bluuebunny/crossref_metadata_2025 huggingface dataset:
A General Computational Method for Converting Normal Spectra into Derivative Spectra
Authors: Yeow Y. Leong , Leong Y. K.
Published: May 2005

The mathematical problem of converting a normal spectrum into the corresponding first- and second-derivative spectra is formulated as an integral equation of the first kind. Tikhonov regularization is then applied to solve the spectral conversion problem. The end result is a set of linear algebraic equations that takes in as input the original spectrum and produces as output the second-derivative spectrum, which is then integrated to yield the first-derivative spectrum. Noise amplification is kept under control by adjusting the regularization parameter (guided by generalized cross-validation) in the algebraic equations. The performance of this procedure is demonstrated by applying it to different types of spectral data taken from the literature.
Raman Scattering Spectroscopic Study of n-Pentane under High Pressure
Authors: Qiao Erwei , Zheng Haifei
Published: May 2005

The Raman spectroscopy of n-pentane was investigated in a Moissanite anvil cell from 0.07 GPa to 4.77 GPa at ambient temperature. The result shows that the CH3 symmetric stretching vibration (2877 cm−1) and asymmetric stretching vibration (2964 cm−1), the CH2 symmetric stretching vibration (2856 cm−1) and asymmetric stretching vibration (2935 cm−1), and –(CH2)n– in-phase twist mode (1303 cm−1) shifted to higher wavenumbers almost linearly with increasing pressure. Around 2.4 GPa an abrupt visible change took place, indicating a sort of phenomenon of freezing due to over-pressurization. In the pressure range of 2.84 to 4.77 GPa a high-pressure phase transition may occur in the crystallized n-pentane. By determining pressure with the method of solid–liquid coexistence, we concluded that the equilibrium freezing pressure of n-pentane is 1.90 ± 0.05 GPa at 27 °C.
Surface-Enhanced Raman Spectra of VX and its Hydrolysis Products
Authors: Farquharson Stuart , Gift Alan , Maksymiuk Paul , Inscore Frank
Published: May 2005

Detection of chemical agents as poisons in water supplies not only requires μg/L sensitivity, but also requires the ability to distinguish their hydrolysis products. We have been investigating the ability of surface-enhanced Raman spectroscopy (SERS) to detect chemical agents at these concentrations. Here we expand these studies and present the SERS spectra of the nerve agent VX (ethyl S-2-diisopropylamino ethyl methylphosphonothioate) and its hydrolysis products, ethyl S-2-diisopropylamino methylphosphonothioate, 2-(diisopropylamino) ethanethiol, ethyl methylphosphonic acid, and methylphosphonic acid. Vibrational mode assignments for the observed SERS peaks are also provided. Overall, each of these chemicals produces a series of peaks between 450 and 900 cm−1 that are sufficiently unique to allow identification. SERS measurements were performed in silver-doped sol-gel-filled capillaries that are being developed as part of an extractive point sensor.
Examination of Some Misconceptions about Near-Infrared Analysis
Authors: Difoggio Rocco
Published: May 2005

There are some recurrent misconceptions about near-infrared (near-IR or NIR) analysis and similar chemometric techniques that have resurfaced as this technology has become more popular and widely used. These misconceptions are that (1) near-IR can never perform better than the primary reference technique from which it was calibrated, (2) near-IR models that are linear in absorbance cannot account for nonlinear effects, and (3) bias and skew adjustments are purely mathematical manipulations without physical assumptions. This paper examines how these misconceptions arise and, using real and synthetic spectra and simulated noise, presents counter examples to them. This paper also shows how one can approximate a change of scale using bias and skew adjustments to the model and lists some conditions on a model's coefficient weights that make a model insensitive to small changes in spectrometer response.
Scintillator-Based Nanosecond Light Sources for Time-Resolved Fluorimetry
Authors: Hobbs Steven E. , Hieftje Gary M.
Published: May 2005

We have investigated a new pulsed light source for time-resolved fluorimetry. The light source consists of a beta emitter, Sr90, and a liquid or plastic scintillator. Time-correlated single photon counting is employed to demonstrate the new pulsed light source. Measured fluorescence lifetimes of standards anthracene (4.97 ± 0.06 ns) and 1-aminoanthracene (21.4 ± 0.2 ns) agree well with literature values. Advantages of the new light source include the low cost, the size (1 cm−3 or smaller), the nanosecond pulse widths, the high pulse rates, and the extremely stable pulse-to-pulse profile. There is no risk of radioactive contamination from the beta emitter since it is bound in a ceramic matrix and encapsulated.
Identification of Tetrol I-2 by Laser-Excited Solution Fluorescence Spectra
Authors: Shu Luchuan , Hurtubise Robert J.
Published: May 2005

The detection and quantitation of the tetrols are important ways to study the extent of chemical damage to DNA. Both room- and low-temperature laser-excited solution fluorescence spectra of the four tetrol isomers were compared for their spectral features. The results showed that the characteristics of the solution spectra obtained at 77 K provided a very reliable means for distinguishing tetrol 1–2 from its isomers. By utilizing both room-temperature solid-matrix (10% α-cyclodextrin/NaCl) fluorescence spectra from earlier work and solution florescence spectra at 77 K obtained in this work, it is possible to identify the four tetrol isomers.
Total Lifetime Distribution Analysis for Fluorescence Fingerprinting and Characterization
Authors: McGown Linda B. , Hemmingsen Sherry L. , Shaver Jeremy M. , Geng Lei
Published: May 2005

