bluuebunny/crossref_metadata_2025 huggingface dataset:
Adsorption Density of Spherical Cetyltrimethylammonium Bromide (CTAB) Micelles at a Silica/Silicon Surface
Authors: Paruchuri Vamsi K. , Fa Keqing , Moudgil Brij M. , Miller Jan D.
Published: May 2005

In situ Fourier transform infrared internal reflection spectroscopy (FT-IR/IRS) was used to calculate the adsorption density values for spherical cetyltrimethylammonium bromide (CTAB) micelles at the silica/silicon (SiO2/Si) surface based on a previously developed adsorption density equation. Recent advances in atomic force microscopy (AFM) imaging methodology have led to the ability to image surface micelles, which was not possible previously. These AFM images have been used to independently calculate adsorption density values through offline fast Fourier transform (FFT) analysis. The adsorption density values measured from in situ FT-IR/IRS spectra and from AFM images showed good agreement and provide further validation of the FT-IR/IRS adsorption density equation in the low concentration range.
Spectroscopic Study of a Novel Bis(Heptamethine Cyanine) Dye and its Interaction with Human Serum Albumin
Authors: Patonay Gabor , Kim Jun Seok , Kodagahally Ravikumar , Strekowski Lucjan
Published: May 2005

A newly synthesized near-infrared (NIR) bis(heptamethine cyanine) dye 7 was evaluated for its utility as a non-covalent label for proteins. This dye forms inter- and intramolecular H-aggregates in polar solvents, even at very low concentrations. The intramolecular dimeric form of the dye can be described as a clam-shell complex with two interacting hydrophobic carbocyanine moieties. In this intramolecular H-aggregate, the chromophore has a low extinction coefficient and low fluorescence quantum yield. In aqueous solution, in the absence of human serum albumin (HSA), dye 7 has characteristic absorption bands at 792 and 435 nm, and its fluorescent emission is significantly diminished in comparison to that in methanol or when compared to its monomeric equivalent 5. Dye 7 seems to be more advantageous than its monomeric counterpart 5 as a non-covalent label for biomolecules. Upon addition of HSA, the H and D bands are decreased and the monomeric band is increased, with concomitant increase in fluorescence intensity, suggesting that clam-shell H-aggregates open up in the complex with HSA. The binding stoichiometry is 1:1. The main advantage of this dimeric dye as a non-covalent label is that the free dye has negligible fluorescence.
Investigation of Selected Baseline Removal Techniques as Candidates for Automated Implementation
Authors: Schulze Georg , Jirasek Andrew , Yu Marcia M. L. , Lim Arnel , Turner Robin F. B. , Blades Michael W.
Published: May 2005

Observed spectra normally contain spurious features along with those of interest and it is common practice to employ one of several available algorithms to remove the unwanted components. Low frequency spurious components are often referred to as ‘baseline’, ‘background’, and/or ‘background noise’. Here we examine a cross-section of non-instrumental methods designed to remove background features from spectra; the particular methods considered here represent approaches with different theoretical underpinnings. We compare and evaluate their relative performance based on synthetic data sets designed to exemplify vibrational spectroscopic signals in realistic contexts and thereby assess their suitability for computer automation. Each method is presented in a modular format with a concise review of the underlying theory, along with a comparison and discussion of their strengths, weaknesses, and amenability to automation, in order to facilitate the selection of methods best suited to particular applications.
Influence of the Metal Film Thickness on the Sensitivity of Surface Plasmon Resonance Biosensors
Authors: Ekgasit Sanong , Thammacharoen Chuchaat , Yu Fang , Knoll Wolfgang
Published: May 2005

The influence of the metal film thickness (i.e., the chromium adhesion promoting film and the gold film) on the sensitivity of surface plasmon resonance (SPR) signals (i.e., resonance angle shift and reflectance change) towards the thickness variation of the nonabsorbing dielectric film is investigated. The sensitivity of reflectance change decreases when a thick chromium film or a thin gold film is employed. Its linear range becomes narrower as the thickness of the metal films increases. The sensitivity and linear range of the resonance angle shift are not affected by the thickness variation of the metal films. The phenomena were theoretically explained based on the attenuated total reflection (ATR) generated evanescent field at the prism/metal interface and the SPR-generated evanescent field at the metal/dielectric interface.
Vibrational Spectroscopic and Ultrasound Analysis for In-Process Characterization of High-Density Polyethylene/Polypropylene Blends during Melt Extrusion
Authors: Barnes S. E. , Brown E. C. , Sibley M. G. , Edwards H. G. M. , Scowen I. J. , Coates P. D.
Published: May 2005

Spectroscopic techniques such as Raman, mid-infrared (MIR), and near-infrared (NIR) have become indispensable analytical tools for rapid chemical quality control and process monitoring. This paper presents the application of in-line Fourier transform near-infrared (FT-NIR) spectroscopy, Raman spectroscopy, and ultrasound transit time measurements for in-line monitoring of the composition of a series of high-density polyethylene (HDPE)/polypropylene (PP) blends during single-screw extrusion. Melt composition was determined by employing univariate analysis of the ultrasound transit time data and partial least squares (PLS) multivariate analysis of the data from both spectroscopic techniques. Each analytical technique was determined to be highly sensitive to changes in melt composition, allowing accurate prediction of blend content to within ±1% w/w (1σ) during monitoring under fixed extrusion conditions. FT-NIR was determined to be the most sensitive of the three techniques to changes in melt composition. A four-factor PLS model of the NIR blend spectra allowed determination of melt content with a standard prediction error of ±0.30% w/w (1σ). However, the NIR transmission probes employed for analysis were invasive into the melt stream, whereas the single probes adopted for Raman and ultrasound analysis were noninvasive, making these two techniques more versatile. All three measurement techniques were robust to the high temperatures and pressures experienced during melt extrusion, demonstrating each system's suitability for process monitoring and control.
Analyzing Raman Maps of Pharmaceutical Products by Sample—Sample Two-Dimensional Correlation
Authors: Šašić Slobodan , Clark Donald A. , Mitchell John C. , Snowden Martin J.
Published: May 2005

