bluuebunny/crossref_metadata_2025 huggingface dataset:
Hadamard Transform Photoacoustic Spectrometry and Depth Profiling
Authors: Wright S. L. , Hammaker R. M. , Fateley W. G.
Published: June 2005

The Hadamard transform technique has been extended to include photoacoustic detection. The feasibility of Hadamard transform photoacoustic spectrometry in the visible spectral region has been demonstrated. Depth profiling has been illustrated in a layered sample consisting of a thin (20 μm) surface layer of neodymium oxide dispersed in a polystyrene matrix on a thick (2.5 mm) interior layer of holmium oxide dispersed in a polystyrene matrix. Depth profiling may be accomplished by varying the modulation frequency or by phase-sensitive detection at the appropriate modulation frequency.
Direct Determination of Trace Elements in Graphite Matrices Using Modulated Glow Discharge Atomic Absorption Spectrometry
Authors: Pan Changkang , King Fred L.
Published: June 2005

The trace element concentrations in high-purity graphites were determined by atomic absorption spectrometry (AAS) with the use of a modulated glow discharge atomizer. Glow discharge power was modulated at SO Hz to enhance sensitivity and to permit time-resolved atomic absorption measurements. The influence of discharge operating parameters including current, pressure, and plasma sampling on the analytical performance of this technique was investigated. This analytical technique was evaluated in terms of stability, sensitivity, reproducibility, and accuracy. The method of standard additions was used to determine the impurity levels of the standard graphite matrix. Linear analytical calibration curves were constructed for four elements of interest in samples of nuclear-grade graphite. Detection limits for these elements were calculated to be in the tens of parts-per-billion range for graphite matrices.
Spectroscopic Studies of the Interaction of Tert-Butylamine and n-Propylamine with the β-Cyclodextrin: Pyrene Complex
Authors: Will A. Yvette , De La Peña Arsenio Muñoz , Ndou Thilivhali T. , Warner Isiah M.
Published: June 2005

The influence of amines on the aqueous beta-cyclodextrin ( β-CD): pyrene complex with the use of steady-state fluorescence measurements is examined. A 2:1 β-CD:pyrene complex is reported in the presence of either tert-butylamine (TBA) or n-propylamine (PA). At low amine concentrations, the role of the amine is to shield pyrene from the bulk aqueous phase. However, at higher TBA concentrations, there exists a competitive equilibrium between the amine and pyrene for the β-CD cavity. The formation constants for the various complexes in the presence of either amine were estimated to be of comparable order of magnitude.
Effect of Addition of Hydrogen to the Argon Sheath of a Unidirectional, High-Voltage Spark
Authors: Cappel Jennifer B. , Scheeline Alexander , Goldberg Joel M.
Published: June 2005

Changes in the spectrum of copper alloys excited with a unidirectional spark discharge in argon are noted when hydrogen is added to the system. Systematic enhancement in erosion of copper, but not of copper in brass or in Muntz metal, is observed. Argon spectra are also perturbed, with some cascades originating near the Ar I ionization limit enhanced while other, nearly isoenergetic, cascades terminating in the Ar I metastable levels are suppressed. Ar II emission is also enhanced in the presence of H2. Both electrode surface chemistry and plasma chemistry are affected by the hydrogen addition.
Nondestructive Characterizations of Polyethylene/Nylon Laminates by Near-Infrared Spectroscopy
Authors: Miller Charles E. , Svendsen Svend A. , Næ Tormod
Published: June 2005

The use of near-infrared (NIR) spectroscopy for the rapid and nondestructive analysis of food packaging laminates containing polyethylene (PE), polyamide-6 (PA-6), and ethylene vinyl alcohol (EVOH) layers is demonstrated. The method of Pathlength Correction with Chemical Modeling (PLC-MC) is used to estimate the total laminate thickness, and Principal Component Regression (PCR), is used to estimate the thickness percentages of PE and EVOH in the laminates, from NIR reflective-transmission spectra in the region 1500–2500 nm. Results indicate that the NIR method can be used to determine the total laminate thickness within 2–4 μm, the PE layer thickness percentage within 0.7–1.8%, and the EVOH layer thickness within 0.7–0.8 μm. In addition, detailed observation of the PCR models indicates that the NIR method is also sensitive to the absorbed water content, the morphology of the polymers, and perhaps the amount of polyurethane adhesive in the laminates. The usefulness of PCR outlier detection, for identification and characterization of strange samples, and principal component rotation, for improvement of PCR model interpretability, is also demonstrated.
Performance of a Holographic Supernotch Filter
Authors: Schoen Christian L. , Sharma Shiv K. , Helsley Charles E. , Owen Harry
Published: June 2005

Results are presented of a comparative evaluation of a holographic supernotch filter (HSNF) and a holographic notch filter (HNF) as a Rayleigh line rejection filter for Raman spectroscopy. The filter permits acquisition of both Stokes and anti-Stokes spectra down to ±200 cm−1 shift from excitation simultaneously, without filter angle adjustment. With slight angle adjustment, spectra can be recorded as close as 41 cm−1 from the excitation line. Performance of the HSNF is evaluated by measuring the low-frequency Raman spectra of Tb2(MoO4)3, water, and naphthalene.
Reflectance FT-IR Microspectroscopy of Fossil Algae Contained in Organic-Rich Shales
Authors: Lin Rui , Ritz G. Patrick
Published: June 2005

