch Henry H. , Thomson Glen T. D.
Published: June 2005

The IR spectra of dry films of synovial fluid from normal and arthritic joints are presented. The spectra suggest the existence of CO2 clathrates in these fluids which are of remarkable stability in comparison to well-known CO2 clathrate hydrates. To our knowledge, this is the first demonstration of the formation of CO2 clathrates in biological media. The proportion of CO2 clathrates found in synovial fluid appears to vary with the state of health of joints and thus may be of use in the clinical diagnosis of arthritis.
VT-DRIFTS: A Two-Dimensional Infrared Thermal Analysis Method
Authors: White Robert L.
Published: June 2005

Thermal analysis by using variable-temperature diffuse reflectance infrared spectroscopy (VT-DRIFTS) is described. Techniques for extracting spectral information from VT-DRIFTS data regarding temperature-dependent solid-state structure changes are discussed. The use of VT-DRIFTS for investigating the thermal degradation mechanisms of calcium oxalate monohydrate and poly(vinyl alcohol) and for profiling the Lewis and Brønsted acid strength distributions for an HZSM-5 zeolite by monitoring pyridine desorption as a function of temperature is described.
ATR/FT-IR Study of a Monolayer Film of Chlorophyll-a on a Germanium Plate
Authors: Sato H. , Ozaki Y. , Uehara K. , Araki T. , Iriyama K.
Published: June 2005

Infrared spectra of one-monolayer Langmuir-Blodgett (LB) films of chlorophyll- a (Chl- a) can be obtained with a high signal-to-noise ratio by using the attenuated total reflection (ATR) technique. The observed spectra indicate that Chl- a assumes a five-coordinated monomer in the LB films; it seems that both the ester and keto C=O groups are free from any interactions, and a water molecule coordinates to the Mg atom. Comparison of the spectra of the one-monolayer LB films with those of the cast films shows that the structure of Chl- a is quite different between the two kinds of films; in contrast to the LB films the cast films are liable to have the dimer or oligomer of Chl-a. The fact that the five-coordinated monomer is predominant in the LB films suggests that Chl- a molecules are highly oriented in the one-monolayer LB films.
Modification of a Research-Grade FT-IR Spectrometer for Optional Step-Scan Operation
Authors: Gregoriou Vasilis G. , Daun Michael , Schauer Mark W. , Chao James L. , Palmer Richard A.
Published: June 2005

The implementation of step-scanning to a research-grade FT-IR spectrometer (Nicolet system 800) is described. This implementation relies on the complete computer control of the retardation, representing a substantial improvement over results from the previous generation of step-scan spectrometers (IBM IR44) available in our laboratory. Specifically, the instrument represents an improvement in speed, stability, and attainable limit of detection. The most distinctive capability of this instrument is that of high-amplitude phase modulation (tested up to 10 ΛHeNe peak to peak) at relatively high phase modulation frequency while maintaining high position certainty. Alternatively, the phase modulation can be turned off completely and the retardation can be maintained within ±1 nm for indefinite periods between steps. The step-scan option for this instrument, along with its continuous-scan “TRS” (stroboscopic) mode, gives it a unique combination of capabilities for dynamic vibrational spectroscopy. The performance of the instrument in the step-scan mode is demonstrated with photoacoustic spectroscopy (PAS).
Modulated Infrared Spectroscopy at the Electrochemical Interface
Authors: Chazalviel J.-N. , Dubin V. M. , Mandal K. C. , Ozanam F.
Published: June 2005

Performing infrared spectroscopy of chemical species at the electrochemical interface represents a difficult challenge in terms of sensitivity (1 monolayer ∼1015 species/cm2) and selectivity (presence of the electrolyte). These problems are efficiently addressed by using modulation coupled with lock-in detection of the optical signal. The electrode potential, which governs the interface behavior, is the most straightforward physical quantity that can be modulated. Such a modulation technique may be combined with Fourier transform spectroscopy by using an interferometer with a very slow scanning speed of the movable mirror (∼1–10 μm/s). This approach allows one to reach high sensitivity (typical minimum detectable signal Δ I/I ∼ 10−6 in a single-reflection arrangement). In some special cases, other modulations may be of interest, for example, modulation of the light at a semiconducting photoelectrode. A common benefit of these modulation techniques is that the resulting response can be analyzed as a function of the modulation frequency or by consideration of the phase of the signal at a given frequency. As can be shown for several examples, this analysis allows one to distinguish between the various physical and electrochemical processes taking place at the interface: change of free-carrier concentration beneath the electrode surface or of ion populations in the ionic double layer, adsorptiondesorption effects, and Faradaic processes, for which useful information on the reaction mechanisms may be obtained.
Vibrational Studies on the Dynamics of Switching between the Surface-Stabilized States of a Ferroelectric Liquid Crystal by Asynchronous Time-Resolved Fourier Transform Infrared Spectroscopy
Authors: Masutani Koji , Yokota Akira , Furukawa Yukio , Tasumi Mitsuo , Yoshizawa Atsushi
Published: June 2005