Sample–sample (SS) two-dimensional (2D) correlation spectroscopy is applied in this study as a spectral selection tool to produce chemical images of real-world pharmaceutical samples consisting of two, three, and four components. The most unique spectra in a Raman mapping spectral matrix are found after analysis of the covariance matrix. (This is obtained by multiplying the original mapping data matrix by itself.) These spectra are identified by analyzing the slices of the covariance matrix at the positions where covariance values are at maxima. Chemical images are subsequently produced in a univariate fashion by visually selecting the wavenumbers in the extracted spectra that are least overlapped. The performance of SS 2D correlation is compared with principal component analysis in terms of highlighting the most prominent spectral differences across the whole data set (which typically comprises several thousand spectra) and determining the total number of species present. In addition, the selection of the unique spectra by SS 2D correlation is compared with the selection obtained by the orthogonal projection approach (OPA). Both comparisons are found to be satisfactory and demonstrate that a quite simple SS 2D correlation routine can be used for producing reliable images of unknown samples. The main benefit of using SS 2D correlation is that it is based on a few data processing commands that can be executed separately and produce results that are closely related to the chemical features of the system.
Binding Properties of 2-Acetylnaphthalene with Hydroxypropyl Cyclodextrins from Fluorescence Quenching Experiments
Authors: Seel Maximilian , Werner T. C.
Published: May 2005

The quenching of 2-acetylnaphthalene (2-AN) fluorescence by hydroxypropyl cyclodextrins (HP-CD) has been analyzed using modified Stern–Volmer plots to obtain binding constants as a function of temperature for 2-AN:HP-CD complexes. The HP-CDs were commercially available and contained 4–7 HP groups per CD molecule for α-CD, β-CD, and γ-CD. HP substitution causes a 12 to over 40% increase in binding constant ( Kave) for 2-AN compared to that for unsubstituted CDs, although the Kave value is not strongly dependent on the extent of HP substitution for β-CD. No evidence of formation of a 2:2 complex, such as that observed with 2-AN and γ-CD, is observed with 2-AN and HP-γ-CD. Thermodynamic parameters (ΔH°o and ΔS°o) suggest that the increase in Kave with HP substitution is due to an enlarged binding site for the HP-CDs that allows greater motional freedom for 2-AN. Comparison is made to the binding of 2-methylnaphthoate (2-MN) to CDs and HP-CDs, and the larger Kave values for 2-MN over 2-AN are attributed to greater dispersion forces for 2-MN complex formation.
Interaction of Enantiomers of Lysyl-7-Azatryptophyl-Lysine with Acidic Phospholipid Vesicles: A Fluorescence Study
Authors: Brennan J. D. , Clark I. D. , Hogue C. W. V. , Ito A. S. , Juliano L. , Paiva A. C. M. , Rajendran B. , Szabo A. G.
Published: May 2005

A tripeptide containing a single 7-azatryptophan (7AW) residue was synthesized with the use of racemic 7AW and purified by high-performance liquid chromatography (HPLC). The peptide NH2-lysyl-7-azatryptophyl-lysine (K7AWK) is analogous to the peptide lysine-tryptophyl-lysine (KWK) whose interactions with acidic lipids are well characterized. It has not been possible to achieve the separation of 7AW D and L enantiomers under HPLC conditions that normally are used to separate enantiomers of amino acids. HPLC of the peptide, however, indicated that there were two main components of nearly equal concentration in the partially purified synthetic peptides. Thin-layer chromatography, paper electrophoresis, amino acid analysis, and steady-state absorption and fluorescence spectra showed that the two HPLC peaks corresponded to peptides with the same composition but with different enantiomers of 7AW. Time-resolved fluorescence measurements of the purified enantiomers indicated that there were differences in the excited-state decay parameters. The nature of the interaction of the different enantiomers of the basic peptide with vesicles of the acidic lipid palmitoyl-oleoyl phosphatidylserine (POPS) at pH 5.0 has been elucidated with the use of steady-state fluorescence measurements. Interaction of the peptide with vesicles in the liquid crystalline phase suggested that proton transfer from the POPS to the 7AW occurs, resulting in enhanced emission at 450 nm. These results are compared to those from the Trp containing peptide KWK, and the unique advantages of 7AW as a spectroscopic probe are described.
NMR Investigation of the Thermolysis of Citric Acid
Authors: Fischer John W. , Merwin Lawrence H. , Nissan Robin A.
Published: May 2005