A microscope sampling accessory interfaced to a Fourier transform infrared (FT-IR) spectrometer has been employed to characterize the remains of individual microscopic fossil algae and algal colonies contained in organic-rich shales. The microspectrometer is able to measure reflectance IR spectra of samples with cross-sectional areas as small as 20 × 20 microns. The fossil algae studied include the colonial green alga Botryococcus braunii, the unicellular green alga Tasmanites, and an unidentified filamentous alga. It was found that IR spectra of the fossil algae, in common, contain intense aliphatic C-H stretching bands in the 2900-cm−1 region relative to the C=C stretching band at 1600 cm−1. The carboxylic acid C=O stretching band at 1710 cm−1 is moderately intense. The relative intensities of these bands vary among the three different fossil algae. Maximum-likelihood spectral restoration and subsequent curve fitting of the stretching vibrations of the aliphatic C-H bands provide greater insight into the aliphatic structures of fossil algae. The CH2/CH3 intensity ratio can be calculated and used to assess the relative average aliphatic chain length and the degree of branching.
Piece-Wise Multiplicative Scatter Correction Applied to Near-Infrared Diffuse Transmittance Data from Meat Products
Authors: Isaksson Tomas , Kowalski Bruce
Published: June 2005

This paper presents a nonlinear scatter correction method, called piece-wise multiplicative scatter correction (PMSC), that is a further development of the multiplicative scatter correction (MSC) method. Near-infrared diffuse transmittance (NIT) data from meat and meat product samples were used to test the predictive performances of the PMSC and the MSC methods. With the use of PMSC, the prediction errors, expressed as the root mean square error of prediction (RMSEP), were improved by up to 36% for protein, up to 55% for fat, and up to 37% for water, in comparison to uncorrected data. The corresponding improvements by using PMSC compared to MSC were up to 22%, 24%, and 31% for protein, fat, and water, respectively.
Detailed Investigation of 2-(p-Toluidinyl)naphthalene-6-Sulfonate (TNS) Binding to Bovine Serum Albumin (BSA) by Steady-State and Time-Resolved Fluorescence Spectroscopy
Authors: Wang Run , Bright Frank V.
Published: June 2005

The complexation of 2-( p-toluidinyl)naphthalene-6-sulfonate (TNS) to the hydrophobic sites of bovine serum albumin (BSA) and the effects of quencher and denaturant were studied by steady-state and dynamic fluorescence spectroscopy. Experimental results show that there are multiple sites in BSA which bind TNS. Fluorescence decay kinetics of BSA-bound TNS were recovered by multifrequency phase-modulation measurements and analyzed by a global analysis scheme. For all the cases, a distributed lifetime model best fits the experimental data—a result of the dynamical nature of BSA/TNS association and of the multiple binding sites in BSA. In addition to the distributed species, a short, discrete component exists, arising from unbound or free TNS. The recovered Stern-Volmer quenching constant for acrylamide from the lifetime data is consistent with the steady-state results. The denaturant, urea, decreases significantly the pre-exponential factor for protein-bound TNS, but affects the center lifetime and the distribution width only at high urea concentrations. The perturbation of probe molecules on the three-dimensional conformation of proteins and the effects of complex (TNS-BSA) age were also studied.
Analysis of Additives in Polyethylene with Desorption Chemical Ionization/Tandem Mass Spectrometry
Authors: Chen S. W. , Her G. R.
Published: June 2005

Desorption chemical ionization with ammonia as the reagent gas in combination with tandem mass spectrometry is described for the analysis of additives in polyethylene. The additives were extracted with toluene and then analyzed directly by desorption chemical ionization and tandem mass spectrometry. With ammonia as the reagent gas, mass spectra of additives were found to contain intense pseudomolecular ions with very little fragmentation. In addition, low-molecular-weight polyethylene molecules extracted with the additives were barely detectable, and thus there was less likelihood of interference. Collision-induced dissociation of the pseudomolecular ions provided great confidence in the assignment of additives.
Infrared Study of Alkyl Isothiocyanates in Carbon Tetrachloride and/or Chloroform Solutions
Authors: Nyquist R. A. , Puehl C. W.
Published: June 2005

The νasym.NCS frequencies for alkyl isothiocyanates occur at higher frequency in CHCl3 or CDCl3 solution than in CCl4 solution. The νasym.NCS mode increases in frequency as the mole % CHCl3/CCl4 increases. The νasym.NCS mode for butyl isothiocyanate occurs at an exceptionally high frequency, and this result is explained in terms of the formation of a pseudo-six-membered intramolecularly hydrogen-bonded ring. The νasym.NCS modes for the alkyl isothiocyanates are corrected for Fermi resonance (FR), with the exception of the propyl analog. The propyl analog appears to have three other modes in FR with νasym.NCS, and an equation has not yet been developed to correct for FR in this case. The unperturbed νasym.NCS frequencies for alkyl isothiocyanates decrease in the alkyl order: methyl, butyl, ethyl, and tert-butyl. The decrease in frequency of νasym.NCS in the order methyl, ethyl, and tert-butyl isothiocyanate is attributed to weakening of the N=C=S bonds due to σ electron donation of each alkyl group. In the case of the butyl analog, the σ electron donation is partially compensated for by the postulated existence of a pseudo-six-membered hydrogen-bonded ring.
Fuel Equivalence Ratio Imaging for Methane Jets
Authors: Ni T. Q. , Melton L. A.
Published: June 2005

