bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectroscopic Determination of Chromium(VI) during the Reduction of Chromium(VI) to Chromium(III)
Authors: Maxcy Thomas A. , Willhite G. Paul , Green Don W. , Mertes Kristin Bowman
Published: July 2005

Reduction of chromium(VI) to chromium(III) by thiourea between pH 3.0 and 5.5 is a key aspect of the chromium(VI)/thiourea/polyacrylamide gel polymer system used in enhanced oil recovery processes. A method has been developed to determine chromium(VI) concentration during the reduction of chromium(VI) to chromium(III) in this pH range. The reduction reaction is run in the presence of an acetic acid/sodium acetate buffer which reacts with the chromium(III) produced and prevents the formation of a brown precipitate which forms in the absence of the buffer. With interference from the precipitate eliminated, chromium(VI) concentration is determined from the visible absorbance of the reaction mixture and the unique molar absorptivity spectra of the five chromium species present in the reaction mixture. An average error of approximately 1% between known and measured chromium(VI) concentrations was demonstrated over a chromium(VI) concentration range from 0.0005 to 0.0025 M.
Three-Dimensional Space- and Time-Resolved Fluorescence Spectroscopy
Authors: Sasaki Keiji , Koshioka Masanori , Masuhara Hiroshi
Published: July 2005

A fluorescence spectroscopic system with both picosecond time resolution and submicrometer three-dimensional space resolution has been developed for elucidating the dynamics of inhomogeneous photophysical/photochemical phenomena. This system is based on a confocal laser scanning fluorescence microscope and a time-correlated single photon counting method. Results on demonstration experiments are shown to specify the performance of the system. Characteristics and limitations of the system are discussed.
Conformational Structure of an L-Asparagine/L-Aspartate Random Copolypeptide as Revealed by Vibrational and CD Spectroscopy
Authors: Carmona P. , Molina M. , Martinez P. , Altabef A. Ben
Published: July 2005

The infrared and Raman spectra of an L-asparagine/L-aspartate random copolypeptide with an L-asparagine residue content of 69% mol have been measured in aqueous solution and in the solid state and analyzed for the first time. The infrared amide I, I', and II bands have been related to the conformational structure of the polypeptide backbone with the aid of CO spectroscopy, whereby it has been concluded that this biopolymer adopts a random coiled secondary structure. The backbone conformation remains unordered even when side-chain carboxyl groups are in the undissociated form (-COOH). The fact that this polypeptide takes this secondary structure in preference to α-helices and β-sheets can be explained by weak hydrophobic bonding between side chains and/or by hydrogen bonding between peptide CONH groups and side-chain polar groups. Another interesting site is the amide III Raman region, which in spite of the above results shows a band in the range usually attributed to α-helical structure. This finding is due to contributions from methine bonds and CH2 groups and indicates that the side chains can influence the position of the bands in the amide III region. Consequently, this result reveals that associating polypeptide backbone conformation with characteristic frequency ranges in the amide III region may be incorrect.
An FT-IR Study of the Atmospheric Hydrolysis of Uranium Hexafluoride
Authors: Armstrong D. P. , Bostick W. D. , Fletcher W. H.
Published: July 2005

The handling and processing of UF6 is accompanied by the potential for a reaction with water, usually as airborne moisture, and the subsequent risk of releasing airborne, particulate UO2F2 and gaseous hydrogen fluoride. We have studied this reaction under the simulated conditions of a “release” of UF6, whereby hot, pressurized UF6 gas suddenly escapes into ambient air. The “release” experiment simulates, on a small scale, the accidental mixing of UF6 gas with the atmosphere in the absence of wind currents. The data obtained with the use of FT-IR spectroscopy have provided information which permits a much better understanding of the behavior of the evolved hydrogen fluoride, the residual water vapor, and the airborne, particulate UO2F2 and of their relation to each other.
A Comparative Study of NIR Diffuse Reflectance of Cottons Grouped According to Fiber Cross-Sectional Dimensions. Part I: Fundamentals
Authors: Montalvo Joseph G.
Published: July 2005

Reported here is the development of a comparative reflectance model that predicts the relative change in NIR diffuse reflectance of cotton, a hollow fiber, according to the cross-sectional dimensions of perimeter, wall thickness, and wall area. Two cotton groupings are considered: paired cottons and any number of cottons of the same perimeter. The model is based on a single wavelength of NIR light and the critical assumption that the total fiber length in the optical path is constant for cottons of the same perimeter. Combinations of paired dimensional variables are derived and classified by selection rules as “allowed” or “forbidden.” Seven allowed nontrivial combinations of perimeter, wall thickness, and wall area are identified. On the basis of the derived equation that optical density (O.D., log 1/ R units) is a linear function of wall thickness at constant perimeter, comparative reflectances are predicted for all seven nontrivial combinations. The predicted comparative reflectances at a single wavelength range from nonunique (i.e., overlap or equivalent O.D.) to unique; those across many wavelengths are all unique. Also, a mechanism is proposed to explain the interaction of photons with fiber. Finally, the fundamental fiber property sensed is elucidated in three-dimensional (3-D) and 2-D fiber space.
Flame Ionization Mass Spectrometry: Isotope Ratio Determinations for Potassium
Authors: Taylor Howard E. , Garbarino John R. , Koirtyohann S. R.
Published: July 2005