A new technique, total lifetime distribution analysis (TLDA), is described for rapid, sensitive, and accurate lifetime characterization of complex samples. Multiharmonic Fourier transform technology in a commercial, frequency-domain fluorescence lifetime instrument allows rapid acquisition of TLDA data. High sensitivity derives from the use of the entire fluorescence emission from the sample in the lifetime measurement. The maximum entropy method (MEM) provides a consistent basis for modeling of the lifetime data for accurate recovery of the total lifetime distribution of the sample. Because MEM is self-modeling, it is not subject to the same sources of bias that influence nonlinear least-squares fits of lifetime data to a priori models. These features make TLDA an effective tool for sample characterization and fingerprinting that is based on the responsiveness of fluorescence lifetime to the chemical composition and dynamic processes that contribute to the uniqueness of the sample. TLDA results are presented for coal liquids and a humic substance. The effect of signal intensity on lifetime recovery is investigated, and comparison is made between MEM and conventional nonlinear least-squares for data analysis.
Analysis of Nitrocresols and Related Compounds by Gas Chromatography/Matrix-Isolation Infrared Spectrometry
Authors: Childers Jeffrey W. , Smith David F. , Wilson Nancy K. , Barbour Ruth K.
Published: May 2005

The capabilities of gas chromatography/matrix-isolation infrared (GC/MIIR) spectrometry for characterizing nitrocresols in air sample extracts were evaluated. The IR spectra of selected nitrocresols were recorded in an argon matrix, in a xenon matrix, in the vapor phase, and in dilute CCl4 solution. The MIIR spectra of the nitrocresols that do not undergo intramolecular hydrogen bonding exhibited split OH stretching bands. Several factors that might cause band splitting, including aggregation, solute–matrix interactions, and the isolation of conformers, were investigated. The presence of aggregates was indicated by a broad band assigned to intermolecular hydrogen bonding in the MIIR spectra of 3-and 4-nitrocresol isomers deposited in an argon matrix at a matrix-to-solute ratio ≤ 283:1. The split OH absorption bands persisted, however, when there was no evidence of aggregate formation. The complexity of the split OH stretching bands was also influenced by steric factors and by the choice of matrix gas. This result suggests that isolation of rotational isomers and solute-matrix interactions also contribute to the band splitting. The presence of the split OH absorption bands did not preclude the use of the GC/MIIR technique to identify several nitrocresols produced from the photooxidation of toluene and NO x.
Characterization of Polymer-Dispersed Liquid Crystal Systems by FT-IR Microspectroscopy
Authors: Challa Sudarsana R. , Wang Shi-Qing , Koenig Jack L.
Published: May 2005

Infrared microspectroscopy was used to generate functional group images of liquid crystal (E7) droplets dispersed in poly( n-butyl methacrylate) (PBMA). The spatial concentration fluctuations that occur within the system were studied as a function of time. This approach is possible because spectral information can be obtained by focusing on regions on the order of tens of micrometers. The peak intensities were used as a measure of concentration of the components. The amount of liquid crystal dissolved in the polymer matrix determines the extent to which the polymer is plasticized, which in turn affects the shape and size of the droplets. The growth of the domains at any temperature is also determined by whether the system is maintained above or below the glass transition temperature of the matrix. It is observed that the growth of the droplets follows temporal power laws. The spatially resolved spectroscopic images provide valuable insight into the phase separation process and the formation of microdroplets of E7 in PBMA.
Optimization of the Self-Quenching Response of Nitrobenzoxadiazole Dipalmitoylphosphatidylethanolamine in Phospholipid Membranes for Biosensor Development
Authors: Shrive Jason D. A. , Brennan John D. , Brown R. Stephen , Krull Ulrich J.
Published: May 2005

Incorporation of the lipid-conjugated fluorescent probe nitrobenzoxadiazole dipalmitoylphosphatidylethanolamine (NBD-PE) into bilayer lipid membranes (BLMs) provides a matrix wherein changes in the structure of the membrane can be transduced into changes in fluorescence intensity or lifetime. In the work reported here, a comparison was made between an empirical model recently developed by our group to account for alterations in the fluorescence lifetime and average fluorescence intensity of NBD-PE as a result of self-quenching and an earlier alternative model which describes self-quenching of membrane-bound chlorophyll a. Our model showed the more satisfactory correlation with self-quenching data obtained from lipid membranes containing 1 to 50 mol % of NBD-PE. This model was used to determine the optimum initial surface concentration of NBD-PE to be incorporated into phospholipid membranes for biosensor development. Optimization was based on the magnitude of the change in fluorescence intensity as a function of changes in the local concentration of the probe. The presence of acidic headgroups in the membrane results in negligible improvement in sensitivity, while a heterogeneous membrane structure greatly enhances the signal magnitude. Experimental results did not provide accurate optimum concentrations, although two NBD-PE surface concentrations were found to yield close agreement with theoretically predicted optimum surface concentrations of 0.027 ± 0.001 and 0.073 ± 0.001 molecules NBD-PE nm−2.
Core-Based Intrinsic Fiber-Optic Absorption Sensor for the Detection of Volatile Organic Compounds
Authors: Klunder Gregory L. , Russo Richard E.
Published: May 2005

