bluuebunny/crossref_metadata_2025 huggingface dataset:
Strategies for Constructing Near-Infrared Spectral Libraries for the Identification of Drug Substances
Authors: Gerhäusser Christina I. , Kovar Karl-Artur
Published: October 2003

The suitability of near-infrared reflectance analysis (NIRA) as a noninvasive method for “real-time” spectral verification of drug substances is evaluated. Strategies for development and optimization of reference libraries by different mathematical means are discussed. In order to compare data preprocessing techniques, factor-based libraries were constructed with the use of raw and second-derivative spectra of 17 benzodiazepines collected over the wavelength range from 1100 to 2500 nm. Validation of the models by predicting the identity of test set samples using the correlation coefficient proved that using the derivatives enhanced the library's selectivity dramatically, as the recognition rates increased from 25 to 100%. Two pattern recognition methods, correlation coefficient and distance, were applied to confirm the identity of 117 drugs by using libraries based on full-range second-derivative spectra. Recognition rates of 99.2% were obtained from a factor-based library with the use of the correlation coefficient. Even structural analogues could be reliably classified among highly dissimilar drugs. The construction of sub-libraries consisting solely of similar drugs offered no advantages. Considerable data reduction by principal component analysis (PCA) made NIRA a rapid and effective method of analysis providing a high degree of reliability.
Association of Near-Infrared Dyes with Bovine Serum Albumin
Authors: Sophianopoulos Alkis J. , Lipowski Jacek , Narayanan Narasimhachari , Patonay Gabor
Published: October 2003

The binding of five near-infrared (near-IR) dyes to bovine serum albumin (BSA) has been evaluated by absorption, fluorescence, and circular dichroism. These dyes have a common squarilic acid polymethine backbone but differ in the substituents on two sites, R1 and R2, symmetrically located on the chromophore. The magnitude of the association constants for the dye–albumin complexes depended on the nature of the side chains and ranged from 34,000 to 1 × 107 M−1. Listed by the kind of side chain and in increasing binding order, the association constants are: [R1 = R2 = butyl phthalimide] < [R1 = R2 = cetyl] < [R1 = R2 = ethyl] < [R1 = butyl phthalimide, R2 = butyl sulfonate] < [R1 = R2 = butyl sulfonate]. The chromophore seems to interact mainly with a hydrophobic cavity on BSA. However, the association constants increase substantially when the side chain or chains are butyl sulfonate. This observation suggests that near the hydrophobic region there is at least one positively charged site with which the butyl sulfonate chain or chains interact. The molar ratio of the dye–albumin complex determined was 1:1. The optical constants of the dye–albumin complexes cannot be determined directly; therefore, a method is described for determining these complexes' optical parameters and thus their association constants.
Reactivity of Nucleic Acids with Ozone: An FT-IR Microspectroscopy Study
Authors: Biondi Giovanna , Zini M. Francesca , Bramanti Emilia , Benedetti Edoardo , Agostini Giovanni , Franzini Marianno , Vergameli Piergiorgio , Benedetti Enzo
Published: October 2003

Chemical changes were observed by Fourier transform microspectroscopy (FT-IR-M) in DNA and RNA samples treated with increasing amounts of ozone. The nucleobase reactivity and conformational changes in nucleic acids were followed through the trend of certain spectroscopic parameters calculated from the spectra. The P1 and P2 parameters (calculated from the ratios of the optical densities of the bands at 1692 and 1654 and at 1728 and 1654 cm−1, respectively), involving base absorptions, are sensitive to the chemical action of ozone on covalent bonds of purinic and pirimidinic bases. The P3 parameter (calculated from the ratios of the optical densities of the bands at 1230 and 1090 cm−1) is sensitive to conformational changes in the phosphate-ribose backbone of nucleic acids. We found that, as the amount of ozone increases, the P1, P2, and P3 parameters increase for both the DNA and RNA sample spectra, but the curve trend and the concentration range that gave significant parameter changes were different for DNA and RNA. DNA spectra showed a sigmoidal increase in P1 and P2 parameters ( C1/2 = 1.6 mg/mL, the concentration of ozone at which the parameters observed changed by 50%), a plateau between 2 and 4.5 mg/mL of ozone, and a slow linear increase for ozone concentrations >5 mg/mL. Instead, a C1/2 = 2.5 mg/mL was evaluated from the P3 vs. ozone concentration plot. The plots of P1, P2, and P3 parameters calculated from the RNA sample spectra vs. ozone concentration showed a saturation-shape curve that reached its maximum value between 0 and 1.9 mg/mL. On the basis of these results, several hypotheses are suggested to explain the reaction mechanism of DNA and RNA nucleobases and the conformational changes in nucleic acids.
Light-Emitting Diodes as Sensors for Colorimetric Analyses
Authors: Berry R. James , Harris Jay E. , Williams Ronald R.
Published: October 2003

A new nondispersive colorimetric analyzer has been developed with the use of light-emitting diodes (LEDs) as optical sensors coupled to an artificial neural network (ANN). In this application, various colored LEDs are used as optical detectors with tuned bandpasses. The device has been evaluated against conventional spectrometric methods in the determination of pH and heavy metals by the use of colorimetric procedures. The spectrometer benefits from a simple design, ease of application, inexpensive cost of construction, and long life.
Europium Bisphthalocyanine—NO2 Interactions in Monolayers: Spectroscopic and Electrical Measurements
Authors: Berno Bob , Nazri Abbas , Aroca Ricardo
Published: October 2003

