bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Solution-Deposited Anions on Glow Discharge Relative Ion Yields
Authors: Hess K. R. , Barshick C. M. , Duckworth D. C. , Smith D. H.
Published: May 2005

When standard addition methods were employed for quantification in glow discharge mass spectrometry (GDMS), relative ion yields for some, but not all, elements were observed to be greater when deposited as a solution residue than as a corresponding solid of the same composition. The origin of these effects was investigated and determined to result from the deposition of anions present in the solution standards. The enhancements could be duplicated from a solid by pretreatment with a solution containing the anion. The mechanism by which the enhancements occur is not well understood, but we believe it involves a form of reactive etching followed by collisional dissociation of the sputtered molecular species into metal ions. Preliminary research suggests that it may be possible to compensate for changes in relative ion yield with solution treatment by employing an appropriate internal reference standard, or to match closely the matrices of the sample and standard in such a manner that quantification by standard addition is possible.
Environmental Monitoring of Hanford Nuclear Facility Effluents by Thermal Ionization Mass Spectrometry
Authors: Stoffel(S) J. J. , Wacker J. F. , Kelley J. M. , Bond L. A. , Kiddy R. A. , Brauer F. P.
Published: May 2005

Thermal ionization mass spectrometry (TIMS) is a sensitive method for environmental monitoring of effluent radionuclides around nuclear material production facilities. Isotopic analysis by positive and negative TIMS is an essential tool for the assessment of both the inventory and migration of radionuclides in the environment. Instrumentation used for trace-level isotope ratio measurements is described. Examples are given of environmental measurements of plutonium and radioiodine at the Hanford Site, a former nuclear material production site. In favorable cases, complete isotopic analyses are obtained on total analytes in the femtogram range, and minor isotopes in the attogram range are measured. The method of direct particle-inlet mass spectrometry (PIMS) for real-time analysis of airborne particles is also described, along with PIMS instrumentation. Examples are given that demonstrate the capability of PIMS to measure uranium isotope ratios in individual particles without isolating them from complex, heterogeneous samples.
Reduction of Space Charge Effects Using a Three-Aperture Gas Dynamic Vacuum Interface for Inductively Coupled Plasma-Mass Spectrometry
Authors: Tanner Scott D. , Cousins Lisa M. , Douglas D. J.
Published: May 2005

A three-aperture gas dynamic vacuum interface for ICP-MS has been developed which reduces the ion current within the ion optics. The effect on performance limitations previously associated with space charge were determined. The gas and ion dynamics within the first stage of the vacuum interface are similar to those of current ICP-MS instruments and allow delineation of the relative effects of space charge in the interface region and within the ion optics. The sensitivity of the instrument to trace elements is similar to that of current commercial instruments. The instrument shows an improvement in the discrimination against low mass ion transmission. It also shows a dramatic improvement in both the magnitude and analyte-ion mass dependence of the signal suppression induced by a high concentration of a heavy concomitant element (Tl). The new design results in more uniform ion kinetic energies as a function of ion mass-to-charge ratio. The performance improvements are ascribed to the reduction of space charge effects resulting from both the reduction of the ion current within the ion optics and the reduction of the mass dependence of the ion kinetic energies. It is concluded that the discrimination against low-mass ions and the magnitude and analyte mass dependence of the signal suppression induced by concomitant heavy elements observed with current ICP-MS instruments derive from space charge effects within the ion optics. These effects are less significant within the first stage of the vacuum interface or within the mass analyzer.
Polarization-Division Interferometry: Far-Infrared Dichroism
Authors: Polavarapu Prasad L. , Chen Gang-Chi
Published: May 2005

We report the first far-infrared dichroism measurements using a polarization-division interferometer (PDI) developed in our laboratory. This interferometer uses a free-standing wire-grid beamsplitter made of tungsten wires. In conjunction with a linear polarizer in front of the source and two roof-top mirrors (one in each arm of the interferometer), the PDI divides the input beam into two orthogonal linear polarization components, recombines them for interference at the beamsplitter, and directs the output beam at 90° to the direction of the input beam. Light exiting the interferometer is manipulated with far-infrared lenses, to avoid polarization distortions that are inherent to the reflecting surfaces of the mirrors. The performance of the PDI is evaluated by measuring the linear dichroism of oriented PVF2 [poly(vinylidenefluoride) and circular dichroism of α-pinene, camphor, and 3-methylcyclohexanone. The dichroic multiplex advantage (ability to measure dichroism in the entire far-infrared region from a single measurement) and throughput advantage are demonstrated. These measurements establish the utility of the PDI in measuring transmission and linear dichroism spectra simultaneously without the need for any additional components. Additional developments appear necessary to establish the circular dichroism measurements when the magnitudes are less than one part in one thousand.
Polarization-Division Interferometry: Approach for Biomedical Infrared Imaging
Authors: Polavarapu Prasad L. , Chen Gang-Chi , Deng Zhengyu
Published: May 2005