The thermolytic decomposition of citric acid in the presence of tin/lead solder has been investigated. The solid reaction products were first examined by solid-state 13C NMR. The samples were then dissolved in D2O, and 1H and 13C 1D and 2D (HMQC, TOCSY) spectra were obtained. Results indicate the presence of a series of compounds including 3-hydroxyglutaric, citraconic, itaconic and aconitic acids, and anhydrides. Solution- and solid-state NMR data are provided for citric acid and a number of metal and alkali metal citrate salts. Results of this work are related to the use of citric acid as a solder flux and to the elimination of chlorofluorocarbon cleaning processes in the electronics industry.
Gas-Phase Absorption and Laser-Induced Fluorescence Measurements of Representative Polychlorinated Dibenzo-p-dioxins, Polychlorinated Dibenzofurans, and a Polycyclic Aromatic Hydrocarbon
Authors: Funk David J. , Oldenburg Richard C. , Dayton Dave-Paul , Lacosse Jeffrey P. , Draves Jeffrey A. , Logan Thomas J.
Published: May 2005

Dioxins and furans are believed to be among the most toxic chemicals known to man. The presence of these compounds in the emission gases of municipal solid waste incinerators and other combustion sources has raised debate over the location and the ultimate utility of incineration as an approach to waste management. Current methods used to measure dioxins and furans in combustion source emissions do not provide the real-time monitoring necessary to track average incinerator performance or upset emission levels. A study to design and develop a laser-induced fluorescence/continuous emission monitoring system to detect and quantify these compounds is being conducted. This paper reports the results of the study to date. Vapor-phase ultraviolet absorption spectra, absorption cross sections, and laser-induced fluorescence profiles are presented for three dioxins and two furans. These spectral data are needed for initial design and evaluation of the laser-induced fluorescence/continuous emission monitoring system approach.
Effects of Particle Size on the Near-Infrared Reflectance Spectra of Wheat and Rape Seed Meal Mixtures
Authors: Devaux Marie-Françoise , Nathier-Dufour Nathalie , Robert Paul , Bertrand Dominique
Published: May 2005

Binary mixtures were jointly studied by near-infrared (near-IR) spectroscopy and image analysis. Fine and coarse fractions of wheat and rape seed meal were mixed in proportions varying from 0 to 100% as follows: fine wheat and fine rape seed meal (FF), coarse wheat and fine rape seed meal (CF), fine wheat and coarse rape seed meal (FC), and coarse wheat and coarse rape seed meal (CC). Principal component analysis (PCA) was applied to the near-IR spectra. Certain deviations were observed in the proportions described by principal component 2, which showed an underestimation of the coarse fractions. Images of the cell were recorded immediately after each near-IR measurement. The logarithm of the mean gray level [log(MGL)] was characteristic of the wheat fractions areas actually visible at the sample surface. The correlation coefficients of log(MGL) with principal component 2 were −0.998, −0.989, −0.997, and −0.991 for series FF, FC, CF, and CC. An interpretation of the principal components was proposed: principal component 1 described the scattering effect, component 2 described the proportions of the fractions at the sample surface, and component 3 contained certain information about the deeper particles.
Equilibrium Composition of Retinal Isomers in Dark-Adapted Bacteriorhodopsin and Effect of High Pressure Probed by Near-Infrared Raman Spectroscopy
Authors: Schulte A. , Bradley L. , Williams C.
Published: May 2005

The combination of near-infrared Raman spectroscopy and variations in external parameters offers new opportunities for site-specific studies of proteins. Using excitation at 840 nm, we have measured the near-infrared Raman spectrum of dark-adapted bacteriorhodopsin at ambient and high pressure. The C=C ethylenic stretching region shows two resolved bands at 1526 and 1534 cm−1, corresponding to the all- trans and 13- cis isomers. From deconvolution of these bands we find an isomeric ratio between 13- cis and all- trans retinal equal to 1 at ambient pressure. The Raman spectrum gives direct spectroscopic evidence that the 13- cis component is favored at high pressure, implying that it has a smaller volume. The pressure dependence of the isomeric ratio yields a molar volume of −6.6 mL/mol, which suggests ionization of one or two residues or the formation of three hydrogen bonds.
Distance-Dependent Quenching of Anthracene Fluorescence by N,N-Diethylaniline Observed by Frequency-Domain Fluorometry
Authors: Zelent Bogumil , Kuśba Józef , Gryczynski Ignacy , Lakowicz Joseph R.
Published: May 2005

We measured the time-dependent fluorescence intensity decays of anthracene and 9,10-dimethylanthracene in propylene glycol quenched by N,N-diethylaniline by frequency-domain fluorometry. The frequency-domain data, for a range of temperatures and diffusion coefficients, are consistent with a rate of quenching which depends exponentially on the fluorophore-quencher separation distance. This type of quenching interaction explains upward curvature in the Stern-Volmer plots. In total, the steady-state and time-resolved data are consistent with a mechanism of quenching due to the electron transfer process from DEA to the singlet excited anthracene molecules.
Depth Profiling of a Photochemically Yellowed Paper. Part I: UV-Visible Reflectance and Fluorescence Spectroscopy
Authors: Forsskåhl Ingegerd , Olkkonen Carola , Tylli Henrik
Published: May 2005

A strongly photochemically yellowed paper having a reflectance at 457 nm of 53% (initial reflectance 73%) containing high-yield pulp from softwood was ground off to varying depths. The resulting papers were studied with the use of UV-visible diffuse reflectance and fluorescence spectroscopy. Yellowing penetration depth was determined and the chromophore distribution in the z direction was characterized with the aid of difference spectra. Expressed as the amount of chromophores based on the specific adsorption coefficient, 25% of the yellowing had occurred at a depth of 10–12 μm, 50% at 15–20 μm, and 75% at 25–30 μm. The fluorescence spectroscopy results showed that 50% of the changes induced by light had occurred at a depth of about 20 μm.
Alternative Design for Improved FT-IR/VCD Capabilities
Authors: Tsankov D. , Eggimann T. , Wieser H.
Published: May 2005