Time-resolved polarized infrared spectra have been observed from a ferroelectric liquid crystal (chiral smectic C phase) consisting of a chiral dopant and a nonchiral smectic base during the course of switching between the surface-stabilized states. A primary fast process and the subsequent slow process have been observed for all infrared bands. The chiral dopant and smectic base molecules move simultaneously. The observed time behavior of the infrared bands can be mostly explained by the reorientation of a rigid molecule whose rotational motion around the molecular long axis is almost free. The static intensities and the time behavior of the ester and keto C=O stretching bands do not seem to be consistent with the simple view on the role of these groups.
Generalized Two-Dimensional Correlation Method Applicable to Infrared, Raman, and other Types of Spectroscopy
Authors: Noda I.
Published: June 2005

A two-dimensional (2D) correlation method generally applicable to various types of spectroscopy, including IR and Raman spectroscopy, is introduced. In the proposed 2D correlation scheme, an external perturbation is applied to a system while being monitored by an electromagnetic probe. With the application of a correlation analysis to spectral intensity fluctuations induced by the perturbation, new types of spectra defined by two independent spectral variable axes are obtained. Such two-dimensional correlation spectra emphasize spectral features not readily observable in conventional one-dimensional spectra. While a similar 2D correlation formalism has already been developed in the past for analysis of simple sinusoidally varying IR signals, the newly proposed formalism is designed to handle signals fluctuating as an arbitrary function of time, or any other physical variable. This development makes the 2D correlation approach a universal spectroscopic tool, generally applicable to a very wide range of applications. The basic property of 2D correlation spectra obtained by the new method is described first, and several spectral data sets are analyzed by the proposed scheme to demonstrate the utility of generalized 2D correlation spectra. Potential applications of this 2D correlation approach are then explored.
Average Dielectric Constant of Coated Spheres: Application to the IR Absorption Spectra of NiO and MgO
Authors: Pecharroman C. , Carreno T. Gonzalez , Iglesias J. E.
Published: June 2005

An analytical expression has been obtained for the average dielectric constant of a sample consisting of small coated spheres interspersed in a matrix, by solving the static boundary value problem and averaging the values of the electric field and polarization over the whole of the sample. Absorption IR data of MgO and NiO samples of this kind, produced by spray pyrolysis, embedded in a KBr matrix, are presented, and the theory developed is employed to fit the observed spectra.
Comparison of Noniterative Factor Analysis Spectral Resolution Algorithms
Authors: Neal Sharon L.
Published: June 2005

The effects of fundamental and ancillary algorithm differences on the performance of three noniterative factor analysis spectral resolution algorithms on noisy and overlapped bilinear matrix-formatted spectral data are evaluated and compared. The evaluation consists of the analysis of simulated fluorescence excitation-emission matrices in which the spectral overlap, noise type, and level were systematically varied. The results indicate that the conventions used to exclude low-intensity, high-noise rows and columns from consideration as component spectra estimates and to choose the first estimates of the component spectra have significant impact on resolution algorithm performance. The results of the application of the algorithms to ideal data are nearly identical; however, there are several distinctions in the performance of the algorithms on noisy data. Verifiable estimates of the component spectra were resolved from data matrices degraded by white and Poisson noise that have signal-to-noise (S/N) ratios above 10 by all three algorithms regardless of the noise level and the degree of spectral overlap. The impact of pink noise was uniformly deleterious at S/N below 15.
Direct Determination of Palladium and Cobalt in Phenol by Atomic Spectroscopy
Authors: Frame E. M. Skelly , King J. A. , Anderson D. A. , Balz W. E.
Published: June 2005

A direct method was developed for the quantitation of catalyst metals in phenol by dissolution in an organic solvent mixture. Both flame atomic absorption spectrometry and ICP emission spectrometry of the organic mixtures proved suitable for the determinations, eliminating the difficulties encountered with conventional sample decomposition techniques. A variety of solvent systems and standard compounds were studied to develop a rapid, simple, sensitive method for the direct determination of Pd and Co in phenol. A comparison of analytical procedures is presented, and the stability of organic matrix standards is discussed.
In Situ IR Study of the Reaction Behavior of [Cr3(μ3-O)(μ-O2CH)6(H2O)2(O2CH)]·xH2O and its Active Fragments for the Addition Reaction of Acetylene
Authors: Weiwen Xie , Yukui Cai , Linna Zhang , Yu Zheng , Lingjie He , Suhua Cai
Published: June 2005

