bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of the Effects of Atmospheric Conditions on the Quantification of Metal Hydrides Using Laser-Induced Breakdown Spectroscopy
Authors: Singh Jagdish P. , Zhang Hansheng , Yueh Fang-Yu , Carney Kevin P.
Published: May 2005

A study was performed to evaluate the performance characteristics of a laser-induced plasma for real-time determination of various gas-phase metal hydrides, specifically Sn and As. The choice of carrier gas composition and the effect of the pressure on the temporal emission behavior of neutral atoms excited by the laser-induced plasma were investigated. Metal hydrides were generated by using a NaBH4-based hydride generation system. The hydrides were equilibrated into an evacuated cell and isolated from the generator prior to measurement. Laser-induced breakdown spectroscopy (LIBS) spectra of Sn and As were recorded in He and N2 atmospheres at 300 and 760 Torr. The temporal behavior of the LIBS signal was most affected by gas composition, gas pressure, and intensity of the laser beam. The Sn neutral atom emission (284.0 nm) in a N2 atmosphere decreased exponentially with time. In contrast, with a He atmosphere and identical experimental conditions, the Sn signal increased logarithmically with time over the first 100 s. Then the signal maintained a steady-state value until approximately 400 s, after which it decreased exponentially. The steady-state time depends on the concentration of metal hydride. The variation of the LIBS signal with time was mirrored for the As neutral atom emission in He and N2 atmospheres. Various experiments have been performed to find the possible reason for the signal variation with time. It was found that chemical reactions in the laser plasma that might deplete the metal from the gas volume were responsible for the decrease in the signal with time.
Rotational Reorientation Dynamics of Aerosol-OT Reverse Micelles Formed in Nearcritical Propane
Authors: Heitz Mark P. , Bright Frank V.
Published: May 2005

The rotational reorientation kinetics of two fluorescent solutes (rhodamine 6G, R6G, and rhodamine 101, R101) have been determined in sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol-OT, AOT) reverse micelles formed in liquid and nearcritical propane. We show that the amount of water loading ([water]/[AOT], R), continuous phase density, and temperature all influence the solute rotational dynamics. In all cases, the decay of anisotropy data (i.e., frequency-dependent differential polarized phase angle and polarized modulation ratio) are well-described by a bi-exponential decay law. We find that the faster rotational correlation times are similar to but slightly less than the values predicted for an individual AOT reverse micelle rotating in propane. The recovered rotational correlation times range from 200 to 500 ps depending on experimental conditions. This faster rotational process is explained in terms of lateral diffusion of the fluorophore along the water/headgroup interfacial region within the reverse micelle. The recovered values for the slower rotational correlation times range from 7 to 18 ns. These larger rotational reorientation times are assigned to varying micelle-micelle (i.e., tail-tail) interactions in the low-density, highly compressible fluid region. We also quantify the contribution of the reverse micellar “aggregate” to the total decay of anisotropy.
Steady-State Fluorescence of Polystyrene Plasticized by Supercritical Carbon Dioxide
Authors: Li Ming , Bright Frank V.
Published: May 2005

A steady-state fluorescence study of low-molecular-weight polystyrene (MW = 1060 g/mol and 13,000 g/mol) plasticized in supercritical CO2 is reported. In addition to excitation wavelength, molecular weight, and polystyrene concentration dependencies, CO2 density also strongly affects the emission spectral contours. A major increase in the steady-state fluorescence intensity and a significant decrease in the polystyrene 320- to 365-nm fluorescence intensity ratio are observed when CO2 density is increased. Concentration and conformational changes in the polystyrene molecules are used to explain the observations, and these results are proposed to arise from changes in the plasticization power of supercritical CO2 over the density range studied. A theoretical model is proposed that is based on the assumption that, at low CO2 densities and low polymer concentrations, polystyrene intermolecular interactions are negligible. The proposed model is able to fit our observed fluorescence data from a CO2 reduced density of 0.3 to 1.4.
Effects of Sampling Parameters on Principal Components Analysis of Raman Line Images
Authors: Hayden Charlene A. , Morris Michael D.
Published: May 2005

Raman images of the distribution of materials in a sample prepared from 10-μm-diameter polystyrene spheres embedded in epoxy were reconstructed from sets of line-scanned images, with the use of univariate and multivariate processing of the spectral data. Multiple sets of microscopic Raman spectral line images were acquired by using line-focused illumination with a cylindrical lens, a motorized translation stage to move the sample perpendicular to the illumination line, and a holographic imaging spectrograph equipped with a 2D charge-coupled device (CCD) detector. Repeat sets of data were obtained at different spectrometer slit width settings and different magnification. The raw spectral data were processed by using both a simple univariate method (single-band integration) and a more sophisticated multivariate method [principal components analysis (PCA) with eigenvector rotation] to generate 2D Raman images representing spatial distribution of the individual polymeric constituents. The repeat data sets were compared to ascertain the effects of the sampling parameters on the PCA method. The results indicated that spectrometer slit width and magnification affect the sampling depth and spatial resolution, but have little effect on the PCA. Moreover, digital sampling (i.e., number of PCA wavelength variables) could be significantly reduced with little or no degradation of the PCA-generated images, particularly if key bands were represented.
Spectral Interpretation and Qualitative Analysis of Organophosphorus Pesticides Using FT-Raman and FT-Infrared Spectroscopy
Authors: Tanner Peter A. , Leung Kim-Hung
Published: May 2005