A Bomem MB100-based vibrational circular dichroism (VCD) spectrometer suitable for chiroptical studies in the infrared region is described. The optical layout utilizes the spectrometer's external collimated beam. Standard VCD optics consisting of a KRS-5 polarizer and a ZnSe photoelastic modulator are mounted on an optical breadboard. A ZnSe meniscus lens focuses the beam on a small-area MCT detector. Several optical designs were examined to find the optimal positions of the optical elements. The experiments aimed to improve the energy throughput, minimize polarization artifacts, and increase signal-to-noise ratio to such an extent that single-enantiomer VCD spectra could be recorded routinely and dependably. Examples are presented illustrating the high-performance characteristics of the instrument.
Model for the Moisture Quenching of Solid-Matrix Phosphorescence via the Young's Modulus of Filter Paper
Authors: Chen J. , Hurtubise Robert J.
Published: May 2005

Experimental Young's modulus values were obtained as a function of adsorbed moisture content for filter paper samples with no absorbed salt and with several different types of salt adsorbed on filter paper. The Young's modulus values were correlated with the room-temperature phosphorescence intensities and room-temperature phosphorescence lifetimes of several phosphors adsorbed on filter paper samples with the use of a theory for the Young's modulus of paper and solid-matrix phosphorescence quenching concepts. Phosphorescence intensity ratios changed much more dramatically than phosphorescence lifetime ratios, both with increasing moisture uptake on the filter paper and with decreasing modulus ratio of the filter paper samples. The changes in the phosphorescence parameters, due to the adsorption of moisture on filter paper, were caused primarily by alterations of the hydrogen-bonding network in the amorphous regions of filter paper.
Fluorescence from the Twisted Intramolecular Charge Transfer Compound Bis(4,4′-dimethylaminophenyl)sulfone in Ethanol/CO2: A Probe of Local Solvent Composition
Authors: Schulte Richard D. , Kauffman John F.
Published: May 2005

Fluorescence spectra and decays of bis(4,4′-dimethylaminophenyl)sulfone (DMAPS) in mixed ethanol/CO2 supercritical fluid solution have been examined in order to evaluate the local solvent polarity of the mixed fluid solvents. Solvatochromic shifts and band intensities have been determined by nonlinear regression analysis, and are compared with shifts and intensities observed in liquid n-alcohols. The spectral parameters of DMAPS in the mixed supercritical fluid solvents have been used to estimate enrichment of the local solvent composition in the polar modifier, under the assumption that the increase in solvent polarity over that calculated for the bulk fluid is the result of augmentation of the fluid composition in the region immediately surrounding the solute molecule. The analysis indicates that the local composition is enriched by a factor of five to ten over the bulk composition.
Solid-Phase Hydride Generation of Silane for Determination of Silicate by ICP-AES
Authors: Kumamaru Takahiro , Uchida Masayuki , Fujiwara Kenji , Okamoto Yasuaki , Fujiwara Kitao
Published: May 2005

A sample introduction method based on in situ solid-phase SiH4 generation for ICP-AES has been proposed for the determination of silicate. The hydride generation procedure is as follows: An aqueous sample solution is dried on a sample cuvette, and LiAlH4 solution is added onto the dehydrated sample and is dried again. The cuvette is then located on a tungsten boat furnace. Silane species are generated by heating the cuvette at 700°C, with the species introduced directly into the ICP to measure the atomic emission of Si. The amount of LiAlH4, the reaction temperature, and the flow rate of the Ar carrier gas were optimized. The calibration curve was linear up to at least 100 ng of Si(IV) and the detection limit (signal-to-noise ratio of 3) was 0.03 ng. The relative standard deviation for 10 replicate measurements of 1.0 ng of Si(IV) was 2.7%. This method was applied to the determination of Si in river water with satisfactory results.
Use of Flow Injection Inductively Coupled Plasma-Mass Spectrometry for the Determination of Niobium, Vanadium, and Titanium in Microalloyed Steels
Authors: Coedo Aurora G. , Dorado Teresa Ma
Published: May 2005

The use of microsampling flow injection inductively coupled plasma-mass spectrometry for the determination of Nb, V, and Ti in microalloyed steels samples is described. A microwave nitric acid digestion procedure, resulting in 0.4% m/v Fe [≈1.75% m/v (NO3)3Fe] test solutions, was used for sample dissolution. The flow injection parameters, such as carrier flow rate and sample loop volume, were optimized with respect to sensitivity and stability. Yttrium, with an ionization potential close to that of the analytes considered, and with a close mass number, was used as internal standard. The obtained detection limits, in μg of analyte per gram of steel, were 0.010 for Nb, 0.017 for Ti, and 0.025 for V. The RSD values, at concentration levels of more than 10 times the detection limit, were less than 1.5%. Three certified reference materials, from the National Institute of Standards and Technology (Gaithersburg, MD)—NIST 2165, 2166, and 2167—were analyzed, from 0.4% m/v steel sample solutions, with 1% v/v HNO3 multielement calibration solutions. The close agreement with the certified values demonstrates the accuracy of the method developed.
Quantitative Evaluation of Selective Fluorescence Quenchers for Polynuclear Aromatic Hydrocarbons
Authors: Ogasawara Faye K. , Wang Yiwen , McGuffin Victoria L.
Published: May 2005