The reaction behavior of the complex [Cr3(μ3-O)(μ-O2CH)6-(H2O)2(O2CH)]· xH2O [shown as (Cr3FF)] has been investigated in the system of acetylene with water vapor by means of in situ IR and TG analyses. It has been observed that some active fragments obtained by the loss of part of the ligands of (Cr3FF) demonstrated activity for the additional reaction of acetylene with water or hydrogen, forming either acetaldehyde or ethylene. On the basis of the study of the thermo-decomposition process, as well as the FAB-MS data, the nature of these active fragments has been elucidated.
Theoretical Development for Depth Profiling of Stratified Layers Using Variable-Angle ATR
Authors: Shick Robert A. , Koenig Jack L. , Ishida Hatsuo
Published: June 2005

The theory allowing depth profile information to be recovered from variable-angle attenuated total reflection spectroscopy is shown for both perpendicular and parallel polarizations. The errors invoked by the necessary approximations are evaluated by comparison with exact optical simulations using dispersion theory.
Improved Precision in a Resonance Ionization Mass Spectrometer by the Use of Stark-Shifted Spectral Lines as a Probe for Extraction Field
Authors: Downey S. W. , Emerson A. B. , Fullowan T. R.
Published: June 2005

High-lying (Rydberg) electronic levels of sputtered Na atoms are spectrally shifted by the strong ion extracting electric field (⩾12 kV/cm) present in a resonance ionization mass spectrometer (Stark effect). The Stark-shifted lines are a beneficial diagnostic to probe the ion source's local electric field, which is related to sample alignment and hence ion transmission efficiency. Changes in electric field of 1% can be detected spectrally, so the sample position is controlled to ⩽ 10 μm by this technique. Results show that by the use of the Na spectrum as an alignment aid prior to sputter depth profiling, the precision of the RIMS instrument, as measured by the reproducibility of either the peak of the integrated signals from Be-implanted GaAs, is improved to about ±3%—at least a fourfold improvement over the best previous results. Spatial variations in the Be-ion implant dose over a GaAs wafer may be detected because of improved precision.
Probing Biosensor Interfaces by Multifrequency Phase and Modulation Total Internal Reflection Fluorescence (MPM-TIRF)
Authors: Bright Frank V.
Published: June 2005

The multifrequency phase and modulation (MPM) technique is used in concert with total internal reflection fluorescence (TIRF) to probe in situ the distribution of free and analyte-bound sites of a fluorescently labeled, silica-immobilized F( ab’) antibody fragment. Using this new technique, one is able to recover the affinity constant (Kf) for the immobilized antibody, determine the effects of storage time on Kf and the excited-state fluorescence decay parameters, and follow time-dependent changes in antibody conformation at the silica substrata. This new technique adds a powerful tool to the study of biosensor interfaces.
Multivariate Determination of Glucose in Whole Blood Using Partial Least-Squares and Artificial Neural Networks Based on Mid-Infrared Spectroscopy
Authors: Bhandare Prashant , Mendelson Yitzhak , Peura Robert A. , Janatsch Günther , Kruse-Jarres Jürgen D. , Marbach Ralf , Heise H. Michael
Published: June 2005

The infrared (IR) spectra of whole blood EDTA samples, in the range between 1500 and 750 cm−1, obtained from the patient population of a general hospital, were used to compare different multivariate calibration techniques for quantitative glucose determination. Ninety-six spectra of whole undiluted blood samples with glucose concentration ranging between 44 and 291 mg/dL were used to create calibration models based on a combination of partial least-squares (PLS) and artificial neural network (ANN) methods. The prediction capabilities of these calibration models were evaluated by comparing their standard errors of prediction (SEP) with those obtained with the use of PLS and principal component regression (PCR) calibration models in an independent prediction set consisting of 31 blood samples. The optimal model based on the combined PLS-ANN produced smaller SEP values (15.6 mg/dL) compared with those produced with the use of either PLS (21.5 mg/dL) or PCR (24.0 mg/dL) methods. Our results revealed that the combined PLS-ANN models can better approximate the deviations from linearity in the relationship between spectral data and concentration, compared with either PLS or PCR models.
Gel Permeation Chromatography/Fourier Transform Infrared Interface for Polymer Analysis
Authors: Wheeler L. M. , Willis J. N.
Published: June 2005