FT-Raman spectroscopy is a selective and safe technique for the qualitative identification of organophosphorus pesticides and is not accompanied by sample photodecomposition. Spectra of 14 target pesticides were recorded, and the phosphorus characteristic group frequencies are discussed. Preliminary investigations of solvent and temperature effects upon the infrared spectra were also carried out.
Measurement of Vibrational Circular Dichroism below ∼600 cm−1: Progress towards Meeting the Challenge
Authors: Polavarapu Prasad L. , Deng Zhengyu
Published: May 2005

The measurement of vibrational circular dichroism (VCD) below ∼600 cm−1 is one of the experimental challenges of the current times. Polarization-division interferometry is considered to be the most efficient approach for realizing these measurements. A crucial component for successful applications of this interferometry is the beamsplitter, which divides the incoming beam according to polarization. Free-standing metal wires and the metal wires deposited on a mylar substrate have been employed as beamsplitters, and their performance has been evaluated for the ∼700–10 cm−1 region. VCD measurements obtained for the enantiomers of α-pinene in the 400–250 cm−1 region are presented. The current status and future developments needed for routine far-infrared VCD measurements are summarized.
Analytical Chiral Purity Verification Using Raman Optical Activity
Authors: Spencer Kevin M. , Edmonds Robert B. , Rauh R. David
Published: May 2005

Current chiral analytical spectroscopic techniques are limited, either in their inability to perform multicomponent analyses or in their need to undergo tedious sample preparation. Vibrational optical activity (VOA) techniques show promise in overcoming current restrictions. The plethora of vibrational bands allows multicomponent analysis, and sample preparation is minimal. Previous analytical evaluation of VOA techniques has been limited. In this paper, a thorough evaluation of Raman optical activity (ROA) reproducibility has been performed to demonstrate that ROA can uniquely identify 100:0% and 99:1% enantiomeric mixtures. Spectra of compounds of industrial and pharmaceutical relevance are also presented.
Spinning Quarter-Wave Plate Polarization Modulator: Test of Feasibility for Vibrational Circular Dichroism Measurements
Authors: Malon Petr , Keiderling Timothy A.
Published: May 2005

A novel polarization modulator design based on a rotating quarter-wave plate and preliminary results of its application for vibrational circular dichroism (VCD) are presented. The device permits quarter-wave retardation in the infrared with alternating senses so that the resultant components of circular polarization can be modulated at frequencies on the order of 100 Hz. We have been able to apply this device to measure VCD with a step-scan FT-IR spectrometer by incorporating a stressed ZnSe optical element as the rotating quarter-wave plate. VCD of α-pinene and camphor were obtained. While these test spectra were of low signal-to-noise ratio (S/N), they exhibited the correct VCD spectral features for these chiral molecules. While not yet of competitive, practical utility, this design is potentially adaptable to extension into the far-IR with alternative optical elements, permits variable-frequency polarization modulation, and should be capable of improved S/N with modifications to increase rotation frequency.
X-ray Fluorescence Analysis of Gold Ore
Authors: De Celis Benito
Published: May 2005

A method to obtain high sensitivity and accuracy for nondestructive analysis of gold ore is proposed. The applied technique is energy-dispersive X-ray fluorescence, using a Co-57 radioisotope source to excite gold K X-rays in the sample, and a high-purity Ge (HPGe) detector with a range of energies from 1 keV to 4 MeV. The use of radioisotope sources and K X-rays gives some advantages in comparison with other analytical techniques and the usual tube excitation L X-ray analysis: the high sensitivity to concentrations of 1 ppm, the absence of interferences from other elements present in the matrix, and the possibility of performing fast and economical nondestructive analyses of large samples.
Fiber-Optic Raman Detection of Trace Levels of Phosphonate Vapors Chemisorbed onto an Alumina Substrate
Authors: Ewing K. J. , Dagenais D. M. , Bucholtz F. , Aggarwal I. D.
Published: May 2005

Detection of ppm(v) levels of the nerve agent simulants dimethyl methylphosphonate (DMMP) and diisopropyl methylphosphonate (DIMP) by chemisorption to an alumina surface followed by fiberoptic Raman spectroscopic determination is described. Real-time measurements of the increase in the Raman line intensities with respect to time for DMMP and DIMP chemisorption to alumina are presented. A detection limit at the 95% confidence interval of 6 ppm(v) is calculated for DMMP vapors at a vapor flow rate of 100 mL/min. Factors which limit lower detection limits are identified and possible solutions presented.
Stratospheric Trace Gas Measurements in the Near-UV and Visible Spectral Range with the Sun as a Light Source Using a Fourier Transform Spectrometer
Authors: Notholt Justus , Pfeilsticker Klaus
Published: May 2005

Spectra of the atmosphere have been measured in the near-UV and visible spectral range for the first time with a Fourier transform spectrometer using direct and zenith scattered sunlight. The observations were performed in the Arctic at 79°N, 12°E in 1994. Spectra were recorded in the wavelength range 310 to 1100 nm up to a resolution of about 0.0008 nm. The use of the FT spectrometer allowed the study of atmospheric trace gas concentrations in the whole spectral region between 500 and 31,000 cm−1 (0.3–20 μm) with one instrument by only changing the beamsplitters and choosing different detectors. At a spectral resolution of 1.2 nm, the atmospheric absorptions of O3 around 505 nm and NO2 at 448 nm were analyzed. Results are compared with observations performed in the infrared with the same instrument, with TOMS data and with ozone balloon data.
Electronic and Vibrational Circular Dichroism of Model β-Lactams: 3-Methyl- and 4-Methylazetidin-2-one
Authors: McCann Jennifer , Rauk Arvi , Shustov Gennadii V. , Wieser Hal , Yang Danya
Published: May 2005