In this investigation, nitromethane, nitrobenzene, and are evaluated for their class selectivity and efficiency as fluorescence quenchers of polynuclear aromatic hydrocarbons (PAHs). Conditional Stern-Volmer quenching constants are utilized for qualitative and quantitative evaluation at known quencher concentration and fluorescence excitation and emission wavelengths. From these measurements, nitromethane is determined to be the most selective quencher for alternant PAHs, 1,2,4-trimethoxybenzene is somewhat less selective for nonalternant PAHs, and nitrobenzene is an effective but nonselective quencher. The utility of this technique is demonstrated by application to a complex coal tar sample after separation of the individual PAH components by microcolumn liquid chromatography.
Polycyclic Aromatic Hydrocarbon Solute Probes. Part XI: Unusual Solvent-Modulated Fluorescence Emission Behavior of 1-Methylcoronene and Select Dimethylcoronenes in Nonelectrolyte Solvents
Authors: Tucker Sheryl A. , Acree William E. , Fetzer John C.
Published: May 2005

Fluorescence emission spectra are reported for 1-methylcoronene, 1,2-dimethylcoronene, 1,4-dimethylcoronene, 1,6-dimethylcoronene, 2,3-dimethylcoronene, and 2,5-dimethylcoronene dissolved in organic nonelectrolyte solvents of varying polarity. Four of the five coronene derivatives were found to exhibit probe character, as evidenced by a systematic variation in emission intensity ratio with solvent poplarity. Mathematical expressions which correlate measured intensity ratios and solvent polarity probe behavior of 1-methylcoronene and 1,2-dimethylcoronene with pyrene in 46 solvents of varying polarity are reported. Also reported is the preferential solvation behavior of both solutes in binary mixtures of n-heptane + tetrahydrofuran and n-heptane + 1,4-dioxane.
FT-Raman Measurements on Cation-Exchange Resins
Authors: Wang Hsiaoling , Mann Charles K. , Vickers Thomas J.
Published: May 2005

The utility of FT-Raman spectroscopy in characterizing ion-exchange resins has been demonstrated. Measurements have been made on strong acid-type cation-exchange resin beads of a sulfonated polystyrene-divinyl benzene copolymer. Spectra are compared for the resin with 10 different cations. Classical least-squares fitting is used to quantitate the amounts of different cations in binary mixtures. On-column determinations are demonstrated for displacement of H+ by Na+ and Na+ by Ag+.
Rotational Reorientation Dynamics of Xanthene Dyes within the Interior of Aerosol-OT Reversed Micelles
Authors: Heitz Mark P. , Bright Frank V.
Published: May 2005

The rotational reorientation kinetics of several xanthene dye molecules [rhodamine 6G (R6G), rhodamine B (RB), rhodamine 101 (R101), and fluorescein (FLR)] have been investigated in sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol-OT; AOT) reverse micelles formed in liquid n-heptane. We show that the water content within the micellar core and the probe structure have a significant effect on the rotational dynamics of the probe. The differential phase and polarized modulation ratio data (decays of anisotropy) are always best described by a bi-exponential decay law. We interpret these results in terms of a two-step model for lateral diffusion and a wobbling-in-a-cone model. The former model described the observed bi-exponential decay by attributing the slower of the two rotational motions to lateral diffusion along the water core/headgroup interfacial region and the faster motion to a more restricted internal motion. The results show that, for the cationic probes, lateral diffusion coefficients vary by more than an order of magnitude across the water-loading range investigated. The wobbling-in-a-cone model serves to quantify the restricted internal motion of the probe in terms of a cone angle (θ) and wobbling diffusion coefficient. The semiangle covers a wide range for the cationic probes (0 ≤ θ ≤ 35) depending on the specific probe structure and R ([water]/[AOT]) value. The anionic probe shows a larger semiangle at each R value relative to the cationic probes.
Pulsed Photothermal Deflection Spectroscopy with Optically Dense Samples
Authors: Li Bingcheng , Deng Yanzhuo , Cheng Jieke
Published: May 2005

The pulsed photothermal deflection spectroscopy (PTDS) method to determine the large optical absorption coefficient from the transverse PTDS magnitude and to measure spectroscopic data of optically dense sample from the normal-to-transverse magnitude ratio of the PTDS signal is presented and has been examined both theoretically and experimentally. Saturation at high absorption, effects of thermal inhomogeneity of the sample, and energy or power fluctuation of both the excitation and probe beams are avoided by this method. Together with the transverse PTDS technique, the dynamic range of spectroscopic measurement is over 9 to 10 orders of magnitude. This technique can be used with sample which is transparent or semitransparent to the probe beam.
Characterization and Application of a Grazing Angle Objective for Quantitative Infrared Reflection Microspectroscopy
Authors: Pepper Stephen V.
Published: May 2005