A 2-D fuel/oxygen equivalence ratio imaging system has been developed. The technique exploits the efficient quenching of the fluorescence of organic molecules by molecular oxygen in order to determine the fuel and oxygen partial pressures simultaneously. Following pulsed planar laser excitation of fluoranthene—a specially selected fluorescent dopant—two images of the fluorescence were recorded, with the second image being delayed by several nanoseconds. Use of a rapid lifetime determination algorithm yielded first a fluorescence lifetime image, and subsequently, with the assumption of Stern-Volmer quenching, an intensity image corrected for quenching. Images of the air pressure, fuel pressure, and the equivalence ratio were obtained. The technique, which uses dual gated intensifiers coupled to a sensitive CCD camera, requires only two integrated fluorescence intensities to calculate the fluorescence lifetime accurately. In the current work, images of the turbulence-induced mixing of a methane jet into quiescent air are displayed. Images can also be obtained in flames, but the analysis of the data is uncertain because the fluorescence lifetime of fluoranthene is temperature dependent.
Comparison between Covalent Attachment and Physisorption of 2-(p-Toluidinyl)naphthalene-6-Sulfonate (TNS) to Proteins
Authors: Wang Run , Bright Frank V.
Published: June 2005

Previously, we studied the physisorption of 2-( p-toluidinyl)naphthalene-6-sulfonate (TNS) to the hydrophobic sites or cavities of bovine serum albumin (BSA) and determined the effects of acrylamide (quencher) and urea (denaturant) on the complex using steady-state and dynamic fluorescence spectroscopy. In this paper, we extend this work to bovine β-lactoglobulin (β-Lg) and immunoglobulin G (IgG), and compare the complexes to the covalently attached TNS. These results show that the hydrophobic sites of different proteins can be probed by TNS with the use of steady-state and time-resolved fluorescence spectroscopy. The TNS binding site in β-Lg is the most hydrophobic in comparison to BSA and IgG. The excited-state decay kinetics for the TNS/protein complexes is best described by a distribution (Gaussian) plus a discrete decay model. TNS/protein adducts (covalent attachment of TNS), whereby the TNS sulfonate is converted to a sulfonamido group, strongly affects the probe photophysics. For example, a red shift is observed in the emission and excitation spectra due to covalent attachment. Acrylamide quenches the fluorescence of TNS/protein complexes, but does not quench 2-( p-toluidinyl)naphthalene-6-(N-propyl)-sulfonamide(TNS-PA) or the covalent TNS/protein adducts. Furthermore, the fluorescence decay kinetics of the covalent TNS/protein adducts is always best described by a double discrete decay model. In all cases studied, added urea does not affect the recovered lifetime values but does decrease the pre-exponential factor for the longer lifetime component. This result suggests a single-step urea denaturation mechanism involving two protein states—folded (native) and unfolded (denatured).
Waveguide CARS Spectroscopy: A New Method for Background Suppression, Using Dielectric Layers as a Model
Authors: De Boeij Wim P. , Kanger Hans S. , Lucassen Gerald W. , Otto Cees , Greve Jan
Published: June 2005

Waveguide Coherent Anti-Stokes Raman Spectroscopy (CARS) can be used to measure Raman-active vibrations in thin-layer dielectric waveguides. In waveguide CARS experiments, background-free spectra can be obtained when asymmetric mode combinations are applied. The degree of suppression depends on the waveguide parameters and the wavelengths used. A new method using scanning pump and Stokes beams in waveguide CARS experiments is presented, which allows the possibility of maintaining full background suppression conditions over large spectral intervals. A small controlled change in the tuning conditions results in a heterodyning of the signal with a small amount of background, thereby enhancing the small resonant signals. Several simulations for dielectric waveguides are given.
Characterization of a Fiber-Optic Evanescent Wave Absorbance Sensor for Nonpolar Organic Compounds
Authors: Conzen J.-P. , Bürck J. , Ache H.-J.
Published: June 2005

A fiber-optic evanescent field absorbance sensor (EFAS) is described, for which the sensing element consists of a commercially available silicone-clad quartz glass fiber, coiled on a Teflon® support. The polydimethylsiloxane cladding fulfills various functions. It protects the brittle fiber core against fracture induced by mechanical stress. Moreover, as a lower-refractive-index medium, it causes total reflection in the fiber and acts as a hydrophobic membrane that enriches nonpolar organic compounds, whereas polar species like water cannot penetrate. Coupled to an NIR spectrometer, the sensor has a potential for remote in situ measurements of organic pollutants in drainage waters originating from contaminated areas. In this study aqueous solutions of typical drainage-water contaminants like dichloromethane, chloroform, and trichloroethylene were measured in the 900–2100 nm spectral range. The influence of refractive index, fiber length and diameter, bend radius, polysiloxane swelling, and ambient temperature on the sensor signal is described and qualitatively compared with theoretical predictions. Kinetics measurements are presented, which allow explanation of the diffusion mechanism of CHC13 enrichment in the polysiloxane cladding. The data show that the rate-determining step for penetration of this substance into the sensor polymer layer can be described mainly by film diffusion through the aqueous boundary layer. In most cases no remarkable influence of gel diffusion in the polysiloxane membrane was observed.
Effects of Sample Dilution and Particle Size/Morphology on Diffuse Reflection Spectra of Carbohydrate Systems in the Near- and Mid-Infrared. Part I: Single Analytes
Authors: Olinger Jill M. , Griffiths Peter R.
Published: June 2005