The electronic and surface-enhanced resonant Raman spectra of europium bisphthalocyanine (EuPc2) are used to monitor the adsorption of NO2 onto EuPc2 Langmuir–Blodgett (LB) monolayer films. The reaction was also monitored in solution, and the complex formed was studied by electron paramagnetic resonance (EPR) spectroscopy. Conductivity measurements of the LB film have shown a two-stage process due to exposure to NO2 gas: adsorption on the surface, and absorption into the film. After a complete desorption by annealing, film conductivity rises continuously with time of exposure to gas to a saturation point. EPR measurements suggest that the EuPc2 structure is irreversibly changed by the material–gas interaction, although the adsorption is reversible.
X-ray Photoelectron Spectroscopic Characterization of Au Collected with Atom Trapping on Silica for Atomic Absorption Spectrometry
Authors: Süzer Ş. , Ertaş N. , Kumser S. , Ataman O. Y.
Published: October 2003

The nature of analyte species collected on a cooled silica tube for atom-trapping atomic absorption spectrometric determination was investigated with the use of X-ray photoelctron spectroscopy (XPS). An XPS spectrum of gold deposited on atom-trapping silica tubes reveals a Au 4f7/2 peak with a binding energy of 84.8 (±0.2) eV, which falls in the middle of the binding energies corresponding to zerovalent Au(0) at 84.0 eV and that of monovalent Au(I) at 85.2 eV. The corresponding energy for Au vapor deposited on silica is also 84.8 eV. Deposition of AuCl4- solution on silica results in two different Au 4f7/2 peaks with binding energies of 84.8 and 87.3 eV corresponding, respectively, to Au(0) and Au(III). Deposition of the same AuCl4- solution on platinum metal again gives two peaks, this time at 84.4 and 87.0 eV energies corresponding again to Au(0) and Au(III). Combining all these data, we conclude that gold is trapped on atom-trapping silica surface as zerovalent Au(0) with a 0.8-eV matrix shift with respect to the metal surface. A similar 0.6-eV shift is also observed between the binding energy of 4f7/2Hg22+ measured in Hg2(NO3)2·2H2O powder and that deposited on silica.
Calibration of an FT-IR Spectrometer for Ambient Air Monitoring Using PLS
Authors: Johansen Ib-Rune , Lines Glenn Terje , Honne Atle , Midtgaard Tonje
Published: October 2003

The objective of this work has been to develop a robust calibration method for simultaneous multigas detection with a Fourier transform infrared (FT-IR) system. Calibration models for the identification and quantification of 23 gases in the presence of high concentrations of background gases such as water vapor, carbon dioxide, and methane have been obtained for an FT-IR instrument with 0.7-cm−1 resolution. The calibration models have been tested on a breadboard instrument for trace gas measurement in manned space missions. The results show that FT-IR combined with multivariate methods such as partial least-squares (PLS) and proper pretreatment of the infrared spectra used in calibration is well suited for this purpose. A procedure for baseline drift compensation has been introduced to make the system insensitive to baseline drift and variations in transmittance. This baseline drift compensation also reduces the need for background measurements. Further, a procedure for incorporating a priori information about the instrument signal-to-noise ratio (SNR) and the absorption strength of interfering absorption lines has been developed. Indoor air monitoring and industrial process monitoring are other possible application areas for these techniques. Parts of this work have been performed in a project for the European Space Agency (ESA) in cooperation with Kayser-Threde GmbH and Daimler-Benz Aerospace, Dornier GmbH.
Direct Injection Nebulizer-Coupled Microwave-Induced Plasma for Atomic Emission Spectroscopy
Authors: Ng Kin C. , Culp Robbey C.
Published: October 2003

A micronebulizer/tangential torch configuration was used for the direct introduction of organic and aqueous aerosols into a 120-W argon Beenakker cavity plasma. Atomic emission was measured for Ca, Mg, Cr, Zn, Li, and Sr. Detection limits (3σ) with the use of aqueous standards were 40, 80, 180, 535, 9, and 90 ng/mL, respectively. Detection limits under similar conditions with the use of 50% methanol-aqueous solutions were 35, 107, 230, 10, and 127 ng/mL for Ca, Mg, Cr, Li, and Sr, respectively. Iodine detection in the helium plasma was evaluated in aqueous, 50% methanol-aqueous, and pure methanol solutions, with detection limits of 17, 25, and 42 μg/mL, respectively.
On the Local Environment Surrounding Pyrene in Near- and Supercritical Water
Authors: Niemeyer Emily D. , Dunbar Richard A. , Bright Frank V.
Published: October 2003

We use steady-state and time-resolved fluorescence spectroscopy to probe local solvent–solute interactions between pyrene (the solute) and supercritical water (SCW). Toward this end, we have developed a new fiber-optic-based titanium high-pressure optical cell which can withstand the temperatures and pressure needed to generate supercritical water. Static fluorescence measurements indicate that there is an increase in the local water density surrounding the pyrene molecules (clustering) up to five times the bulk fluid density. This extent of clustering is most prevalent at about one-half the critical density. Consistent with previous work on more mild supercritical fluids (e.g., CO2, CF3H, C2H6), the extent of this solute–fluid clustering decreases as the system temperature and pressure are increased. Time-resolved fluorescence measurements show that the excited-state decay kinetics are exponentially activated and not themselves affected by this solute–fluid clustering process.
Valence Discrimination Effects with Thermospray Sample Introduction: Characterization and Prevention
Authors: Yang Jinfu , Koropchak John A.
Published: October 2003