The air/acetylene flame provides a convenient ion source for the determination of potassium isotopic ratios by mass spectrometry. Unlike the argon inductively coupled plasma (ICP), the flame provides low background in the mass region of interest. Ion production is quite satisfactory for isotope ratio measurements at the micrograms per milliliter ( µg/mL) level and slightly below, with 1 µg/mL potassium giving about 105counts/second at a nominal mass-to-charge ratio of 39. The detection limit for potassium was 2–3 nanograms per milliliter (ng/mL). The ratio of 41K/39K was measured with 0.5–1% relative standard deviation, and a 41K spike representing 0.2% of the total potassium was readily detected. Both signal levels and signal stability were improved by adding a second easily ionized element such as cesium to samples and standards. Alternatively, a cesium solution could be aspirated for about 1 minute between sample measurements to ensure signal stability.
Infrared Study of β-Propiolactone in Various Solvent Systems and other Lactones
Authors: Nyquist R. A. , Fouchea H. A. , Hoffman G. A. , Hasha D. L.
Published: July 2005

Many lactones exhibit two significant bands in the carbonyl stretching region which result from Fermi resonance interaction between vC = O and a combination or overtone of a lower-lying fundamental (or fundamentals). However, for β-propiolactone, three significant bands in the carbonyl stretching region of the spectrum are observed. These bands result from vC = O in Fermi resonance between the combination tone v6 + v13, A′ and 2 v10, A'. The extent of Fermi resonance interaction between vC = O and the combination and/or overtone is dependent upon the solvent system. Approximate unperturbed vC = O frequencies have been calculated, and these vC = O frequencies decrease in frequency in the solvent order n-hexane, carbon tetrachloride, and chloroform. The unperturbed vC = O frequencies were also calculated with the use of reported frequencies and band intensities for many other lactones, and the unperturbed vC = O frequencies decrease significantly as the amount of ring strain is reduced in the lactone structures. An equation, based on perturbation theory for obtaining approximate unperturbed vC = O frequencies for situations where three modes are in Fermi resonance, was developed and used to assign the unperturbed vC = O frequencies for β-propiolactone in various solvent systems. This method assumes that all or nearly all of the intensity in the three bands in Fermi resonance arises from the vC = O mode.
Correlation of Infrared and Nuclear Magnetic Resonance Data for Some Substituted Benzenes
Authors: Nyquist R. A. , Hasha D. L.
Published: July 2005

Infrared (IR) and/or Nuclear Magnetic Resonance (NMR) carbon-13 data are presented for mono-substituted benzenes, acetophenones, benzaldehydes, benzophenones, benzoic acids, methyl and ethyl benzoates, and acetanilides. Correlations are developed between Taft σR• values for 3- x and 4- x atoms or groups versus δ13C-4 or vs. the out-of-plane hydrogen deformation modes I and II for mono-substituted benzenes. Correlations are also developed between Hammett σ values vs. δl3CN for 3- x- and 4- x-benzonitriles. Correlations are also developed between Hammett σ values or Taft σR• values for x atom or group vs. δ13C-1 or vC = O for certain members of the above classes of compounds. Correlations are also noted between δ13C-1 and vC = O in certain classes of C = O-containing compounds.
Characterization of Holographic Band-Reject Filters Designed for Raman Spectroscopy
Authors: Pelletier M. J. , Reeder R. C.
Published: July 2005

We report the optical transmission properties of holographic band-reject filters designed for Raman spectroscopy using excitation at 514.5 nm and at 632.8 nm. We use these data to quantitatively evaluate the compromise between rejection of elastic scatter and transmission of Raman bands as a function of Raman shift. We demonstrate the use of a single filter for the rejection of elastically scattered light from the Raman spectra of a white powder and of a clear liquid.
Pattern Recognition in 2D NMR Contour Maps for Studying Molecules Containing Fluorines. Part I: Study of Organofluorine Ethers
Authors: Cholli A. L.
Published: July 2005

The procedure described here is useful in the study of molecules containing fluorines, especially organofluorine ethers. It provides all the basic information about fluorines without actually performing 19F NMR. With the use of the two-dimensional NMR technique, identifying the position of fluorine in a molecule is simple and straightforward. The contour patterns in the two-dimensional NMR plot are distinctively different for many fluorinated functional groups, thereby providing a means for locating the position of fluorine(s) in the molecule without any difficulty. In addition, other relevant NMR parameters can be easily derived directly from the plot. The suggested experiment is easy to implement on any basic pulse NMR spectrometer with a 13C/1H probe for the study of organofluorine compounds. Experimental, as well as theoretical, two-dimensional contour patterns for commonly occurring functional groups of organofluorine ethers are also presented.
A Size-Exclusion Chromatography/FT-IR (SEC/FT-IR) Technique for Improved FTIR Spectroscopy of Proteins in D2O Solution
Authors: Remsen Edward E. , Freeman John J.
Published: July 2005

A size-exclusion chromatography/Fourier transform infrared spectroscopic (SEC/FT-IR) method for improving the FT-IR spectroscopy of proteins in D2O solution is described. The technique employs low-volume SEC columns to exchange protein solutions into buffered D2O and effectively removes spectral interference from H2O and other low-molecular-weight compounds in the region of the protein amide carbonyl stretching band (1600–1700 cm−1). Application of the method with protein solutions prepared in deuterated, denaturing buffers completely exchanges labile protein hydrogens with deuterium and refolds the proteins into their native conformations for subsequent spectral characterization. Potential applications of the SEC/FT-IR method for kinetic monitoring of dynamic processes in proteins (e.g., secondary structure formation during protein folding) are also discussed.
A New Beam Condenser Design for Studies on Solutions and Single Crystals with a UV-Vis Spectrophotometer
Authors: Mullica Donald F. , Wesson Greg A. , Leschnitzer Dale Hugo
Published: July 2005