The chiroptical properties of the simplest chiral β-lactams, 3- and 4-methylazetidin-2-one, 1 and 2, respectively, were investigated. The experimental vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) spectra were measured and compared with ab initio predictions. Both compounds were found to form dimers with calculated binding enthalpies and free energies of about −51 kJ/mol and −6 to −8 kJ/mol, respectively. The experimentally measured IR and VCD spectra were measured in concentrated nonpolar (CCl4) solution and are in agreement with the predicted IR and VCD spectra of the dimeric forms, 12 and 22, but not the monomers. The most intense dimer VCD bands originate from in-plane N-H wags, which perturb the H-bonded cyclic array. At the more dilute concentrations employed for the ECD spectra, the experimental ECD spectra in heptane were interpreted satisfactorily as arising from a mixture consisting predominantly of monomers. In protic solvent (H2O, MeOH), the ECD spectra are consistent with H-bonded monomers. Simple modeling suggests that the rotational strengths of the first electronic transition gain most of their intensity from the nonplanarity of the amide chromophore, the contributions of which follow a spiral rule previously enunciated.
Atr/Ft-Ir Difference Spectroscopy of Biological Matter with Microsecond Time Resolution
Authors: Heberle Joachim , Zscherp Christian
Published: May 2005

Attenuated total reflection (ATR) spectroscopy allows precise control of external parameters vital for proper functioning of biological matter. For the first time in biospectroscopy, ATR difference spectroscopy has been combined with the step-scan technique. The current setup integrates a broad frequency range (800–25,000 cm−1) with high temporal resolution (5 μs). Vibrations are detected that arise from single amino acids (<10−3 absorbance units) of the chromoprotein bacteriorhodopsin. Time-resolved ATR/FT-IR difference spectra are compared with conventional transmission spectra. The high mirror stability enables time-resolved FT-vis spectroscopy of the same sample with the same instrument. Potential applications even to non-light-absorbing biomaterial are discussed.
Measurement of Dispersive Vibrational Circular Dichroism: Signal Optimization and Artifact Reduction
Authors: Xie Ping , Diem Max
Published: May 2005

Artifacts, or spurious signals, are common problems in the measurement of optical activity. Until recently they have limited the applicability of vibrational circular dichroism (VCD) in cases of weak ellipticity—for example, in structural studies of small peptides. The artifacts in dispersive VCD to be discussed here can be from the optical and electronic hardware as well as from the data processing methods in the software. The data acquisition and processing methods reported here reduce system artifacts in VCD measurements, particularly for samples with weak ellipticity.
Depth Profiling of Poly(Methyl Methacrylate), Poly(Vinyl Alcohol) Laminates by Confocal Raman Microspectroscopy
Authors: Hajatdoost Sohail , Yarwood Jack
Published: May 2005

We report a molecular depth profiling study of a PMMA/PVOH laminate on quartz using confocal Raman microspectroscopy. It is demonstrated that this technique can be successfully employed to study the hydrogen-bonding interaction between the ester and alcohol groups near the interfacial region. The carbonyl, v(C=O), band of PMMA shows significant broadening in the interfacial region. Various PMMA/PVOH laminates with different PMMA molecular weights have been studied, and it is demonstrated that the PMMA layers with lower molecular weight show a greater degree of interpenetration for a given annealing time.
Development of an Ultrafast Laser Apparatus for Time-Resolved UV-Visible and Infrared Spectroscopy
Authors: Ye Tian-Qing , Arnold Caroline J. , Pattison David I. , Anderton Clare L. , Dukic Davor , Perutz Robin N. , Hester Ronald E. , Moore John N.
Published: May 2005

An ultrafast laser apparatus has been developed that allows time-resolved UV-visible and infrared spectroscopy to be performed with a time resolution of 200 fs. The instrument design allows UV-vis and IR data to be collected either as spectra or as kinetic profiles. Solution flow and cell translation sampling systems have been developed that allow the handling of chemical and biochemical systems, including highly air-sensitive materials and volumes as small as 50 μL. The apparatus performance has been evaluated with the use of trans-stilbene in hexane (UV-vis) and silicon (IR) test samples, and the techniques have been applied in combination to study both native carbonmonoxymyoglobin and the novel H64L mutant.
Optimization of Discharge Parameters for a Flat-Type Radio-Frequency Glow Discharge Source Coupled to a Quadrupole Mass Spectrometer System
Authors: Shick Charles R. , Marcus R. Kenneth
Published: May 2005

A radio-frequency (rf)-powered glow discharge (GD) atomization/ionization source for nominally flat sample types (>6 mm o.d.) has been designed and coupled to a commercial GD mass spectrometer system, the VG GloQuad. This source was evaluated and optimized for conducting as well as nonconducting samples. A parametric study has been conducted on this rf-GDMS system with respect to discharge power, Ar flow (cell pressure), limiting orifice plate (anode) diameter, and ion sampling distance. Analytical characteristics under the optimized source parameters—including stabilization times (5 min for conducting samples, 60 min for nonconducting samples); repeatability (overall internal <2% RSD, overall external <8% RSD employing ion beam ratios); quantification; and detection limits—were evaluated for both conducting and nonconducting samples.
High-Resolution Spectroscopy Using an Acousto-Optic Tunable Filter and a Fiber-Optic Fabry-Perot Interferometer
Authors: Baldwin David P. , Zamzow Daniel S. , D'Silva Arthur P.
Published: May 2005