The mid- and near-infrared diffuse reflection spectra of three carbohydrates—microcrystalline cellulose, wheat starch, and sucrose—are examined to determine whether dilution is necessary in either spectral region in order to avoid the effects of specular reflection. As expected, it was found that dilution was not necessary to obtain valid diffuse reflection spectra of samples in the near-infrared, but that dilution was necessary for measuring mid-infrared diffuse reflection spectra free of the effects of specular reflection. The effects of particle size and sample morphology were investigated for sucrose crystals up to 2 mm in dimension. Depending upon the particle size and orientation, the effects of specular reflection can be observed in both near- and mid-infrared diffuse reflection spectra of sucrose. Surface roughness can allow a diffuse reflection component to be measured in the spectra of very large particles where a specular reflection mechanism would typically be expected to predominate.
Feasibility of On-Line Monitoring of the BTU Content of Natural Gas with a Near-Infrared Fiber Optic System
Authors: Brown Chris W. , Lo Su-Chin
Published: June 2005

Optical-fiber measurements coupled with near-infrared spectra in the range of 5500 to 10,000 cm−1 are used to determine the optimum spectral region for remotely monitoring the energy content of natural gas at above ambient pressures. The system was configured with a Fourier transform near-infrared spectrometer and a fused-silica fiber bundle. The total energy values at a pressure of 100 psi were determined by the partial least-squares (PLS) calibration algorithm. The precision and accuracy for predicting the BTU content of an industry standard gas sample were less than 0.4% in the lower-frequency region of 5700 to 6400 cm−1.
Analysis of Selected Chemical Groups by Liquid Chromatography/Mass Spectrometry
Authors: Krost Kenneth J.
Published: June 2005

The use of a moving-belt liquid chromatography/mass spectrometry interface for identifying selected members of various chemical classes has been investigated. Among the chemical groups examined with this system were benzidines, nitrosoamines, anilines, nitroaromatics, dinitroaromatics, hydrazines, amides, phenylenediamines, organophosphites, acrylates, pyridines, phthalates, nitrophenols, halogenated triazines, pesticides, halogenated pyridines, and alkyl tins. Selective ion monitoring was used for detection in all cases, in view of the lack of sensitivity in the full-scan mode. The lower limit of detection for the present technique is approximately 10 nanograms of compounds. Compounds of molecular weight exceeding 250 amu generally show a diminished response. Presumably, some lower-molecular-weight compounds within given groups exhibit similar behavior because of volatilization losses in the inlet.
Quantification of Silica in Mine Dusts Using Diffuse Reflectance Infrared Spectroscopy
Authors: Babu V. Suresh , Seehra Mohindar S.
Published: June 2005

Following up on the recent work by Pandurangi and Seehra, a new method for the quantification of silica in mine dust samples, with the use of diffuse reflectance spectroscopy (DRS) of the 1875-cm−1 band of silica, is proposed. The 1875-cm−1 band does not suffer interference from other minerals usually present in mine dusts, and a linear calibration curve of the integrated intensity of this band with silica concentration is obtained with concentration up to about 100 mg. This calibration is employed to determine silica concentration in six mine dust samples collected in a roof bolter box and one coal sample. These results are compared with the independent results obtained by x-ray diffraction (with CaF2 as the standard), and a good agreement is obtained in most cases.
Measuring the Concentration of Minor Species from the Modulation Dip of the Nonresonant Background of Broad-Band CARS Spectra
Authors: Hahn J. W. , Park S. N. , Lee E. S. , Rhee C. , Kang K. T. , Chung S. H. , Choi C. Y. , Huh Y. D.
Published: June 2005

A new technique for measuring the concentration of species from the modulation dip of the nonresonant background of broad-band CARS spectra has been proposed. To reduce the mode noise superimposed on the CARS spectra, we used a modeless laser generating amplified spontaneous emission as the Stokes beam of the broad-band CARS. The modulation dip induced by a minor species, CO in Ar, was numerically calculated and fitted as a function of CO concentration and temperature. We applied this technique in measuring CO concentration in a static cell and also the profile of CO concentration in a CH4/air premixed flame of a counterflow burner.
Ultraviolet Spectroscopic Determination of Five Lanthanide Elements without Prior Separation
Authors: Citron Irvin M. , Hanlon Patrick M. , Arthur Stephen
Published: June 2005

This investigation has resulted in an analytical method for the quantitative determination of total lanthanide concentration in aqueous solution by absorbance at 240 nm in the ultraviolet followed by quantitative determination of individual lanthanide ion concentrations by the use of concentration-responsive absorption peaks in the 190–235 nm region. The 240-nm peak is present and is proportional to concentration regardless of the ligand employed to complex the lanthanides (including H2O). The individual lanthanide/ligand peaks in the 190–235 nm region were selected on the basis of their separation from one another, their linearity of absorbance vs. concentration, and their statistical reliability based on replicate sample analyses. Lanthanides involved in this investigation were La+3, Nd+3, Eu+3, Ho+3, and Yb+3. Ligands ultimately selected for complexation were citrate for La+3, Nd+3, and Ho+3, and DTPA for Eu+3, Ho+3, and Yb+3. When large amounts of heavy metal ions were present, a modified method was developed with citrate as the only complexing ligand for all five lanthanides. The method here developed permits the analyses of lanthanide ions in aqueous solution without prior separation and involves the use of comparatively inexpensive instrumentation (UV absorption spectrophotometer).
Application of DRIFT Spectroscopy and Chemometrics for the Comparison of Cotton Fabrics
Authors: Gilbert Christina , Kokot Serge , Meyer Ulrich
Published: June 2005