A core-based intrinsic fiber-optic absorption sensor has been developed and tested for the detection of volatile organic compounds. The distal ends of transmitting and receiving fibers are connected by a small cylindrical section of an optically clear silicone rubber. The silicone rubber acts both as a light pipe and as a selective membrane into which the analyte molecules can diffuse. The sensor has been used to detect volatile organics (trichloroethylene, 1,1-dichloroethylene, and benzene) in both aqueous solutions and in the vapor phase or headspace. Absorption spectra obtained in the near-infrared (near-IR) provide qualitative and quantitative information about the analyte. Water, which has strong broad-band absorption in the near-IR, is excluded from the spectra because of the hydrophobic properties of the silicone rubber. The rate-limiting step is shown to be the diffusion through the Nernstian boundary layer surrounding the sensor and not the diffusion through the silicone polymer. The rate of analyte diffusion into the sensor, as measured by the t90 values (the time required for the sensor to reach 90% of the equilibrium value), is 30 min for measurements in aqueous solutions and approximately 3 min for measurements made in the headspace. The limit of detection obtained with this sensor is approximately 1.1 ppm for trichloroethylene in an aqueous solution.
Curve Fitting and Deconvolution of Instrumental Broadening: A Simulated Annealing Approach
Authors: Ferry A. , Jacobsson P.
Published: May 2005

A curve-fitting procedure based on the simulated annealing algorithm has been developed for the analysis of spectral Raman data. By the inclusion of a priori information about the instrumental broadening in the definition of the cost function that is minimized, effects of the finite instrumental resolution are eliminated from the resulting fit. The ability of the method to reproduce original band shapes is tested on synthesized spectra and FT-Raman spectra of diamond recorded at different resolutions with different apodization functions. The procedure yields the global optimum of the fitted parameters and is easily implemented on a personal computer.
Time-Dependent Fluorescence Depolarization Analysis in Three-Dimensional Microspectroscopy
Authors: Koshioka Masanori , Sasaki Keiji , Masuhara Hiroshi
Published: May 2005

Three-dimensional space- and time-resolved fluorescence depolarization spectroscopy has been developed for elucidating picosecond rotational relaxation processes occurring in micrometer-sized volumes. Anisotropy decays are obtained by a new analytical method which is adapted to the large-solid-angle characteristic of the microscope optics. System parameters introduced in this method were determined by measuring a reference sample. The fluorescence dynamics of p-terphenyl in a thin liquid layer was analyzed as a demonstration experiment.
Infrared Mapping of Surface-Modified Kevlar Fiber-Reinforced Epoxy Systems
Authors: Mavrich Angela M. , Ishida Hatsuo , Koenig Jack L.
Published: May 2005

Epoxy-reacted Kevlar-49/epoxy systems were studied with the use of localized infrared microspectroscopy and IR imaging. Spectral evidence was acquired that indicated the modification of the fiber's surface with epoxy functionalities. Thin films of amine-cured epoxy resin, deposited on single filaments of unreacted and epoxy-reacted Kevlar, were examined with the use of FT-IR microspectroscopy. IR images of these samples reveal higher levels of cure along the reacted fiber surface in comparison with the unreacted fiber and bulk matrix. Finally, thin films of curing agent were deposited on the surface of reacted and unreacted single Kevlar filaments. IR functional group images from this sample reveal a preferential attraction of the curing agent, DEH 26, to the epoxyreacted surface.
Mössbauer, Far-Infrared, and XPS Investigations of SnCl2 and SnCl4 Introduced in Polyconjugated Monosubstituted Acetylene Matrices
Authors: Alonzo Giuseppe , Bertazzi Nuccio , Ferraro John R. , Furlani Anita , Iucci Giovanna , Polzonetti Giovanni , Russo Maria V.
Published: May 2005

Mössbauer, far-infrared, and X-ray photoemission spectroscopy (XPS) studies have been made on doped (SnCl2 or SnCl4) (PEFl) and polyphenylacetylene (PPA). The nature of the tin as it is incorporated into the polymer is examined. The resistance values of the doped polymers are followed with relative humidity. Results point to tetrahedral (SnCl4 and octahedral (SnCl4 · 2H2O) species in the SnCl4 doping. With SnCl2 doping, the nature of the species is less certain, although both Sn(II) and hexacoordinated Sn(IV) appear to be present. Index Headings: Mössbauer
Hybrid Substrates for Real-Time SERS-Based Chemical Sensors
Authors: Wachter E. A. , Storey J. M. E. , Sharp S. L. , Carron K. T. , Jiang Y.
Published: May 2005

Since the discovery of the surface-enhanced Raman scattering (SERS) effect, numerous substrate designs have been proposed for a variety of analytical applications. Although many of these have offered exceptional electromagnetic enhancement, the durability and reusability of substrates have not always been acceptable for routine analytical use. This paper discusses the design and testing of a new class of hybrid SERS substrates specifically designed to optimize electromagnetic enhancement while also affording exceptional ruggedness and reversibility of response under challenging conditions. Substrate templates are fabricated lithographically into a quartz surface, then a thin metal film is deposited, and finally the entire surface is coated with a protective layer. Examples of inorganic and organic protective coatings are provided. Analytes are measured in flowing streams of airborne vapor and aqueous liquid. Properly designed surface coatings serve a dual role as both a protective layer and as a rapidly reversible selective adsorbent for specific analytes.
Polarization-Division Interferometry: Time-Resolved Infrared Vibrational Dichroism Spectroscopy
Authors: Polavarapu Prasad L. , Deng Zhengyu , Chen Gang-Chi
Published: May 2005