A new solvent elimination interface capable of operating at elevated temperatures, here 145°C, has been used to collect polymer molecular weight fractions eluting from a gel permeation chromatogram and to prepare them for IR analysis. The sample is deposited continuously onto a rotating germanium disk which can subsequently be scanned with the use of GC/FT-IR software, allowing direct access to the polymer or copolymer composition as a function of molecular weight. Data are presented here for an ethylene-propylene copolymer which has a distinct bimodal molecular weight distribution. Both the concentration profile and the “composition distribution” are examined. For the polymer concentration profile, comparison is made between the chromatogram obtained with a differential refractive index (DRI) detector and the IR detector (plotting the absorbance as a function of time using Gram-Schmidt vector orthogonalization). The copolymer composition is determined from the relative absorbance of methyl and methylene groups in the CH stretching region. The results show a small change in propylene content as a function of molecular weight, and there is good agreement between composition calculated with the use of the Gram-Schmidt and point-to-point methods.
Direct Imaging Raman Microscope Based on Tunable Wavelength Excitation and Narrow-Band Emission Detection
Authors: Puppels G. J. , Grond M. , Greve J.
Published: June 2005

A new type of imaging Raman microscope is described. First the advantages and disadvantages of the two possible approaches to Raman microscopy based on signal detection by means of a charge-coupled-device camera (i.e., direct imaging and image reconstruction) are discussed. Arguments are given to show that in most cases direct imaging is to be preferred over image reconstruction, because it provides the desired information in less time. In the direct imaging Raman microscope presented in this communication, detection of scattered light occurs in a narrow interval around a fixed wavelength. Selection of the Raman wavenumber shift at which an image is recorded is established by tuning the wavelength of the exciting laser light in such a way that the wavelength of the Raman scattered light with the desired Raman shift coincides with the detected wavelength. The microscope has been incorporated in a Raman microspectrometer in a way that enables easy switching between the imaging and the multichannel spectroscopy modes of operation. Bright field, fluorescence, and Raman microscopic images can be obtained.
Development, Justification, and Applications of a Mid-Infrared Polarization-Division Interferometer
Authors: Polavarapu Prasad L. , Chen Gang-Chi , Weibel Stephen
Published: May 2005

We report the development of a polarization-division interferometer (PDI) for the mid-infrared region. This interferometer uses a self-designed beamsplitter constructed in-house from a BaF2 polarizer and a matching substrate. In conjunction with a linear polarizer in front of the source and two roof-top mirrors, one in each arm of the interferometer, the PDI divides the input beam into two orthogonal linear polarization components, recombines them for interference at the beamsplitter, and directs the output beam at 90° to the direction of the input beam. Light exiting the interferometer is manipulated entirely with lenses, to avoid polarization distortions that are inherent to the reflecting surfaces of the mirrors. Details of the instrumental design for this mid-infrared PDI are presented. The performance of the PDI is evaluated by measuring the circular dichroism of α-pinene and camphor and the linear dichroism of oriented polypropylene and polystyrene. These measurements establish the utility of the PDI to measure transmission, circular dichroism, and linear dichroism spectra simultaneously without need for any additional components. The dichroic multiplex advantage (ability to measure dichroism in the entire mid-infrared region from a single measurement) and throughput advantage are demonstrated.
Surface-Enhanced Raman Spectroscopy as a Detection Method in Gas Chromatography
Authors: Roth E. , Kiefer W.
Published: May 2005

The use of surface-enhanced Raman scattering (SERS) as a detection method in gas chromatography (GC) was investigated by two different approaches; GC eluates were trapped either in liquid silver sol or on solid thin-layer chromatography (TLC) plates, previously coated with silver colloidal solution. Subsequently, the trapped analytes were monitored by their SERS spectrum. Pyridine was successfully used as probe molecule for both interfaces. The extension of this static system for application in on-line detection of GC eluates is discussed.
Corrections to the Baseline Distortions in the OH-Stretch Region of Aqueous Solutions
Authors: Fischer Wolfgang B. , Eysel Hans H. , Nielsen Ole F. , Bertie John E.
Published: May 2005

The intensity gains or intensity losses of the OH-stretch vibrations and their changes of band shapes as observed in IR or Raman spectra of dilute aqueous solutions of carboxylic acids, amino acids, and amines were able to be simulated. The difference spectra of the type {sample solution} – {standard} x {empirical factor} displayed essentially flat baselines throughout the OH-stretch region of isotropic Raman scattering. Peaks of the solute spectra which had been hidden by the OH-stretch contour emerged from the background. At concentrations below 1 M, pure water was the standard. Distortions of the isotropic Raman spectra at higher solute concentrations (1 M to 4 M) could be mimicked by phosphoric acid or sulfuric acid solutions as standards. The influence of solutes on the reorientational motions of water molecules made baseline corrections of anisotropic Raman scattering and IR absorption of the more concentrated solutions difficult, if not impossible.
2-D Light Diffraction from CCD and Intensified Reticon Multichannel Detectors Causes Spectrometer Stray Light Problems
Authors: Bormett Richard W. , Asher Sanford A.
Published: May 2005

