bluuebunny/crossref_metadata_2025 huggingface dataset:
Flame Front Observation of Ammonia Decomposition and Oxidation Using 193 nm Two-Photon Photolysis and Photofragment Fluorescence
Authors: Chadwick Bruce L. , Charlston-Goch Denise , Campisi Anthony , Morrison Richard J. S.
Published: October 2003

The 193 nm output of an ArF laser is utilized in the detection of gas-phase ammonia in methane–air flames of varying stoichiometry. Photolysis of ammonia with the 193 nm radiation results in NH photofragment fluorescence—the intensity of which is found to be proportional to the concentration of the ammonia present. Detection limits of <1 ppm of gas-phase ammonia are readily achievable under atmospheric flame conditions. Two-dimensional images of ammonia decomposition have been obtained for a laminar premixed flame, clearly revealing the conical reaction zone. Thermal decomposition of the ammonia is observed in the pre-flame zone of the burner in addition to its oxidation in the reaction zone.
Effect of Spectral Resolution on Pattern Recognition Analysis Using Passive Fourier Transform Infrared Sensor Data
Authors: Bangalore Arjun S. , Demirgian Jack C. , Boparai Amrit S. , Small Gary W.
Published: October 2003

The Fourier transform infrared (FT-IR) spectral data of two nerve agent simulants, diisopropyl methyl phosphonate (DIMP) and dimethyl methyl phosphonate (DMMP), are used as test cases to determine the spectral resolution that gives optimal pattern recognition performance. DIMP is used as the target analyte for detection, while DMMP is used to test the ability of the automated pattern recognition methodology to detect the analyte selectively. Interferogram data are collected by using a Midac passive FT-IR instrument. The methodology is based on the application of pattern recognition techniques to short segments of single-beam spectra obtained by Fourier processing the collected interferogram data. The work described in this article evaluates the effect of varying spectral resolution on the pattern recognition results. The objective is to determine the optimal spectral resolution to be used for data collection. The results of this study indicate that the data with a nominal spectral resolution of 16 cm−1 provide sufficient selectivity to give pattern recognition results comparable to that obtained by using higher resolution data. We found that, while higher resolution does not increase selectivity sufficiently to provide better pattern recognition results, lower resolution decreases selectivity and degrades the pattern recognition results. These results can be used as guidelines to maximize detection sensitivity, to minimize the time needed for data collection, and to reduce data storage requirements.
Thermal Volatilization Analysis: A Versatile Platform for Spectroscopic Investigations of Polymer Degradation Processes
Authors: Guo Xiaoyen (Kathy) , Huang Bin , Dyakonov Tania , Chen Yan , Padron Laz , Vickstrom Thayne , Kuhn John , Hodkiewicz Joseph , Stevenson William T. K.
Published: October 2003

The thermal volatilization analysis (TVA) and subambient thermal volatilization analysis (SATVA) techniques are described. In addition to rate profiling of the volatile product flux of thermal degradation under high-vacuum conditions through measurement of pressure in the vacuum line as a function of sample temperature, the TVA technique is shown to afford a convenient method for an isolation, on the basis of volatility under high-vacuum conditions, of product fractions of thermal degradation for subsequent spectroscopic analysis. The capacity and flexibility of TVA as a platform for these analyses are illustrated in a case study format by degrading poly(bisphenol A, 2-hydroxy propylether). The overall degradation process is quantified, and most significant pathways of thermolysis are identified through subsequent spectroscopic analysis of products of decomposition. The design and construction of a modified vacuum-tight long-path gas IR cell, as an interface allowing for the application of Fourier transform infrared spectroscopy (FT-IR) for the on-line analysis of volatile products of polymer degradation, is detailed. Proof of concept and application of this new analytical technique, subsequently referred to as TVA/FT-IR, is illustrated through the examination of appropriate aspects of the thermal degradation of polymethyl methacrylate polymers.
Noninvasive, On-Line Monitoring of the Biotransformation by Yeast of Glucose to Ethanol Using Dispersive Raman Spectroscopy and Chemometrics
Authors: Shaw Adrian D. , Kaderbhai Naheed , Jones Alun , Woodward Andrew M. , Goodacre Royston , Rowland Jem J. , Kell Douglas B.
Published: October 2003

We describe the first application of dispersive Raman spectroscopy using a diode laser exciting at 780 nm and a charge-coupled device (CCD) detector to the noninvasive, on-line determination of the biotransformation by yeast of glucose to ethanol. Software was developed which automatically removed the effects of cosmic rays and other noise, normalized the spectra to an invariant peak, then removed the “baseline” arising from interference by fluorescent impurities, to obtain the “true” Raman spectra. Variable selection was automatically performed on the parameters of relevant Raman peaks (height, width, position of top and center, area and skewness), and a small subset used as the input to cross-validated models based on partial least-squares (PLS) regression. The multivariate calibration models so formed were sufficiently robust to be able to predict the concentration of glucose and ethanol in a completely different fermentation with a precision better than 5%. Dispersive Raman spectroscopy, when coupled with the appropriate chemometrics, is a very useful approach to the noninvasive, on-line determination of the progress of microbial fermentations.
Raman Microscopy of a Mediaeval Spanish Cantoral
Authors: Edwards H. G. M. , Farwell D. W. , Perez F. Rull , Villar S. Jorge
Published: October 2003