Conventional Fourier transform infrared absorption spectroscopy is not suitable for most biological and biomedical studies because of strong infrared absorption by water. For wavelengths where samples absorb more than one unit of absorbance, most measurements with conventional Fourier transform infrared spectroscopy suffer from photometric inaccuracies. However, water is not sensitive to the polarization of the infrared light, but living systems can exhibit differential interaction to the polarized nature of light. In a method where the measured signal directly represents the difference in polarized absorptions, the water component becomes spectrally transparent (although the number of photons reaching the detector is still attenuated by water) and facilitates the measurements appropriate for biological systems. Verification of this principle is reported here for the use of a new midinfrared polarizationdivision interferometer developed in our laboratory. With the amide I vibrational band of a nylonll film which overlaps with the water absorption band at 1647 cm-', the associated dichroism is measured in the presence of varying amounts of interfering water absorption. It is found that dichroism can be measured even in the presence of strong interfering absorption from water. This observation suggests that the present method provides a unique approach, as well as the necessary impetus, for initiating biomedical infrared imaging studies.
Gas and Ion Dynamics of a Three-Aperture Vacuum Interface for Inductively Coupled Plasma-Mass Spectrometry
Authors: Tanner Scott D. , Douglas D. J. , French J. B.
Published: May 2005

The equations describing the pressure, density, and temperature characteristics of isentropic flow and of the formation of a shock structure due to the sudden termination of the directed motion of a flowing plasma are reviewed. The results are applied to describe the flow characteristics of a novel ICP-MS vacuum interface which consists of three apertures: a conventional sampler and skimmer and a third aperture contained in a blunt support which is normal to (or nearly normal to) the axis of the primary expansion through the sampler and skimmer. The flow through the interface apertures is characterized as continuum, effusive, or transitional, and the impact of these forms of expansion on the ion dynamics (kinetic energies and plasma neutrality) is examined. A shock wave may form in front of the third aperture. The effect of this flow disturbance on the gas and ion dynamics in the vicinity of the aperture is discussed. Experimental neutral and ion flow results are compared to the theoretical predictions. It is concluded that the plasma retains its charge neutrality as it flows through the sampler and skimmer and, under the conditions studied, also through the shock and subsequent expansion through the third aperture. The gas behind the shock flows across the surface of the blunt tip of the third aperture, and the aperture itself may be offset from the axis of the original expansion to eliminate clogging of the aperture by unvaporized particles and condensed salts from the plasma and to prevent source plasma photons from contributing to the background signal continuum. The reduction in the ion current introduced into the ion optics region of the mass spectrometer reduces the magnitude of the space charge field and results in a gain in ion transmission efficiency which offsets the reduction of the ion flow.
Direct Evidence for β-Cyclodextrin-Induced Aggregation of Ionic Surfactant below Critical Micelle Concentration
Authors: Jiang Yun-Bao , Wang Xiu-Juan
Published: May 2005

The fluorescence emission of p-dimethylaminochalcone (DMAC) has been monitored in β-cyclodextrin (β-CD) and cetyltrimethylammonium bromide (CTMAB) or sodium dodecylsulfate (SDS) mixture. In the presence of a fixed amount of β-CD, a peak-shaped variation is observed in the curve of DMAC fluorescence intensity vs. surfactant concentration below critical micelle concentration (cmc). The peak height is dependent on β-CD concentration, and no peak is noted in the absence of β-CD. Such a peak-shaped variation in DMAC fluorescence emission is shown to be direct evidence for β-CD-induced aggregation of the surfactant below cmc in aqueous solution. The 1:1 surfactant/β-CD inclusion complex is the hydrophobic source inducing the aggregation.
In situ Raman Spectroscopy of Aza-Arenes Adsorbed at the Aqueous/Silica Interface
Authors: Matzner Robert A. , Bales Roger C. , Pemberton Jeanne E.
Published: May 2005

Raman spectroscopy is used to study the effect of pH on the solute/sorbent interactions and the chemical nature of the adsorbed species at the aqueous/silica interface for the aza-arenes acridine, quinoline, and pyridine. The neutral aza-arene is hydrogen-bonded to surface sites in aqueous media in which the pH is above the p Ka of the compound. A protonated aza-arene/ClO4− ion pair interacts with surface sites in aqueous solutions in which the pH is below the pKa of the compound. These results may be useful in predicting the fate of these environmentally significant compounds in groundwater.
Fourier Transform Infrared Spectroscopy Studies of the Secondary Structure in mt-PA6 and mt-PA6 Treated with L-Arginine, L-Asparagine, and (+)-Citrulline in Aqueous Solution
Authors: Kirsch J. L. , Zimmerman R. E. , Tensmeyer L. G.
Published: May 2005

FT-IR studies of the secondary structure of mt-PA6 and mt-PA6 treated with L-arginine, (+)-citrulline, and L-asparagine were carried out in aqueous buffer solution. Spectral subtraction was used to remove the interfering water bands in the amide absorption region, and the amide I absorptions were monitored to investigate changes in the secondary structure of the mt-PA6 induced by the binding of these amino acids. The spectral data showed a narrowing of the amide I absorption of mt-PA6 on treatment with L-arginine, (+)-cirrulline, and L-asparagine. Deconvolution of the amide I absorption revealed vibrational bands characteristic of β-sheet (1632 cm−1), disordered or bound water (1644 cm−1), and turns (1660 cm−1) secondary structures for the mt-PA6. Curve-fitting methods were also used to examine the changes in spectra and secondary structure of the mt-PA6 resulting from amino acid treatment. Analysis of the spectral data shows that loss in intensity of the bands near 1644 and 1660 cm−1 is responsible for the amino acid-induced narrowing of the mt-PA6 amide I absorption. In addition, the spectral data could suggest different binding interactions for L-arginine to mt-PA6 compared to the L-asparagine and (+)-citrulline.
Mass Spectral Recording and Storing System Based on GPIB Data Transfer for Laser Ionization Time-of-Flight Mass Spectrometry
Authors: Coulson Larry D. , Nagra Davinder S. , Guo Xijian , Whittal Randy M. , Li Liang
Published: May 2005