Intensified diode arrays and charge-coupled detectors (CCD) which are used as multichannel detectors for spectroscopy exhibit strong 2-D diffraction of light due to the micro-channel plate intensifier and the CCD surface microelectronic structures. The strong 2-D diffraction of light by the intensified diode arrays shows hexagonal symmetry due to the hexagonal packing of the hollow glass fibers of the micro-channel plate intensifier. The 2-D diffraction of light from the CCD detectors shows square symmetry due to the almost square symmetry of the individual surface microelectronic structures. Light incident on the detector surfaces is diffracted into numerous angles which depend upon the incident angle and the light wavelength. This diffracted light can be redispersed and/ or reflected and scattered by optical elements inside the spectrometer. This diffracted light can then contribute to spectrometer diffuse stray light or it can be directly reimaged onto the detector to cause spectral artifacts. Backthinned CCD detectors do not show 2-D light diffraction and thus avoid these 2-D diffraction stray light limitations.
Depth Profile Analysis of Keratin Fibers by FT-IR Photoacoustic Spectroscopy
Authors: Jurdana Lucia E. , Ghiggino Kenneth P. , Leaver Ian H. , Barraclough Colin G. , Cole-Clarke Peter
Published: May 2005

The depth profiling capability of Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS) has been used to distinguish spectroscopically between the surface layer (cuticle) and the interior (cortex) of intact keratin fibers. The thermal diffusion lengths of wool and hair fibers, calculated as a function of the wavenumber and optical scanning velocity of the interferometer, indicate a depth resolution of the order of a micrometer. Shifts in the amide I and II bands to lower wavenumbers were observed with increasing velocity of the interferometer, consistent with differences in protein structure between the bulk and surface regions of the fiber. On the basis of these spectral changes, the location of the cuticle/cortex interface below the fiber surface can be determined.
Quantitative Simultaneous Elemental Determinations in Alloys Using Laser-Induced Breakdown Spectroscopy (LIBS) in an Ultra-High Vacuum
Authors: Thiem T. L. , Salter R. H. , Gardner J. A. , Lee Y. I. , Sneddon J.
Published: May 2005

Laser-induced breakdown spectroscopy (LIBS) in an ultra-high vacuum is used in simultaneous quantitative elemental analysis of NIST transition metal alloy samples. A plasma is formed by focusing a Nd:YAG laser onto the sample's surface inside a vacuum chamber. UV-visible emission from excited species is monitored with the use of an optical multichannel analyzer (OMA). Linear calibration curves are shown for the elements (percent composition) Al (0.2–1.2%), Cu (0.021–0.49%), Fe (4.5–51.0%), Ni (30.8–80.3%), and Zn (6–12.8%) with the use of nonresonant lines. Detection limits (signal-to-noise = 3) vary with sample composition complexity from 0.0001% for Ni in a simple copper alloy (SRM 1111) to 0.16% for Al in a complex granular sample (SRM 349a). Absolute detection limits are estimated to be in the 20–200 μg/g range for the elements of interest. Simultaneous mass spectra were taken by sweeping the magnetic field of a mass spectrometer. Preliminary results showed the magnet could not be swept fast enough for multielement analysis. The use of a position-sensitive ion detection system is proposed.
Binding of 2-Acetylnaphthalene to Cyclodextrins Studied by Fluorescence Quenching
Authors: Fraiji Elie K. , Cregan Timothy R. , Werner T. C.
Published: May 2005

The molecule 2-acetylnaphthalene (2-AN) exhibits significant room-temperature fluorescence only in strong hydrogen-bonding solvents, such as water and fluorinated alcohols. As a consequence, the fluorescence of 2-AN is strongly quenched when it binds in the relatively nonpolar cavity of cyclodextrins (CDs). Fluorescence lifetime data confirm that the quenching is static rather than dynamic, and thus the slope of the Stern-Volmer quenching plot (F°/F vs . [CD]) is equal to K, the binding constant. We have used these plots to measure K for 1:1 complexes formed between 2-AN and several CDs, including unsubstituted α;-, β-, and γ-CD and a dimethyl substituted β-CD. In addition, we have determined Δ H° and Δ S° of binding from the temperature dependence of these plots. The room-temperature binding constants vary over a 50-fold range for the 2-AN:CD complexes studied herein, and the variability stems primarily from the Δ S° term. We report here the results of this work and also show evidence for observations other than 1:1 complexes, including emission from the excimer of 2-AN in the presence of γ-CD.
Measuring Infrared Absorption in the Visible: Sensitive Determinations of Chemical and Isotopic Purity of Solvents by the Thermal Lens Effect
Authors: Tran Chieu D. , Grishko Victor I.
Published: May 2005