A Raman microscopic study of a 14th century Spanish choir book (cantoral) from Burgos has revealed information about the pigments used in the historiated initials, the ruled lines of Latin verse, the musical staves, and the script itself. The predominant red pigment is cinnabar, mercury(II) sulfide, which appears to have been possibly extracted and refined from local mineral sources. The black notes constituting the musical staves are comprised of lamp black. Sparse decoration with blue and purple pigments is also present; azurite is present in both of these, but the purple pigment also shows bands which are characteristic of an as-yet-unidentified organic-based red pigment. The parchment substrate spectrum shows evidence for amide I and amide III bands, with some evidence of degradation.
Towards Faster FT-IR Imaging by Reducing Noise
Authors: Bhargava Rohit , Ribar Travis , Koenig Jack L.
Published: October 2003

Fourier transform infrared (FT-IR) imaging is a powerful technique that can be used to obtain spatially resolved chemical information from a large sample area in a relatively short time. However, temporal resolution of fast FT-IR imaging is limited by rapid degradation of data quality (due to increased noise) with faster image acquisition. We present various coaddition schemes to reduce noise and improve the quality of images acquired from such systems. The application of the proposed schemes allows for improved signal-to-noise ratio (SNR) characteristics in the resulting data. These schemes are tested by monitoring the dissolution of a polymer film [poly(α-methyl styrene)] by a low-molecular-weight solvent [methyl isobutyl ketone (MIBK)]. Pseudo coaddition improved the SNR by ∼ 45%, while the SNR for sampling coaddition was found to scale as ∼ N0.5 where N is the number of coadded pixels. A total acquisition time of about 100 s was achieved, allowing the dissolution process to be monitored by using image acquisitions separated by 3 min. Low noise concentration profiles, linear solvent penetration rate, and polymer dissolution rate were measured. Detection limits of ∼ 5% and quantification limits of ∼ 20% were achieved by using optimal coaddition strategies. This result represents an order of magnitude improvement over untreated data.
Thermal Dependence of the Cr-to-Nd Energy Transfer in Lanthanum Lutetium Gallium Garnet
Authors: Özen G. , Dibartolo B.
Published: October 2003

Photoluminescence, excitation, and response to pulsed excitation measurements show the existence of the Cr3+ -to-Nd3+ energy transfer in lanthanum lutetium gallium garnet with an efficiency η = 0.59 at room temperature. The transfer occurs radiatively and non-radiatively, and both transfer rates are temperature dependent within 15–550 K. The nonradiative transfer rate, calculated as a function of temperature by using the lifetime data of the Cr3+ ion in the crystal, increases slowly with increasing temperature.
The Red-Shift Cascade: Investigations into the Concentration-Dependent Wavelength Shifts in Three-Dimensional Fluorescence Spectra of Petroleum Samples
Authors: Smith Garon C. , Sinski Joseph F.
Published: October 2003

Samples of motor oil and creosote are subjected to three-dimensional fluorescence spectroscopy to document the shifting of excitation/emission maxima as the solutions undergo serial dilutions. Effects such as self-quenching of individual polycyclic aromatic hydrocarbons (PAHs) and energy transfer between PAHs combine to produce large red-shifts in the resulting fluorescence emission spectra. The concentration-imposed complications are also demonstrated for several synthetic ternary PAH mixtures and a diesel residue mimic.
Solid-Phase Extraction in Conjunction with Matrix-Assisted Laser Desorption Ionization/Quadrupole Ion Trap Mass Spectrometry for the Determination of Benzoylecgonine in Urine
Authors: Hall Brad J. , Goolsby Brian , Brodbelt Jennifer S.
Published: October 2003

A matrix-assisted laser desorption ionization/quadrupole ion trap/mass spectrometer (MALDI-QIT-MS) system is evaluated for the rapid analysis of benzoylecgonine, a cocaine metabolite, from human urine after solid-phase extraction (SPE). Collisionally activated dissociation (CAD) is utilized to provide unambiguous confirmation of benzyolecgonine. In addition, MALDI-QIT-MS is shown to be a viable, rapid quantitative method of analysis for benzoylecgonine with the inclusion of a deuterated benzoylecgonine internal standard. Linearity was established from 1 to 10 μg/mL of benzoylecgonine in urine. A clinical urine sample known positive for benzoylecgonine was analyzed by MALDI-QIT-MS. The results indicate a mean concentration of 6.2 μg/mL [7.4% relative standard deviation (RSD), n = 3] of benzoylecgonine by the MALDI method, which is in good agreement with the result of 7.1 μg/mL (7.0% RSD, n = 3) obtained by a standard gas chromatography (GC)-MS procedure. Therefore, the MALDI method is demonstrated to be a rapid method for the quantitation of benzoylecgonine without post-SPE derivatization and chromatographic separation. Finally, the MALDI method is briefly extended to another class of analyte, methadone, and [(±)-2-ethyl-1,5-dimethyl-3,3-diphenyl-pyrrolinium] (EDDP), a methadone metabolite, to demonstrate that the technique holds potential for a wide range of analytes.
Determination of the Hydration of Methylene Blue Aggregates and Their Dissociation Constants Using Visible Spectroscopy
Authors: Zhao Zhouming , Malinowski Edmund R.
Published: October 2003