We report the first direct measurements of time-resolved Fourier transform infrared vibrational dichroism (TR/FT-IR/VD). The central component for these measurements is a polarization-division interferometer (PDI). This interferometer uses an in-house-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 rooftop 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 input beam. The signals measured as a function of the moving mirror position in the PDI represent the linear/circular dichroism interferograms, whose cosine/sine Fourier transforms yield linear/circular dichroism spectra. Time-resolved dichroism interferograms were measured with the use of this PDI with the asynchronous external perturbation method. Microsecond time-resolved linear dichroism spectra of a nematic liquid crystal, under the influence of bipolar electric field oscillating at 2 kHz, were measured and presented as the first examples.
Design and Use of Background-Reduced 27Al NMR Probes for the Study of Dilute Samples from the Environment
Authors: MacFall Janet S. , Ribeiro Anthony A. , Cofer Gary P. , Dai Ko-Hsiu G. , Labiosa William , Faust Bruce C. , Richter D. D.
Published: May 2005

Development of methods for the detection and measurement of aluminum (Al) is crucial for our understanding of Al(III) chemistry and toxicity in natural waters, soil solutions, and environmental samples. Traditional colorimetric assays, by their very nature, alter solution Al(III) chemistry, potentially biasing measurements. Methods based on 27Al NMR spectroscopy have the advantage of being nondestructive and of not altering the chemistry of the solution. Standard commercial NMR probes and sample tubes, unfortunately, are constructed from aluminum-containing components. These materials give substantial background signal, which is detected as a large, broad hump, overwhelming signals from dilute samples. We describe here the construction of two novel NMR probes and a sample container built from a variety of materials with low Al content. The designs feature the use of transversely mounted solenoid coils with aluminum-free sample holders. The sample container features a second chamber which can be filled with an external reference solution. These novel 27Al NMR probes are being used for the NMR spectroscopic investigation and quantitation of natural, dilute (10−6 M) Al(III) samples from the environment.
Continuously Tuneable, Quasi-Continuous-Wave Source for Ultraviolet Resonance Raman Spectroscopy
Authors: Doig Stephen J. , Prendergast Franklyn G.
Published: May 2005

A continuously tuneable, quasi-continuous-wave (cw), ultraviolet source for resonance Raman spectroscopy has been developed. The third and fourth harmonics of a picosecond mode-locked titanium: sapphire laser were generated in nonlinear crystals. The pulses which resulted from these processes were spectrally narrow (10–15 cm−1) and had low peak powers (<1 kW), while the system as a whole provides high average powers. Fourth-harmonic wavelengths were generated from 208 to 230 nm with average powers from 15 to 40 mW, while the third harmonic ranged from 255 to 305 nm with over 90 mW of power. The UV light was well collimated and focused well, and the power was stable for hours. Resonance Raman spectra of tryptophan and phenylalanine were recorded to demonstrate the practical application of this system. Spectra with excellent signal-to-noise ratios were recorded in 6 min with no deleterious effects from nonlinear processes. The selective enhancement of tryptophan scattering in a 1:10 molar solution of tryptophan to phenylalanine makes clear the advantage of a continuously tuneable UV source. Elaboration of this system to the full tuning range of titanium: sapphire lasers will create a laser source suitable for resonance Raman spectroscopy throughout the ultraviolet region (205–400 nm).
Determination of Water in Slurries by Fiber-Optic Raman Spectroscopy
Authors: Lombardi Daniel R. , Mann Charles K. , Vickers Thomas J.
Published: May 2005

We have examined the feasibility of the remote determination of water in a sodium nitrate matrix by fiber-optic Raman spectroscopy with multichannel detection. The direct determination based on the Raman line due to OH bending is shown to be possible but relatively insensitive. A determination based on the ratio of signals due to dissolved and solid nitrate is shown to provide a water detection limit of less than 1% for a measurement time of one minute.
Evaluation and Mapping of Heat-Shield Flight Temperature and Composition with Raman Spectroscopic Techniques
Authors: Tallant D. R. , Auerbach I. , Higgins K. L.
Published: May 2005

A Raman spectroscopic technique has been developed which can measure the maximum temperatures experienced by charring heat-shield materials and determine their post-test compositions (char, pyrolysis zone, and virgin resin). The technique has the capabilities of analyzing circular areas less than 0.1 mm in diameter or rectangles 0.1 mm in width and 2 mm in length. It can provide fine detailed surface and internal mappings and perform the analyses rapidly and conveniently in the laboratory following testing or flight recovery. Representative plots of temperature and composition profiles are provided. The data are compared with computations from the Charring Material Ablation (CMA) code.
Optimization of Excitation and Detection Geometry for Multiplexed Capillary Array Electrophoresis of DNA Fragments
Authors: Lu Xiandan , Yeung Edward S.
Published: May 2005