The need for accurate absorption data on small single crystals has led to the development of a new optical beam condenser design for UV-Vis spectroscopy. This design is based on the style of beam condensers used in IR spectrophotometers as opposed to the standard light pipes and lens focusing devices. The six-mirrored unit focuses the slit image on samples as small as 300 µm. The design and standardization of the beam condenser unit are presented.
Surface-Enhanced Raman Scattering (SERS) and Surface-Enhanced Resonance Raman Scattering (SERRS) on HNO3-Roughened Copper Foil
Authors: Xue Gi , Dong Jian , Zhang Mingsheng
Published: July 2005

Copper foils for a Raman study were prepared by a chemical etching method with HNO3. These foils were found to exhibit a strong SERS effect. SERS or SERRS spectra of cobalt phthalocyanine, cystamine dihydrochloride, benzylamine, and p-thiocresol have been taken to illustrate the usefulness of this sample preparation technique. The enhancement effect of HNO3-roughened copper foil shows better thermal stability than that of vacuum-deposited Ag/CaF2 substrate. The HNO3-roughened copper foil seems to be a more easily prepared substrate system for SERS studies. There is a high potential that this technique could be used in studies of adsorption, molecular orientation, surface reaction, and surface catalysis at room or elevated temperatures.
Polycyclic Aromatic Nitrogen Heterocycles. Part III: Effect of Solvent Polarity and Solvent Acidity on the Fluorescence Emission Behavior of Select Azapyrenes and Phenanthroisoquinolines
Authors: Tucker Sheryl A. , Acree William E. , Tanga Mary J.
Published: July 2005

Fluorescence emission spectra are reported for 1-azapyrene, 2-azapyrene, 4-azapyrene, 12-azabenzo[a|pyrene, phenanthro[9,10g]isoquinoline, phenanthro[2,3h|isoquinoline, and phenanthro[3,2h]isoquinoline dissolved in organic nonelectrolyte solvents of varying polarity and acidity. Results of these measurements indicate that 12-azabenzo[a]pyrene, phenanthro[2,3h]isoquinoline, and phenanthro[3,2h]isoquinoline exhibit modest probe character as evidenced by decreased I/II or I/III band emission intensity ratios with increasing solvent polarity. Alcoholic solvents such as trifluoroethanol protonate the nitrogen hetero-atom, resulting in loss of emission fine structure accompanied by a sizeable red-shift in emission wavelength(s). For 1-azapyrene and 2-azapyrene the observed fluorescence emission spectra showed both neutral and protonated forms of the solute in trifluoroethanol.
A Comparative Study of NIR Diffuse Reflectance of Cottons Grouped According to Fiber Cross-Sectional Dimensions. Part II: Optical Path Simulations
Authors: Montalvo Joseph G.
Published: July 2005

In Part I of this series, a model was proposed to predict the comparative NIR reflectance of cottons grouped according to cross-sectional dimensions. The critical assumption in the model is that total fiber length in the diffuse reflectance optical path is constant among cottons of the same perimeter. This paper introduces an alternative assumption: that the volume of solid cellulose (i.e., mass) in the diffuse reflectance optical path is constant for cottons of the same perimeter. Optical path simulations are used to predict the consequences of either assumption. One method of simulation is based on diffuse reflectance calculations and the other on relating diffuse reflectance to diffuse transmittance. In the diffuse reflectance calculations, 13 variables are included in the simulation model. Relating reflectance to transmittance is justified because sample weights for the latter can be selected a priori to produce either a constant total fiber length or a constant volume of solid cellulose in the optical path. The simulations support the premise that the critical assumption in the comparative reflectance model is correct. The study goes further to produce diagnostic criteria from the simulation results for testing the assumptions.
FT-IR Diagnostics of Tungsten-Halogen Lamps: Role of Halogen Concentration, Phosphorus, Wall Material, and Burning Environment
Authors: Bigio Laurence , Kubickl Brian , Codella Peter J.
Published: July 2005

A 24 factorial design matrix experiment is conducted to measure the effects of four different parameters on the HBr and CO levels in tungsten-halogen lamps as a function of burn time. The two gas species are measured at room temperature with the use of Fourier Transform Infrared (FT-IR) spectroscopy. The four parameters varied are (1) initial halogen concentration (as CH3Br); (2) presence or lack of phosphorus; (3) bulb wall material; and (4) burning environment. The effects of these parameters on lamp efficacy and life are also analyzed. In addition, separate oven results show that a small amount of HBr is initially adsorbed onto the bulb surfaces. Also, results are given for separate CO measurements over a wider range of initial CH3Br fill for bulbs with and without phosphorus.
Rapid, Quantitative Measurements Using Time-Correlated Single-Photon Counting and Time-Filtered Detection
Authors: Nowak Steven A. , Lytle Fred E.
Published: July 2005

One-second quantitative measurements are achieved by employing time-correlated single-photon counting detection and a software time-filter for signal-to-noise ratio enhancement. Fast collection times are accomplished by configuring a commercial time-to-amplitude converter in the reverse-interactive mode. In such a configuration, instrumental sensitivity is enhanced sixfold over that for the conventional-noninteractive configuration, and photon-processing rates can be as high as 125 kHz. The linear range for the one-second measurement is greater than three orders in magnitude, the sensitivity is 4.6 × 1014 counts M−1 s−1, and the extrapolated lower limit of detection for solutions of β-carboline in 0.5 M sulfuric acid is about 2 × 10−13 M.
FT-IR Emission Spectroscopy Studies of Molybdenum Oxide and Supported Molybdena on Alumina, Silica, Zirconia, and Titania
Authors: Li Can , Xin Qin , Wang Kai-Li , Guo Xiexian
Published: July 2005