The visible spectra of methylene blue (MB) in aqueous-methanol solutions were used to determine the extent of hydration of MB aggregates. The investigation was carried out at MB concentrations of 1.000 × 10−4 M and 1.000 × 10−3 M. Abstract factor analysis (AFA) was used to determine the number of chemical species responsible for the spectral data. The species were identified as aqueous MB monomer, dimer, and trimer, and a methanoic MB monomer. The absorptivity spectra of the aqueous MB species obtained from the previous studies were used to extract their concentration profiles in methanol–water mixtures. With the addition of methanol to the aqueous solvent, the concentration of water could be varied from 0% to 100%. This variation was used to determine the extent of hydration and solvation of each of the four MB species, as well as their mutual equilibria. The species were identified as (1) MB+CH3OH, MB monomer monomethanol; (2) MB+H2O, MB monomer monohydrate; (3) (MB)2++ 6H2O, MB dimer hexahydrate; and (4) (MB)3Cl++ (H2O)13, MB trimer monochloro tridecahydrate. The dissociation constants for the hydrated monomer, dimer, and trimer were determined to be 0.48, 1.29 × 103 M5 and 7.2 × 106 M13, respectively.
Improving Complex Near-IR Calibrations Using a New Wavelength Selection Algorithm
Authors: McShane Michael J. , Cameron Brent D. , Coté Gerard L. , Spiegelman Clifford H.
Published: October 2003

Near-infrared spectroscopy is being considered as a tool for the noninvasive determination of important cell culture media constituents, which would allow frequent, harmless sampling and computer interfacing for closed-loop control. Partial least-squares calibration models for glucose and lactate are constructed for cell culture media and aqueous media comprised of several absorbing species. Wavelength selection, having failed in previous attempts with these data, is shown to reduce the error prediction and number of required wavelengths when performed with the use of a newly developed “peak-hopping” algorithm. The selection method reduces prediction errors in every case considered here and is extendable to combined calibration models that are built for use with a particular type of sample with the aid of high-quality spectra from simpler mixtures. The new selection algorithm leads to calibrations producing accurate predictions with fewer wavelengths, in support of previous results obtained when applied to single-component Raman spectroscopy data. The findings continue to suggest that the algorithm can be used as a simple alternative to the difficult-to-configure genetic algorithm.
Analysis of Near-Infrared Spectra of Complicated Biological Fluids by Two-Dimensional Correlation Spectroscopy: Protein and Fat Concentration-Dependent Spectral Changes of Milk
Authors: Czarnik-Matusewicz Bogusława , Murayama Koichi , Tsenkova Roumianna , Ozaki Yukihiro
Published: October 2003

Generalized two-dimensional (2D) correlation spectroscopy has been applied to analyze near-infrared (NIR) spectra of milk with different protein and fat concentrations. The NIR spectra of milk show rather poor signal-to-noise ratios compared with those of a protein or fat solution and have changing baselines from one spectrum to another. Poor signal-to-noise ratio and variations in baseline are common problems for NIR spectra of real-world samples. This study aims at expanding the utility of generalized 2D correlation spectroscopy to complicated multicomponent biological systems. In order to overcome the above two problems, we have employed multiplicative scatter correction (MSC) and smoothing as pretreatment procedures of the milk spectra selected for the calculation of 2D NIR correlation. 2D synchronous correlation spectra in the 2000–2400 nm region constructed from protein or fat concentration-dependent spectral changes of milk sharply enhance bands assignable to proteins or fats, respectively. It has been found that a power spectrum along the diagonal line in a synchronous spectrum very effectively shows the contribution of a particular component to the NIR spectra of milk. In fact, for example, the power spectrum for the fat concentration-dependent spectral changes of milk is very close to an NIR spectrum of fat itself. Two-dimensional asynchronous correlation spectra demonstrate the existence of bands that cannot be identified even by calculation of second derivatives and chemometrics analysis of the spectra. The asynchronous spectra also elucidate interaction between fats, proteins, and water.
Optical Emission Analysis of 15N: Pressure Effects and Identification of NO and Gaydon—Herman N2 Bands in the Discharge
Authors: Preston Caroline M.
Published: October 2003

The optical emission method, an alternative to mass spectrometry for 15N analysis, is based on measuring ratios of the intensities of the 14N2(28), 14N 15N (29), and 15N2 (30) lines of the 2→0 band of the C(3πu)→B(3πg) N2 transition near 298 nm. However, properties of the discharge are not well understood, and interferences that affect the analysis have never been explicitly identified. An efficient low-energy radio-frequency source and home-built spectrometer were used to obtain spectra over a wide range and with multiple scans. Weak extraneous bands were identified as the overlapping β andγ series of NO, not CO or OH as previously thought. Bands identified as the third positive system of CO were only observed under conditions far removed from normal practice. As tube pressure was increased from 0.3 to 1.8 kPa, the N2 intensity decreased relative to that of NO peaks. The 29/28 intensity ratio also varied with pressure, although not in a completely consistent way. A weak band underlying the 14N15N transition was identified as part of the Gaydon–Herman singlet series of N2; this interference rather than peaks from other species, may be the single factor most limiting analytical performance. Implications for the analytical method are discussed.
Theoretical Study of the Electric Field Distribution in the Cathode Fall Region of a Spherical Hollow Cathode Discharge
Authors: Mixon P. D.
Published: October 2003

A theory is presented for a simplified, one-dimensional model of a spherical hollow cathode discharge. Analytical expressions are derived for the electric field distribution and cathode fall voltage as functions of radial distance across the cathode dark space. The model assumes that the drift velocity of ions obeys the high-field approximation. An empirically derived discharge maintenance condition is assumed which, in addition to the secondary electron emission due to ions, includes the secondary electron emission effects of photons and metastable atoms from the negative glow region. The electric field and cathode fall voltage are shown to be monotonic functions of radial distance across the cathode dark space, which agrees qualitatively with previous theoretical and experimental work on cylindrical hollow cathodes. The sublinear mathematical form obtained for the electric field and its relationship to other cathode geometries is briefly discussed.
Fiber-Optic Resonance-Enhanced Multiphoton Ionization Probe for in situ Detection of Aromatic Contamination
Authors: Cullum Brian M. , Shealy Slade K. , Angel S. Michael
Published: October 2003