A data acquisition scheme based on a general-purpose interface bus (GPIB) for data transfer from a digital storage oscilloscope (DSO) to a PC is investigated for recording and storing transient signals generated by laser-induced multiphoton ionization or laser desorption ionization time-of-flight mass spectrometry. With this scheme and the use of commercial software, the data acquisition rate is generally low, typically 1 or 2 Hz for 20-Kbyte transients. We have developed a software to maximize the speed of data transfer and storage. This software is incorporated into LabWindows for data analysis. We demonstrate that it is possible to record and store mass spectra at a speed ranging from 14 spectra/s for a transient record length of 20 Kbytes to 50 spectra/s for a record length of 1 Kbyte by using this DSO-GPIB-PC scheme. This simple and readily adaptable system is found to be adequate and useful for many operations in laser work where relatively higher repetition rates are required. The applications of the system are demonstrated for recording and constructing ion chromatograms in liquid chromatography/time-of-flight mass spectrometry. In addition, it is shown that the data system can not only replace the traditional boxcar integrator for signal monitoring but also provide multiple ion monitoring for recording wavelength spectra in laser ionization spectroscopy.
Fluorescence Spectroscopic Investigation of the Effect of α-Cyclodextrin on the Twisted Intramolecular Charge Transfer of p-Dimethylaminobenzoic Acid in Aqueous Media
Authors: Jiang Yun-Bao
Published: May 2005

The effect of α-cyclodextrin (α-CD) on the twisted intramolecular charge transfer (TICT) of p-dimethylaminobenzoic acid (DMABOA) in aqueous media is investigated with the use of TICT-typical dual fluorescence. With the increase of α-CD concentration in aqueous DMABOA solution, the LE fluorescence is slightly quenched and is not shifted in position, while the TICT fluorescence is strongly enhanced and shifted to blue. The correlation of the intensity ratio of the TICT band to the normal band, Ia/ Ib, of DMABOA with medium polarity in aqueous α-CD media is opposite to that in pure organic solvent, which is explained in terms of the different TICT behavior in aqueous solution. The p Ka of DMABOA is not affected by the presence of α-CD, and the orientation of the DMABOA molecule in the DMABOA/α-CD inclusion complex is determined to be with the dimethylamino group in the cavity. The stoichiometry and association constant of the DMABOA/α-CD inclusion complex are investigated by monitoring the Ib/ Ia of DMABOA as a function of α-CD concentration. The Ia/ Ib value of DMABOA in α-CD media is generally much lower than that of DMABN in the same media, which is interpreted by the difference in the energy barrier from the locally excited (LE) to the TICT state and in the orientation of the guest molecules in the α-CD cavity. The effect of the cyclodextrin cavity is clearly demonstrated to be a micro-environmental effect.
Optical Depth Profiling of Thin Films by Impulse Mirage Effect Spectroscopy. Part II: Measurements Using Wide-Band Modulated Excitation
Authors: Schweitzer M. A. , Power J. F.
Published: May 2005

Laser mirage effect (photothermal deflection) spectroscopy was used in this work to determine depth profiles of the optical absorptivity of thin polymer films whose thermal properties were approximately invariant with depth. A variety of well-characterized laminates and continuous samples were examined. The key experimental variables affecting optical depth profile resolution were the offset of the probe beam above the surface, the thermal properties of the fluid medium in which optical deflection occurs, and the relative depths of the subsurface features to be resolved. The accuracy of the experimental signal was found to depend on several key factors which included the electrical bandwidth of the electronic detection system and the linearity of the photothermal deflection signal. Experimental procedures for ensuring quantitative signal recovery are described, and a theoretical interpretation of the depth dependence of the mirage signal was made by means of a model presented in a companion paper.
Surface-Enhanced Resonance Raman Spectroscopy of Flavins on Silver Nitrate-Modified Cu and Fe as Well as Cu-Zn-Pb and Fe-C-Cr-Ni Surfaces
Authors: Liang E. J. , Göttges D. , Kiefer W.
Published: May 2005

Surface-enhanced resonance Raman spectroscopy (SERRS) of riboflavin, flavin adenine dinucleotide (FAD), and flavin mononucleotide (FMN) on Cu, Cu-Zn-Pb, and Fe as well as Fe-C-Cr-Ni has been performed by means of the modification of these substrates with silver nitrate. It is found that the SERR spectrum of a flavin molecule on the alloy Cu-Zn-Pb is different from that on the pure Cu, and this is also the case for a flavin molecule on the alloy Fe-C-Cr-Ni and on pure Fe. This result indicates possibly that Zn, rather than Cu, and Ni or Cr, rather than Fe, in the alloys also interact with the flavin molecules. In addition, the three flavins on the same supporting metal surfaces also exhibit some differences in the SERR spectra. This result implies an involvement of the side chains of the flavin molecules in the enhancement. The SERR spectra of the three flavins are compared with their resonance Raman (RR) spectra. On the basis of our experimental results, a direct interaction of N–5 and possibly also O–4 in the flavins with silver is suggested. The general effectiveness of this method for obtaining SERS is demonstrated, and the enhancement mechanism of these substrates is also briefly discussed.
Fourier Transform Near-Infrared Spectra of N-Methylacetamide: Dissociation and Thermodynamic Properties in Pure Liquid Form and in CCl4 Solutions
Authors: Liu Yongliang , Czarnecki Mirosław A. , Ozaki Yukihiro
Published: May 2005