Fourier transform infrared (FT-IR) emission spectroscopy has been used to study both molybdenum oxide and supported molybdenum oxide catalysts. An infrared emission cell was specially designed to treat the samples in vacuo or in various gases over a wide temperature range (25–700°C). The experimental conditions including sample preparation, effects of temperature, and sample thickness on the emission spectrum are detailed. The infrared emission spectrum of pure MoO3 was nearly identical to the spectrum obtained by the KBr disc transmission method. An infrared emission study on the reduction and the oxidation of molybdenum oxide is presented. In situ infrared emission spectra were recorded for supported molybdena on Al2O3, SiO2, ZrO2, and TiO2 at elevated temperatures, and the nature of the molybdenum-containing species on these supports is discussed on the basis of the infrared emission results.
Relative Raman Scattering Cross-Section Measurements with Suspended Particles
Authors: Fung K. H. , Tang I. N.
Published: July 2005

An experimental technique using individual aerosol particles for relative Raman scattering cross-section measurement is described. An electrostatically charged particle of known chemical composition, 10 to 15 µm in diameter, is suspended in an electrodynamic cell. A single line (4880 Å) from an argon-ion laser is selected to induce the Raman scattering. The minute size and free rotation of the suspended particle ensure uniform sample illumination. The present results show very good linearity between the scattering intensity ratio and the molar mixing ratio. Sodium nitrate, ammonium nitrate, sodium sulfate, and ammonium sulfate are examined, and their respective Raman cross sections relative to that of sodium nitrate are determined to be 1, 0.9, 0.61, and 0.94. The uncertainty in this work is estimated to be less than 10%.
Optical Sensors for High Acidities Based on Fluorescent Polymers
Authors: Carey W. Patrick , Jorgensen Betty S.
Published: July 2005

An indirect method for monitoring acid concentrations from 0.1 to 10 M was developed on the basis of the fluorescence of linear-chain, rigid-rod polymers. These linear polymers have high strength and acid-resistant properties that are ideal for support materials, as well as having chemical functionalities that can be protonated under highly acidic conditions to provide a sensing mechanism. By immobilization of the polymers on the endface of an optical fiber, an acidity sensor for monitoring nitric and hydrochloric acids was developed with the use of the change in fluorescent emission as a function of acid concentration. Polymers tested for sensor applications include poly(phenylquinoline), poly(biphenylquinoline), and poly(phenylquinoxaline). The quinoxaline responded from 0.1 to 2 M nitric acid, and the quinolines responded from 2 to 10 M nitric acid. The performance of sensors developed with these materials resulted in a relative standard deviation of approximately 10%.
Multivariate Calibration Applied to Infrared Spectroscopy for Quantitative Determination of Crystalline and Amorphous Silica
Authors: Bjørsvik Hans-René , Bye Erik
Published: July 2005

The application of infrared spectroscopy for quantitative microanalysis of silica is hindered by one severe difficulty. There is an almost complete spectral overlap in the region around wavelength 800 cm−1, where the various forms of silica have their main absorption band. Multivariate analysis with the use of plsr techniques has been applied to mixtures of α-quartz and fumed amorphous silica, by the calibration of the wavelength region 900-600 cm−1 at 10-cm−1 intervals. The two silica components could be determined simultaneously in concentrations relevant for occupational hygiene control work. The standard deviation of the method is ±1.8%, whereas the relative prediction error is better than ±5.2%. The plsr multivariate calibration techniques are found to be more robust and more accurate than a combined method of infrared spectroscopy and x-ray diffraction for the quantitative determination of silica mixtures. Thus, multivariate calibration offers a rapid, low-cost, and reliable method for the determination of silica polymorphs in low concentrations by infrared spectroscopy, excluding the use of x-ray diffraction. The ability to extract qualitative spectral information from plsr calibrations is demonstrated, and the principle of matrix specific calibration sets is discussed.
Noninvasive Polymer Reaction Monitoring by Infrared Emission Spectroscopy with Multivariate Statistical Modeling
Authors: Pell Randy J. , Callis James B. , Kowalski Bruce R.
Published: July 2005

Infrared absorption and emission spectroscopy have been used to monitor the curing of a commercial paint product. Principal component analysis of the absorption data indicates that three factors are needed to explain the observed spectral/temporal variance. The interpretation of this finding in terms of changes in the physical state of the reaction mixture is discussed. A similar analysis of the emission data proved more difficult due to a nonlinear concentration/response relationship. A linearization step based on an approximate theoretical model is suggested. The absorption, linearized emittance, and raw emittance data are fit to a two-step sequential rate model using multivariate nonlinear optimization and error estimates derived by Monte Carlo calculations. Better agreement of the model parameters between the absorbance and emittance data is found after linearization, but it is found that linearization introduces large errors in the nonlinear parameter estimates. Comparisons of model parameters for the raw emittance data at different temperatures are made.
The Infrared Spectroscopic Determination of Moisture in HCl for the Characterization of HCl Gas Drying Resin Performance
Authors: Pivonka Don E.
Published: July 2005