With thermospray sample introduction for atomic spectrometry, sensitivity for certain elements can be valence-dependent (valence discrimination effect). To this point, this effect appears to be significant only for nonmetals with easily reducible lower oxidation states, such as arsenic, antimony, and selenium. In this work, the valence discrimination effects for these elements were studied in detail with inductively coupled plasma atomic emission spectrometry detection. The sensitivities for As(III), Sb(III), and Se(IV) were found to be significantly lower than those for As(V), Sb(V), and Se(VI), respectively. In general, the sensitivity difference between the low- and high-valence species increases with thermospray temperature but decreases with an increase in HCl or HNO3 concentration in solution. The low sensitivity for the low-valence species proved to arise from their reduction to corresponding metals within the thermospray process, after which the metals were trapped on the vaporizer and desolvation system. An effective way to prevent the valence discrimination effect is by means of the addition of a suitable oxidant into the solution.
Optimization of Single-Molecule Fluorescence Burst Detection of ds-DNA: Application to Capillary Electrophoresis Separations of 100–1000 Basepair Fragments
Authors: Haab Brian B. , Mathies Richard A.
Published: October 2003

Methods for optimizing the dye labeling, laser excitation, and data analysis for single-molecule fluorescence burst detection of ds-DNA have been developed and then validated through capillary electrophoresis (CE) separations of 100–1000 basepair (bp) DNA. Confocal microscopy is used to observe fluorescence bursts from individual DNA fragments labeled with the intercalation dye TO6 as they pass through the ∼ 2-μm-diameter focused laser beam. The dye concentration and laser power were optimized by studying fluorescence burst intensities from pBluescript DNA fragments. The optimal TO6 concentration was ≤100 nM, and the optimal laser power was ≤1 mW. Single-molecule counting was then used to detect CE separations of a 100–1000 bp DNA sizing ladder in 3% linear polyacrylamide. Discrete and baseline-resolved fluorescence bursts were observed in bands as small as 100 bp, and the average burst size within each band increased linearly with fragment size. By counting events using a single optimally chosen discriminator level, we achieve maximum signal-to-noise ratio (S/N) for each fragment size. If the discriminator level is ramped linearly with fragment size to achieve a constant detection efficiency, then the number of events properly reflects the relative fragment concentrations.
Characterization of Surface Contaminants by a Silver Film-Enhanced IR—Johnson Method
Authors: Marino Nobuaki , Murai Kiichirou , Kataora Yoshinori
Published: October 2003

Characterization of nanometer-order organic contaminants on polymer film and silicon wafer surface has been investigated by a modified IR–Johnson method. We have proposed a silver film-enhanced IR–Johnson method that is useful for surface contaminant analysis. In the present method, organic traces are transferred from the surface of a polymer film or silicon wafer onto the KBr particles deposited with silver film, and then the KBr particles are analyzed directly by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Infrared absorption of organic traces was enhanced by the presence of silver island film. With this method, a spectrum of nanometer-order organic traces can be obtained without any interference from the polymer film substrate. The present method is as surface-sensitive as X-ray photoelectron spectroscopy (XPS) and provides a large amount of information on the chemical structure of surface contaminants. This is a promising method for the surface characterization of polymer films and silicon wafer. Index Headings: Infrared; Diffuse reflectance; Surface enhancement.
Electrospray Ionization Time-Of-Flight Mass Spectrometer for Elemental Analysis
Authors: Mahoney Patrick P. , Guzowski John P. , Ray Steven J. , Hieftje Gary M.
Published: October 2003

Electrospray ionization (ESI) has been combined with a time-of-flight (TOF) mass spectrometer for elemental analysis. With the use of a heated-capillary interface, the instrument is shown to be stable to within 5% relative standard deviation (RSD) over a 60-min period. The ratio between the isotopes of rubidium is measured with a precision of 0.4% RSD for a 1-min integration time. With the addition of a supporting electrolyte as a spray stabilizer and internal standard, the dynamic range is linear over at least three orders of magnitude. The extent of solvent-cluster fragmentation is found to be governed primarily by the voltage differential between the capillary and skimmer and, to a lesser extent, by the capillary temperature. The capillary voltage also affects the distribution of species among the parent and its fragment ions for ferrocene and tetraethyllead. Under “mild” interface conditions, a resolving power of 1400 is achieved for an organolead complex. A spectrum for a larger molecule, polypropylene glycol, is presented to show the versatility of the ESI-TOF instrument for both atomic and molecular analysis.
Flow-Injection Chemiluminescence Method for the Determination of Hydrocortisone and Progesterone
Authors: Li Huai-Na , Ci Yun-Xing
Published: October 2003

A simple flow injection chemiluminescence (CL) method for the determination of progesterone and hydrocortisones (HCRs) is described. The method is based on their sensitizing effect on the chemiluminescence reaction of a mercapto-group (-SH) with cerium(IV) in sulfuric acid. This method allows determination in the ranges 0.28–8.0 μg/mL for hydrocortisones (HCRs) and 0.5–8.0 μg/mL for progesterone with a detection limit of 0.10 μg/mL for HCRs and 0.26 μg/mL for progesterone. The experimental conditions for the reaction are optimized. The possible reaction mechanism is discussed.
NMR Characterization of Liquid Crystal—Polymer Interactions in Polymer-Dispersed Liquid Crystals
Authors: Mirau Peter A. , Srentvasarao Mohan
Published: October 2003