FT-NIR spectra have been measured for N-methylacetamide (NMA) in pure liquid form and in carbon tetrachloride (CCl4) solutions over temperature ranges of 303–368 K and 283–343 K, respectively. For the pure liquid, the FT-NIR spectra give one band due to a free NH group, at least five bands due to free end NH groups, and at least six bands due to hydrogen-bonded NH groups in the region of the first overtone of the NH stretching mode, demonstrating the potential of FT-NIR spectroscopy for investigating the hydrogen-bonding of NMA. The temperature-dependent spectral changes of NMA in the pure liquid indicate that, with increasing temperature, longer-chain oligomers of NMA dissociate into monomeric and dimeric species. For the CCl4 solutions, the intensity of a band assigned to the first overtone of the NH stretching mode of the monomeric NMA has been employed to study the degree of dissociation and thermodynamic properties for the dissociation process. Below 4 × 10−3 M, NMA exists completely in the monomer form, and from the absorbance-concentration plot, the molar absorption coefficient of the first overtone of the NH stretching mode has been obtained. The degree of dissociation and dissociation equilibrium constant K have been calculated for the solutions at various concentrations, and then they have been employed to evaluate the thermodynamic parameters (Δ H, Δ S, and Δ G) for the dissociation of hydrogen-bonded NMA into its monomeric species. The results show that the contribution of the entropy (Δ S) to the standard free energy (Δ G) becomes larger with a reduction in the concentration. It seems very likely that in the dilute solutions shorter-chain oligomers exist predominantly, and they easily dissociate into the monomeric species.
Discussion of the Stray Light Rejection Efficiency of FT-IR Spectrometers: The Effects of Sample Emission on FT-IR Spectra
Authors: Tripp C. P. , McFarlane R. A.
Published: May 2005

The effects of emitted radiation at the sample position in FT-IR spectrometers can produce spectral distortions and artifacts. Because of the high stray light rejection efficiency of FT-IR, these distortions are presumed to arise from the constant (dc) emission leading to nonlinearity in detector response or to a rise in temperature of the optical bench caused by the hot sample which leads to a drop-off in spectrometer performance. We show that the stray light advantage of FT-IR may not be valid for hot samples because some sample emission makes its way back to the interferometer, where it is modulated and can be passed back to the sample to produce distortions in peak shapes and relative intensities. Several approaches to eliminate these problems are provided.

Although we have addressed only emission phenomena in this work, reflection from samples also leads to distortions, notably the presence of signal at n ( n = 2, 3, 4 …) times the frequency. As discussed by Hirschfeld,12,13 these effects can be eliminated by using a half-beam blocking aperture or by tilting the sample. From the above experiments, clearly these effects can also be eliminated by using the corner-cubed FT-IR.
Synthesis and Characterization of the Surfactant Terbium 3-[[1,2-Bis-[[(2-Ethylhexyl)Oxy]Carbonyl]Ethyl]Thio]Succinate as a Reagent for Determining Organic Analytes
Authors: Mwalupindi Averrin G. , Agbaria Rezik A. , Warner Isiah M.
Published: May 2005

The surfactant terbium 3-[[1,2-bis[[(2-ethylhexyl)oxy]carbonyl]ethyl]thio]succinate has been synthesized and characterized by use of its absorption, luminescence, and microviscosity properties. In the presence of small amounts of water, this surfactant aggregates in cyclohexane to form reversed micelles containing Tb(III) counterions. The critical reverse micelle concentration has been determined to be 5.7 × 10−5 M with the use of an optical probe. Organic analytes solubilized in reverse micelles have been detected indirectly with the use of the luminescence characteristics of Tb(III) counterions. The detection scheme is based on energy transfer from the solubilized organic donor to acceptor Tb(III) counterions. Analytical figures of merit for the micellar system in the presence of organic analytes are presented. The microviscosity of the reverse micellar core has been estimated with the use of a viscosity-sensitive luminescent probe.
Measurements of the Collisionally Quenched Lifetime of CO in Hydrocarbon Flames
Authors: Agrup Sara , Aldén Marcus
Published: May 2005

Time-resolved laser-induced fluorescence (LIF) from CO molecules in hydrocarbon flames was studied. Collisional quenching constants were evaluated on the basis of the exponential decays. Effective lifetime in a methane/oxygen flame was observed to vary between 250 and 400 ps depending on the position within the flame, and from 400 to 600 ps in the non-sooty parts of an ethylene/air flame. Fluorescence, constituting simultaneous spatially and temporally resolved decays, was also registered from various sections along a laser beam that probed different parts of the flame. Spectral recordings revealed not only the expected CO peaks but also, in the ethylene flame, laser-induced emission from C2 Swan bands and from polyaromatic hydrocarbon (PAH) emission that affected the fluorescence time decay in the sooty part of the flame.
Determination of Hexavalent Chromium in Environmental Fly Ash Samples by an Inductively Coupled Plasma-Atomic Emission Spectrometer with Ammonium Ion Complexation
Authors: Hwang J. David , Wang Wen-Jwu
Published: May 2005