A Fourier transform infrared spectroscopic method has been developed for the determination of trace moisture in HCl gas. Calibration of moisture was performed as a two-step process. First, an FT-IR spectrometer equipped with a 10-m-pathlength cell was placed in series with a DuPont 5700 Moisture Analzyer to yield an absorbance vs. concentration curve of H2O in N2. In the second step, the moisture analyzer was replaced with a water scrubber, and the correlation of molar absorbance values for moisture in HCl vs. moisture in N2 was obtained through dilution of a fixed-concentration moist nitrogen stream into alternate streams of dry HCl and N2 gas. The effects of hydrogen bonding with the HCl matrix on H2O absorbance bandwidth and intensity were investigated at 2 cm−1 and 0.5 cm−1 spectral resolutions for the O-H stretching absorbance region. Matrix correlation data resulted in a linear calibration of moisture in HCl gas for the 0.1–25 ppm range. The infrared methodology has been further utilized to characterize the performance of several HCl gas purifiers designed for use in semiconductor applications. The in-line configuration of this method permits direct quantitation of HCl gas dryer efficiency, capacity, and flow rate specifications. Instrumental considerations including corrosion-resistant optics, inert seals, fittings, valves, purge techniques, and calibration procedure details and results are discussed.
Evaluation of Gas Chromatography/Matrix Isolation-Infrared Spectroscopy for the Quantitative Analysis of Environmental Samples
Authors: Schneider John F. , Schneider Ken R. , Spiro Stephanie E. , Bierma Douglas R. , Sytsma Louis F.
Published: July 2005

Gas chromatography/matrix isolation-infrared spectrometry (GC/MI-IR) is being applied to many analyses previously done only by gas chromatography/mass spectrometry (GC/MS). Qualitatively, the infrared spectra of matrix-isolated compounds contain much information about their structure. The information obtained from the infrared spectrum is complementary to the information obtained from mass spectrometry. The technique of GC/MI-IR should also be useful as a quantitative detector. In this study, semivolatile priority pollutant mixtures were analyzed quantitatively by GC/MI-IR. Results were compared with results obtained by GC/MS. Calibration curves were obtained on the GC/MI-IR for several semivolatile priority pollutants to measure the precision and linearity of this technique. The results indicated that GC/MI-IR, in its current form, is only suitable for semiquantitative work.
Factors Affecting Sensitivity in Lightpipe Gas Chromatography Fourier Transform Infrared Interfaces
Authors: Brown R. S. , Lennon J. J.
Published: July 2005

A variety of experimental parameters are evaluated which are important in maximizing the sensitivity of the combination of gas chromatography and Fourier transform infrared spectrometry (GC/FT-IR) for the detection and identification of mixtures of volatile organic compounds. Basic parameters can be optimized such as the mirror scan velocity and the detector bias current employed to reduce the overall system noise, thus improving the signal-to-noise ratio (S/N) of the resulting spectra. Quantitation of the resulting trade-off between using a lower-noise narrow-spectral-range mercury-cadmium-telluride (MCT) detector versus a wider-spectral-range MCT detector with somewhat higher noise characteristics is examined. An optical design incorporating a variable aperture to reduce the amount of unmodulated infrared radiation from the heated lightpipe which reaches the detector is evaluated. Linearity in sample absorbance is shown to be unaffected by the amount of unmodulated heat reaching the detector despite the nonlinear behavior of the detector observed as interferogram signal loss at elevated detector temperatures. By flowing a fixed concentration of isobutane in helium through the lightpipe, one can monitor the absorbance; it is observed to change significantly from ambient to operating temperature, mostly due to temperature broadening of the absorbance bands. However, no discernible change in the absorbance is observed as a function of the amount of unmodulated light reaching the detector. Finally, lightpipe dimensions are examined as they affect sensitivity. A comparison of the performance of a 1.1-mm i.d. and a 0.6-mm i.d. lightpipe shows increased chromatographic performance of the latter, as expected, but similar signal losses with temperature. Little or no evidence for the counter Jacquinot (sometimes referred to as the Hirschfeld) advantage is found, and reasons for this inconsistency are discussed.
On the Possibility of Observing Negative Fluorescence Dips in Laser-Induced Fluorescence Experiments
Authors: Simeonsson J. B. , Smith B. W. , Winefordner J. D. , Omenetto N.
Published: July 2005

Some theoretical considerations are given which show how a negative fluorescence dip (i.e., an increase in the monitored fluorescence signal) can be obtained when one is performing two-step excitation experiments in atmospheric pressure atomizers. Such an inverted dip is due to an increased population of the fluorescent level, caused by cascade de-excitation, both radiational and collisional, from the upper level(s) reached with the second excitation step. No coherence effects are involved. These considerations are supported by the experimental observation of the inverted dip in the stepwise, nonresonance fluorescence of silver atoms present in an inductively coupled argon plasma.
Vibrational Spectroscopic Evidence for the Associated-Anion Promotion of the Helical Structure of N-Acylglycine Oligomers
Authors: Okabayashi Hirofumi , Taga Keijiro , Yoshida Tadayoshi , Ohshima Kunihiro , Etori Hideki , Uehara Toshiyuki , Nishio Etsuo
Published: July 2005

