bluuebunny/crossref_metadata_2025 huggingface dataset:
Analytical Performance in Flow Injection—Simultaneous Multielement—Inductively Coupled Plasma—Optical Emission Spectrometry Employing a Cyclonic Spray Chamber
Authors: Hettipathirana Terrance D. , Davey David E.
Published: May 2005

Simultaneous multielement–inductively coupled plasma–optical emission spectrometry (ICP-OES) with flow injection (FI) and a small-volume cyclonic spray chamber is described. Analytical performance of FI-ICP-OES was studied with the use of a concentric nebulizer and the cyclonic spray chamber for carrier nebulization. A noise study using Fourier transformation analysis was also carried out to identify the factors that affect the analytical figures of merit of FI-ICP-OES. At a carrier flow rate of 1.0 mL/min, the major source of noise, between 0 and 15 Hz, was the peristaltic pump's roller rotation; this pump noise disappeared at a flow rate of 3.5 mL/min. A number of other discrete low-frequency noise sources were also observed at flow rates below 2.5 mL/min, with resultant degradation of precision and detection limit.
Spectral Distortions in Near-Infrared Spectroscopy of Turbid Materials
Authors: Schmitt J. M. , Kumar G.
Published: May 2005

A liquid suspension consisting of a mixture of H2O, D2O, and polystyrene latex microspheres was used to study the effects of multiple scattering on the near-infrared (800–1600 nm) spectrum of a pure absorber (H2O) in a turbid medium. This simple experimental model enabled us to isolate and explain the spectral distortions introduced by variations in the optical pathlength of scattered photons. We observe the following: (1) Reflectance spectra measured with the detector positioned close to and far from the point of illumination have distinctly different sensitivities to background scattering variations. Within a certain range of detector positions, the use of spectral derivatives to correct for multiplicative scattering effects is most effective. (2) The wavelength dependence of the scattering background of the log(1/ R) spectrum depends not only on particle size but also on the separation between the source and detector probes. And (3) the ratio of the magnitudes of the spectral peaks caused by absorption within the background medium and absorption within the scattering particles decreases as multiple scattering increases. We explain these observations in the context of photon-diffusion theory and point out their significance with respect to the design of diffuse-reflectance spectrometers. Photon diffusion theory proves to be valuable for interpretation of diffuse spectra, but it fails to account for spectral distortions introduced by low-order backscattering at close source–detector separations.
Kinetic Study of the Decomposition of Nitrite to Nitrate in Acid Samples Using Raman Spectroscopy
Authors: van Staden J. F. , Makhafola M. A. , de Waal D.
Published: May 2005

Raman spectroscopy was employed as a means of determining the rate of decomposition of nitrite in solutions at various pH values. Nitrite decomposes with time in acidic medium, with an increase in decomposition rate as the concentration of acid increases. The mean decomposition rate of 0.625 mol/L NO−2 in 1 mol/L HCl is 1.18 × 10−5 s−1, with t1/2 = 16 h. This rate explains the problems encountered when the flow injection analysis (FIA) version of the Shinn reaction is applied to certain nitrite samples mainly from acidic origin. Nitrite is potentially unstable, and all food and water samples should be analyzed as soon as possible after collection. If it is necessary to store the samples prior to analysis, the effects of the storage conditions on the stability of the analyte must be established in prior trials.
Comparison of IR Techniques for the Characterization of Construction Cement Minerals and Hydrated Products
Authors: Delgado Ana. H. , Paroli Ralph M. , Beaudoin James J.
Published: May 2005

The influence of FT-IR sampling techniques on the characterization of cement systems was investigated. Three FT-IR techniques were used to study tricalcium silicate (C3S), hydrated C3S, calcium hydroxide, and calcium silicate hydrate (C–S–H). They include transmission spectroscopy (TS), photoacoustic spectroscopy (PAS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The TS technique (using KBr pellets) was the most labor-intensive but was found to give the simplest spectra with well-defined bands. The PAS technique was found to be the simplest technique but yielded bands at lower wavenumber than TS. DRIFTS was determined to be a good alternative for cement powders since it provided spectra similar to those for the TS technique. DRIFTS required more sample preparation than PAS but less sample preparation than the KBr pellet technique.
Theoretical and Experimental Uncertainty in Temperature Measurement of Materials by Raman Spectroscopy
Authors: LaPlant Fred , Laurence George , Ben-Amotz Dor
Published: May 2005

Previous work has shown the potential of the Stokes/anti-Stokes intensity ratio from Raman spectroscopy for optically probing the temperature of materials. This paper uses the statistics of photon counting to set theoretical limits on the temperature accuracy of the technique, as well as developing an expression whereby the theoretical temperature uncertainty for any Raman band at a given temperature can be predicted. Comparison of the theory to experimental data is shown, and experimental limitations are discussed.
Remote Raman Microimaging Using an AOTF and a Spatially Coherent Microfiber Optical Probe
Authors: Skinner H. Trey , Cooney Thomas F. , Sharma S. K. , Angel S. M.
Published: May 2005