A grazing angle objective on an infrared microspectrometer is studied for quantitative spectroscopy by considering the angular dependence of the incident intensity within the objective's angular aperture. The assumption that there is no angular dependence is tested by comparing the experimental reflectance of Si and KBr surfaces with the reflectance calculated by integrating the Fresnel reflection coefficient over the angular aperture under this assumption. Good agreement was found, indicating that the specular reflectance of surfaces can straightforwardly be quantitatively integrated over the angular aperture without considering nonuniform incident intensity. This quantitative approach is applied to the thickness determination of dipcoated Krytox on gold. The infrared optical constants of both materials are known, allowing the integration to be carried out. The thickness obtained is in fair agreement with the value determined by ellipsometry in the visible. Therefore, this paper illustrates a method for more quantitative use of a grazing angle objective for infrared reflectance microspectroscopy.
Effect of Operating Parameters on Analyte Signals in Elemental Electrospray Mass Spectrometry
Authors: Agnes George R. , Horlick Gary
Published: May 2005

A parametric investigation of an electrospray ion source and interface has been carried out with a focus on elemental analysis. The source and interface variables investigated were the curtain-gas flow rate and the voltage biases of the electrospray capillary tip, the front plate, the sampling plate, the skimmer, and the barrel ion extractor lens. The analytes studied (M+ and M++) included the alkali metals, the alkaline earth metals, and cobalt—all prepared in methanol (MeOH) solutions. The two most important interface parameters in terms of their effect on the nature of the resulting mass spectrum were the curtain-gas flow rate and the sampling-plate voltage bias. A minimum, but modest, flow rate of curtain gas was required in order to observe analyte ion signals, and, when combined with a low sampling-plate voltage, the observed signal species were primarily analyte ion–solvent clusters [M(MeOH) n+1 and M(MeOH) m+2]. As the values of these two parameters were increased, these species were declustered, plus-two analyte ions were reduced to plus-one species, and ultimately the mass spectra were dominated by the bare singly charged analyte ion (M+). Also, these two variables (curtain-gas flow rate and sampling-plate voltage) seem to act in a synergistic manner, with neither variable alone able to effect complete declustering and charge reduction.
Temperature and Gatewidth Dependence of the Solid-Matrix Fluorescence Spectra of Stereoisomeric Tetrols
Authors: Shu Luchuan , Hurtubise Robert J.
Published: May 2005

A unique laser-based method was developed for the solid-matrix fluorescence characterization and identification of tetrols, which are the hydrolysis products from benzo[ a]pyrene-DNA adducts. By employing different gatewidths with a boxcar integrator, we obtained the fluorescence spectra of the four tetrol isomers adsorbed on 10% α-cyclodextrin/NaCl at several temperatures. The data showed that the fluorescence spectral characteristics of the tetrols were both gatewidth- and temperature-dependent. The experimental conditions were optimized to identify the tetrols which had only minor structural differences. Applications of the gatewidth-dependence method both at room temperature and low temperature were considered. The low-temperature approach has the potential for the application to several species over a range of fluorescence lifetimes. The differences in the fluorescence spectral properties were partially explained by the rotation of functional groups in the tetrols and the solid matrix during the time frame of obtaining the spectra. Comparisons were made among the solid-matrix fluorescence spectra and the solution fluorescence spectra of the tetrols, and the solution fluorescence spectra of pyrene and the solid-matrix fluorescence spectra of pyrene.
Comparison of Room-Temperature Phosphorescence Properties of Three Purine Compounds with Cadmium Acetate as a Source of Heavy Atom Perturbation
Authors: Jin Wei Jun , Zhang Hai Rong , Yang Xin , Liu Chang Song
Published: May 2005

Cadmium acetate salts can greatly enhance room-temperature phosphorescence (RTP) of purine and 6-mercaptopurine. 6-Mercapto-substituent and 6-hydroxy-substituent appear quite different in their effect on the RTP of purine. The effects of cadium salt matrix and pH on the RTP of purine compounds were also investigated in detail. With cadmium acetate as a source of heavy atom perturbation, nanogram or subnanogram amounts of purines can be detected.
Application of FT-IR Step-Scan Photoacoustic Phase Modulation Methods to Keratin Fibers
Authors: Jurdana Lucia E. , Ghiggino Kenneth P. , Leaver Ian H. , Cole-Clarke Peter
Published: May 2005

Step-scan FT-IR/PAS is shown to be a powerful tool for the nondestructive analysis of keratin fibers. Depth profiling studies were performed either by varying the optical velocity of the interferometer (scanning FT-IR/PAS depth profiling) or by a phase modulation method, utilizing a lock-in amplifier to separate the surface and bulk components of the signal phase. Both methods were shown to be capable of distinguishing spectroscopically between the cuticle and cortex of wool and hair fibers, the different spectral features being consistent with the differences in protein composition between these components. Phase-modulated spectra exhibited improved signal-to-noise ratios, with relatively little interference from saturation effects, compared with scanning FT-IR/PAS depth profile spectra.
Routine Absorbance Spectroscopy at the Air/Water Interface
Authors: Moore Jeffrey L. , De Bry Beth A. , Hughes Kenneth D.
Published: May 2005

A Langmuir–Blodgett instrument has been assembled that is capable of providing side-by-side comparisons of two separate monolayers in a true double-beam absorption geometry with no moving parts. Absorbance spectra of two different films are monitored at the air/water interface, with the use of fiber optics in conjunction with a charge-coupled-device detector and a single-stage spectrograph. The utility of this instrument is demonstrated by simultaneous measurement of monomer, dimer, and aggregate components in a single-component carbocyanine dye monolayer and a mixed carbocyanine dye/phospholipid monolayer, as the isotherm of each of these films is generated. A linear relationship between number density and the carbocyanine monomer/dimer ratio is observed.
Near- versus Mid-Infrared Spectroscopy: Relationships between Spectral Changes Induced by Water and Relative Information Content of the Two Spectral Regions in Regard to High-Moisture Samples
Authors: Reeves James B.
Published: May 2005