Solid-state nuclear magnetic resonance (NMR) and optical microscopy have been used to study liquid crystal–polymer interactions in polymer-dispersed liquid crystals (PDLCs) composed of the E7 liquid crystal mixture and poly( n-butyl methacrylate) or poly(isobutyl methacrylate). As previously reported, the droplets adopt a bipolar configuration in the PDLCs using poly( n-butyl methacrylate) as the matrix material and a radial configuration in those using poly(isobutyl methacrylate). The NMR signals from the E7 cannot be detected in the bulk state by using magic angle spinning and cross-polarization because of its liquid-like properties. The E7 and the polymer signals are only weakly cross-polarized in 60:40 E7/poly( n-butyl methacrylate) PDLCs but are strongly cross-polarized in the PDLCs with poly(isobutyl methacrylate). We suggest that the differences are due to a change in the surface-anchoring conditions and that NMR spectroscopy may provide a molecular-level probe of the forces that control droplet configuration and the electro-optical properties of these materials.
Identification of Xylene Isomers in High-Pressure Liquid Chromatography Eluates by Raman Spectroscopy
Authors: Steinert Roland , Bettermann Hans , Kleinermanns Karl
Published: October 2003

This contribution presents a combination of high-pressure liquid chromatography (HPLC) with a Raman spectrometer. With this approach, we have identified both isomer m-xylene and isomer p-xylene in solution at concentrations down to 10−5 mol/L. The setup was developed to analyze compounds that cannot be separated by using standard HPLC techniques.
Rapid-Scan Two-Dimensional FT-IR: An Efficient Approach to Dynamic Infrared Spectroscopy
Authors: Steeman Paul A. M.
Published: October 2003

It is shown that it is possible to use a standard rapid-scan Fourier transform infrared FT-IR spectrometer for dynamic infrared measurements. Spectrum acquisition time is significantly reduced in comparison with two-dimensional infrared (2D IR) spectrometers employing the step-scan technique. In the case of polymers, for which stress relaxation often occurs over time, the reduction of the total measurement time proves to be an essential feature. Experimental and mathematical details are discussed. Application of the rapid-scan technique is illustrated with some results for a styrene–acrylonitrile/butadiene copolymer.
Multichannel FT-Raman Spectroscopy: Noise Analysis and Performance Assessment
Authors: Zhao Jun , McCreery Richard L.
Published: October 2003

A Raman spectrometer based on forming an interferogram on a charge-coupled device (CCD) detector is evaluated further with respect to signal-to-noise ratio (SNR), stability, response correction, and resolution. The multichannel Fourier transform technique differs fundamentally from dispersive spectrometers and FT-Raman systems based on Michelson interferometers. Changes in entrance optics permitted multitrack operation and an improvement in collection efficiency. Both hardware and a more facile software procedure were examined for correction of noise caused by nonuniformity of the CCD response. The instrumental linewidth (ILW) for the multichannel Fourier transform (MCFT) system examined here was 14 cm−1 (full width at half-maximum), close to the 13.5 cm−1 predicted theoretically. An optical heterodyne method was used to downshift the observed Raman features and further reduce the ILW to 8 cm−1. The unheterodyned MCFT spectrometer has a lower SNR than do dispersive systems for most samples, but has the advantages of frequency precision and large throughput. Several applications of MCFT are discussed, including examination of photolabile samples, multiple sample monitoring with fiber optics, and identification of MCFT spectra with a dispersive library.
Two-Dimensional Correlation Analysis of Time-Resolved Step-Scan FT-IR Spectra of a Liquid Crystalline Guest—Host System in an Electric Field
Authors: Czarnecki Miroslaw A. , Jordanov Bojidar , Okretic Stefano , Siesler Heinz W.
Published: October 2003

The time-resolved step-scan FT-IR spectra of a solution of 2-naphthaldehyde in a nematic solvent were recorded during switching of an electric field. The mesogen of the nematic solvent consisted of a nitrile-substituted bicyclohexyl unit and had a flexible aliphatic chain attached to it. Two-dimensional (2D) correlation analysis of the dynamic spectra was undertaken in order to investigate the details of the molecular orientation and relaxation of the sample under the influence of this electric field. In addition, from the time-resolved spectra the relaxation times of selected functionalities were estimated. The results yield strong evidence that both the nematic solvent and the solute reorient in phase at similar rates. However, the movement of the hydrocarbon chain of the nematic solvent seems to be slightly delayed with respect to the mesogen and the solute. It has been shown that the rigidity of the mesogen plays an important role in the mechanism of the electric-field-induced reorientation of the aliphatic chain.
Phase Structure of Polymers by Dipolar-Induced Spin Diffusion: Model Spin Diffusion Calculations
Authors: Cheung T. T. P.
Published: October 2003