A simple fiber-optic probe suitable for remote analysis with the use of resonance-enhanced multiphoton ionization has been developed and demonstrated by measuring vapor-phase toluene and gasoline above aqueous solutions. An optical fiber transmits a high-power laser pulse (266 nm or 532 nm) to the sample, ionizing it, and the subsequent ions are collected with a platinum electrode mounted at the fiber tip. Measurements take approximately 100 s to perform, require no sample preparation, and have been demonstrated over a distance of five meters. The limit of detection for toluene in water with the use of this probe is 1.47 ± 0.02 ppb (wt/wt). In addition to two-photon excitation at 266 nm, the feasibility of a 2+2 excitation scheme using 532 nm has also been shown.
On-the-Fly Fluorescence Lifetime Detection in Liquid Chromatography with Data Collected Simultaneously at Multiple Emission Wavelengths
Authors: Burt J. A. , Dvorak M. A. , Gillispie G. D. , Oswald G. A.
Published: October 2003

A novel liquid chromatography (LC) fluorescence detector simultaneously generates fluorescence decay curves at multiple emission wavelengths. The fourth harmonic (266 nm) excitation light from a pulsed Nd:YAG laser is focused into a standard LC flow cell. A small spectrograph disperses the fluorescence. Fiber-optic delay lines positioned in the exit focal plane time the arrival of photons at the photomultiplier tube detector. Four wavelength channels with 50 ns channel spacing were used in this study. The intensity-decay time waveform is averaged with a digital storage oscilloscope. Temporal overlap between adjacent wavelength channels is removed during the post-processing of the data. System performance was characterized for chromatographic elution of polycyclic aromatic hydrocarbons (PAHs). Detection limits are 1.6 ppb for naphthalene and 0.14 ppb for fluorene. Resolution of co-eluting 1,4-dimethyl-naphthalene and anthracene components on the basis of differences in their lifetimes and spectral distributions is demonstrated.
Longitudinal Light Profile Microscopy: A New Method for Seeing below the Surfaces of Thin-Film Materials
Authors: Power J. F. , Fu S. W.
Published: October 2003

Longitudinal light profile microscopy (LLPM) is introduced in this work as a new optical method for depth profiling the properties of thin-film materials. The method uses irradiation of an optically polished cross section of a prepared thin film sample, by a laser beam propagating along the depth (longitudinal) axis of the material. An observation microscope, aligned along an orthogonal axis to the sample cross section, transfers an image of the light profile propagating along the material's longitudinal (depth) axis to a recording camera. While depth attenuation of the optical beam in the sample is dominated by light absorption, and turbid scatter (which our analysis neglects), light profile images recovered by the microscope use contrast mechanisms based on luminescence and elastic or inelastic light scatter. Blur contributions to the images arising from axial thickness of the light profile “object” are shown to be minimal in our microscope. Our experimental setup, moreover, is constructed from relatively inexpensive, easily available components. A number of different image contrast mechanisms, including luminescence and elastic scattering contrast, were demonstrated on materials with known optical properties, including continuous media and laminates. The sample dimensions and depth-dependent image features were directly observable and unambiguous to identify. Images recovered on the basis of elastic scattering showed unusual contrast for optical interfaces in materials which were transparent at the analysis wavelength. The method holds promise for providing a plethora of new depth-resolved imaging mechanisms.
Infrared Spectra and Elemental Composition in Recent Biogenic Calcites: Relationships between the ν4 Band Wavelength and Sr and Mg Concentrations
Authors: Dauphin Y.
Published: October 2003

Biogenic calcites show various chemical contents (Sr and Mg) related to the systematic position of the organisms. It is well known that algae, octocorallia, and echinoderm tests are composed of high Mg calcites, whereas mollusc shells are composed of lower Mg calcites. DRIFT (diffuse reflectance infrared Fourier transform) spectra show that the frequency of the ν4 band significantly differs in the high Mg calcite and low-Mg calcite set. The ν1 band and the doublet ν2 do not seem to be altered. There is a strong positive linear correlation between the ν4 wavelength and Mg concentrations in these biological calcites. The linear correlation between the ν4 wavelength and Sr concentrations is only 0.59. It is known that the calcite dolomite transition shifts the wavelength of the ν4 band, but such a shift has not been observed in the single calcite.
Multi-Instrument Calibration with Genetic Regression in UV-Visible Spectroscopy
Authors: Ozdemir Durmus , Williams Ron
Published: October 2003

The applicability of genetic regression (GR) to multi-instrument calibration was demonstrated by using several UV-visible spectrophotometers. GR is a calibration technique that optimizes linear regression using a genetic algorithm (GA). Sample spectra of ternary and quaternary mixtures of the pharmaceuticals furaltadone (Fd), doxycycline (Dx), sulfadiazine (Sd), and trimethoprim (Tm) were collected on four different UV-visible spectrophotometers, including one single-beam diode array and three double-beam dispersive instruments. Hybrid calibration models (HCMs) were generated by combining the data collected on multiple instruments into one calibration model as if they had all been collected on a single instrument. For comparison, single-instrument calibration models were also generated for each instrument. Both HCMs and single-instrument models were tested by using a validation set measured on all four instruments. Results obtained from single-instrument models were comparable with a previous study in which partial least-squares (PLS) regression was used for multivariate calibration of these compounds. HCMs for double-instrument cases performed equally well as single-instrument models and slightly worse for the four-instruments models.
Measurement of Carboxyhemoglobin in Forensic Blood Samples Using UV-Visible Spectrometry and Improved Principal Component Regression
Authors: Egan William J. , Brewer William E. , Morgan Stephen L.
Published: October 2003