A compact, solid-state, high-resolution spectrometer consisting of an acousto-optic tunable filter (AOTF) and a fiber-optic Fabry-Perot (FFP) interferometer has been developed. The system has been designed for high-resolution inductively coupled plasma atomic emission spectroscopy (ICP-AES) applications. A description of the AOTF-FFP and its performance is presented. The resolution of the AOTF-FFP was determined by measuring the physical widths of ICP emission lines using a 1.5-m-focal-length grating spectrometer and deconvoluting the physical line shapes from the acquired AOTF-FFP spectra. Over the optimum range of the FFP mirror coatings, the resolution is sufficient for the determination of isotopic and hyperfine emission features in ICP-AES experiments, and approaches that of the 1.5-m spectrometer. The application of the AOTF-FFP to the determination of uranium isotopes (U-235 and U-238) introduced into the ICP is presented.
Identification of Electrolytes in Aqueous Solutions from Near-IR Spectra
Authors: Lin Jie , Zhou Jing , Brown Chris W.
Published: May 2005

Dissolution of electrolytes causes characteristic changes in the near-IR spectrum of water. These changes result from a decrease in the concentration of water; charge-dipole interactions between ions and water molecules; formation of hydrogen bonds between oxygen or nitrogen atoms in some ions and water molecules; production of H+ and OH− ions from dissociation and hydrolysis; absorptions due to OH, NH, and CH groups in some ions; and intrinsic colors of some transition metal ions. Changes in spectra were used for identification of electrolytes in aqueous solutions. Near-IR spectra of 71 solutions of single electrolytes were measured and used to develop a spectral library. This near-IR spectral library was processed with principal component regression (PCR) and used for the identification of single and multiple electrolytes in aqueous solutions with the use of their spectra. Most of the unknown electrolytes were identified correctly. For the others, very similar electrolytes were selected with one ion identified correctly. The near-IR spectral library of aqueous solutions of electrolytes can be used as a simple and fast approach for the identification of electrolytes.
Atmospheric-Pressure Helium Inductively Coupled Plasmas for Elemental Mass Spectrometry
Authors: Zhang Hao , Nam Sang-Ho , Cai Mingxiang , Montaser Akbar
Published: May 2005

Analytical and fundamental characteristics of helium inductively coupled plasma mass spectrometry (He ICPMS) were explored for atmospheric-pressure plasmas generated in a 13-mm He ICP torch with the use of a prototype ICPMS equipped with an analogue detector. Four sets of operating conditions were identified for the detection of four categories of elements at levels lower than or similar to those of the Ar ICPMS. In general, detection limits of He ICPMS were improved by two to four orders of magnitude for metals, compared to results from our previous study with the same torch. For the easy-to-atomize elements (Li, Na, K, Ga, Rb, In, Cs, Tl, Pb, and Bi), the detection limits ranged from 0.1 to 7 pg/mL at 500–600 W forward power. Detection limits of the fourth-period transition metals (Cr, Mn, Fe, Co, Ni, and Cu), i.e., elements subject to the spectral interferences in Ar ICPMS, were 4 to 100 pg/mL at a power level of 560–700 W. The detection limits of hard-to-atomize elements (Ti, V, Sr, Y, Rh, Pr, Tm, Th) ranged from 4 to 90 pg/mL at 800 W. For hard-to-ionize elements (As, Se, Br, Sn Sb, I), detection limits of 0.05 to 1 ng/mL were obtained at 820 W. Ion kinetic energies were measured under two diverse sets of operating conditions. At 600 W, the ion kinetic energies were very low (2.6–6.6 eV for mass range 39–209 amu), indicating the absence of a secondary discharge at the sampler tip of the MS interface. The gas-kinetic temperature estimated in this measurement was 600 K for the 600-W He ICP. In contrast, very high ion kinetic energies (31–66 eV for mass range 51–232 amu) were obtained at 800 W. The estimated plasma potential and gas kinetic temperature were 22 V and 3500 K, respectively. Ion kinetic energies of polyatomic ions were slightly lower than those of atomic ions at the same mass, suggesting that polyatomic ions were formed in the low-temperature zones of the He ICP.
Effects of a Heavy-Atom Salt on the Solid-Matrix Luminescence Properties of the (±)-Trans-7,8-Dihydroxy-Anti-9,10-Epoxy-7,8,9,10-Tetrahydrobenzo[a]Pyrene-DNA Adducts and Tetrol I-1 Adsorbed on Several Solid Matrices
Authors: Chu Yu , Hurtubise Robert J.
Published: May 2005