A new technique has been developed in which the absorption in the infrared region is measured in the visible. This was accomplished by use of the visible (probe) laser to monitor the thermal lens effect that was induced in a sample as a consequence of its absorption of the radiation in the infrared. The sensitivity of the technique is much higher than that of conventional transmission measurements because, in addition to its inherent ultrasensitivity, the infrared absorption is measured in the visible region, which has relatively less noise, and is detected by a phase-lock detecting method. With the use of the partial least-squares method to analyze the data, this technique can be used for the nondestructive, noninvasive, and sensitive determination of the chemical and isotopic purity of samples. Specifically, it is capable of measuring water in D2O and in tetrahydrofuran at levels as low as 3.75 × 10−4 and 1.20 × 10−4% (w/w), respectively.
Characteristics of Backpropagation Neural Networks Employed in the Identification of Neurotransmitter Raman Spectra
Authors: Schulze H. Georg , Blades Michael W. , Bree Alan V. , Gorzalka Boris B. , Greek L. Shane , Turner Robin F. B.
Published: May 2005

We have shown that neural networks are capable of accurately identifying the Raman spectra of aqueous solutions of small-molecule neurotransmitters. It was found that the networks performed optimally when the ratio of the number of hidden nodes to the number of input nodes was 0.16, that network accuracy increased with the number of input layer nodes, and that input features influenced the abilities of networks to discriminate or generalize between spectra. Furthermore, networks employing sine transfer functions for their hidden layers trained faster and were better at discriminating between closely related spectra, but they were less tolerant of spectral distortions than the networks using sigmoid transfer functions. The latter type of network produced superior results where generalization between spectra was required.
Spectral Observation of Defects in Space Using Polymer Chain Irradiated by Oxygen Ion Beam
Authors: Yokota Toshiaki , Sasaki Susumu , Kawashima Nobuki , Ota Masahiro , Usui Motofumi
Published: May 2005

We discuss some effects of oxygen ions on a polymer, on the basis of spectroscopic data analysis related to the study of the effect of the space medium in the lower earth orbit (LEO). Oxygen and UV light have an influence upon the surface of spacecraft in LEO. The light transmittance of polymers decreases with time during oxygen ion beam irradiation. The signals of CO2and C=O in the ATR spectra indicate that the surface of the polymer is oxidized and the chain of the polyimide partially cut. When the oxygen ion beam hits the aluminum coated on the polymer, the mass loss of aluminum can be clearly detected by measuring the change of the transmittance.
Experimental Studies in EDXRF on a New Linear Relationship for Fluorescence
Authors: Yap C. T. , Hua Younan
Published: May 2005

An experiment was carried out to verify a previously described linear relationship between ln(fluorescent intensity ratio of analyte to pure analyte/concentration of analyte) and ln(fluorescent energy) or, mathematically, ln( Ii/ciIi0 = a ln( Ei) + b. The best fit to our experimental data for elements from manganese to molybdenum for porcelain matrix is given by ln( Ii/ciIi0) = 2.401 ln( Ei) – 8.701 with a value of the gradient in agreement with the theoretical prediction.
Characterization of a Radio-Frequency Glow Discharge/Time-of-Flight Mass Spectrometer
Authors: Myers D. P. , Heintz M. J. , Mahoney P. P. , Li G. , Hieftje G. M.
Published: May 2005

A radio-frequency glow discharge/time-of-flight mass spectrometer (RFGD-TOFMS) has been developed by simple modification of the interface to an ICP-TOFMS. The work described here evaluates the interface and operating conditions of the RFGD-TOFMS. The ion optics which focus ions toward the entrance of the TOFMS are the same as those used in the original ICP-TOFMS instrument. By means of pin-shaped brass samples of varied lengths, the sample-skimmer distance in the RFGD-TOFMS has been optimized at 4 mm. The discharge pressure and power have been found to be optimal at 50–60 W and 0.3 Torr, respectively. The application of small negative potentials to the skimmer cone (extraction orifice) was found to improve signals marginally. However, higher negative potentials reduced both signal levels and resolving power. The skimmer potential also affects the final kinetic energy of the ions before their extraction into the TOFMS. At 0.3 Torr all ions extracted for mass analysis have approximately the same kinetic energy, which can be estimated in the orthogonal TOFMS. Detection limits for several standard samples are at the single-ppm level, which is not unexpected; with the same ion-optical system, the current ICP-TOFMS also produces detection limits that are 2–3 orders of magnitude worse than those of many commercial instruments.
Use of Rough Sets and Spectral Data for Building Predictive Models of Reaction Rate Constants
Authors: Collette Timothy W. , Szladow Adam J.
Published: May 2005