The forensic determination of carboxyhemoglobin (COHb) in blood was performed by using an improved principal component regression (PCR) technique applied to UV-visible spectra. Calibration data were decomposed into principal components, and the principal components useful for prediction were selected by their correlation with calibration spectra. Cross-validation of prediction results was done by leverage-corrected residuals. Confidence and prediction intervals derived from classical regression theory were found to be reasonable in size. The results compared favorably to a comparison study conducted by using a CO Oximeter method. In analysis of forensic case study samples, the improved PCR method allowed detection of abnormal samples and successfully predicted percentages of COHb and methemoglobin (MetHb), and provided error estimates for those predictions.
Near-Infrared Excited Surface-Enhanced Raman Scattering of Biological Molecules on Gold Colloid I: Effects of pH of the Solutions of Amino Acids and of Their Polymerization
Authors: Dou Xiaoming , Jung Young Mee , Yamamoto Hiroshi , Doi Shigeru , Ozaki Yukihiro
Published: October 2003

Near-infrared (NIR) excited surface-enhanced Raman scattering (SERS) has been measured for lysine (Lys) on gold colloid at pH 10.8 and 12.0 where its -amino group is ionized and both the α -and -amino groups are neutralized, respectively. The intensities of SERS signals from Lys are much stronger at pH 10.8 than at pH 12.0. This result suggests that the electrostatic interaction between the positive charge of the -NH+3 group and the negative charge of the gold surface is one of the most important factors which determine the intensities of the SERS signals. A similar SERS study has been carried out for glycine (Gly) on gold colloid at various pH. The SERS spectra of Gly on gold colloid are quite different in terms of both the frequencies and the band intensities from those of Gly on silver colloid, previously reported; the zwitter ion is dominant on the surface of the gold colloid, while the anion form is major on the silver colloid surface. The chemical interactions are much less important for the emergence of SERS of Gly on the gold colloid. NIR SERS has also been performed for oligomers and polymers of Lys and Gly. The intensities of the SERS signals decrease markedly with their polymerization. The effects of the steric hindrance due to the polymerization and of the distance between the gold surface and amino acid unit probably determine the SERS intensities.
Identification of Major Species in Industrial Metal-Refining Solutions with Raman Spectroscopy
Authors: Schmidt K. J. , Michaelian K. H. , Loppnow G. R.
Published: October 2003

Raman and resonance Raman spectroscopies were used to characterize industrial metal-refining solutions containing nitrogen, sulfur, and Ni, Co, Zn, and Cu ammine complex species. To identify the species present in these solutions, we also recorded Raman spectra of model compounds in similar matrices. The results indicate that clearly resolved diagnostic bands in the Raman spectrum can be used to identify and discriminate free ammonia, metal-bound ammonia, sulfate, sulfamate, and metal species in industrially relevant plant solutions. We roughly estimate that Raman can determine cobalt at the 0.3 g Co/L level, nickel at the ∼5 g Ni/L level, and copper at the 2–3 g Cu/L level in these solutions. Also, sulfate and sulfamate can be detected at the 1 g/L level with Raman spectroscopy. Finally, the Raman spectrum can be used to determine bound ammonia with detection limits of about 20 g/L. The detection of free ammonia depends on the concentration ratio of free to bound ammonia because of their overlapping vibrational bands and the weaker intensity of free ammonia Raman scattering.
Infrared and Raman Analysis of In-Plane Microtomed Thermoplastic Olefins
Authors: Coleman Patricia B. , Ramamurthy A. C.
Published: October 2003

The distribution of chemical composition of as-molded thermoplastic elastomers: polyolefinic (TEOs), commonly called TPO, has been studied. Fifty in-plane sections, each 10 μm thick, were microtomed from the surface to a depth of 510 μm into the sample. These sections were studied by transmission infrared to compare the level of polypropylene (PP) and polyethylene (PE) at the surface and throughout the 510 μm thickness. No compositional differences were observed. These same sections were studied by optical microscopy. Birefringent spherulites were observed beginning about 100 μm into the sample. Deeper into the sample, these spherulites became larger, approaching 20 μm. Infrared microscopy was used to analyze several 20 μm by 20 μm spots on these sections. Still no compositional difference could be found. A Raman microprobe using a 2 μm diameter sampling spot was also used to analyze these sections. Once again no compositional differences in the amount of PP and PE were observed at the surface as compared to 500 μm into the sample.
Characterizing the Performance of a Fast FT-IR Imaging Spectrometer
Authors: Snively C. M. , Koenig J. L.
Published: October 2003

The noise sources present in fast FT-IR imaging instrumentation are analyzed in order to ascertain the limits of the quantitative ability of this technique. Methods to increase the quality of spectral and spatial information are presented. It is shown that a technique comparable to the coaddition of multiple mirror scans in standard FT-IR spectroscopy is able to increase the signal-to-noise ratio of the spectral data obtained, and that the expected square root behavior is obeyed. A method of distinguishing real image features from artifacts is also presented.
Two-Dimensional FT-IR Correlation Analysis of the Chemisorption of Nitric Oxide on Pt(100)
Authors: Magtoto Noel P. , Sefara Nelson L. , Richardson Hugh H.
Published: October 2003