The effects of a heavy-atom salt on the room-temperature solid-matrix luminescence properties of the (±)- trans-7,8-dihydroxy- anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[ a]pyrene-DNA adducts [(±)- anti-BPDE-DNA adducts] and benzo[ a]pyrene- r-7, t-8,9, c-10-tetrahydrotetrol (tetrol I-1) on several solid matrices were investigated. TlNO3 was found to be very effective in enhancing the room-temperature phosphorescence of the (±)- anti-BPDE-DNA adducts and tetrol I-1. However, the room-temperature fluorescence signals were quenched from the (±)- anti-BPDE-DNA adducts and tetrol I-1 on the solid matrices with the heavy-atom salt. It was found that 1% α-cyclodextrin/TlNO3, 10% trehalose/TlNO3, and 30% TlNO3/sodium acetate (NaOAc) yielded very strong RTP signals from the (±)- anti-BPDE-DNA adducts. The greatest enhancement of the RTP intensities from the (±)- anti-BPDE-DNA adducts was achieved with 30% TlNO3/NaOAc. In addition, a very low limit of detection (0.14 fmole/mg) for tetrol I-1 was acquired with 30% TlNO3/NaOAc. With its tremendous enhancement of RTP signals from the adducts and tetrol I-1 and the sub-femtomole limit of detection obtained for tetrol I-1, 30% TlNO3/NaOAc is ideal for the characterization and analysis of DNA adducts and their tetrol products.
Novel In situ Probe for Monitoring Polymer Curing
Authors: Aust Jeffrey F. , Booksh Karl S. , Myrick Michael L.
Published: May 2005

A novel probe design for in situ fiber-optic Raman spectroscopy has been tested and employed for real-time monitoring of an epoxy curing. The epoxy system consists of diglycidylether of bisphenol-A and polyoxypropylenetriamine. The probe consists of a single fiber optic and a small section of Teflon® tubing. The tube acts as a waveguide and sample holder. Raman signal enhancements of 15 x were observed with the employment of the tube compared to those of spectra acquired with the single fiber alone. This analysis studied the C-H stretching region of the epoxide, where previously studies have centered around the fingerprint region. The small volume of the probe and large surface area allow it to be used effectively as a method of polymer thin-film measurement. It is also effective in bulk polymer measurements because of a negligible amount of heat trapped in the sample during curing. This gives the probe a temperature and reaction rate characteristic of the polymer surrounding it. Multivariate analysis was employed to interpret and analyze the numerous spectra taken during analyses. Multivariate techniques show that both curing and sample internal temperature information can be derived from the Raman spectra.
Dynamic Step-Scan Two-Dimensional Fourier Transform Infrared Studies of Uniaxially Drawn Poly(Ethylene Terephthalate) Film
Authors: Sonoyama Masashi , Shoda Kunihiro , Katagiri Gen , Ishida Hideyuki
Published: May 2005

Dynamic infrared spectra of uniaxially drawn poly(ethylene terephthalate) (PET) under a sinusoidal strain were examined. A very intense dynamic band at 973 cm−1 assigned to the trans C-O stretching mode indicated stress-induced high mobility around the C-O bond in the ethylene glycol units. It was supposed that derivative-like skeletal bands observed in the dynamic spectra originated from the stress-induced frequency shift. Two-dimensional correlation analyses of the dynamic spectra were also carried out and revealed that the phenyl ring 18a band at 1018 cm−1 and the phenyl ring 19b band at 1410 cm−1 were composed of three and two independent components, respectively. The correlation peaks between the phenyl ring and CH2 vibrational modes showed that orientation of the methylene group in the ethylene glycol unit, induced by mechanical stretching, is faster than that of the phenyl ring in the terephthalate unit.
Investigation of Sample Atomization Using a Power-Modulated Radio-Frequency Glow Discharge Source
Authors: Parker Mark , Marcus R. Kenneth
Published: May 2005

A power-modulated (pulsed), radio-frequency glow discharge source by atomic absorption spectrophotometry (rf-GD-AAS) atomizer was used to evaluate the roles of applied power, pressure, orifice diameter, duty cycle, and power-on time in the production of gas-phase sample atoms. As expected, the response of the modulated rf-GD-AAS source generally followed the same trends as those exhibited by the more common continuous-powering scheme. The effects of discharge power and pressure on the observed plasma emission and absorbance transients are presented. Use of small duty cycles and higher instantaneous powers, thus keeping the same overall average power as in the continuous mode, was shown to increase the production of ground-state atoms. However, using very high instantaneous powers may more efficiently populate excited states of the atomic species, thus decreasing the observed absorption signal for resonant transitions. Individual pulse transients were shown to be distorted if the plasma “on” times approached periods down to 2 ms. Plasma stabilization times for measurements taken in the “dark” portion of the pulse cycle (i.e., after pulse termination) were comparable to those obtained in the continuous mode (on the order of a few seconds) with the use of the same source and sample. Calibration curves were used to investigate the analytical utility of different temporal regions of the absorption transients with comparisons made between the plasma “on” and “off” portions of the cycle in the quantification of continuous plasma operation.
Determination of Copper in A533b Steel for the Assessment of Radiation Embrittlement Using Laser-Induced Breakdown Spectroscopy
Authors: Ernst Wolfgang E. , Farson Dave F. , Sames D. Jason
Published: May 2005