The evolution of the spatial inhomogeneity of magnetization induced by spin diffusion is investigated theoretically for different models of a multiphase polymer solid. It is shown that the decay of the total magnetization associated with the domains where the magnetization initially resides is affected by the distributions in the size of the domains and the separation between them. The models examined include the two-phase/multidomain (2P-MD) case, in which the system consists of two phases with an infinite number of domains in each phase, and the two-phase/four-domain (2P-4D) model, in which the system has two phases with two domains in each. The spin diffusion equation is solved for these models by using a simple two-value distribution in the domain width or the domain separation. The solutions for the magnetization of the 2P-MD model show a slower decay in the long-time regime in comparison to those of the 2P-4D case. The solutions of the latter give a reasonable approximation to the former, provided that the spread in the distribution is sufficiently smaller than the average of the distribution. The simple two-phase/two-domain (2P-2D) model, in which the two phases are represented by a single domain each, is also investigated. In this case, the effect of the distribution is incorporated by taking an ensemble average. It is shown that there is no correct way of taking the average, and the results always yield erroneous long-time behavior for the magnetization. The results of the 2P-MD, 2P-4D, and 2P-2D models are applied to the spin diffusion experiment of a semicrystalline polypropylene film.
Raman Imaging of Dental Adhesive Diffusion
Authors: Wieliczka D. M. , Kruger M. B. , Spencer P.
Published: October 2003

The clinical success of dental composites depends critically upon the adhesive bond that secures it to the tooth. Previous efforts to characterize the adhesive/dentin interface have generally required sample preparation that alters or damages the interface. Using micro-Raman spectroscopy, we have collected chemical and morphologic information on the dentin/adhesive interface with minimal sample preparation. Results from this technique have provided direct evidence of adhesive penetration and demineralization depth for two adhesive systems.
FT-IR TRS of Liquid Crystalline 5CB in ac, dc, and ac + dc Electric Fields
Authors: Leyte J. C. , Van Woerkom P. C. M.
Published: October 2003

Time-resolved (TR) spectra of 5CB in the millisecond domain were obtained during excitation with electric fields of different time dependence: ac, dc, and ac + dc. The response to ac excitation occurs mainly at twice the modulating frequency. The effect of the addition of dc to an ac field is the induction of an additional response at the ac frequency. The additional “single frequency” response persists indefinitely, even though the response to the application of only a permanent dc field relaxes within roughly 200 ms. The amplitude of the oscillating responses diminishes with increasing ac frequency. This result is in accordance with the expected response to the torque exerted by the ac field. Different functional group absorptions respond without a significant phase difference in this time scale.
Spatial and Temporal Profiles of Indium in a Furnace Atomization Plasma Excitation Spectrometry Source
Authors: Blanc C. W. Le , Blades M. W.
Published: October 2003

Spatially resolved emission and absorption intensities from the indium 303.94-nm resonance line were measured in a furnace atomization plasma excitation spectrometry (FAPES) source. These measurements show that the spatial structure observed in the analyte emission is due to two effects. The first is the spatial distribution of analyte atoms in the source. The absorption measurements show that this spatial distribution is fairly uniform. There is a slight gradient, with analyte concentrations increasing from the cuvette wall to the center electrode. The fine structure in the emission intensity profiles must therefore be caused by the dependence of the degree of analyte excitation on position within the cuvette. This structure suggests that the FAPES source operates as an atmospheric-pressure radio-frequency glow discharge. Negative glows are seen adjacent to the graphite cuvette wall and center electrode.
Dielectric Stack Filters for Ex Situ and In Situ UV Optical-Fiber Probe Raman Spectroscopic Measurements
Authors: Munro Calum H. , Pajceni Vasil , Asher Sanford A.
Published: October 2003

Dielectric stack interference filters can be used in conjunction with a high-throughput single-stage spectrograph to facilitate the measurement of high signal-to-noise (S/N) ultraviolet (UV) Raman spectra with 228.9-nm and 244-nm excitation wavelengths. Placed between the sample and the spectrograph, these filters reflect Rayleigh scattering while transmitting Stokes-shifted Raman scattering. We have measured UV Raman bands from solid, highly scattering samples down to a 290-cm−1 shift from the Rayleigh line. The high throughput of the filtered single-stage spectrograph enables the measurement of UV Raman spectra from photo-labile samples, including DNA and the energetic materials pentaerythritol tetranitrate (PETN) and trinitrotoluene (TNT), with sufficiently low excitation powers and short accumulation times to minimize photo-alteration. High S/N UV preresonance and resonance Raman are obtained for PETN and TNT within 1 s, indicating the possible application of UV Raman spectroscopy as a rapid, highly selective screening methodology for the detection of trace levels of contraband explosives. Furthermore, the incorporation of these dielectric filters within a UV optical-fiber Raman probe head provides simultaneous Rayleigh rejection and removal of background silica Raman scattering. With the use of a 244-nm UV optical-fiber probe, we measured Raman spectra from 100 nM to 10 μM concentrations of polycyclic aromatic hydrocarbon (PAH) in water, even in the presence of an equimolar concentration of the visible fluorophore rhodamine 6G (R6G). Thus, we demonstrate the potential of UV Raman optical-fiber probes for minimally invasive in situ real-time monitoring at low analyte concentrations and within environments in which fluorescence backgrounds would prevent measurements with visible Raman optical-fiber probes.
Quantitative Analysis of Mineral Powders by DRIFTS: Determination of SrCO3 in Superconductor Precursor Powders
Authors: Bak Jimmy , Kindl Bruno
Published: October 2003