Two sets of cotton fabrics—one consisting of different types of fabric and the other of a fabric sampled sequentially during its normal processing stages—were investigated by DRIFT spectroscopy. The band assignments were consistent with previous work but, in general, the spectra could not be differentiated on visual examination. However, they were successfully qualitatively and quantitatively distinguished with the use of chemometrics; a chemical basis for fabric clustering was also indicated. This approach is a significant improvement on previously reported work with KBr disk IR sampling.
Quantitative Analysis of Mixed Volatile Fluids by Raman Microprobe Spectroscopy: A Cautionary Note on Spectral Resolution and Peak Shape
Authors: Seitz Jeffery C. , Pasteris Jill D. , Morgan George B.
Published: June 2005

Raman analyses of fluid inclusions can yield quantitative information on composition (from peak areas and heights) and density (from peak position and width). In this study, we examine the effect of instrumental spectral resolution on the ratios of these spectral parameters, and the selection of appropriate integration limits for the determination of peak areas in the CO2-CH4-N2 system. Spectral resolution was varied from about 1 to 9 cm−1 by co-varying the widths of all spectrometer slits. Changes in resolution produced a modest effect on peak-area ratios and a significant effect on peak-height ratios. Measured peak-width ratios varied strongly as a function of the spectral resolution. In addition, we observed a moderate shift in the measured peak position of N2, which can be related to the asymmetry of the band. These results indicate that accurate analysis requires careful attention to the selection of quantification factors, especially if the selected values were derived from studies at different spectral resolutions. Another factor that can have a significant effect on the calculated compositions of CH4- and H2-bearing fluid mixtures is the band broadening that occurs with increasing pressure.
Effects of Sample Dilution and Particle Size/Morphology on Diffuse Reflection Spectra of Carbohydrate Systems in the Near- and Mid-Infrared. Part II: Durum Wheat
Authors: Olinger Jill M. , Griffiths Peter R.
Published: June 2005

It is shown that reduction of particle size for ground durum wheat does not cause a concomitant decrease in the amount of specular reflection observed in the mid-infrared spectrum of the neat sample. Specular reflection can be reduced, but not completely eliminated, by dilution of the wheat in a nonabsorbing matrix such as KCl. The lack of dependence of mid-infrared diffuse reflection spectra of neat ground durum wheat on particle size is explained by the morphology of the surface of each particle and the low effective depth of penetration of mid-infrared radiation into particles of very high absorptivity. It is concluded that mid-infrared diffuse reflection spectra of wheats do not provide information characteristic of the overall composition of the wheat when the particle size exceeds a few micrometers, but that near-infrared diffuse reflection spectra will provide representative analytical data even when the particle size is large.
Time-Resolved Polarization of Luminescence Spectroscopy: An Accurate and Versatile Digital Instrument for the Sub-μs Time Domain
Authors: Rexwinkel R. B. , Schakel P. , Meskers S. C. J. , Dekkers H. P. J. M.
Published: June 2005

An instrument is described for the measurement of circular and linear polarizations of the luminescence with a time resolution up to 50 ns. The spectrometer, which makes use of a 50-kHz photoelastic modulator and a differential photon-counting technique, is accurate and absolute and is capable of detecting small degrees of polarization. Making use of excitation light pulses which lie randomly in the modulator's duty cycle, the instrument can be readily interfaced with a variety of externally triggered or free running pulsed light sources.
Exciplex-Based Vapor/Liquid Visualization Systems Appropriate for Automotive Gasolines
Authors: Melton Lynn A.
Published: June 2005

This paper reports the development of exciplex-based vapor/liquid visualization systems based on exciplexes formed from tertiary amines and fluorine-substituted benzene and/or toluene. These systems are expected to be virtually coevaporative with solvents (fuels) boiling in the temperature range 70 to 110°C and thus are expected to track the vaporization of automotive gasoline effectively. A system consisting of 10% triethylamine/0.5% fluorobenzene/89.5% hexane should be coevaporative with a normal boiling point of 69°C. A system consisting of 10% n-propyldiethylamine/0.5% 4-fluorotoluene/89.5% isooctane should be coevaporative with a normal boiling point of approximately 100°C. Although the coevaporation of these systems is excellent, the exciplexes revert to varying extents to excited monomer at temperatures near 100°C. Thus there is considerable cross talk from the liquid into the vapor spectral region. The tertiary amines generally require excitation at wavelengths below 250 nm; the fluorobenzene or 4-fluorotoluene can be excited at 266 nm. Monomer emission peaks at 290 nm; exciplex emission peaks at 350 nm.
Applications of the Theory of Optical Spectroscopy to Numerical Simulations
Authors: Milosevic M. , Berets S. L.
Published: June 2005

A numerical simulation has been developed to extract the optical constants from experimental spectra. In particular, transmission, internal reflection, and external reflection spectra can be simulated for any incident angle, polarization, and sample thickness. The simulation is used here to determine the optical constants of two materials and to illustrate differences in spectral features that arise from variations in experimental conditions. Other potential applications of this method include determining film thicknesses from experimental data, selecting the best spectroscopic technique for a particular sample, and cross-referencing spectroscopic techniques.
Observing Crystallization Molecule-By-Molecule Using Exciton Transfer/Emission Spectroscopy
Authors: Graham Daniel J. , Labrake Dwayne L.
Published: June 2005