Determination of radiation embrittlement in nuclear reactor pressure vessels is crucial to assessing safe operative lifetimes for many aging nuclear power plants. Conservative nuclear fluence estimates and trace impurity diagnosis of the weldment material are the basis of radiation embrittlement analysis. Copper is thought to be a key impurity contributing to radiation embrittlement. In this paper, the application of laser-induced breakdown spectroscopy (LIBS) as a means to assess radiation embrittlement by the detection and quantification of copper in A553b steel was investigated. A LIBS configuration completely coupled by fiber optics was attempted, but because of low laser power and fiber losses, fiber-optic delivery of the laser beam was unsuccessful. Consequently, hard optics (lenses and mirrors) were employed for laser beam delivery. The plasma emission was delivered successfully via fiber optics to the detection apparatus. Copper measurements were made from custom-fabricated steel samples. Comparison of the LIBS results to an independent atomic absorption spectrophotometry (AAS) analysis showed LIBS to be of comparable accuracy, especially in low-level copper samples.
Class of Photostable, Highly Efficient UV Dyes: 2-Phenylbenzoxazoles
Authors: Kanegae Yukie , Peariso Katrina , Martinez Shannon Studer
Published: May 2005

The photophysics and lasing properties of 2-phenylbenzoxazole,2-(4'-methoxyphenyl)benzoxazole and 2-(4'-diethylaminophenyl)-benzoxazole in nonpolar solvents are reported. This class of 2-phenylbenzoxazoles provides near-UV laser generation with a wide range of tunability (330–380 nm). The efficient laser output and extreme photostability of this class of dyes make their practical application feasible when pumped by a nitrogen laser (337 nm), XeCl excimer laser (308 nm), or Nd:YAG laser (fourth harmonic, 266 nm).
Application of the Fast Wavelet Transform Method to Compress Ultraviolet-Visible Spectra
Authors: Chau F. T. , Shih T. M. , Gao J. B. , Chan C. K.
Published: May 2005

Data compression methods based on the fast wavelet transform and the multiresolution signal decomposition algorithms were devised and applied to ultraviolet-visible absorption spectra. Wavelet functions of the Daubechies type were employed for the purpose. In addition, two data pretreatment procedures were proposed and used to cope with the side-lobe problem. The performance of these methods was evaluated by using both synthetic and experimental data. It was found that the storage space of the spectral information under study can be reduced significantly by using the suggested methods with good-quality spectra generated from the compressed data.
FT-IR Spectroscopic Investigation of 4,4'-Bipyridine Adsorption on Metal Oxide Surfaces
Authors: Bagshaw Stephen A. , Cooney Ralph P.
Published: May 2005

4,4‘-Bipyridine (4bipy) adsorption on the surfaces of silica, alumina, and titania and the infrared (IR) spectra obtained therefrom are reported for the first time. This paper constitutes the second part of a multi-faceted investigation into the development of a vibrational spectroscopic technique for the determination of distances between surface acid sites of three-dimensional solid acids. The aforementioned oxides were chosen because their surface chemistries are generally well understood and because they constitute the pillars within pillar interlayered clay (PILC) catalysts. However, there is little information in the literature regarding the surface interactions of this novel and potentially useful spectroscopic probe. The pore structures of PILC materials have been investigated through 4bipy adsorption, the results of which will be reported in a later paper. The spectra obtained for adsorption on the parent oxides are discussed with reference to earlier 4bipy and 2,2’-bipyridine (2bipy) adsorption studies and indicate that the mode of adsorption is a unidentate, “end-on” arrangement in agreement with that observed for adsorption on MgO. This mode of adsorption results in a reduction in molecular symmetry of the adsorbed 4bipy from D2 h to C2γ. A previously unreported observation involving the high-temperature cleavage of the inter-ring bond of 4bipy adsorbed on γ-alumina and titania Lewis acid sites is described.
Quantitative Analysis of Copolymers by GPC/FT-IR
Authors: Liu Michael X. , Dwyer James L.
Published: May 2005

A combined method of chromatography and infrared spectroscopy is employed to map the distribution of monomers in copolymer samples. The method relies on the measurement of spectral peak ratios of the sample, using polymer samples of known composition as calibration standards. The inherent variation of the method was established by measuring a homopolymer of invariant composition. The samples examined were styrene/butadiene copolymers, synthesized by two different polymerization protocols. The technique provided sensitive measurement of comonomer composition across the molecular weight distribution of the samples and is generally applicable to copolymers that can be fractionated by chromatographic methods.
Near-Infrared Surface-Enhanced Raman Scattering Spectra of Heterocyclic and Aromatic Species Adsorbed on TLC Plates Activated with Silver
Authors: Matějka P. , Stávek J. , Volka K. , Schrader B.
Published: May 2005

Near-infrared surface-enhanced Raman scattering (NIR SERS) spectra were obtained for 2,2-bipyridine, 5,6-benzoquinoline, pyrene, anthracene, and fluoranthene on SERS pre-activated thin-layer chromatography (TLC) plates by Fourier transform (FT) Raman spectroscopy. The pre-activation of TLC plates was based on a procedure of dipping the plates into a solution of silver oxalate and the subsequent pyrolysis of adsorbed silver oxalate forming silver particles on the plates. The effects of the type of TLC plates, the time of immersion in the silver oxalate solution, and the time of pyrolysis are discussed with respect to the SERS activity of the systems formed.
Laser-Induced Solid-Surface Room-Temperature Phosphorimetry of Polycyclic Aromatic Hydrocarbons
Authors: Campiglia A. D. , Hueber D. M. , Vo-Dinh T.
Published: May 2005