The objectives of this work were to examine similarities and differences in the near-infrared and mid-infrared spectral regions when one is working with high-moisture materials and to study spectral changes in these regions as a method to identify the relationship of spectral information in the near-IR to fundamental absorptions in the mid-IR. Near- and mid-infrared spectra were taken with a Digilab FTS-65 Fourier transform spectrometer. Liquids were examined by transmission and solids by reflectance. Results with solutions showed that less spectral distortion arises when one is subtracting water from mid- rather than from near-infrared spectra. It was also easier to produce high-quality spectra in the mid-infrared by using attenuated total reflectance than by using transmission in the near-infrared. While mid-infrared spectra showed changes (induced by water, pH, physical state, and ionic strength) similar to those found in the near-infrared, there appeared to be more information available in the mid-infrared, even in the presence of water.
Speciation of Uranyl Species in Nitric Acid Medium by Time-Resolved Laser-Induced Fluorescence
Authors: Couston Laurent , Pouyat Dominique , Moulin Christophe , Decambox Pierre
Published: May 2005

The aim of this work is the development of an on-line analytical procedure for uranyl trace determination in the nuclear fuel reprocessing process using time-resolved laser-induced fluorescence. Because the uranyl fluorescence spectrum is strongly affected by the nitrate concentration, knowledge of composition of the medium is necessary to normalize measurements. This paper reports the assumptions made on the spectral distortion, leading to a spectral deconvolution model. Uranyl complex formation constants are obtained from the spectral deconvolution and validate the method. In this way, spectral distortion allows the determination of the nitrate concentration with good accuracy.
Nondestructive Method for Analyzing Irreplaceable Objects
Authors: Poslusny Matthew , Daniel Meredith
Published: May 2005

Current studies are focusing on newspaper samples and the question of authenticity. They will also be extended to look at collectible stamps, pieces of art work, and a variety of other materials that require nondestructive analysis but are too large to fit into conventional sampling accessories.
Evaluation of a Direct-Injection Nebulizer (DIN) for Liquid Sample Introduction in Helium Microwave-Induced Plasma Mass Spectrometry (MIP-MS)
Authors: Giglio Jeffrey J. , Wang Jianshang , Caruso Joseph A.
Published: May 2005

A direct-injection nebulizer (DIN) has been evaluated for liquid sample introduction in helium microwave-induced plasma mass spectrometry (MIP-MS). A short-term stability test with the direct-injection nebulizer was found to give less than 0.5% RSD for twenty minutes. Isotope abundances for K, Ca, Cr, and Se were determined with less than 10% error on all isotopes. All elements have linear dynamic ranges of two to three orders of magnitude. Detection limits are low to sub-ppb for all elements. Ion lens tuning plays an important role in multielement determinations. Oxide, hydroxide, and doubly charged ions are determined for Cr, As, Sr, Cs, Ba, and Pb. The effect of 10% methanol and high-dissolved salts is investigated.
Novel Experimental Technique for Measuring High-Temperature Spectral Emissivities
Authors: Ballico Mark J. , Jones Trebor P.
Published: May 2005

A novel experimental technique for the measurement of spectral emissivities in the temperature range 500 to 1000°C of materials that are both poorly thermally conducting and have a high level of transparency is presented. A Fourier transform infrared spectrometer (FT-IR) is used to compare the spectral radiance from a nearly isothermal, but rapidly cooling, sample to that of a reference blackbody. Experimental results obtained from metal metaborate samples and a theoretical analysis of the technique show the effectiveness of this method, particularly for the case of molten samples.
Low-Temperature Transient Optical Spectroscopy of Polydiacetylene DCHD: Evidence for a Distribution of Side Group Orientations
Authors: Hambir S. A. , Blanchard G. J. , Baker G. L.
Published: May 2005

We report on the transient optical response of the polydiacetylene DCHD at low temperature. Ultrafast pump-probe spectroscopic measurements reveal that excitation of the polymer N-methyl carbazolyl side group results in instantaneous (<10 ps) excitation transfer to the polymer backbone at 10 K. The slow population recovery signal seen subsequent to excitation transfer to the polymer backbone exhibits an excitation energy dependence that is indicative of the existence of multiple conformers. The energy barrier between these conformers is inferred to be <0.5 kcal/mol.
Optimization of the Surface Characterization of Carbon Fiber by FT-IR Internal Reflection Spectroscopy
Authors: Ohwaki T. , Ishida H.
Published: May 2005

Infrared spectra of surface-oxidized carbon fibers have been obtained with different angles of incidence, polarization states, and internal reflection elements (IREs) to find the optimal condition by internal reflection spectroscopy. It has been found that the maximum peak area of a surface functional group is obtained by using s-polarized light at a 30° angle of incidence for the multiple reflection technique. However, the highest signal-to-noise ratio is observed if unpolarized light is used. Spectral simulations have been performed to understand the observed spectra of the surface-oxidized carbon fibers according to exact optical theory. In the spectral simulations, Fresnel's three-layered system has been adopted to model the “IRE/oxidized layer/bulk of carbon fiber” system.
Combined Vibrational and Rotational CARS for Simultaneous Measurements of Temperature and Concentrations of Fuel, Oxygen, and Nitrogen
Authors: Bengtsson Per-Erik , Martinsson Lars , Aldén Marcus
Published: May 2005