A new on-column excitation and detection geometry for multiplexed array capillary electrophoresis is evaluated. The detection limit is improved 100-fold for the same laser power because of more efficient coupling of the laser beam. The illumination is also more uniform over the entire array. Stray light and cross-talk are effectively suppressed by immersing the capillaries in water to roughly match the refractive index. A charge-coupled-device (CCD) camera combined with cutoff filters provides adequate sensitivity and speed for high-speed DNA sequencing based on sieving in a polymer-matrix solution.
Picosecond Time-Resolved Fourier Transform Raman Spectroscopy of 9,10-Diphenylanthracene in the Excited Singlet State
Authors: Jas Gouri S. , Wan Chaozhi , Johnson Carey K.
Published: May 2005

Time-resolved Fourier transform Raman spectroscopy of the highly fluorescent chromophore 9,10-diphenylanthracene (DPA) in cyclohexane and ethanol is described. Raman spectra of the first excited singlet state of DPA were obtained with 100-ps resolution at several time delays between pump pulses at 355 nm and probe pulses at 1064 nm. The near-infrared excited-state Raman scattering is enhanced by resonance with an excited-state transition of DPA. The excited-state Raman bands decay in about 5–6 ns. Evidence for interaction of the solvent with the DPA excited state is observed in the cyclohexane C-H stretching bands.
Fluorescence Rejection in Raman Spectroscopy by Shifted-Spectra, Edge Detection, and FFT Filtering Techniques
Authors: Mosier-Boss P. A. , Lieberman S. H. , Newbery R.
Published: May 2005

The use of shifted-spectra, first-derivative spectroscopy (or edge detection), and fast Fourier transform filtering techniques for fluorescence rejection in Raman spectra is demonstrated. These techniques take advantage of the fact that Raman signals are very narrow in comparison to fluorescence bands in order to discriminate between the two. None of these techniques require modification of existing instrumentation. Fast Fourier transform filtering and deconvolution techniques also provide a means of improving spectral resolution and the signal-to-noise ratio.
Wavelength Calibration Transfer between Diode Array UV-Visible Spectrophotometers
Authors: Blanco Marcelo , Coello Jordi , Iturriaga Hortensia , Maspoch Santiago , Rovira Esther
Published: May 2005

The need to obtain expeditious results in control analyses of complex mixtures has turned multivariate calibration procedures into major choices for routine analyses. The inherent complexity of the calibration process and the practical need for analyses to be carried out as near the manufacturing line as possible occasionally entail calibrating with a different instrument from that subsequently employed for the analytical measurements proper. This paper exposes the problems potentially arising in transferring calibrations between diode array UV-Vis spectrophotometers. Basically, such problems originate in wavelength differences between spectrophotometers, even if they meet the manufacturer's specifications and the pharmacopoeia recommendations. We developed a straightforward method for harmonizing instrumental responses on the basis of reference wavelengths corresponding to zero values in the first-derivative spectra for potassium dichromate and benzoic acid standards. The method was applied to the analysis of binary mixtures of theophylline and doxylamine by multiple linear and partial least-squares regression with the use of one spectrophotometer for calibration and four others for analyses.
Remote Fiber-Optic Raman Analysis of Xylene Isomers in Mock Petroleum Fuels Using a Low-Cost Dispersive Instrument and Partial Least-Squares Regression Analysis
Authors: Cooper John B. , Flecher Philip E. , Vess Thomas M. , Welch William T.
Published: May 2005

We report the use of a low-cost dispersive Raman instrument with charge-coupled-device (CCD) detection, near-infrared (near-IR) diode laser excitation, and remote fiber-optic sampling to analyze mock petroleum samples which contain high benzene, toluene, ethylbenzene, and xylene (BTEX) concentrations. Partial least-squares regression (PLSR) analysis is used to correlate the individual xylene isomer concentrations to the Raman spectral signal without the use of an internal standard. The resulting PLSR model is used to predict the concentration of individual xylene isomers, and it is found that, at a 95% confidence level, samples containing between ∼1.5 and 15% xylene isomer can be predicted to better than ±0.1% for meta- and para-xylene, and to ±0.15% for ortho-xylene. The use of PLS model leverage plots provides a facile statistical method by which to identify Raman spectra which involve diode laser mode hops or significant fiber backscatter.
Implementation of the Scanning Multichannel Technique in Raman Spectroscopy and the Application for the Characterization of Oxides
Authors: Spielbauer D.
Published: May 2005

The scanning multichannel technique (SMT) has proved to be a good method to compensate for the disadvantages of diode arrays as detectors in Raman spectroscopy. A method is presented for implementation of SMT with a system which is equipped with a conventional MT software package. Additional programs were developed for controlling the MT software and for calculation the SMT spectra from the recorded raw data. Additional functions for filtering defective channels of the diode array and for suppressing defective individual spectra were added to improve the quality of the SMT spectra. Sulfate on γ-Al2O3 was investigated as a model system for an intermediate of a proposed transfer catalyst for the removal of SO x from fluid catalytic cracking (FCC) catalysts. The recorded MT spectra were disturbed by the characteristics of the diode array that was used and by a high (fluorescence-like) background of γ-AL2O3. As a consequence, the correction of the spectra by the spectrometer function is complicated. In this case, the application of SMT led to Raman spectra with significantly improved quality. The Raman spectra suggest a tridentate structure of the sulfate on the surface of γ-A12O3 having C, or C3 v symmetry.
Influence of Triethanolamine on Aqueous β-Cyclodextrin/Pyrene Complexes
Authors: Will A. Yvette , De La Peña Arsenio Muñoz , Ndou Thilivhali T. , Warner Isiah M.
Published: May 2005