A method to determine hexavalent chromium in environmental solid waste has been developed by using an ammonium complexation technique in ICP-AES. This method consists of a two-step extraction and the complexation of ammonium ion. An ammonium hydroxide solution was used to extract the chromium(VI) out of the fly ash sample into the solution. Interfering metal ions, such as Pb, Fe, and Zn in the fly ash sample, were effectively removed by extracting them as diethyldithiocarbamate (DDTC) complexes at pH 9.5 into an MIBK (methyl isobutyl ketone) solution. The pH of the aqueous phase of the sample is then transferred and adjusted to 6.0, and the Cr(VI) is extracted as its complex with MIBK prior to the organic ICP analysis. A method detection limit of 50 ng/g or better, as well as spike recoveries of 90 to 110% (at a spike concentration level of 500 ng/g), is obtained when this method is applied to determine chromium(VI) in fly ash samples.
Identification and Quantification of Organic Solvents in Flammable Hazardous Wastes by GC/FT-IR
Authors: Beihoffer Jon , Milam Nicole , Reschl John J. , Seidel Jimmy L.
Published: May 2005

A wide variety of organic solvents within flammable hazardous wastes were determined by GC/FT-IR using external calibration. The hazardous waste samples were prepared for analysis by dilution with hexane. The type of compounds analyzed included acetate esters, alcohols, aromatics, ethylene glycol ethers, chlorinated hydrocarbons, ketones, and other industrial solvents. The instrumental detection limits for the various compounds ranged from 4 to 240 μg/mL. Calibration curves were linear over one to two orders of magnitude and stable for several months. The percent relative standard deviation ranged from 0.9 to 10.0% and the percent bias was within ±23% for all analytes.
Optical Depth Profiling of Thin Films by Impulse Mirage Effect Spectroscopy. Part I: Theory
Authors: Schweitzer M. A. , Power J. F.
Published: May 2005

Impulse mirage effect/photothermal deflection spectrometry may be used to detect depth-dependent optical absorption in materials, through the time dependence of the probe beam deflection signal occurring in response to sample irradiation with a short excitation pulse. In this work a theoretical expression was derived for the normal and transverse photothermal deflection signals which occur in a sample with homogeneous thermal properties but where optical absorptivity varies with depth from the surface. An analytical solution of moderate simplicity is obtained for several cases of experimental interest, with three-dimensional heat conduction effects included. The depth profile resolution obtained with the mirage effect method is critically dependent on the distance between the sample layer probed and the offset position of the probe beam in the fluid layer above the sample. Saturation conditions and conditions for obtaining optimal depth resolution of continuous and discrete optical profiles are examined in detail.
Surface-Enhanced Resonance Raman Scattering of R-Phycoerythrin Adsorbed by Silver Hydrosols
Authors: Xu Yiming , Liang Li
Published: May 2005

Surface-enhanced resonance Raman scattering (SERRS) of R-phycoerythrin adsorbed by silver hydrosols was obtained. There are thirty-five lines in its SERRS spectra. However, there is a “fluorescent packet” in its Raman spectra only. All lines are covered up by the “packet”. The SERRS spectra were enhanced and the fluorescence was quenched rapidly because of the formation of the hydrosol/phycoerythrobilin (PEB) complex and the interaction with the SERS-active surface of the metallic base. The R-phycoerythrin consists of PEB and its surrounding protein matrix, but the lines of PEB appeared in R-phycoerythrin SERRS spectra only. This result indicates again that a competitive binding exists in the binding of protein-bound chromophore (R-phycoerythrin) components with silver hydrosols; thus, the chromophores (PEB) are mainly responsible for the SERRS effect. Therefore, the SERRS technique is very useful for studying protein-bound chromophores.
Comparative Study of Photovoltaic and Photoconductive Detection Methods for Liquid-Phase Photoionization
Authors: Judge John W. , McGuffin Victoria L.
Published: May 2005

The photovoltaic method for the detection of liquid-phase photoionization in the absence of an applied electric field is compared to the traditional photoconductive method. Each system is characterized by means of signal and signal-to-noise ratio measurements with respect to laser pulse energy, applied voltage, electrode separation distance, solute concentration, and solvent composition. Although both techniques exhibit similar detection limits (1 × 10−7 M) for solutes in polar solvents such as methanol and water, the photovoltaic technique has a more extensive linear dynamic range (103). Moreover, this technique allows detection of solutes in ionic solutions with comparable detectability and linearity.
Optical Monitoring of Laser-Induced Plasma Derived from Graphite and Characterization of the Deposited Carbon Film
Authors: Iida Yasuo , Yeung Edward S.
Published: May 2005

Mechanisms of the deposition of carbon thin films by the laser ablation of graphite were investigated by monitoring the plasma emission. Parameters such as electron density, ionization temperature, and vibrational temperature during plasma growth were evaluated as a function of the laser power density and the surrounding atmosphere. Also, Raman spectra of the deposited films were measured so that the particle size can be estimated from the intensity ratio of the Raman bands around 1360 and 1580 cm−1. The increase in power density caused an increase in ionization temperature and vibrational temperature of carbon species in the plasma but a decrease of particle size of the deposited thin films. The existence of 10 Torr of helium as a surrounding atmosphere caused drastic changes in the plasma parameters. The films deposited with helium atmosphere showed a low optical band gap, which indicates heat restructuring of ablated graphite particles in the hot plasma. The results can be explained with a simple model of laser ablation and the subsequent interaction of ablated particles with the laser-induced plasma.
Raman Imaging System with Dual Holographic Grating Tunable Filter
Authors: Pallister David M. , Govil Anurag , Morris Michael D. , Colburn Willis S.
Published: May 2005