In addition to the previously reported vibrational frequencies of NO stretch at 1591–1650 cm−1 and 1770–1800 cm−1 on Pt(100) surface at 300 K, we observed an infrared spectral band centered around 1689–1692 cm−1. With the use of two-dimensional IR correlation analysis, we were able to distinguish the various adsorption sites of NO under the present experimental conditions. The infrared band at 1689–1692 cm−1 developed independently of the band at 1639–1654 cm−1. By varying the pressure of NO and the surface temperature, we were able to demonstrate that the 1689–1692 cm−1 band grows only at higher NO pressure and lower surface temperature.
Direct Qualitative and Quantitative Analysis of Triterpenes Using 13C NMR Spectroscopy Exemplified by Dichloromethanic Extracts of Cork
Authors: Castola Vincent , Bighelli Ange , Casanova Joseph
Published: October 2003

We describe a methodology which allows identification and quantitation of individual triterpenes in natural mixtures, using the computer-aided analysis of their 13C NMR spectra, without previous separation. The analytical procedure was validated on artificial mixtures and applied to authentic extracts of cork. Identification of triterpenes was possible with the use of either reference spectra recorded in our laboratory or literature data.
Spectroscopy of Hydrothermal Reactions. Part XI: Infrared Absorptivity of CO2 and N2O in Water at Elevated Temperature and Pressure
Authors: Maiella P. G. , Schoppelrei J. W. , Brill T. B.
Published: October 2003

The temperature dependence of the infrared absorptivity of the asymmetric stretch of CO2 and N2O dissolved in H2O was determined at 300–600 K under 275 atm. These results are essential for using these species as internal calibrants of the rate of many hydrothermal reactions by infrared spectroscopy. The absorptivity (band area) for ν3(CO2) at constant number density increases from 1.58 × 104 cm/mmol at 300 K to 2.68 × 104 cm/mmol at 600 K. The absorptivity of ν3(N2O) is 8.57 × 103 cm/mmol at 300 K and 1.33 × 104 cm/mmol at 525 K. The absorptivity is suppressed in the presence of H2O by a factor of about 5 compared to results for the gas phase. The absorptivity increases, however, with increasing temperature in H2O solution, which is opposite the trend for the gas phase. The Lorentzian line shape in H2O solution provides a global relaxation time of <1 ps, which is more consistent with relaxation by vibrational energy transfer among associated molecules than by collisions or stochastic modulation by the surrounding H2O field.
Raman Microscopic Study of Some Borate Minerals: Ulexite, Kernite, and Inderite
Authors: Kloprogge J. Theo , Frost Ray L.
Published: October 2003

Three borate minerals—inderite, kernite, and ulexite—have been studied by Raman microscopy in the region between 4000 and 100 cm−1. The spectra are very complex due to the presence of four possible boron clusters in either trigonal or tetrahedral coordination. All three minerals contain clusters containing one or more of both the trigonal and tetrahedral boron clusters. Ulexite is characterized by bands at 3490, 3433, 3401, 1133, 1111, 1005, 745, 668, 639, 617, 602, 551, 491, 475, 421, 412, 367, and 305 cm−1. Kernite is characterized by bands at 3585, 3543, 3421, 3352, 3247, 3122, 2987, 2855, 2729, 1465, 1388, 1349, 1061, 929, 880, 869, 841, 801, 778, 736, 584, 541, 494, 458, 424, 386, 372, 316, and 301 cm−1. Inderite shows the most complex spectrum with bands at 3616, 3479, 3365, 3292, 3254, 3127, 3067, 2988, 2931, 2843, 2750, 1397, 1349, 1282, 1249, 1195, 1167, 1138, 1058, 1006, 948, 879, 811, 743, 664, 637, 580, 551, 492, 440, 420, 379, 347, and 313 cm−1. The region between 3600 and 3000 cm−1 is characteristic for the OH stretching modes; between 1500 and 1300 cm−1 one will observe the asymmetric stretching modes of the trigonal boron cluster, whereas the symmetric stretching region is generally between 950 and 850 cm−1. The asymmetric stretching mode for the tetrahedral boron clusters is observed between approximately 1100 and 850 cm−1, while the symmetric stretching modes are observed between 850 and 700 cm−1 together with the OH out-of-plane bending modes. The OH in-plane bending modes are visible between 1300 and 1000 cm−1. Finally, the bending modes for both the trigonal and the tetrahedral boron clusters are found below 700 cm−1.
Combining X-Ray Fluorescence Spectrometry and Vibrational Microscopy to Assess Highly Heterogeneous, Actinide-Contaminated Materials
Authors: Schoonover Jon R. , Havrilla George J.
Published: October 2003

Combining X-ray fluorescence (XRF) spectrometry with micro-Raman and infrared spectroscopies is shown to be a powerful experimental approach in providing information on components present in highly heterogeneous materials which contain or have been in contact with actinides. In this initial study, the quantitative XRF data demonstrate a correlation in the relative amounts of plutonium with other elements such as strontium and yttrium. The XRF mapping provides further evidence for correlation of these (and other) elements and identifies regions of interest within the sample to be further studied. These regions were then examined by vibrational microscopy to supply information on molecular species present and their spatial distribution. This experimental approach provides insight into very complex samples and provides a technique capable of exploring interactions of molecular components with actinides in complex media.
Characterization of Tantalum Films on Analytical Surfaces: Insights into Sputtering of Nonconductors in a Direct-Current Glow Discharge Using Secondary Cathodes
Authors: Wayne David M. , Schulze Roland K. , Maggiore Carl , Cooke D. Wayne , Havrilla George
Published: October 2003