Vibrational spectroscopic evidence for conformational change of the anions of N-acylglycine oligomers (trimers, tetramers, and pentamers) in aqueous solution is reported. The infrared absorption spectra of sample solutions diluted below the critical micelle concentration (cmc) can be explained by the coexistence of several conformations containing the polyglycine I-like extended form and the polyglycine II-like helix. However, above the cmc the infrared bands arising from the polyglycine II-like helix are intensified. This result is due to preferential stabilization of the helical structure, promoted by intermolecular association of the anions. The helical structure is also stable in the hydrophobic environment of micelles.
Signal-to-Noise Considerations in Flame/Furnace Infrared Emission Spectroscopy
Authors: Busch Marianna A. , Busch Kenneth W.
Published: July 2005

A theoretical model for the signal-to-noise ratio (SNR) performance of a flame/furnace infrared emission (FIRE) radiometer using a PbSe detector has been developed. The model uses readily available, published PbSe detector parameters to predict the SNR for situations involving only detector noise as well as for situations involving detector noise in the presence of residual, uncorrected flame noise remaining after background subtraction. The theoretical SNR values were found to be in good agreement (6%) with previously published, experimentally determined SNR values for Freon-113®, obtained with a dual-channel FIRE radiometer operating in the carbon mode. The model was used to show the effect of source modulation frequency on the SNR obtained with the FIRE radiometer. At room temperature under detector-noise-limited conditions, it was found that: 1/ f noise > background photon noise > generation-recombination noise » Johnson noise. The PbSe detector was found to exhibit 1/ f-noise behavior out to about 1000 Hz when operated at room temperature. The model predicts that, even for a dual-channel FIRE radiometer in the presence of residual flame background noise, some SNR improvement should be possible by increasing the chopping frequency out to around 3 kHz.
Analytical Accuracy in Unpolarized ATR Spectroscopy: Effects of the Spectrometer Polarization Ratio
Authors: Sperline R. P.
Published: July 2005

A method for the determination of the wavelength-dependent polarization ratio [PR(λ)] for any spectrometer is described. Equations are also developed for an averaged effective thickness for use in analyses of unpolarized ATR spectra, and for parallel and perpendicular effective thicknesses for use with external polarizers of known efficiency. Polarization ratios for one Fourier transform IR spectrometer and one grating IR spectrometer are presented and compared. In unpolarized ATR spectrophotometry using the grating spectrometer, the assumption of PR = 1.0 for all wavelengths introduces a Beer's law pathlength uncertainty of approximately a factor of 1.8.
Raman Spectroscopic Identification of Phosphate-Type Kidney Stones
Authors: Kodati Venkata Ramana , Tomasi Gordon E. , Turumin Jacob L. , Tu Anthony T.
Published: July 2005

Phosphate-type kidney stones have been examined by the Raman spectroscopic technique by merely focusing laser light on the cut surface of the stones. Before examination of the kidney stones, Raman spectra of several standard phosphate compounds—such as calcium monobasic phosphate [Ca(H2PO4)2], calcium dibasic phosphate (CaHPO4), calcium tribasic phosphate [Ca10(PO4)6(OH)2], calcium orthophosphate [Ca3(PO4)2], brushite (CaHPO·2H2O), struvite (MgNH4PO4·6H2O), and hydroxyapatite [Ca10(PO4)6(OH)9]—were obtained. Hydroxyapatite has a distinctive line at 961 cm−1, and one kidney stone examined showed a comparable band. It was concluded that one stone is primarily hydroxyapatite and another one is brushite. The analysis of the kidney stones by Raman spectroscopy is direct, fast, and nondestructive, and does not require tedious sample preparation.
The Development of a Fourier Transform Raman Microprobe
Authors: Sommer A. J. , Katon J. E.
Published: July 2005

An FT-Raman microprobe based on a refracting microscope and proprietary beamsplitter is detailed and characterized with regard to spatial resolution, Rayleigh rejection, and performance as compared to a 180° backscattering macro-geometry. Several examples are presented which demonstrate the microprobe's capabilities in analyzing micro-samples with moderate Raman-scattering cross sections. Further improvements to the integrated system are also discussed and highlighted.
NMR Imaging of Water in Model Porous Materials
Authors: Sarkar Subhendra N. , Wooten E. Wrenn , Komoroski Richard A.
Published: July 2005

Nuclear magnetic resonance images have been obtained for four porous glass disks of different porosities as models of materials such as oil cores. The mottled appearance often seen for such images is attributed largely to insufficient signal-to-noise ratio, and not pore structures. Comparison of spin-echo and gradient-echo images demonstrates the defect-magnification effect of the gradient-echo sequence seen previously for elastomers. The advantages of volume imaging, isotropic voxels in thin slices, and higher resolution are demonstrated for porous materials. Images with isotropic voxels of 80 to 100 μm on a side were obtained in several hours. Dramatic differences are not seen at 100-μm resolution for disks of average pore size 15 to 200 μm because the images are dominated by the large-pore tail of the size distribution.
Infrared Studies of Wood Weathering. Part I: Softwoods
Authors: Anderson Erin L. , Pawlak Zenon , Owen Noel L. , Feist William C.
Published: July 2005

Infrared spectra, in the diffuse reflectance mode, are presented for three common softwoods (Western redcedar, southern pine, and Douglas fir) that have been subjected to a variety of artificial weathering conditions. The surface spectra of the three unweathered woods have distinctly different characteristic features, but after 2400 hours of full artificial weathering the surface features are virtually identical and correspond closely with those of the cellulosic polymer components. Weathering with light alone has a less pronounced effect on the wood surfaces, whereas weathering with water alone has virtually no effect in comparison to the result of both light and water used in conjunction. A photochemically induced reaction pathway for the weathering process, consistent with the experimental findings, is discussed.
Bridging the Gap between What Mass Spectrometrists Want and What Spectroscopists Can Do: An Instrument for Spectroscopic Investigation of Matrix-Isolated, Mass-Selected Ions
Authors: Sabo Mark S. , Allison John , Gilbert Jeffrey R. , Leroi George E.
Published: July 2005