Simultaneous measurements of temperature and relative concentrations of fuel, oxygen, and nitrogen using combined vibrational coherent anti-Stokes Raman Spectroscopy (CARS) and dual-broad-band rotational CARS have been demonstrated with the use of a Nd:YAG laser and a single dye laser. With the use of a double-folded BOXCARS phase-matching scheme, both the vibrational and the rotational CARS signals were generated in such a way that the signals were superimposed at the spectrograph. With an additional mirror arrangement inside the spectrograph, both signals were recorded simultaneously on a single diode-array detector. The accuracy of single-shot fuel concentration measurements has been investigated, and measurements in a methane/air diffusion flame have been demonstrated. The influence of systematic errors on measured concentrations is discussed.
Stray Light Rejection in Double Monochromators with Multichannel Detection
Authors: Deckert V. , Fickert C. , Gernet D. , Vogt P. , Michelis T. , Kiefer W.
Published: May 2005

There is, of course, a disadvantage because of the slightly increasing measurement time since the number of active elements on the multichannel detector is reduced. However, a combination of measurements with small middle slits in the low-frequency Raman region and middle or even wide slit width in the higher-frequency Raman region combined with the use of the full detector size can yield complete Raman spectra in much shorter times than is possible by means of single-channel detection. Appropriate slit setting could be made computer-controlled during a scanning multichannel measurement.
Time-Resolved Pyrene Fluorescence for Determination of Polymer Surface Polarity: Correlations with Surface Tension
Authors: Chang Kaisyang , Forcé R. Ken
Published: May 2005

Pyrene time-resolved fluorescence has been applied to correlate the surface tension levels obtained for polyethylene and polypropylene films after exposure to corona-discharge treatment. The surface tension level of the films was validated with surface tension test fluids according to the ASTM D2578 standard test method. Although in direct contact with air, pyrene showed an extremely long lifetime upon deposition on the polymer films, which approached the lifetime of pyrene in freeze/pump/thaw deoxygenated hexane. The I/III ratio of pyrene fluorescence at 373 and 384 nm, designated as bands I and III, was determined at 150-ns delay relative to the time at laser maximum. Prolonged time delay was imposed before fluorescence measurement in order to minimize the background interferences from the blank films. Measurements of the time-resolved pyrene fluorescence I/III ratio from pyrene/ethanol depositions showed averages of 0.63, 0.56, and 0.49 for 42, 35, and 30 dyne/cm treated films. The uncertainty of the measurements was estimated to be 1–2 dyne/cm. Application of the pyrene I/III ratio can be used easily to monitor incorrectly and nonuniformly treated polymer film surfaces.
Determination of Chlorophyll a and Pheophytin a Concentrations in Acetone Extracts by Laser Fluorometry
Authors: Demidov Andrey A. , Baulin Evgenii V.
Published: May 2005

We have used the technique of laser fluorometry for chlorophyll a and pheophytin a measurements in 90% acetone/water extracts of sea-water phytoplankton. In our method, the acetone Raman signal is used as an internal standard. We have shown that use of the second harmonic of a pulsed Nd:YAG laser (λ = 532 nm) makes it possible to measure pigment concentrations as low as 10 ng/L. It creates favorable conditions for high-efficiency analysis of the phytoplankton pigments in the oligotrophic areas of the world ocean and for investigations of the feed process of individual zooplankton samples.
Depth Profiling of a Photochemically Yellowed Paper. Part II: FT-IR Techniques
Authors: Forsskåhl Ingegerd , Kenttä Eija , Kyyrönen Pirjo , Sundström Olavi
Published: May 2005

A strongly photo-yellowed paper, whose surface had been ground off to different depths, was subjected to various Fourier transform infrared (FT-IR) techniques, including attenuated total reflectance (ATR), diffuse reflectance (DRIFT), photoacoustic (PA), and potassium bromide pellet (KBr) spectroscopy. Depth profiling of the paper was accomplished by monitoring specific infrared bands which showed systematic and consistent changes caused by irradiation. The results from the different Fourier transform infrared techniques were compared.
Contribution of Spectrometric Methods to the Study of the Constituents of Chromating Layers
Authors: Petit François , Debontride Henri , Lenglet Michel , Juhel Gérard , Verchere Didier
Published: May 2005

The amorphous constituents of a chromating layer may be defined by the simultaneous use of diffuse reflection spectrometry in the ultraviolet and visible, and of Fourier transform infrared spectrometry. The PO4 group is characterized in the infrared reflection spectrum by bands located near 1070, 1030, and 900 cm−1 for chromium phosphate. The CrO4 group induces bands at 960, 860, and 820 cm−1 for zinc chromate and at about 980, 950, and 860 cm−1 for chromium chromates. The ligandmetal charge transfer bands (LMCT) characteristic of the chromates are situated in the region 3.35 to 4.20 eV. The study of the thermal behavior of chromium phosphate CrPO4 and zinc chromate ZnCrO4 shows that these compounds are stable up to 300°C. Complex chromates of Cr(III) may be observed in the range 150 to 300°C. These analytical data show the contribution of these methods which, used in the reflection mode, are demonstrably the best suited to the analysis of chromating layers on coated steel, of which the primary constituents are chromium phosphate and complex Cr(III) chromates. These results allow the interpretation of the thermal behavior of chromating layers.