The influence of triethanolamine (TEA) on the aqueous β-CD/pyrene fluorescence is examined. Collisional quenching of pyrene by TEA is indicated by Stern-Volmer plots. However, a decrease in the quenching is observed in the presence of β-cyclodextrin, which indicates an effective protection of the included pyrene molecules against quenching from TEA. A decrease in the apparent formation constant of the β-CD/pyrene complex also occurs in the presence of TEA. This phenomenon is attributed to a combination of an increased bulk solvent hydrophobicity and a competitive equilibrium between pyrene and TEA for the β-CD cavity. The present study indicates that TEA is not co-included in the β-CD/pyrene complex.
Decomposition Kinetics of EGDN on ZnO by Diffuse Reflectance Infrared Fourier Transform Spectroscopy
Authors: Henderson D. O. , Mu R. , Tung Y. S. , Huston G. C.
Published: May 2005

Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to follow the decomposition kinetics of ethylene glycol dinitrate (EGDN) adsorbed on a zinc oxide surface at 313 K. The principal decomposition products are most likely a variety of carbonyl, carboxylate, and carbonate species. The appearance of these products follows zeroth-order Langmuir kinetics. Another decomposition product, carbon monoxide, exhibited more complex kinetics. Overall, because of its reactivity with EGDN, ZnO does not appear to be a suitable material for an explosive preconcentrator device.
ATR Spectroscopic Study of PMMA/PDMS Graft Copolymers Using a Barrier Layer Method
Authors: Marand Eva , Smartt L. Mike
Published: May 2005

The use of an intermediate barrier layer to vary the penetration depth in an ATR experiment is investigated. Both theoretical and experimental results suggest that this method may be useful in probing concentration profiles away from the interface, particularly in the case of thin films, where variable-angle methods have limitations. Application of this technique in the study of poly(methylmethacrylate)/poly(dimethylsiloxane) (PMMA/PDMS) graft copolymers deposited onto a copper oxide surface indicates a preferential presence of the siloxane component at the oxide interface, a concentration which tends to decrease with increasing distance into the bulk of the sample film.
Molecular Orientation and Stacking of Perylenetetracarboxylic Diimide Derivatives in Langmuir-Blodgett Monolayers: Part II
Authors: Aroca Eric Johnson Ricardo
Published: May 2005

Molecular overlapping of perylene tetracarboxylic diimides (PTCD) in Langmuir–Blodgett (LB) films is discussed. With the use of Kuhn's extended dipole model and spectral data in the visible and infrared regions, the degree of molecular overlap in a series of PTCD derivatives was determined. The results are in general agreement with the overlap values reported in X-ray studies for crystal packing of similar molecules.
Quantitative Analysis of Aluminum Alloys by Laser-Induced Breakdown Spectroscopy and Plasma Characterization
Authors: Sabsabi Mohamad , Cielo Paolo
Published: May 2005

Laser-induced breakdown spectroscopy has been applied to perform elemental analysis of aluminum alloy targets. The plasma is generated by focusing a pulsed Nd:YAG laser on the target in air at atmospheric pressure. Such a plasma was characterized in terms of its appearance, emission spectrum, space-integrated excitation temperature, and electron density. The electron density is inferred from the Stark broadening of the profiles of ionized aluminum lines. The temperature is obtained by using Boltzmann plots of the neutral iron lines. Calibration curves for magnesium, manganese, copper, and silicon were produced. The detection limits are element-dependent but are on the order of 10 ppm.
Molecular Orientation and Stacking of Perylenetetracarboxylic Diimide Derivatives in Langmuir-Blodgett Monolayers: Part I
Authors: Aroca Ricardo , Johnson Eric , Maiti Asim Kumar
Published: May 2005

The molecular organization in Langmuir-Blodgett (LB) monolayers for five organic dyes with a common chromophore moiety was studied. With the use of transmission and reflection-absorption (FT)IR spectroscopy (RAIRS), the orientation of the chromophore units in the LB monolayer was determined. The results obtained with carbonyl and C=C stretching vibrations exclude a flat-on orientation of the chromophore moiety and may be rationalized in terms of a tilted head-on organization of the chromophore on the Ag, ZnS, and Ge surfaces. The tilt angle, φ, formed between the direction of the dynamic dipole moment and the normal to the surface of the film was determined from the combined infrared data obtained in a transmission geometry and in RAIRS. The aromatic-aromatic interaction plays a significant role in determining the molecular alignment in the Langmuir and LB monolayers.
Infrared Intensities of Liquids XVIII: Accurate Optical Constants and Molar Absorption Coefficients between 6500 and 800 cm−1 of Dichloromethane at 25°C, from Spectra Recorded in Several Laboratories
Authors: Bertie John E. , Lan Zhida , Jones R. Norman , Apelblat Yoram
Published: May 2005