A method for observing crystallization molecule-by-molecule is presented. The method is based on the properties of exciton transfer and emission spectroscopy, as established by several research groups during the sixties. The discussion centers on benzophenone (BZP) crystallization, although the ideas can be adapted to other molecular systems. It is the purpose here to pose a timely, relatively inexpensive way to monitor crystallization on an Ångstrom scale.
A Miniaturized, No-Moving-Parts Raman Spectrometer
Authors: Lewis E. Neil , Treado Patrick J. , Levin Ira W.
Published: June 2005

A solid-state acousto-optic tunable filter (AOTF) is combined with krypton laser excitation (647 nm), holographic Raman filters, and photon-counting silicon avalanche photodiode (APD) detection to construct a miniaturized Raman spectrometer with no moving parts. The physically compact AOTF and the highly integrated APD provide a rugged, digitally controlled spectrometer of moderate spectral resolution and with a footprint comparable in size to a laboratory notebook. Instrument design details are considered and representative spectra are reported. Potential areas of application for this prototype Raman spectrometer are also discussed.
Classification of Condensed-Phase Infrared Spectra by Substructures Using Principal Components Analysis
Authors: Hasenoehrl Erik J. , Griffiths Peter R.
Published: June 2005

Expert system rules have been developed through the use of principal components analysis (PCA) for discriminating compounds containing large molecular substructures from their condensed-phase infrared spectra. With the use of this approach, the presence of substructures such as those of barbiturates, cocaines, and amphetamines can be recognized automatically. The classification rule can be generated from a PCA of a small training set of infrared spectra of compounds containing the substructure of interest. One important use of this type of expert system is the analysis of direct-deposition capillary gas and supercritical fluid chromatographic separations in which many peaks are eluted and analyzed by FT-IR spectrometry but only one or two contain the substructure of interest. Classification rules for substructures are easy to generate with little or no knowledge of characteristic group frequencies.
Fiber-Optic Time-Resolved Fluorescence Sensor for in Vitro Serotonin Determination
Authors: Mottin Stephane , Tran-Minh Canh , Laporte Pierre , Cespuglio Raymond , Jouvet Michel
Published: June 2005

At pH 7 and with the excitation at wavelengths above 315 nm, previously unreported fluorescence of 5-HT (5-hydroxytryptamine) is observed. Two fluorescence bands were observed for 5-HT; the first emits at around 390 nm with an associated lifetime near 1 ns, and the other (well known) emits at 340 nm with an associated lifetime of 2.7 ns. With both static and time-resolved fluorescences, the spectral and temporal effects of the excitation wavelength were studied between 285 and 340 nm. With these basic spectroscopic properties as a starting point, a fiber-optic chemical sensor (FOCS) was developed in order to measure 5-HT with a single-fiber configuration, nitrogen laser excitation, and fast digitizing techniques. Temporal effects including fluorescence of the optical fiber were studied and compared with measurements both directly in cuvette and through the fiber-optic sensor. Less than thirty seconds are required for each measurement. A detection limit of 5-HT is reached in the range of 5 μM. Our system, with an improved sensitivity, could therefore be a possible and convenient “tool” for in vivo determination of 5-HT.
Trading Wavelength for Absorbance Resolution: Predicting the Performance of Array Detection Systems
Authors: Brown Chris W.
Published: June 2005

Mid-infrared spectra of liquid mixtures measured at 4 cm−1 resolution and near-infrared spectra of synthetic natural gas samples measured at 2 cm−1 resolution were convoluted to determine the effect of low resolution on multicomponent analyses of these samples. The resolution of the liquid samples could be degraded to almost 100 cm−1 before significant effects on the quantitative results were observed. The minor components in the natural gas samples were sensitive to degrading the resolution; however, the major components, methane and ethane, and the BTU values were unaffected until the resolution was degraded to over 100 nm (∼600 cm−1 at 1225 nm). The convoluted spectra were also displayed across a simulated array detector to determine the effect of the number of pixels on quantitative analysis. Excellent results were obtained on the convoluted spectra of both the liquid and gas mixtures with 32 elements. The liquid samples could be analyzed with as few as 8 pixels.
Theory and Reduction of Artifacts in Incident, Scattered, and Dual Circular Polarization Forms of Raman Optical Activity
Authors: Che Diping , Nafie Laurence A.
Published: June 2005

A simplified Stokes-Mueller theory of the dominant artifacts encountered in the measurement of incident (ICP), scattered (SCP), and dual (DCP) circular polarization (CP) Raman optical activity (ROA) is presented for forward, right-angle and backward-scattering geometries. Sources of common artifacts in CP ROA measurements are identified, and examples of artifacts in spectra are presented. Procedures are given for the elimination or significant reduction of ROA artifacts.
Atmospheric-Pressure Argon Surface-Wave Plasma (SWP) as an Ion Source in Elemental Mass Spectrometry
Authors: Boudreau D. , Hubert J.
Published: June 2005

Results of the study of a high-power argon surface-wave plasma as an ion source for mass spectrometric elemental analysis of aqueous solutions are presented. The plasma is operated at power levels between 475 and 800 W and at gas flow rates between 4 and 6 L/min. The wet aerosol obtained by ultrasonic nebulization is directly carried into the plasma, without the use of a desolvation system. Effects on the mass spectrum of parameters such as sampling depth and applied power were studied. With this source, indicative detection limits for most of the studied elements were in the range of 0.5 to 5 ng/mL, and the dynamic range covered 4 to 5 orders of magnitude. Analytical figures of merit obtained with the surface-wave plasma are compared with those of an inductively coupled plasma with the use of the same mass spectrometer system.
Use of Halocarbon Oils as a Matrix for Transmission Spectroscopic Studies of Solid Inorganic Materials in the Near-Infrared and Visible Regions
Authors: Guyot-Sionnest N. S. , Maroni V. A.
Published: June 2005