Laser-induced solid-surface room-temperature phosphorimetry (SSRTP) has been employed for the detection of polycyclic aromatic hydrocarbons. A nitrogen-pumped laser and a dye laser were used as excitation sources. The effects of sample volume, laser irradiation, and background reduction treatment on the precision and sensitivity of the method were studied. With the use of thallium(I) acetate as a phosphorescence enhancer, picogram limits of detection were estimated for phenanthrene, pyrene, benzo[ g,h,i]perylene, chrysene, coronene, and 1,2-benzofluorene. The study demonstrates that laser excitation can improve the sensitivity of SSRTP by up to three orders of magnitude.
Near-Infrared FT-SERS Microspectroscopy on Silver and Gold Surfaces: Technical Development, Mass Sensitivity, and Biological Applications
Authors: Beljebbar A. , Sockalingum G. D. , Angiboust J. F. , Manfait M.
Published: May 2005

An FT-Raman and FT-SERS microprobe with the spatial resolution on the micrometer scale has been developed. The main interfacing components are discussed and the whole setup is validated with the use of different SERS-active substrates: silver and gold colloids and gold island films. Micro-FT-SERS spectra of crocetin, mitoxantrone, and mitoxantrone/DNA complexes have been obtained, and the mass detection limits are found to be on the order of 5 × 102 molecules. Adsorption on the SERS-active substrates does not induce any detectable changes in the all-trans configuration of the crocetin. Adsorption of the mitoxantrone/DNA complex does not induce detectable perturbations of the molecular interactions within the complex. Moreover, interactions between the drug and DNA induces very similar effects in both the resonance Raman and FT-SERS spectra of the drugs. These effects were found to be consistent with the model of mitoxantrone/DNA intercalation proposed from nuclear magnetic resonance and resonance Raman data. The signal-to-noise ratios found indicate that submonolayer amounts of intracellularly localized drugs totaling less than 10−18 mole can be detected by means of the FT-SERS microprobe. Hence, both the extra-low mass detection limit of the technique and its sensitivity to interactions within the supramolecular complexes will in the future allow the drug to be followed within the living cell.
Breakdown Characteristics in Argon-Helium Mixtures Using an Improved Microcavity Hollow Cathode Emission Source
Authors: Chen Yixin , Williams J. C.
Published: May 2005

Improvements to the microcavity hollow cathode source are reported. These include a lower breakdown voltage and a larger operating range of fill-gas pressures of argon, helium, and mixtures of each. Data showing the effect of size, shape, and materials (copper and stainless steel) of the cathodes and anodes on the breakdown voltage are presented. The minimum discharge current required for the discharge to enter the cathode cavity is profoundly affected by the size of the cathode cavity.
Laser Diode Reflectometry and Infrared Emission Measurements of Permeating Gases at High Driving Pressures and Temperatures
Authors: Funk David J. , Breshears W. Dale , Laabs Gary W. , Asay Blaine W.
Published: May 2005

We report the use of infrared diode lasers in a diffuse reflection geometry for detection of the cyclotetramethylentetranitramine (HMX) combustion product CO permeating through a silicon carbide bed. We find that infrared emission and transient absorption are coincident with these pressure waves and demonstrate the feasibility of these diagnostics for detecting molecular species in hostile environments. We conclude from the experimental evidence that macroscopic convective heating may play a limited role in the deflagration-to-detonation transition (DDT) of porous explosives.
Reduced-Pressure Inductively Coupled Plasma Mass Spectrometry for Nonmetallic Elements
Authors: Yan Xiaomei , Tanaka Tomokazu , Kawaguchi Hiroshi
Published: May 2005

A reduced-pressure argon inductively coupled plasma (ICP) is interfaced to a mass spectrometer to evaluate its possibility of increasing the sensitivity of nonmetallic elements. An electrostatically shielded water-cooled torch is used for the investigation of the secondary discharge at the sampling orifice. Iodine vapor is continuously introduced into the torch as an analyte by using a peristaltic pump. The effects of plasma operating parameters such as gas flow rate, pressure, and power on the intensities of background and iodine ions are studied. It is shown that when the pressure is less than about 30 Torr, an intensive secondary discharge occurs at the sampling orifice if the torch shield is not grounded. The background ion intensity and secondary discharge effect decrease with increasing pressure. The pressure in the torch has an important effect on both polyatomic and analyte intensities. At about 130 Torr of torch pressure, the iodine signal is more than one order of magnitude higher than that obtained at atmospheric pressure, which suggests that low-pressure ICP provides a sensitive ion source for the elements with high ionization potential.
Near-Infrared Acousto-Optic Tunable Filter Hadamard Transform Spectroscopy
Authors: Turner John F. , Treado Patrick J.
Published: May 2005

The acousto-optic tunable filter (AOTF) is a digitally accessible, compact, solid-state spectrometer that is well suited to high-frequency optical switching and wavelength selection. With injection of a combination of radio-frequency signals into its transducer, the AOTF acts as an electronically controllable, multiplexing spectrometer. The multiplexing AOTF in this study is employed in two distinct fashions. The first of these utilizes the multiplexing AOTF as a matched filter whose intended spectral profile (i.e., bandpass and band symmetry) is controlled almost at will, providing unprecedented flexibility and high throughput. Second, the multiplexing AOTF is employed for the first time as a Hadamard transform spectrometer. In operation, the integrated intensity on the detector measures combinations of the diffracted wavelengths. The light encodement is performed without the use of physical masks and is governed by HT mathematics, which allow efficient recovery of the optical spectrum. Appreciable signal-to-noise enhancement is demonstrated with the HT AOTF spectrometer.
Polarization-Division Beamsplitters with KBr and KRS-5 Substrates for Fourier Transform Infrared Spectroscopy
Authors: Polavarapu Prasad L. , Deng Zhengyu , Weibel Stephen
Published: May 2005