A tunable filter is described for microscopic Raman imaging. The filter employes two matched-volume holographic transmission gratings in a dispersion/dedispersion configuration and is useful throughout the visible wavelength region. Average transmission is greater than 75%. The filter performance is demonstrated with brightfield images of a bar target, Raman images of a silicon integrated circuit, and brightfield images of mineral inclusions in glass.
Analysis of Carbon Black-Filled Rubber Materials by External Reflection FT-IR Spectrometry
Authors: Lutz E. T. G. , Luinge H. J. , van der Maas J. H. , van Agen R.
Published: May 2005

External reflection Fourier transform infrared (FT-IR) spectrometry in combination with partial least-squares regression allows qualitative and quantitative analysis of rubber materials with a high carbon black content (up to 35% w/w) on a routine level. The method developed proves to be reproducible and yields reliable qualitative information. The prediction potential of the method is shown to be sufficient for (semi)-quantitative analysis. Proper selection of spectral windows greatly improves the results. It is shown that natural, butadiene, and styrenebutadiene rubber can be determined with a precision of 9, 8, and 6% w/w, respectively.
Database of Standard Raman Spectra of Minerals and Related Inorganic Crystals
Authors: Wang Alian , Han Jingyi , Guo Lihe , Yu Jianyuan , Zeng Pei
Published: May 2005

Establishing a standard Raman spectral database for minerals and related inorganic crystals is a very important basis for further increasing the applications of Raman spectroscopy in the geosciences. However, the Raman spectral pattern of a crystal is a function not only of its composition and structure but also of the scattering geometry during the measurement. Therefore, the standard Raman spectrum of a crystal must be measured under well-defined standard conditions. It would be of great interest to establish a standard measuring configuration with which the characteristic Raman spectra of all mineral crystals could be obtained. Factor-group analysis of the main types of minerals indicates that almost all of them possess a Raman-active totally symmetric (TS) vibrational mode. Therefore, we propose a scheme to measure standard Raman spectra under a scattering geometry set up on the basis of these TS modes. Using this scheme, we were able to establish a database for standard Raman spectra of minerals and related inorganic crystals.
ESR Study of the Radical Cations 1,1′-Dimethylene and 1,1′-Trimethylene 2,2′-Bipyridinium: Charge-Transfer Complexes between Their Dications and the Donor Cysteine
Authors: Sánchez-Palacios Angela , Delgado Rut
Published: May 2005

In order to compare the acceptor properties of 1,1′-dimethylene and 1,1′-trimethylene 2,2′-bipyridinium dications opposite to a donor cysteine and the stabilities of their cation radicals, UV-visible spectrophotometric and ESR studies were carried out. The diquat dication (DQ2+) forms a red charge-transfer (CT) complex with cysteine (Cys2–) of the ion-pair type. The complex presents two CT bands at 348 and 494 nm, respectively. By use of the Benesi-Hildebrand and other treatments (Scott, Foster, and Scatchard), the association constant for the ion association and ελ were determined. The results obtained by all the procedures are in fair agreement. The triquat dication (TQ2+) does not form a CT complex with cysteine (Cys2–). The triquat radical (TQ+) was generated by its reduction with alkaline sodium dithionite, and it was detected by electron spin resonance spectroscopy at room temperature. The ESR spectrum of the diquat radical (DQ+) was reinvestigated. The corresponding hyperfine coupling and g factors of the radicals DQ+ and TQ+ were given.
What is Wrong with “What is Wrong with MEM?”
Authors: Leclerc Gervais , Pireaux J. J.
Published: May 2005

A theoretical derivation of autoregressive spectral estimation is briefly presented, at variance with a recent paper by Kauppinen and Saario.
Surface-Enhanced Raman Detection of Aqueous Cyanide
Authors: Shelton Robert D. , Haas John W. , Wachter Eric A.
Published: May 2005

Cyanide ion (CN−) has been the subject of numerous studies probing the mechanisms underlying the surface-enhanced Raman scattering (SERS) phenomenon. This work examines various aspects critical to application of SERS for direct detection of trace cyanide in groundwater and in wastewater streams. A new method for direct quantitation of cyanide in aqueous electrolyte has been developed that uses an ex situ oxidation-reduction cycle to precondition a planar silver electrode. Cyanide ion can be detected in 0.1 M KCl with a linear response between 100 ppm and 10 ppb. The estimated limit of detection is approximately 8 ppb. The effects of pH, electrolyte level, and two common background ions, nitrate (NO3−) and sulfate (SO42–), have been characterized. Cyanide response was found to be sensitive to pH, with optimal performance observed at neutral to basic pH. Electrolyte concentrations of 0.001 M reduced response to cyanide by a factor of five, while levels above 0.1 M had no significant effect. The addition of 10-ppm sulfate ion decreased response approximately 40%, while the presence of nitrate ion at concentrations up to 100 ppm had a negligible effect on SERS response. These results suggest that cyanide ion can be detected directly in high-ionic-strength aqueous solutions, such as groundwater.
Double-Chamber Flow Cell for in situ Infrared Spectroscopy Studies of Chemical Reactions in Ziegler-Natta Catalyst Systems
Authors: Bache Øystein , Ystenes Martin
Published: May 2005