This is the last of four papers that present the detailed measnrements and results that led to the acceptance by the International Union of Pure and Applied Chemistry of Secondary Infrared Absorption Intensity Standards for liquids. In this paper accurate infrared absorption intensities of liquid dichloromethane at 25°C are presented. The accuracy was estimated from the ±1.5% average agreement of integrated intensities over specific wavenumber ranges between spectra measured by five spectroscopists in four laboratories. The use of data from different instruments in different laboratories has significantly included the effect of systematic instrumental errors. The spectra from the different spectroscopists have been averaged, unweighted, to give intensity spectra of dichloromethane that are presented as the best available. The results obtained agree with the only measurements that have been made against a primary standard, the estimated accuracy of which is about 5.5%. The spectra of the molar absorption coefficient and or the real and imaginary refractive indices are reported as tables and graphs between 6500 and 800 cm−1. Also reported are the peak heights and the areas under band groups in the molar absorption coefficient and imaginary refractive index spectra. The imaginary refractive index, k(ν˜), and molar absorption coefficient, Em(ν˜), values are believed to be accurate to an average ±2.3% over the 36 measured bands. The baseline k(ν˜) values are believed to be accurate to ∼8% below 6000 cm−1, ∼1% below 4500 cm−1, and ∼25% above 6000 cm−1, where the absorption is extremely weak. The areas under band groups in the k(ν˜) and Em(ν˜) spectra are believed to be accurate to 1.5% averaged over the 15 measured band groups and to 1.0% over the 10 band groups below 3600 cm−1. The real refractive index, n(ν˜), values are believed to be accurate to 0.2%.
Visible and Near-Infrared Fluorescence of Crude Oils
Authors: Downare Taggart D. , Mullins Oliver C.
Published: May 2005

Fluorescence emission spectra and absolute quantum yields have been measured for ten diverse crude oils at various concentrations over a broad range of excitation and emission wavelengths in the visible and the near-infrared. Energy transfer produces large red shifts and large widths in the fluorescence emission spectra for shorter wavelength excitation particularly for heavier crude oils. However, the effects of energy transfer are nearly absent for near-infrared excitation; all crude oils exhibit nearly the same emission spectra for long wavelength excitation. In addition, the fraction of emission resulting from collisional energy transfer relative to nascent emission is almost independent of oil type; it is governed by quantum yield characteristics. Absolute fluorescence quantum yields of ten crude oils (and three rhodamine dyes for validation) were measured with respect to scattering of latex microspheres in distilled water. Fluorescence quantum yields vary systematically with crude oil type as well as excitation wavelength; quantum yields are lower for high fluorophore concentrations (heavy crude oils) and for longer wavelength excitation. Stern-Volmer analyses of the quantum yields indicate that simple models apply and show the relative quenching rates for different excitation wavelengths.
On the Scales Associated with Near-Infrared Reflectance Difference Spectra
Authors: Dhanoa M. S. , Lister S. J. , Barnes R. J.
Published: May 2005

Scale differences of individual near-infrared spectra are identified when set-independent standard normal variate (SNV) and de-trend (DT) transformations are applied in either SNV followed by DT or DT then SNV order. The relationship of set-dependent multiplicative scatter correction (MSC) to SNV is also referred to. A simple correction factor is proposed to convert derived spectra from one order to the other. It is suggested that the suitable order for the study of changes using difference spectra (when removing baselines) should be DT followed by SNV, which leads to all derived spectra on the scale of mean zero and variance equal to one. If baselines are identical, then SNV scale spectra can be used to calculate differences.
Time-Resolved Step-Scan FT-IR Spectroscopy of the Photodynamics of Carbonmonoxymyoglobin
Authors: Plunkett Susan E. , Chao James L. , Tague Thomas J. , Palmer Richard A.
Published: May 2005

The kinetics of protein response and of CO recombination after photolysis of the Fe-CO bond in carbonmonoxymyoglobin have been monitored via time-resolved step-scan FT-IR absorption difference spectroscopy in D2O solution. Although the initial photodissociation is too fast to observe with currently available FT-IR instrumentation, we have been able to correlate the CO recombination kinetics with protein secondary structural changes via changes in the amide I band of the polypeptide chain with microsecond time resolution. The spectral and kinetic data corroborate and confirm previously published single-frequency infrared studies. This is the first application of time-resolved step-scan FT-IR spectroscopy in the absorbance difference mode to study the photodynamics of an aqueous protein solution at room temperature. This work also demonstrates the potential of the technique for the sub-microsecond kinetic analysis of other biological molecules of interest.
Mass Spectrometry Study of a Magnetron Planar Glow Discharge Excited in the Direct-Current and in the Radio-Frequency Mode: An Experimental Design Approach
Authors: Molle Christel , Springael Sabine , Wautelet Michel , Dauchot Jean-Pierre , Hecq Michel
Published: May 2005

A magnetron glow discharge is studied by a differentially pumped quadrupole mass spectrometer measuring the positive ions as well their energy. The 1-in.-diameter target is made in an aluminum base alloy. An “experimental design” procedure was used to study the influence of geometrical and electrical parameters of the discharge on the intensity and the energy of the ions collected by the mass filter. The ion intensity increases, in the dc mode, by two orders of magnitude when the pressure drops from 450 mTorr to 20 mTorr, whereas, in the rf mode, a maximum is observed at 60 mTorr. For both discharge modes, the ion energy increases with a drop of the pressure and the ion intensity rises proportionally to the electric power. The energy of the ions entering into the mass filter is about 10 eV higher in the rf mode than in the dc mode for the same power and pressure. For most of the ions, their energy does not vary with the power. In the rf mode and at high pressure, a rise of their energy is observed when the target is eroded.
Temperature and Emission Spatial Profiles of Laser-Induced Plasmas during Ablation Using Time-Integrated Emission Spectroscopy
Authors: Mao Xianglei L. , Shannon Mark A. , Fernandez Alberto J. , Russo Richard E.
Published: May 2005