An application of diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) has been demonstrated to be able to determine small concentrations, down to the 100-ppm level, of carbonates in powdery superconductor (SPC) precursor samples. The detection of carbonates in SPC precursor powders is important because of degradation effects on the electrical properties of the final product. Qualitative analysis carried out by DRIFTS shows that strontium carbonate (SrCO3) is the major carbonate present in a batch of SPC precursor powder. Two different calibration approaches are employed in order to determine the SrCO3 concentrations in the SPC powders. The concentrations found by the two methods are in good agreement.
Characterization of Denture Acrylic Resin Surfaces Modified by Glow Discharges
Authors: Süzer Şefik , Özden Nehir , Akaltan Funda , Akovali Güneri
Published: October 2003

Resin samples prepared by compression molding using a poly(methyl methacrylate) (PMMA) denture base material were exposed to radio-frequency (rf) glow discharges to improve the wettability of the material. Fourier transform infrared (FT-IR) reflectance, X-ray photoelectron spectroscopy (XPS), and contact-angle measurements have been employed to characterize the changes introduced by the glow discharge plasma. FT-IR measurements cannot detect any modification. XPS reveals an increase in the O/C atomic ratio. Contact angles of the plasma-treated samples are always lower when compared with untreated ones. The increased O atomic concentration is attributed to formation of –COH groups on the surface during plasma treatment. The O/C atomic ratio decreases upon heating the samples in vacuum to 100 °C for 1–2 min and exposing the samples to liquid CH2Cl2 for 1–2 min. Exposure to distilled water for prolonged periods causes a slight decrease during the initial 1–20 days but levels off to a constant value up to a period of 60 days. Plasma treatment seems to offer a durable increase in the wettability for these materials left in air or distilled water.
Development of a Novel Fluorimeter Based on Superluminescent Light-Emitting Diodes and Acousto-Optic Tunable Filter and its Application in the Determination of Chlorophylls a and b
Authors: Alexander Troy A. , Gao Guan-Hong , Tran Chieu D.
Published: October 2003

A novel, compact, inexpensive fluorimeter that has high sensitivity and no moving parts has been developed by using super luminescent (bright-blue) light-emitting diodes (SLEDs) and an acousto-optic tunable filter (AOTF). In this instrument, the recently developed gallium nitride SLEDs were used in a counterpropagating configuration to provide excitation light. These SLEDs provide not only high intensity (several milliwatts) but also wide spectral bandwidth in the blue region (from 370 to 570 nm). The AOTF can be placed before the sample to facilitate the measurements of excitation spectra or after the sample for the emission spectra measurements. This fluorimeter is suitable for the sensitive and general fluorescent analysis of a variety of compounds. It has been used, as an example, for the sensitive and simultaneous determination of chlorophylls a and b. Detection limits of 2.30 × 10−9 and 1.10 × 10−9 M have been achieved for chlorophyll a and chlorophyll b, respectively. Index Headings: Superluminescent light-emitting diode; Acousto-optic tunable filter; Fluorescence; Chlorophyll.
Line-Scan Raman Microspectrometry for Biological Applications
Authors: De Grauw C. J. , Otto C. , Greve J.
Published: October 2003

A high-resolution confocal line-scan Raman microscope was developed for the study of biological samples such as cells and chromosomes. With the illumination of a line on the sample, all the spectral information of the line is recorded. The line-scan microscope was attained by the introduction of one scanning mirror, a slit, and two cylindrical lenses in a standard confocal Raman microscope. The resolution, for an ideal sample, is 0.5 μm in the lateral direction and 3.5 μm in the axial direction. Line-scan experiments were performed to demonstrate the applicability of the instrument for biological samples. Line-scan images of calcium phosphate bone implant coatings and of the banding pattern of polytene chromosomes are presented.
Investigation of the Effect of Target Water Content on a Laser-Induced Plasma
Authors: Rusak D. A. , Clara M. , Austin E. E. , Visser K. , Niessner R. , Smith B. W. , Winefordner J. D.
Published: October 2003

Because of difficulties with matrix matching in a number of laser solid sampling techniques, plasma diagnostics are often employed directly or indirectly (through internal standardization) as a means of generating working curves. In this study, the effects of water content of CaCO3 powder on size, shape, excitation temperature, electron number density, continuum emission, and line emission of plasmas generated on the powder are investigated. Although the specific wetting properties of the matrix will determine the magnitude of the water content effects, the observations made for CaCO3 powder indicate that emission and electron number density are the two parameters affected significantly by water content, both decreasing with increasing weight % water. In laser-induced breakdown spectroscopy of samples that may have an inhomogeneous distribution of water or of samples in which water content can vary significantly, accounting for the effects of this water is essential to an accurate analysis.
Two-Dimensional Spatial Distribution of the Time-Integrated Emission from Laser-Produced Plasmas in Air at Atmospheric Pressure
Authors: Aragón C. , Aguilera J. A.
Published: October 2003

Emission from Nd:YAG laser-produced plasmas generated in air at atmospheric pressure has been studied with spatial resolution. With the use of a charge-coupled device (CCD), two-dimensional spatial distributions of the time-integrated line emission from plasmas of metallic (copper and stainless steel) and ceramic (alumina) samples were measured for laser power densities in the range 80–900 GW/cm2. Geometrical parameters (distance of the maximum, width in two directions) and the total space- and time-integrated emission were obtained as a function of power density. At the range 100–700 GW/cm2, the formation of a plasma in air for the metallic samples was shown to be responsible for a decrease in the total intensity of lines emitted from the sample plasma, accompanied by effects in the spatial profiles along the laser direction. Beyond 700 GW/cm2, a sharp increase of the line intensities was observed, related to the absence of the shielding air plasma.
Characteristics of the Secondary Plasma Induced by Focusing a 10-mJ XeCl Laser Pulse at Low Pressures
Authors: Kurniawan Hendrik , Ishikawa Yoko , Nakajima Sadao , Kagawa Kiichiro
Published: October 2003