Polarization-division beamsplitters with KBr and KRS-5 substrates were constructed and evaluated for their performance in Fourier transform infrared spectroscopy. It is found that the beamsplitter with a KRS-5 substrate is not practically useful; the one with a KBr substrate has good potential, although its current performance is significantly poorer than the performance of a beamsplitter with a BaF2 substrate. Representative spectra obtained with a KBr beamsplitter are presented.
Diode Laser-Based Absorption Detector for Conventional-Size Liquid Chromatography
Authors: Mank A. J. G. , de Nijs H. , Lingeman H. , Brinkman U. A. Th. , Velthorst N. H. , Gooijer C.
Published: May 2005

A diode laser-based absorption detector is designed for conventional-size liquid chromatography (LC). To this end, various detection setups and individual components have been evaluated. A ratioing system using a 10-mW 670-nm diode laser allowed the detection of 6 × 10−10 M mitoxantrone [signal-to-noise (S/N) = 3; N = root-mean-square (rms) noise], an anti-tumor drug, in a biological matrix without any sample cleanup. Multipass detection and intensity modulation of the excitation light did not improve the detection limit. A fiber-optic detector cell, utilizing a gradient-index lens on the light-guiding fiber, was a good and robust alternative for the standard absorption detector cell. Detection limits with the use of the diode laser-based detector are 20-fold better than those obtained with a commercial absorption detector for LC.
Secondary Structure of Bovine Albumin as Studied by Polarization-Sensitive Multiplex CARS Spectroscopy
Authors: Voroshilov Artemy , Otto Cees , Greve Jan
Published: May 2005

The first application of polarization-sensitive multiplex coherent anti-Stokes Raman spectroscopy (MCARS) in the absence of resonance enhancement to the resolution of the secondary structure of a protein in solution is reported. Polarization MCARS spectra of bovine albumin in D2O were obtained in the range 1370 to 1730 cm−1 with the aid of the background suppression technique. The spectra were fitted simultaneously with a single set of parameters (band positions, bandwidths, amplitudes, and depolarization ratios). Polarized Raman spectra simulated with these parameters revealed a good correspondence with the spontaneous Raman spectra measured. The broad amide I′ band was decomposed assuming the three major secondary conformations of protein, of which the contribution of β-sheet structure was found to be negligible. Relative weights of α-helix and random coil conformations agree well with the estimates obtained with Raman and circular dichroism (CD) spectroscopies.
Fuzzy Optimal Associative Memory for Background Prediction of Near-Infrared Spectra
Authors: Wabuyele Busolo Wa , Harrington Peter De B.
Published: May 2005

A fuzzy optimal associative memory (FOAM) has been devised for background correction of near-infrared spectra. The FOAM yields improved predicted background scans for calculation of near-IR absorbance spectra of glucose in plasma matrices from single-beam data. The FOAM is an enhanced optimal associative memory (OAM) that uses a fuzzy function for encoding the spectra. The FOAM can predict a matching reference spectrum for a near-IR absorbance spectrum with low glucose absorbances by using second-derivative spectra. Glucose concentrations were predicted from calibration models furnished by partial least-squares (PLS). The FOAM stored reference spectra obtained from either water/phosphate buffer or plasma/glucose solutions. Both of these associative memories were evaluated. The standard error of prediction (SEP) for glucose concentration from an optimal PLS calibration model based on FOAM-corrected spectra was 0.60 mM for the water/phosphate buffer spectra. For FOAM-corrected spectra from plasma/glucose reference spectra, the SEP was 0.68 mM. The SEP of conventionally corrected double-beam second-derivative spectra was 0.81 mM. FOAM-corrected spectra generally furnish improved calibration models.
Infrared Spectral Imaging of the Interphase of Epoxy-Glass Fiber-Reinforced Composites under Wet Conditions
Authors: Arvanitopoulos Constantinos D. , Koenig Jack L.
Published: May 2005

Infrared imaging was utilized to analyze the behavior of epoxy-glass fiber composites when exposed to moist conditions. With the use of mapping subtraction, the differences in the water uptake were revealed when different types of glass fibers were used. Composites prepared with as-received glass fibers exhibit the highest water uptake at the interphase as opposed to those prepared with silane-treated glass fibers, which exhibit the lowest uptake. Moreover, the epoxide deformation band was examined in order to analyze the effect of water on the curing of the composites. Water was found to catalyze a polymerization reaction at the interphase, but only if a certain level of water concentration is present is the above phenomenon detectable.
Differential Polarized Reflectance Spectroscopy at Air/Water and Air/Metal Interfaces
Authors: Polavarapu Prasad L. , Deng Zhengyu
Published: May 2005

We report the direct measurement of differential polarized reflectance spectra for samples at air/water and air/metal interfaces. 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 the input beam. Collimated light rays exiting the interferometer are focused by an f/5 lens and bent from the horizontal propagating axis by a ZnSe wedge to give an angle of incidence of ∼75°, at the sample. The reflected rays are brought back to the horizontal propagation direction by another ZnSe wedge and focused onto the detector by an f/1 lens. The interferogram obtained in this manner represents the differential polarized reflectance interferogram whose cosine Fourier transform directly gives the differential polarized reflectance spectrum. Thus, these spectra were obtained without need for the commonly used photoelastic modulator. Representative spectra for monolayers on a water surface and for samples on a gold surface are presented.