A complete experimental setup for in situ infrared transmission spectroscopy studies of solid/liquid reactions in Ziegler-Natta catalysts has been developed. The main part of the apparatus, the flow cell, facilitates separate recording of the liquid-phase spectrum and the superimposed solid/liquid spectrum, and thus allows solid and dissolved species during reactions to be distinguished. Addition of solutes and exchange of solution during the experiments are made possible, thus allowing subsequent reactions to be studied. The setup is suited also for liquid reactions, and, in principle, for other chemical systems as well. The construction of the flow cell and the operation conditions are based on pressure-drop calculations of the flow in the apparatus. Two experimental studies are included to demonstrate the use and to document the performance of the setup: (1) the reaction of MgCl2 with dissolved ethyl benzoate and AlEt3 in succession, and (2) the interaction of a MgCl2/ethyI benzoate support during TiCl4 treatment. In the latter, a hitherto unknown TiCl4/EB complex is discovered in the TiCl4 solution.
Fluorescence Lifetime Studies of Crude Oils
Authors: Wang Xin , Mullins Oliver C.
Published: May 2005

The fluorescence lifetimes of a series of crude oils at various concentrations have been measured for UV-visible excitation and emission wavelengths. The lifetime results are compared with fluorescence spectra and quantum yields for these solutions. The concentration effects of energy transfer and quenching are large and result in a significant decrease in fluorescence lifetimes for high concentrations and for heavy crude oils. Thus, radiationless processes dominate in energy transfer. At high concentrations, energy transfer produces large red shifts in fluorescence emission spectra, while quenching produces a large reduction in quantum yields. Stern-Volmer analyses of lifetime and quenching data show a linear dependence of energy transfer and quenching rates on concentration. The rate constants are consistent with collisions which are very efficient at energy transfer and quenching, and the rates of these two processes are comparable.
Luminescence Study of the Thermal Decomposition of Europium Trichloride Hexahydrate, EuCl3·6H2O
Authors: Stump Nathan A. , Schweitzer George K. , Gibson John K. , Haire Richard G. , Peterson Joseph R.
Published: May 2005

We have studied the thermal decomposition of EuCl3·6H2O using in situ measurements of the Eu3+ ion luminescence spectrum. The luminescence spectrum proved to be extremely sensitive to structural and compositional changes undergone by the title compound during the decomposition process. There appeared to be no change in the oxidation state of the europium throughout the decomposition process. Four differently hydrated species of EuCl3· nH2O ( n = 6, 3, 2, or 1) were identified via luminescence spectroscopy. We also observed another intermediate compound formed from the monohydrate prior to the final product EuOCl. Our analysis of this intermediate's spectrum indicates a single Eu3+ ion site, which is consistent with a formulation of Eu(OH)Cl2 rather than a mixed EuOCl·2EuCl3 product, both of which have been postulated by others on the basis of their thermogravimetric measurements.
Measurement of Ammonia with the Differential Optical Absorption Technique Combined with Fourier Transform
Authors: Axelsson L.
Published: May 2005

By using the differential optical absorption technique combined with Fourier transformation, we have achieved a good separation of ammonia from sulfur dioxide in the wavelength range 207 to 217 nm. Measurements show that, with a pathlength of two decimeters and a measuring time of one minute, we can measure less than 1.32 mg/m3 [1.9 ppm (volume)] of ammonia with a standard deviation of 0.46 mg/m3 [0.66 ppm (volume)] with interference from 408.73 mg/m3 [156 ppm (volume)] sulfur dioxide.
Near-Infrared Surface-Enhanced Raman Scattering (NIR SERS) on Colloidal Silver and Gold
Authors: Kneipp Katrin , Dasari Ramachandra R. , Wang Yang
Published: May 2005

Near-infrared surface-enhanced Raman scattering (NIR SERS) was detected with high sensitivity for two model compounds, crystal violet and the DNA base adenine, adsorbed on silver and gold colloidal particles in aqueous solutions. The NIR SERS spectra were measured with a fiber-optic probe with the use of a Ti:sapphire laser at 850 nm as the excitation source and a charge-coupled device (CCD) as the detection system. In a step to achieve the optimal electromagnetic SERS-enhancement conditions, silver and gold sols were modified to shift their extinction spectra more to the NIR region. Surface enhancement factors for both crystal violet and adenine were estimated to be on the order of 106 and 108 for gold and silver, respectively. A larger enhancement factor was observed for adenine with NIR excitation than with visible excitation. The benefits of NIR SERS and its potential applications are discussed.
Fluorimetric Analysis on Individual Nanoliter Sample Droplets
Authors: Mahoney Patrick P. , Hieftje Gary M.
Published: May 2005

Fluorescence from rhodamine 6G molecules in 225-μm-diameter (6-nL) droplets of ethanol is measured as they fall through a 514.5-nm Ar-ion laser beam, which is operated at a power density of 250 W/cm2. The fluorescence, measured at 555 nm, is imaged onto the entrance slit of a monochromator and measured with a photomultiplier tube. The droplets are produced by repeatedly plunging a 190-μm glass stylus into and out of a sample solution. The frequency of droplet production (150 Hz) corresponds to a flow rate of about 50 μL/min. The present detection limit of 3.7 fg, or 7.8 amol of rhodamine 6G, is limited by stray light and dark-current fluctuations.
Noninvasive Spectroscopic Detection of Bulk Polymerization by Stimulated Raman Scattering
Authors: Lai Edward P. C. , Ghaziaskar Hassan S.
Published: May 2005