We performed glow discharge mass spectrometry (GDMS) analyses on several nonconducting ceramic materials: a glass microscope slide, Nd-doped yttrium aluminum garnet (Nd:YAG), potassium titanyl phosphate (KTP), and several National Institute of Standards and Technology (NIST) Standard Reference Materials (e.g., Trace Elements in Glass SRM 610 and SRM 612). The sputtering of the nonconductor in the GD source results in the formation of a circular sputter crater whose surface profile varies with changing conditions in the GD cell. Following GD analysis, examination of the sample surfaces within, and adjacent to, the sputter crater by micro-X-ray fluorescence (MXRF) and scanning electron microscopy (SEM) indicated that the sputter-deposited Ta film is nonuniform. In several samples, a sharp discontinuity is observable in both Ta concentration and average Z-number approximately 0.5 mm from the crater perimeter. This discontinuity probably corresponds to the physical contact between the Ta cathode and the nonconducting sample beneath. Rutherford backscattering spectrometry (RBS) was then used to characterize Ta film thickness for each of the materials. The data presented here indicate that both crater shape and film thickness are dependent on GD sputtering parameters and on the nature of the material being sputtered.
Spatially and Temporally Resolved Absorption Studies of YO in the Plume of Laser-Ablated Y2O3
Authors: Yang Xinju , Tang Yongxin , Liu Xiannian , Qin Qizong
Published: October 2003

A spatially and temporally resolved transient absorption technique has been employed to investigate the dynamics of ground-state YO during 355 nm laser ablation of Y2O3. Time-of-flight (TOF) measurements of the expanding YO plume in vacuum and in Ar or O2 ambient are reported. During the initial expansion of YO in vacuum, the center-of-mass velocity and the expansion velocity increase with distance up to the boundary of the Knudsen layer. In the presence of oxygen, reactions of the ablated atomic species with oxygen take place, resulting in the formation of YO with broad velocity distribution. From the peak time of the observed TOF distributions, the most probable velocities of YO are found to be 2.6 km/s in vacuum, 2.2 km/s in 50 mTorr Ar, and 1.8 km/s in 50 mTorr O2, respectively. The dependence of the peak time on distance shows that the experimental data can be well fitted with a shock wave model at higher ambient gas pressure.
Novel Time-Resolved Surface-Enhanced (Resonance) Raman Spectroscopic Technique for Studying the Dynamics of Interfacial Processes: Application to the Electron Transfer Reaction of Cytochrome c at a Silver Electrode
Authors: Wackerbarth Hainer , Klar Udo , Günther Walter , Hildebrandt Peter
Published: October 2003

A novel approach for time-resolved (TR) surface-enhanced (resonance) Raman (SE(R)R) spectroscopy is presented for probing potential-dependent processes of molecules adsorbed on a silver electrode. TR SE(R)R spectroscopy offers the unique advantage of providing structural and kinetic data exclusively of the adsorbed species and their reactions. These processes are initiated by a rapid potential jump and monitored by SE(R)R spectroscopy after a delay time δ for the probe interval Δ t. The synchronization is achieved by a mechanical chopper that triggers the potential jump via a photodiode and gates the exciting continuous-wave laser beam. After the probe event, the potential is reset to its initial value. Thus, the original equilibrium is restored to allow a continuous repetition of the sequence of potential jumps and probe events. During the entire experiment, the detection system, a liquid nitrogen-cooled charge-coupled device (CCD) detector, is active so that the signal-to-noise ratio (SNR) can be iteratively improved. This mode of detection does not limit the time resolution, so that the present approach allows TR SE(R)R experiments down to the microsecond time scale without lowering the SNR. The possibilities and limitations of this method are discussed. As an example we present preliminary results of a TR SERR study on yeast iso-1 cytochrome c (Cyt- c) adsorbed on a Ag electrode by applying a potential jump from −0.4 V to +0.05 V (vs. saturated calomel electrode). The experiments are carried out with a rotating electrode to avoid photoinduced degradation and desorption processes. The SERR spectra, which were measured with delay times between 45 to 175 ms, were analyzed quantitively in terms of the various states of the adsorbed Cyt- c that are formed in this potential range. The results show that under these conditions the relaxation processes include the electron transfer of the adsorbed Cyt- c to the electrode and a subsequent conformational transition. The analysis of the data reveals a heterogenous oxidation rate constant of 10.3 s−1 and rate constant for the conformational transition of 4.3 s−1, supporting the view that the biological electron transfer of Cyt- c is coupled with conformational transitions.
Stopped-Flow Rapid-Scan Fourier Transform Infrared Spectroscopy
Authors: Dunn Brian C. , Eyring Edward M.
Published: October 2003