A model for predicting the log of the rate constants for alkaline hydrolysis of organic esters has been developed with the use of gas-phase mid-infrared library spectra and a rule-building software system based on the mathematical theory of rough sets. A diverse set of 41 esters was used as training compounds. The model is an advance in the development of a generalized system for predicting environmentally important reactivity parameters based on spectroscopic data. By comparison to a previously developed model using the same training set with multiple linear regression (MLR), the rough-sets model provided better predictive power, was more widely applicable, and required less spectral data manipulation. [For the previous MLR model, a standard error of prediction (SEP) of 0.59 was calculated for 88% of the training set data under leave-one-out cross-validation. In the present study using rough sets, an SEP of 0.52 was calculated for 95% of the data set.] More importantly, analysis of the decision rules generated by rough-sets analysis can lead to a better understanding of both the reaction process under study and important trends in the spectral data, as well as underlying relationships between the two.
Chevron-Type Dielectric Filter Set for Efficient Narrow-Band Laser Line Rejection in Raman Microspectrometers
Authors: Puppels Gerwin J. , de Grauw Cees G. , Plate Maurice B. J. te , Greve Jan
Published: May 2005

A chevron-type dielectric bandpass filter set is described which combines laser line rejection by a factor >108 with a high throughput of Raman scattered light (70%). The rejection bandwidth is 60 cm−1 full width at half-maximum. Stokes and anti-Stokes Raman spectra can be recorded simultaneously from approximately 20 cm−1 from the laser line. The filter set, moreover, takes care of efficient coupling of microscope and spectrometer, replacing an otherwise necessary beamsplitter.
On-Line Trace Enrichment and Determination of Uranium in Waters by Flow Injection Inductively Coupled Plasma Mass Spectrometry
Authors: Dadfarnia Shayessteh , McLeod Cameron W.
Published: May 2005

A flow injection system incorporating a microcolumn of activated alumina was combined with inductively coupled plasma mass spectrometry for on-line trace enrichment and determination of uranium in surface waters and sea water. Deposition of uranium was effected with the use of a basic alumina microcolumn, and injection of nitric acid (250 μL, 2M) served to elute retained species to the ICP. A sample volume of 14 mL resulted in a preconcentration factor of 40, and precision at the 50-ng 1−1 level was 4.5% (RSD). The procedure was applied to mineral waters, river water, and sea water, and accuracy was assessed through either analysis of certified reference waters or recovery experiments.
Evaluation of Calibration Methods for Zeeman Graphite Furnace Atomic Absorption Spectrometry Using Computer Modeling
Authors: Harnly James M.
Published: May 2005

Computer modeling was used to compare calibration curves and relative concentration errors for normal, linearized, and three-field Zeeman GF-AAS. The model assumed that either photon shot noise or the combination of photon shot and analyte fluctuation noise were limiting and that the sole source of nonlinearity was stray light. For absorbance, the calibration range and the relative concentration error for all three methods are almost identical. The difference is a reduced-sensitivity curve for three-field Zeeman, which offers a relative concentration error advantage in the concentration region where the most sensitive curve rolls over. For integrated absorbance, the sum of absorbances over the analytical peak, linearized Zeeman provides a significant relative concentration error advantage over the other methods at the high concentration end of the calibration curve. The calibration range is effectively extended by at least 1.5 orders of magnitude. This advantage arises from integration of absorbances which have a linear relationship to concentration. At high concentrations, absorbances computed for normal and three-field Zeeman are nonlinear with respect to concentration. Three-field Zeeman offers no advantage over normal Zeeman for integrated absorbance.
Raman and Fluorescence Spectra of Single Optically Trapped Microdroplets in Emulsions
Authors: Lankers M. , Popp J. , Kiefer W.
Published: May 2005

By means of an optical trapping technique we have been able to trap single microdroplets in emulsions and to observe their Raman and/or fluorescence spectra. In the fluorescence spectra we could observe additional morphology-dependent electromagnetic resonances, from which the radius of the sphere can be determined.
Design and Performance Characteristics of a Near-Infrared Scanning Multichannel Raman Spectrometer
Authors: Engert C. , Deckert V. , Kiefer W. , Umapathy S. , Hamaguchi H.
Published: May 2005