Halocarbon oils are shown to be a useful matrix for transmission spectroscopic studies of solid inorganic materials in the near-infrared and visible regions. Absorption spectra of these oils are flat and featureless between 5000 and 32,000 cm−1. The halocarbon oils are inert to virtually all types of inorganic substances at room temperature. Light scattering appeared to be reduced for the more viscous of two halocarbon oils investigated. Examples of the application of the halocarbon oil mull technique are given for three inorganic substances: chromium(III) potassium sulfate dodecahydrate, nickel(II) hydroxide, and silicotungstic acid.
Interfacing a Fiber-Optic Probe to a Diode Array UV-Visible Spectrophotometer for Drug Dissolution Tests
Authors: Brown Chris W. , Lin Jie
Published: June 2005

A fiber-optic probe and an optical interface have been developed for drug dissolution testing with UV spectroscopy. A simple light cone was used to launch the light into the fiber; this increased the efficiency of light collection and reduced the dependence of the interface on the position of the source fiber. A principal component regression model was developed with the use of Fourier transformed spectra. The backgrounds and noise were reduced by the elimination of the first three terms and the use of the following 32 terms in the Fourier transforms. A commercial therapeutic drug, Sudafed Plus®, was tested, and the dissolution curves were very close to those obtained with a cuvette. The fiber-optic probe and the interface developed in this investigation can potentially be used in automated drug dissolution tests with spectroscopy.
Correlation of the Molecular Structure and Spectral Characteristics of Some Hydroxamic Acid Derivatives
Authors: Badei Mohamed M. Abdel , Moustafa Moustafa M. , Mohamed Talaat Y. , El-Shahat Mohamed F.
Published: June 2005

The electronic absorption spectra of some hydroxamic acid oxime derivatives and Schiff's base derivatives in polar (ethanol) and nonpolar (CCl4) solvents, as well as in some other organic solvents of different polarities, were investigated; the variation of absorbance with pH was utilized for the determination of pKa, and Δ G* values. The important bands in the IR spectra as well as the main signals of the NMR spectra are also discussed in relation to the molecular structure.
Magic Angle Lifetime Measurements in Evanescent Wave Fluorometry
Authors: Wirth Mary J.
Published: June 2005

For fluorescence lifetime measurements in isotropic solutions, it is well known that detection using an emission polarization of 54.7°, the so-called magic angle, eliminates contribution of molecular reorientation to the fluorescence decay function. For macroscopically oriented samples and evanescent wave excitation, the magic angle may not necessarily be the 54.7°. With the use of a typical optical scheme of evanescent wave excitation and detection along the surface normal, a mathematical expression is derived for the magic angle condition. The magic excitation angle is shown to be a function of the angle of incidence of the excitation beam and the refractive indices of the two media involved in total internal reflection. The magic angle relations are valid regardless of the orientational distribution of molecules along the surface normal. The magic angle relations apply to cases where the in-plane orientational distribution is isotropic.
Comparison of the Amide I/II Intensity Ratio of Solution and Solid-State Proteins Sampled by Transmission, Attenuated Total Reflectance, and Diffuse Reflectance Spectrometry
Authors: Ishida Kenneth P. , Griffiths Peter R.
Published: June 2005

The absolute and relative differences in amide I and amide II band intensities of albumin, β-lactoglobulin, and myoglobin as measured by attenuated total reflection infrared (ATR-IR) spectrometry, transmission of aqueous solutions, and KBr disks and diffuse reflectance (DR) spectrometry are compared. The amide I/II intensity ratios of the proteins sampled by ATR, DR, and transmission spectrometry of KBr disks were similar and were significantly different from the intensity ratios of the proteins in solution. The absolute amide II band intensity of dissolved proteins did not vary significantly with changes in pH. The difference in amide I/II intensity ratios between solution and adsorbed proteins was attributed to differences in secondary and possible tertiary structure. The thickness of each protein film was estimated with the use of the absorptivities calculated from the amide II band intensities of the KBr disk spectra. pH had a significant influence on the thickness of the adsorbed films. Differences in film thickness were attributed to a difference in the orientation of the protein molecules at the surface of the germanium internal reflection element.
Infrared Study of Solute/Solvent Interactions between Separate Chloroform Solutions of Alkanes, Cycloalkanes, Alkenes, Cycloalkenes, Cyclohexadienes, Benzene, and Carbon Tetrachloride
Authors: Nyquist R. A.
Published: June 2005

The intermolecular deuteron bonds formed between Cl3CD and ClCCl3, are stronger than between Cl3CD and ClCCl2D, since the Cl atoms of CCl4, are more basic than Cl atoms for CDCl3. The n-alkanes act as a diluent for CDCl3 molecules, and the strength of the intermolecular proton bond in (Cl3CD:ClCCl2D) n complexes increases as n becomes larger. Solvent density also plays an important role in solute/solvent interaction. Increased solvent density causes the CD:Cl or CD:π (of C=C group) intermolecular bond distance to decrease, causing the bond to be stronger. A repulsion exists between the intermolecular π electron system of benzene, 1,3-cyclohexadiene, or 1,4-cyclohexadiene and the chlorine atom δ electrons of CDCl3, and this repulsive effect is a factor in establishing the equilibrium intermolecular bond distance formed between the CD:π bonds of benzene (or cyclohexadienes) and the proton of CDCl3. These conclusions are based on the study of the vCD, vC=C, and v(C=C)2 frequencies vs. mole % CDCl3 (or CHCl3)/solvent system.
Determination of Carbon Content in Molten Steel Using Laser-Induced Breakdown Spectroscopy
Authors: Aragón C. , Aguilera J. A. , Campos J.
Published: June 2005