A stopped-flow rapid-mixing device interfaced with a rapid-scan FT-IR spectrometer and a diode-array UV-visible spectrophotometer permits the observation of reaction transient intermediates over a broad range of wavelengths at minimal cost. The system has been evaluated for both spectral regions with the use of two different chemical reaction systems. The presence of a transient intermediate is clearly indicated in one case. Unexpected reactivity was observed in the other case. This approach will allow the study of chemical reactions even when no spectral changes occur in the UV-visible region.
New Method for Monitoring the Reaction of Glass-Ionomer Cements: A Spectroscopic Study of the Effects of Polyacid Structure on the Decomposition of Calcium Aluminosilicate Glasses
Authors: Ouyang Zheng , Sneckenberger Sharon K. , Kao Elizabeth C. , Culbertson Bill M. , Jagodzinski Paul W.
Published: October 2003

A method has been developed that permits monitoring of the reaction of basic glass powders with various polyacids during the formation of glass-ionomer dental cements. Decomposition of the calcium aluminosilicate glass is followed via laser-induced emission signals from trace elements introduced into the powder with the aluminum oxide component or from imperfections in the glass matrix. The method that is reported is significantly easier than previously reported methods and does not require the reaction to be quenched. The change in the intensity of the emission bands was correlated with the extent of branching in the side chains of seven polyacids, indicating that the structure of the polyacid affects the rate of decomposition of the glass powders. The polyacids with longer side chains and more branching extract metal ions from the glass powder more efficiently than the conventional polyacids that have reactive carboxylic groups attached uniformly and directly on the polymer backbone.
Attenuated Total Internal Reflection Microspectroscopy of Isolated Particles: An Alternative Approach to Current Methods
Authors: Lewis Lori , Sommer André J.
Published: October 2003

An alternative approach to conduct attenuated total internal reflection infrared microspectroscopy is described with the use of cartridge-based hemispherical internal reflection elements. The study demonstrates that the devices can be employed on any infrared microscope having reflectance capabilities. A comparison shows that the method provides the same signal-to-noise ratio in comparison to transmission studies for equal sample sizes. In addition, a 4× decrease in the sampled areas inherent with the method was verified for samples 60 μm in diameter and larger. Examples are presented that demonstrate the method's capability of studying small isolated samples without the use of a contaminating mounting media. Examples are also presented that demonstrate the potential to study samples without the effects of diffraction.
Enhancing IR Detection Limits for Trace Polar Organics in Aqueous Solutions with Surface-Modified Sol-Gel-Coated ATR Sensors
Authors: Han Ling , Niemczyk Thomas M. , Haaland David M. , Lopez Gabriel P.
Published: October 2003

An experimental investigation into the use of surface-modified sol-gel-coated Si attenuated total reflectance (ATR) mid-infrared sensors was completed to determine the detection limits for trace amounts of polar organic molecules in aqueous solutions. The surfaces of porous sol-gel films were modified to be mostly hydrophobic in order to concentrate the polar organic analytes in the film while largely excluding the water solvent. This modification of the Si ATR sensor coupled with multivariate partial least-squares calibration methods allowed approximately three orders of magnitude improvement in detection limits for acetone when compared to detection limits from univariate analysis of spectra obtained on uncoated Si ATR sensors. The comparable improvement for isopropanol in aqueous solution was over two orders of magnitude. Studies performed on mixtures of acetone and isopropanol in water confirmed that quantitative analyses could be performed on these mixture systems with cross-validated standard errors of prediction (CVSEP) of 0.5 and 8.7 ppm, respectively. Using three times the CVSEP as an estimate of the detection limit translates to detection limits of 1.5 and 26 ppm for acetone and isopropanol, respectively.
Vibrational Spectroscopy and Dehydroxylation of Aluminum (Oxo)Hydroxides: Gibbsite
Authors: Frost Ray L. , Kloprogge J. Theo , Russell Shane C. , Szetu Jennifer L.
Published: October 2003

The infrared absorption, infrared emission, and Fourier transform (FT)-Raman spectra of a series of gibbsites well defined by X-ray diffraction have been obtained. Hydroxyl stretching frequencies were found ∼ at 3670, 3620, 3524, 3452, 3395, 3375, and ∼ 3300 cm−1. Hydroxyl deformation vibrations were observed at 1059, 1023, 969, 938, and 915 cm−1. Hydroxyl stretching bands were observed in the Raman spectra at 3524, 3436, and 3365 cm−1 and correspond well with the three infrared bands. These bands are both Raman and infrared active. The bands at ∼ 3670, 3620, and 3395 cm−1 are infrared active only. The hydroxyl stretching frequencies show a pronounced blue shift, while the hydroxyl deformation modes show a pronounced red shift. Infrared absorption bands were observed at 3413, 3283, and 3096 cm−1 for the hydroxyl stretching frequencies and at 1024, 969, and 914 cm−1 for the hydroxyl deformation frequencies. Low-frequency infrared absorption vibrations were found at ∼ 860, 838, 800, 747, 666, ∼ 625, 585, 560, 522, 452, and 423 cm−1 and infrared emission bands at 834, 778, 728, 652, 640, 609, 580, 512, and 489 cm−1. The infrared emission low-frequency bands moved to higher frequencies upon thermal treatment. The dehydroxylation of gibbsite was followed by the combination of infrared emission spectroscopy and differential thermal analysis over the 200 to 750 °C temperature ranges. Dehydroxylation is followed by the loss of intensity of the hydroxyl stretching frequencies observed at 3620 and 3351 cm−1 and by the loss of intensity of the hydroxyl deformation modes at 1024 cm−1. Dehydroxylation starts at 220 °C and is complete by 350 °C. Some variation in the gibbsite endotherms was found between the synthetic and natural gibbsite dehydroxylations. Spectral changes in the low-frequency bands confirm that dehydroxylation commenced at 220 °C.