A XeCl excimer laser (20 ns, 10 mJ) was focused on a copper target at a relatively high power density (1010 W/cm2) in a surrounding gas of air in the pressure range from 1 Torr to about 10 Torr. Plasma characteristics were examined in detail with the use of a time-resolved spatial distribution technique on the emission lines Cu(I) 5218 Å, Cu(I) 5105 Å, and Cu(II) 4674 Å. The results show that the majority of atoms are ablated in the form of neutral atoms, and that the temperature of the plasma increases with time in the initial explosion stage. These facts suggest that the secondary plasma is excited by a shock wave and the recombination emission process is not predominant. It was also demonstrated that the plasma produced at 1 Torr is due to another excitation mechanism; namely, the collision of ultrafast atoms with surrounding gas molecules. This plasma is also suitable for analytical spectrochemical application.
Classification of Chemically Modified Celluloses Using a Near-Infrared Spectrometer and Soft Independent Modeling of Class Analogies
Authors: Svensson Olof , Josefson Mats , Langkilde Frans W.
Published: October 2003

A method for classification of eleven chemically modified celluloses has been developed with the use of near-infrared (NIR) spectroscopy and soft independent modeling of class analogies (SIMCA). The sample set consisted of 440 different batches from eleven different cellulose derivatives. A full factorial design in temperature and moisture was made for one sample from each class in order to introduce climate variations in the calibration sample set. Principal components analysis (PCA) models were made for each class, and samples not present in the calibration set were classified according to the SIMCA method. Only one type II error (acceptance of an unacceptable sample) was detected in the classification of the different celluloses. The number of type I errors (rejection of an acceptable sample) ranged from 0 to 14%. Subgroups, due to different manufacturers, viscosities, particle sizes, and degrees of substitution, were detected and correctly classified. The sample presentation, focus of the instrument, number of reference measurements, depth of penetration, and selection of training set samples are discussed.
Discrete Particle Detection and Metal Emissions Monitoring Using Laser-Induced Breakdown Spectroscopy
Authors: Hahn D. W. , Flower W. L. , Hencken K. R.
Published: October 2003

The unique conditions for the application of laser-induced breakdown spectroscopy (LIBS) as a metal emissions monitoring technology have been discussed. Because of the discrete, particulate nature of effluent metals, the utilization of LIBS is considered in part as a statistical sampling problem involving the finite laser-induced plasma volume, as well as the concentration and size distribution of the target metal species. Particle sampling rates are evaluated and Monte Carlo simulations are presented for relevant LIBS parameters and wastestream conditions. For low metal effluent levels and submicrometer-sized particles, a LIBS-based technique may become sample limited. An approach based on random LIBS sampling and the conditional analysis of the resulting data is proposed as a means to enhance the LIBS sensitivity in actual wastestreams. Monte Carlo simulations and experimental results from a pyrolytic waste processing facility are presented, which demonstrate that a significant enhancement of LIBS performance, greater than an order of magnitude, may be realized by taking advantage of the discrete particulate nature of metals.
Rapid Micro-Raman Imaging Using Fiber-Bundle Image Compression
Authors: Ma Jiaying , Ben-Amotz Dor
Published: October 2003

A new technique for rapid Raman imaging and chemical analysis of micro-composites and biomaterials, with potential applications in real-time robotic vision, automated manufacturing, and medical imaging, is described and demonstrated. The key feature of this new instrument is a fiber-optic bundle used to compress two-dimensional images onto a one-dimensional fiber stack, which serves as the entrance slit of an imaging optical spectrograph. Thus a complete Raman spectrum is simultaneously collected from every point within a sample in a single scan of a charge-coupled-device (CCD) detector. The method is demonstrated by using Raman imaging of a microscopic mixed-salt sample. Its efficiency relative to alternative Raman imaging methods is quantitatively evaluated, and potential applications in other spectral imaging measurements are discussed. Index Headings: Raman spectroscopy; Spectral imaging; Chemical imaging; Fiber optics; Chemical sensor.
Spectroscopic Studies of Heavily Carbon-Doped GaAs Grown by Metal Organic Chemical Vapor Epitaxy
Authors: Wu H. Z. , Li Z. Z. , Ye S. T. , Tian Z. W.
Published: October 2003

Spectroscopic studies of the minority electron lifetimes and photo-luminescence efficiencies of heavily carbon-doped GaAs are reported. The GaAs layers were grown by metal organic chemical vapor epitaxy (MOVPE) at 650 °C with carbon tetrabromide used as a dopant source. Combined minority electron lifetime and internal quantum efficiency measurements allowed us to determine the radiative decay times in heavily carbon-doped GaAs to be longer than that we would expect if a value for the radiative recombination constant of B = 2.0 × 10−10 cm3 s−1 were used. Taking into account the effects of hole–hole and hole–ionized impurity scattering, we show that B decreases as hole density increases in heavily carbon-doped GaAs. With the use of the revised values for B, the calculated radiative decay times were compatible with our measurements. Index Headings: Radiative decay times; Luminescence efficiency; Radiative recombination constant; Carrier–carrier interaction; Band structure changes.
Interpretation of Raman Spectra of Nitro-Containing Explosive Materials. Part I: Group Frequency and Structural Class Membership
Authors: Lewis Ian R. , Daniel Nelson W. , Griffiths Peter R.
Published: October 2003