An instrument designed to trap mass-selected ions from mass spectrometers in a low-temperature inert gas matrix, for subsequent structural analysis via vibrational and electronic spectroscopy, is described. Isolation of mass-selected CS2+ in an argon matrix is confirmed with the use of laser-induced fluorescence (LIF) spectroscopy. The role of counter-ions in matrix isolation of ions is discussed, as well as implications of the LIF results to infrared spectroscopic studies of matrix-isolated, mass-selected ions. Early infrared experiments suggest that some ion neutralization may occur.
SERS Microscopy: Laser Illumination Effects
Authors: McGlashen Michael L. , Guhathakurta Urmi , Davis Kevin L. , Morris Michael D.
Published: July 2005

Hadamard transform SERS microscopy of pyridine at Ag electrodes with focused 514.5-nm, 532.0-nm, and 632.8-nm excitation is reported. It is shown that focused 514.5-nm and 532.0-nm laser excitation produces photochemical or photothermal damage at roughened Ag electrodes. Photo-damage limits the spatial resolution of SERS microprobe and raster-scanned point imaging techniques which use focused green excitation at Ag electrodes.
Solution Infrared and Nuclear Magnetic Resonance Studies of Cellulose Nitrates
Authors: Saunders C. William , Taylor Larry T.
Published: July 2005

This study has identified the infrared asymmetric nitrate absorptions of cellulose nitrates observed in THF solution. Independent absorptions for the primary nitrate at C6 and secondary nitrate at C3 were observed at 1651 cm−1 and 1639 cm−1, respectively. In addition, a third absorption at 1667 cm−1 was observed to be dependent upon the degree of nitration of the cellulose nitrate. This absorption was found to be due to steric hindrance between secondary nitrate groups on the C2 and C3 sites.
Hybrid Rotating Arc-Tube Furnace Device for Microsolution Analysis
Authors: Slinkman David , Sacks Richard
Published: July 2005

A hybrid arc-furnace system using a magnetically rotated, concentric-electrode arc connected to a pyrolytic graphite tube furnace is described. The arc is formed between a 5-mm-i.d. graphite tube anode and a W/Th wire cathode. A 0.9-kG magnetic field from a ceramic permanent magnet causes the arc plasma to rotate at about 1.4 kHz, thus forming a diffuse plasma dome covering the end of the anode cylinder. A 10-mm-long ceramic tube connects the furnace to the arc anode. The graphite anode and graphite furnace are housed in the same chamber. Rotation around a horizontal axis allows the system to quickly convert between a sample loading position and a plasma discharge position. Detection limits for various metallic elements are in the ppb and sub-ppb range. Design features and performance data are presented.
Infrared Emission Spectroscopy: A Theoretical and Experimental Review
Authors: Deblase Frank J. , Compton Senja
Published: July 2005

Thermal-induced infrared emission spectroscopy is reviewed, with emphasis on developments in theory and experiment. The theory associated with obtaining thermal-induced infrared emittance spectra as a function of sampling optics is discussed. The FT-IR configuration and data reduction methods needed to properly obtain high-quality spectra, close to room temperature, are also considered. Optical and experimental parameters which affect the spectrum are demonstrated by example, with a discussion of methods which optimize the signal-to-noise ratio. The applications shown range from polymer films on both metal and semiconductor surfaces to a single filament analyzed by micro-emission spectroscopy.
Measurement of Incident Intensity of UV Radiation Delivered by Optical Fibers
Authors: Xu Hong , Kenny Jonathan E.
Published: July 2005

Fiber optics are being used more and more frequently to deliver light to a sample for remote spectroscopic analysis, or to induce photochemistry or photoablation on an otherwise inaccessible sample, e.g., living tissue. For accurate quantitative results, the photon flux at the sample must be known. This paper presents two techniques for simple and accurate measurement of the intensity of ultraviolet light in the range 260 to 369 nm delivered to a distant sample by a fused-silica optical fiber. One technique uses a home-built evanescent wave coupler near the sample to couple excitation light into a monitoring fiber; the other uses a twin-fiber system, with equal amounts of source radiation launched into an excitation and a monitoring fiber. In each method, two Rhodamine B quantum-counter photomultiplier tube detectors are used simultaneously to assess the effectiveness with which the incident intensity is monitored. A critical evaluation of the results is presented. The twin fiber method is, theoretically, very simple; in practice, however, it is difficult to obtain a good wavelength-independent match between the two outputs. The evanescent wave coupling is also wavelength-dependent, but the observed results are in agreement with the predictions of simple evanescent field theory.
Applications of Fourier Transform Infrared Photoacoustic Spectroscopy to Solid Propellant Characterization
Authors: Pesce-Rodriguez Rose Ann , Fifer Robert A.
Published: July 2005

Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS) has been used to examine surfaces of composite solid propellants. Depletion of crystalline energetic material from extruded surfaces, and of plasticizer from aged surfaces, has been documented. In addition, a method has been developed to determine the mass per unit area of graphite on coated propellant surfaces.
Near-Infrared Probe for Determination of Solvent Hydrophobicity
Authors: Patonay Gabor , Antoine Miquel D. , Devanathan Shrinivasan , Strekowski Lucjan
Published: July 2005