Laser-induced breakdown spectroscopy has been applied to the determination of carbon content in steel samples melted in a laboratory induction furnace. A focused Nd:YAG laser beam was used to generate the plasma on the liquid surface in argon atmosphere. The precision obtained is 10% for carbon contents in the range 150–1100 ppm, and the detection limit is 250 ppm. The present results show that this technique can be applied for direct composition determination in molten alloys.
Time-Resolved Step-Scan FT-IR Investigations of the Transition from KL to L in the Bacteriorhodopsin Photocycle: Identification of Chromophore Twists by Assigning Hydrogen-Out-Of-Plane (HOOP) Bending Vibrations
Authors: Weidlich Olaf , Siebert Friedrich
Published: June 2005

Sub-microsecond time-resolved step-scan FT-IR spectroscopy is applied to the study of the molecular changes and their dynamics occurring during the KL-L transition of bacteriorhodopsin. The time-resolved difference spectra are compared to the static low-temperature BR → K and BR → L difference spectra. Our data show that the protein part in KL is similar to that in K. However, the chromophore is more relaxed and is differently twisted. A strong hydrogen-out-of-plane (HOOP) mode in KL is assigned to the 15-HOOP. As is the case for L, a strong deformation of the C14-C15 single bond is deduced for KL. Evidence of a KL → L equilibrium is presented. In N, a 15-HOOP mode similar to that in L is observed, indicating very similar twists of the C14-C15 single bond. This observation excludes major contributions of this deformation to the reduction of the pKa of the Schiff base in L. From the spectral changes, important molecular events are deduced that occur in the transitions to KL, L, and N.
Time-Resolved and Two-Dimensional NIR FT-Raman Spectroscopy
Authors: Schrader B. , Baranović G. , Epding A. , Hoffmann G. G. , Van Kan P. J. M. , Keller S. , Hildebrandt P. , Lehner C. , Sawatzki J.
Published: June 2005

The near-infrared Fourier transform (NIR FT) Raman technique permits the measurement of Raman spectra without interference by fluorescence. Absorption by molecules containing X-H bonds in the NIR range requires a 180° scattering geometry. In this way, Raman spectroscopy of samples on surfaces is possible, both the detecting of small spots and the mapping of the sample distribution over larger areas. The spatial resolution extends into the micrometer range. Mapping of the inorganic pigment distribution of an initial letter of a mediaeval manuscript is demonstrated. For time-resolved measurements, the step-scan technique, previously developed for infrared spectroscopy, may be used in NIR FT-Raman spectroscopy as well. It allows the study of photochemical and photophysical processes, the application of modulation techniques, and the investigation of “noisy” samples. Photo-isomerization of the dye merocyanine 540 has been observed with the step-scan technique upon periodic excitation with a flash lamp.
Pulsed Laser Photolysis Time-Resolved FT-IR Emission Studies of Molecular Dynamics
Authors: Rogers Steven A. , Leone Stephen R.
Published: June 2005

Time-resolved Fourier transform infrared (FT-IR) emission experiments are used to study photofragmentation processes, single collision reactions, energy transfer events, and laser-initiated radical-radical reactions. In the experimental apparatus, a 200-Hz ArF excimer laser is coupled to a commercial 0.01-cm−1 resolution Fourier transform infrared spectrometer. Fringes from the He:Ne reference laser are used for time synchronization of the laser pulses to the FT-IR mirror retardation. Following a short delay after the laser pulse, the analog-to-digital converter samples the signal on the infrared detector at several time delays. A number of fringes are then skipped and the process is repeated. At the start of the next mirror sweep, data for the first time points are acquired at different mirror positions, and the process is repeated until multiple interferograms are obtained at all time delays. Through the use of improved background-limited detectors and multipass collection optics, spectra from a number of small molecules have been obtained in various processes. We report here on the comprehensive details of our experimental apparatus and discuss several of the processes studied with the use of this apparatus.
Time-Resolved FT-IR Study on Reorientation of Ferroelectric Liquid Crystal, (S)-4-Methylhexyl 4-[4-(Decyloxy) Phenylethynyl]-2-Fluorobenzate
Authors: Czarnecki M. A. , Katayama N. , Ozaki Y. , Satoh M. , Yoshio K. , Watanabe T. , Yanagi T.
Published: June 2005

The electric-field-induced reorientation of (S)-4-methylhexyl 4-[4-(decyloxy) phenylethynyl]-2-fluorobenzate in the Sc* phase was investigated by using an asynchronous time-resolved FT-IR technique. The band assignments were made on the basis of the polarized FT-IR spectra and FT-Raman spectrum. The time-resolved study indicates that the reorientation occurs immediately after the electric field is applied. The molecule reorients as a unit; however the rigid core of the molecule seems to be more mobile than the hydrocarbon chains and needs a shorter period of time for the reorientation. The change of orientation is not completely finished in a 500-μs time period. Of particular note is the behavior of the carbonyl band; this band, usually strong in infrared spectra, is very weak in the time-resolved spectra.