Fourier transform (FT)-Raman spectroscopy has been used to obtain high-quality spectra of 32 explosive materials. The majority of the spectra of these explosives have not previously been reported. Twenty-eight of the explosives have been categorized into three classes (nitrates esters, nitro-aromatics, and nitramines) based on their chemical structure, the position of the antisymmetric and symmetric stretching vibrations of the nitro group, and the shapes of the band envelopes. The spectra of exceptional explosives are discussed in terms of their unique structures or compositions.
Interpretation of Raman Spectra of Nitro-Containing Explosive Materials. Part II: The Implementation of Neural, Fuzzy, and Statistical Models for Unsupervised Pattern Recognition
Authors: Daniel Nelson W. , Lewis Ian R. , Griffiths Peter R.
Published: October 2003

The implementation of neural, fuzzy, and statistical models for the unsupervised pattern recognition and clustering of Fourier transform (FT)-Raman spectra of explosive materials is reported. In this work a statistical pattern recognition technique based on the concept of nearest-neighbors classification is described. Also the first application of both fuzzy clustering and a fuzzified Kohonen clustering network for the analysis of vibrational spectra is presented. Fuzzified Kohonen networks were found to perform as well as or better than the traditional fuzzy clustering technique. The unsupervised pattern recognition techniques, without the need for a priori structural information, yielded results which were comparable with those obtained by using a combination of a priori structural information and manual group-frequency analysis. This work demonstrates, via the use of a nitro-containing explosive data set, the utility of unsupervised pattern recognition techniques for the clustering, novelty detection, prototyping, and feature mapping of Raman spectra. The results of this work are directly applicable to the characterization of Raman spectra of explosives recorded with fiber-optic sampling.
Comparative Studies of Hydrogen Termination on Single-Crystal Silicon Surfaces by FT-IR and Contact-Angle Measurements
Authors: Chyan Oliver M. R. , Wu Junjun , Chen Jin-Jian
Published: October 2003

The hydrogen termination process on a Si(100) surface has been studied by multiple internal reflection infrared spectroscopy (MIR-IS) and contact-angle measurements. Three main silicon hydride absorption peaks at 2087, 2104, and 2114 cm−1 were found to gradually increase with the hydrofluoric (HF) acid etching. Eventually, a constant peak height was reached as an indication of complete hydrogen termination. Integration of all the surface hydrides absorption peaks (2000 to 2200 cm−1) provides direct quantitative evaluation of the hydrogen termination process. On the other hand, water contact-angle data were shown to consistently lag behind the IR measurement in determining the extent of hydrogen termination on the silicon surface. Analysis of the surface free energy of HF-etched silicon surfaces indicates that the degree of the hydrogen termination determined by water contact-angle measurements is subjected to inaccuracies due to the preferential hydrogen-bonding interaction between the water and silicon surface oxide.
Characterization of Quaternary Metal Oxide Films by Synchrotron X-ray Fluorescence Microprobe
Authors: Perry D. L. , Thompson A. C. , Russo R. E. , Mao X. L. , Chapman K. L.
Published: October 2003

A synchrotron X-ray fluorescence microprobe has been used to study the composition and microstructure of pulsed-laser ablation-deposited films of calcium–nickel–potassium oxides that have applications in heterogeneous catalysis. The films, whose individual metal oxide components have widely varying boiling points and thus prevent a solid-phase synthesis with the use of standard thermal techniques, represent a new quaternary metal oxide phase containing the three elements. Experimental conditions for preparing the films are given. The X-ray fluorescence microprobe data are discussed with respect to both the distribution of the three metals in the films at the micrometer lateral spatial resolution level and the presence of trace amounts of metals that were introduced into the films as contaminants in targets made of the parent three-metal oxide.
Effect of Ambient Pressure on the Generation and the Propagation of Plasmas Produced by Pulsed Laser Ablation of Metal Al in Air
Authors: Man B. Y. , Wang X. T. , Wang G. T.
Published: October 2003

Simultaneous time- and space-resolved emission spectra from a Nd: YAG laser-ablated plasma on an Al target have yielded quantitative information on the generation and the propagation of species in the plasma. Five ambient pressures from atmosphere to 5 Pa were chosen. The experimental results showed that the characteristics of the species in the plasma were strongly influenced by the ambient pressure. The mean spatially projected ranges of Al2+ ions in the atmosphere of different densities were calculated in theory, and the slowing-down processes were simulated by using a popular Monte Carlo simulation program, TRIM90. The calculated results can be used to explain observed experimental phenomena.
Separation and Identification of Sulfonamide Drugs via SFC/FT-IR Mobile-Phase Elimination Interface
Authors: Ashraf-Khorassani Mehdi , Combs Michael T. , Taylor Larry T. , Willis Jim , Liu Xiaojun , Frey Charles R.
Published: October 2003

Packed-column supercritical fluid chromatography with a mobile-phase gradient of carbon dioxide and methanol has been performed on a mixture of eight sulfonamides. The analytes were detected and identified with Fourier transform infrared spectrometry. A commercial mobile-phase elimination interface (LC-Transform®) was employed. A fixed-integral restrictor afforded the decompression zone between the column and germanium disk where the analytes were deposited. Excellent-quality infrared spectra were obtained for all eight separated analytes.