The composition of aqueous solvents plays an important role in the spectroscopic characteristics of near-infrared (NIR) dyes. The effects of solvent hydrophobicity on NIR spectral characteristics have been studied with the use of different NIR dyes. An NIR dye (I) that belongs to the diethylthiacarbocyanine family was found to be the most sensitive to changes in the hydrophobicity of the environment. Dye I was used as a model dye to evaluate the analytical utility of this change. In pure water-miscible organic solvents, the absorption maximum for I appears in the region of 807 to 818 nm. If the hydrophobicity of the solvent mixture decreases by an increase in water concentration, an additional, well-separated absorption peak, which can be attributed to the dimer, appears at 698 nm. The relative intensity of these two peaks can be exploited for the determination of the composition of the solvent mixture. The method is evaluated with the use of the polarity parameter (P) for different solvent systems. The described method can be useful for quick spectroscopic determination of P values that are important for several analytical applications, e.g., in spectroscopy or reversed-phase chromatography.
Time-Resolved FT-IR Absorption Spectroscopy Using a Step-Scan Interferometer
Authors: Uhmann Wolfgang , Becker Andreas , Taran Christoph , Siebert Friedrich
Published: July 2005

The implementation of time-resolved step-scan FT-IR spectroscopy with a commercial interferometer is described. With the use of the photo-reaction of the biological system bacteriorhodopsin as an example which exhibits infrared spectral changes smaller than 10−2 absorbance units, the quality of the method is demonstrated. A comparison with conventional flash-photolysis experiments with a monochromatic infrared monitoring beam clearly demonstrates the multiplex advantage. The advantage of covering the total time course of the reaction allows for a variety of data analysis, such as forming difference spectra between intermediates of the reaction and the deduction of time courses of absorbance changes at selected wavenumbers. The mirror stability is better than ±1.5 nm, which is sufficient for the reliable measurement of small absorbance changes.
Characterization of Diffuse Reflectance FT-IR Spectrometry for Heterogeneous Catalyst Studies
Authors: Van Every Kenneth W. , Griffiths Peter R.
Published: July 2005

The characteristics of diffuse reflectance (DR) infrared spectrometry for the study of adsorbed species were investigated. DR spectra of adsorbed CO on supported catalysts with a high surface area may be obtained at high signal-to-noise ratio with detection limits approaching 10−6 monolayer coverage on the metal surface. Band intensities of adsorbed species as they appear in the Kubelka-Munk (KM) spectra are linear with surface coverage over a low coverage range but show a negative deviation from linearity at high coverage. This effect is due either to a nonlinear response of the KM function with analyte concentration or possibly to a change in the absorptivities of adsorbates with increasing coverage. Several factors affect band intensity reproducibility including: (1) gas equilibration in the sample, (2) baseline variations due to changes in the scattering coefficient, and (3) signal loss at elevated sample temperatures when a mercury-cadmium-telluride detector is used, because unmodulated radiation leads to conduction band or preamplifier saturation. Reproducibility between different catalyst samples is affected by sample packing and treatment history.
Polycyclic Aromatic Hydrocarbon Solute Probes. Part IX: Evaluation of Additional Pentaphene, Pentacene, and Pyranthrene Compounds as Possible Solvent Polarity Probes
Authors: Tucker Sheryl A. , Zvaigzne Anita I. , Acree William E. , Fetzer John C. , Zander Maximilian
Published: July 2005

Fluorescence emission spectra are reported for benzo[rst]dinaphtho[2,1,-8,7defg;2′1′8′,7′ijkl]pentaphene, dibenzo[a,rst]naphtho[8,l,2cde]pentaphene, dibenzo[fg,ij]pentaphene (also called dibenzo[b,n]perylene), dibenzo[de,kl]naphtho[l,2,3,4rst]pentaphene, dibenzo[h,rst]pentaphene, pyranthrene, tetrabenzo[de,hi,op,st]pentacene, and dinaphtho[2,l,8,7de fg;2′,l′,8′,7′opqr]pentacene dissolved in various organic solvents. Results of these measurements are used to screen PAHs for potential solvent polarity behavior. Of the eight PAHs examined, only dibenzo-[h,rst]pentaphene exhibited probe behavior as evidenced by selective, systematic emission intensity enhancement of band I with increasing solvent polarity.
Rotational Temperature of He2 in a DC Capillary Discharge
Authors: Sekine Shigeyuki , Hirose Chiaki
Published: July 2005

An experimental evaluation was made for the approximation which is used in the determination of rotational temperature from the analysis of electronic-rotational perturbation, and the approximation presented by Kovács was found to be adequate. The rotational temperature in the dc capillary discharge of He as derived by the present study was 500 ± 100 K.
Laser SRS Diagnostics of HBr in Tungsten Halogen Lamps
Authors: Bigio Laurence
Published: July 2005

The generation of infrared radiation by stimulated electronic Raman scattering (SRS) in a cesium vapor heat pipe is used to obtain diagnostic information on HBr in a tungsten halogen lamp. The IR beam traverses through the center of the coiled filament of a General Electric projection lamp, and spectra are taken of the R branch in the fundamental band for the lamp lit from 0 to 148 W, corresponding to filament temperatures of 296-2387 K. Molecular rotational temperatures and absolute HBr densities are then derived from the spectra. The results demonstrate the method to be a useful diagnostic tool for spatially resolved measurements of a key partner in the tungsten halogen cycle.