The polymerization of styrene in a 15-cm storage bottle and of methyl methacrylate (MMA) inside a 50-cm reactor cell was monitored non-invasively by stimulated Raman scattering (SRS) for spectroscopic analysis. A pulsed laser was required to stimulate Raman scattering while a photodiode array detector measured the monochromator-dispersed Stokes lines. The results demonstrate that SRS is a useful spectroscopic technique for the real-time probing of polymerization in a large sample volume. Its signal intensity is related to the average analyte concentration integrated over the laser interaction path, which can better represent the bulk property of extended sample dimensions.
Quantitative and Qualitative Analysis of Some Inorganic Compounds by Raman Spectroscopy
Authors: Lombardi Daniel R. , Wang Chao , Sun Bin , Fountain Augustus W. , Vickers Thomas J. , Mann Charles K. , Reich Frederich R. , Douglas James G. , Crawford Beverly A. , Kohlasch Frank L.
Published: May 2005

Raman spectra have been measured for a number of nitrates, nitrites, sulfates, ferrocyanides, and ferricyanides, both in the solid phase and in aqueous solution. Accurate locations of peak maxima are given. Limits of detection for some of the compounds are given for solutions and for solid mixtures in NaNO3. Preliminary measurements have been made on core material recovered from the storage tanks on the Hanford site in Richland, Washington. Representative spectra are presented, showing that it is possible to observe responses of individual components from measurements made directly on untreated cores, with the use of a fiberoptic sampling probe.
Imaging Spectrometers for Fluorescence and Raman Microscopy: Acousto-Optic and Liquid Crystal Tunable Filters
Authors: Morris Hannah R. , Hoyt Clifford C. , Treado Patrick J.
Published: May 2005

Acousto-optic tunable filters (AOTF) and liquid crystal tunable filters (LCTF) are evaluated for their suitability as fluorescence microscopy imaging spectrometers. AOTFs are solid-state birefringent crystals that provide an electronically tunable spectral notch passband in response to an applied acoustic field. LCTFs also provide a notch passband that can be controlled by incorporating liquid crystal waveplate retarders within a Lyot birefringent filter. In this paper, spectroscopic performance and imaging quality are contrasted by evaluation of model systems. Studies include transmission imaging of standard resolution targets, multispectral fluorescence emission imaging of tagged polystyrene microspheres, and immunofluorescence imaging of neurotransmitters within rat-brainstem thin sections. In addition, the first use of LCTFs for Raman microscopy is demonstrated. Raman microscopy is a noninvasive spectral imaging technique that can provide chemically significant image contrast complementary to fluorescence microscopy without the use of stains or tags.
Nondestructive and Nonintrusive Determination of Chemical and Isotopic Purity of Solvents by Near-Infrared Thermal Lens Spectrometry
Authors: Tran Chieu D. , Grishko Victor I. , Baptista Mauricio S.
Published: May 2005

A novel instrument which is based on the use of the thermal lens effect to facilitate the sensitive measurements of the absorption in the near-infrared region has been developed. In this instrument, the near-IR excitation light was provided by a solid-state, spectra-tunable (from 860 to 1060 nm) titanium:sapphire laser. The heat generated as a consequence of the sample absorption of the excitation beam was monitored in the visible region by a He-Ne laser. The data obtained were analyzed by multivariate calibration methods for the nondestructive, noninvasive determinations of chemical and isotopic impurities in solvents. Water in D2O and in tetrahydrofuran can be detected at levels as low as 0.006 and 0.3% (v/v). The method can also be used for the simultaneous determination of water and DMSO- h6 in DMSO- d6 and CD3OH in CD3OH, CD2HOH, and CDH2OH at levels as low as 10−3% (w/w).
Fourier Transform Raman and Brillouin Spectroscopy Using Atomic Vapor Filters
Authors: Horoyski P. J. , Thewalt M. L. W.
Published: May 2005

This paper presents Raman and Brillouin scattering measurements obtained with a Fourier transform interferometer, in which the laser light rejection was provided by an alkali-metal vapor cell. The narrow absorption band of the vapor cell allowed for the detection of energy shifts as low as 0.85 cm−1(∼26 GHz) while completely blocking scattered light at the laser frequency. Since, unlike a Fabry-Perot interferometer, a Fourier transform interferometer does not have a free spectral range placing an upper bound on the energy shifts which it can detect without ambiguity, the energy regimes of both Brillouin and Raman scattering are for the first time accessible with a single instrument.
Resonance Raman Study of the Binding of the Anticancer Drug Amsacrine to DNA
Authors: Butler Catherine A. , Cooney Ralph P. , Denny William A.
Published: May 2005

The binding of amsacrine [4′-(9-acridinylamino)methanesulfon- m-anisidide] to calf thymus DNA was studied by UV-visible and resonance Raman spectroscopy. A shift of the UV-visible absorption band of amsacrine at 434 to 442 nm together with a decrease in the intensity of this band is observed upon amsacrine-DNA binding. The resonance Raman spectrum of DNA-bound amsacrine shows a general slight decrease in intensity relative to the spectrum of the free species. The significant decrease in intensity of the bands at 1165, 1265, and 1380 cm−1 upon binding to DNA is attributed to the formation of a single amsacrine-DNA species. The assignment of these bands (1165, 1265, and 1380 cm−1), which was based upon a previous normal coordinate analysis (NCA) and molecular neglect of diatomic overlap (MNDO) calculation, and the observed lack of shift in the band positions upon binding are consistent with intercalation being the major binding mode of amsacrine, as inferred previously by other techniques.