This paper provides comprehensive evidence for the performance of a highly sensitive NIR Raman spectrometer that is based on a single monochromator, a holographic edge filter, and a germanium photodiode array and that employs the scanning multichannel technique. In terms of signal-to-noise ratio, resolution, band intensities, and band shape accuracy, the spectra presented are the best reported so far with the use of a multichannel NIR Raman spectrometer. We believe that the design proposed here can yield data at least as good as FT-Raman data, for any given sample.
Noise Characterization of the Microwave Plasma Torch (MPT) Source
Authors: Madrid Yolanda , Borer Matthew W. , Zhu Chu , Jin Qinhan , Hieftje Gary M.
Published: May 2005

Noise characteristics of emission signals from the Ar microwave plasma torch (MPT) discharge have been analyzed. Noise spectra are reported with the use of a nebulizer sample introduction system for desolvated and undesolvated aerosols, for varying analyte concentrations, and for background emission from argon and water vapor. The analytical system appears to be flicker-noise limited at frequencies below about 1 Hz. White noise was found to be dominant below 100 Hz, but discrete noise peaks were detected in the frequency region extending to 300 Hz. The noise frequency characteristics are independent of the plasma viewing position, analyte concentration, and sample introduction method but strongly dependent on the argon carrier flow rate and on the introduction of water vapor. The discrete-frequency peaks presumably have a fluid-dynamics origin, caused by flow fluctuations as argon exits the top of the torch. Noise from the measurement system and from external sources was not significant compared with the noise level observed from the plasma.
Heuristic and Statistical Algorithms for Automated Emission Spectral Background Intensity Estimation
Authors: Salit M. L. , Collins J. B. , Yates D. A.
Published: May 2005

Two algorithms for the complete automation of background estimation in ICP emission spectroscopy are presented and evaluated. One of these algorithms is based on heuristic spectral interpretation, while the other is based on statistical spectral interpretation. These algorithms both address the weaknesses of the conventionally employed approaches of blank subtraction in calibration and background estimation through interpolation from analyst-selected wavelengths adjacent to the analyte peak. In a rigorous evaluation with synthetic spectra, these algorithms are characterized for performance in terms of accuracy, precision, and robustness. As a demonstration of the algorithms' performance with experimentally measured spectra, a determination of uranium in the presence of a calcium background interference is performed. These algorithms require no analyst interaction for their operation, and they estimate the background for every spectrum measured.
Determination of the Fluorescence Lifetime and Oxygen Quenching Rate of Vapor-Phase Fluoranthene at High Oxygen Pressures
Authors: Haug Michael , Schulpin Hans-Joachim
Published: May 2005

The fluorescence lifetime and oxygen quenching rate for vapor-phase fluoranthene are reported for oxygen pressures up to 5.2 bar and temperatures up to 553 K. The unquenched lifetime is found to be 27 ns at an excitation wavelength of 308 nm. Furthermore, the emission spectrum is shown to be dependent on the oxygen pressure.
Interpretation of Reflection and Transmission Spectra for Thin Films: Reflection
Authors: Yamamoto Kiyoshi , Ishida Hatsuo
Published: May 2005

The optical behavior of a thin film (i.e., peak positions and intensities of infrared spectra) has been discussed for reflection under a thin-film approximation. The reflection spectra of anisotropic and isotropic thin films on various substrates (transparent, dielectric and absorbing, and semi-metal) have been simulated at various angles of incidence in the infrared region for external and internal reflection. For spectral simulation, the matrix method has been used in conjunction with noise-free complex refractive indices based on dispersion theory. The peak positions in the simulated spectra have been compared with transverse optic and longitudinal optic frequencies based on macroscopic theory. The simulated peak intensities for the films have been compared with the prediction based on the thin-film approximation. The optical behavior of reflection spectra has also been examined in detail for a thin film on water or highly oriented pyrolytic graphite.
On-Line Radioisotope XRF Analysis of Copper, Arsenic, and Sulfur in Copper Electrolyte Purification Solutions
Authors: Davidson Robert A. , Walker Edward B. , Barrow Craig R. , Davidson Charles F.
Published: May 2005

The U.S. Bureau of Mines (USBM) and Weber State University (WSU) have developed an on-line analysis system for copper electrolytic solutions in a laboratory-scale decopperization electrolytic cell using a portable energy-dispersive X-ray fluorescence (XRF) unit. The portable XRF unit utilizes Fe-55 and Cm-244 radioactive isotope sources for sample analysis. Copper, sulfur, and arsenic were successfully analyzed directly in electrolytic purification solutions without any dilution or sample alteration. Interelement deconvolution was conducted to compensate for interferences resulting from matrix absorption of copper fluorescence by sulfur. The ubiquitous presence of sulfur in copper refining operations necessitates sulfur correction in the analysis of copper by XRF. A unique flow-through sampling cell was engineered and constructed for the portable XRF unit which allowed real-time analysis of a continuously pumped sample stream from the electrolytic cell.