Emission spectra and excitation temperature spatial profiles, within laser-induced plasmas from solid copper targets, are characterized as a function of laser power density with the use of time-integrated emission spectroscopy. This research shows how the measured axial spatial emission intensity of the expanding plasma can be influenced by the time integration. The excitation temperatures calculated from these integrated emission-line intensities may not coincide with the actual temperature spatial profile. Transient plasma dynamics during time-integrated intensity measurements can influence both the excitation temperature and the atomic number density of the emitting species. As a demonstration of the influence of fluid dynamics on time-integrated emission measurements, a shock-wave model was used as an example to show how the spatial emission intensity profile of a laser-induced plasma can be affected by transient expansion. Even for time-resolved emission measurements, the high velocity of a laser-induced plasma can influence spatial intensity data close to the target surface. The ability to accurately measure spatial emission intensity and temperature behavior is shown to be related to the integration time vs. plasma expansion velocity.
Laser-Excited Atomic Fluorescence of Eu, Y, and Tm in a Miniature Glow Discharge Atom Reservoir
Authors: Davis Cheryl L. , Smith Benjamin W. , Bolshov Mikhail A. , Winefordner James D.
Published: May 2005

A miniature glow discharge (GD) is evaluated as an atom reservoir for laser-excited atomic fluorescence spectrometric measurements of Eu, Y, and Tm. Nanoliter-sized aqueous samples are deposited and dried on the Ni cathode and atomized upon ignition of the GD. The atom population is probed by a copper vapor laser pumped dye laser, and direct-line fluorescence is detected. The optimum chamber pressures and operating currents are 1 Torr and 10 mA for Eu, 2 Torr and 10 mA for Y, and 3 Torr and 40 mA for Tm. The fluorescence temporal profiles are found to consist of short (∼20-ms duration) transient spikes, followed by long tails which last more than 60 s as a result of sample redeposition on the cathode surface. The limits of detection (3a) are 2 fg, 1.2 pg, and 0.08 fg for Eu, Y, and Tm, respectively, with the use of signal area integration over a 6-s duration. Theoretically simulated signals for a particular sample mass, considering the geometry of the GD atomizer, were found to fall within one order of magnitude of those obtained by experiment.
UV-Visible Spectral Library Search with Mixtures
Authors: Brown Chris W. , Okafor Anne E. , Donahue Steven M. , Lo Su-Chin
Published: May 2005

A library mixture search method originally developed for infrared spectra has been successfully applied to UV-visible spectra. This novel approach for searching a spectral library performs a principal component analysis (PCA) on the entire library of spectra for pure compounds. The library spectra are represented by their PCA scores, and the concentrations (assumed to be unity) are regressed onto these scores. The scores for an unknown spectrum projected onto the PCA basis set are multiplied by the regression matrix to predict pseudo-concentrations or composition indices. After the first pass through the library, a subgroup of the top 20 hits (10% of the library) is selected and the PCR analysis is repeated on this set to improve the selection process. Spectra of each of the individual target components are adaptively filtered from the subgroup of library spectra and from the unknown spectrum prior to the repeat of the PCR analysis. The application of the adaptive filter greatly improves the success rate on hitting the second and third components by removing the first hit during each pass through the library. Computation times for training and applying the Mix-Match algorithm are greatly reduced by pre-processing with Fourier Transforms. A 200-compound library could be trained in 45 min and searched in 9 s; a 20-compound subgroup could be adaptively filtered and searched in 37 s. Both components in 12 two-component mixtures and one component in each of two two-component mixtures were correctly identified; the algorithm failed on both components in only one out of 15 two-component mixtures. All three components were correctly identified in one three-component mixture, and one component was correctly identified in another three-component mixture.
Evaluation of Secondary Cathodes for Glow Discharge Mass Spectrometry Analysis of Different Nonconducting Sample Types
Authors: Schelles Wim , De Gendt Stefan , Muller Victor , Van Grieken René
Published: May 2005

The use of different secondary cathodes is evaluated for the analysis of solid, nonconducting samples by means of dc glow discharge mass spectrometry. Optimum discharge conditions and analytical characteristics are reported for the analysis of a compacted iron ore sinter and a solid glass sample, both with known composition. These conditions seem to differ significantly for the two samples under consideration. This difference is assumed to be caused mainly by the electrical characteristics of the sample. The electrical resistivity of the sample is indeed found to be an important factor, determining the capabilities of the technique, especially with respect to the detection power.
Time-Resolved Studies of the Effects of Water Vapor in Glow Discharge Mass Spectrometry
Authors: Ratliff P. H. , Harrison W. W.
Published: May 2005

The role of water vapor as an impurity in glow discharge mass spectrometry is examined by means of pulsed injection of water into an argon discharge. The effect of water vapor on both analyte and intrinsic gas species is determined. Water dissociates in the discharge to produce reactants that can influence analytical results. The extent of this effect is dependent on the reactivity of the cathode sample with water and its dissociation products. Metal oxides are observed during and shortly after the pulsed water injection. Three different cathode materials (titanium, iron, and copper) are studied, with a range of metal oxide bond strengths. Titanium, which has strong gettering action in the glow discharge plasma, exhibits the shortest perturbation time after addition of water vapor. The experiments show the need to remove trace water from glow discharges for best analytical results.