A fiber-optic Raman microimaging probe is described that is suitable for acquiring high-spatial-resolution Raman images in sampling situations with no clear line of sight. A high-power near-infrared diode laser combined with an acousto-optic tunable filter and a spatially coherent optical fiber bundle allow fluorescence-free Raman images of remotely located samples to be acquired at distances up to several meters. The feasibility of this technique is demonstrated with Raman images of (1) a pellet containing a mixture of a highly scattering sample, bis-methylstyrylbenzene (BMSB), KCl, and graphite, and (2) a partially graphitized diamond. These images clearly show phase boundaries over an area of approximately 0.1 mm2 with ∼4-μm resolution.
Fluorescence Studies of the Effects of t-Butyl Functionalities on the Formation of Ternary β-Cyclodextrin Complexes with Pyrene
Authors: Anigbogu Vincent C. , Warner Isiah M.
Published: May 2005

The effects of t-butyl (TB) compounds on the formation of β-cyclodextrin (CD)/pyrene complexes have been examined by monitoring changes in the fluorescence I/III band ratio of 1.0 × 10−7 M pyrene in 0.075 M of the t-butyl compounds and in various concentrations of β-CD in a solvent mixture consisting of 60% v/v methanol/40% water solution. For the compounds tested, the strongest effects were observed in the presence of the following (in decreasing order): TB-carbamate, TB-carbazate, TB-( N-hydroxy) carbamate, TB-( N-butoxy carbonyl) glycine, and TB-formate. In terms of enhancement of the pyrene/β-CD binding constant, all exhibited effects stronger than those previously reported for t-butyl alcohol. In contrast, TB-amine, TB-acetic acid, and TB-acetoacetate exhibited very little effect. There appears to be a relationship between the chemical structure of the modifier molecules and the magnitude of their concomitant effects on the I/III ratio. In fact, the t-butyl modifiers which exhibited moderate to strong effects have a common caboxy, –C–O–, skeleton attached to the t-butyl moiety in their general structure: (CH3)3C–O–R. The modifier effect was also found to be independent of the pH of the solutions. A detailed explanation has been offered for the observed changes in the I/III ratio relative to t-butyl functionalities.
Infrared Intensities of Liquids XIX: A Simple and Effective Approximate Method for the Calculation of Infrared Optical Constant Spectra of Liquids from Transmission Measurements
Authors: Bertie John E. , Apelblat Yoram
Published: May 2005

A simple and effective approximate method is presented for the calculation of the optical constants of neat liquids from transmission measurements. The method calculates the apparent absorbance due to reflection losses by treating the liquid cell as a single slab of the window material. This approach makes the method far simpler than the exact iterative method that has been used to develop secondary infrared intensity standards and that applies Fresnel's equations to each interface in the cell. However, for all but the strongest absorption bands, the approximate method gives imaginary refractive indices that are within ∼1% of those from the exact method. The method is, thus, useful for nearly all common liquids in cells with alkali halide windows for all but the strongest bands. The effect of the size of the mismatch between the real refractive indices of sample and windows has been explored to some extent. It is recommended that results from the approximate method be regarded with caution if the refractive indices of the sample and windows differ by more than 0.15.
Construction of a Multichannel Fourier Transform Infrared Spectrometer for Single-Event Time-Resolved Spectroscopy
Authors: Hashimoto Mamoru , Hamaguchi Hiro-O
Published: May 2005

A newly designed multichannel Fourier transform infrared spectrometer has been constructed for single-event time-resolved spectroscopy. It is capable of measuring unrepeatable transient events such as phase transitions, explosions, etc., with a time resolution of up to 5.14 ms. The mid-infrared region of 4500–2500 cm−1 is covered with a maximum spectral resolution of 13 cm−1. The developed system is used to measure the phase transitions of alkanes. The solid–solid and solid–liquid phase transitions of octadecane and nonadecane have been studied with time resolutions of 5–50 ms.
Depth Profiling of Stratified Layers Using Variable-Angle ATR
Authors: Shick Robert A. , Koenig Jack L. , Ishida Hatsuo
Published: May 2005

It is shown that variable-angle attenuated total reflectance Fourier transform infrared spectroscopy is a viable technique to recover depth profile information on the molecular level. A number of known step profiles are measured to determine the limits of applicability for this method. Thickness results obtained by using the internal reflection technique are compared with thickness determination with the use of a profilometer.
Coupling Efficiency of Directional Fiber Couplers in the Mid-Infrared
Authors: Tugendhaft I. , Bornstein A. , Weissman Y. , Hardy A.
Published: May 2005

Coupling efficiency characterization in the mid-IR region (2–10 μm) of contact couplers made of step index multimode As2Se3 fiber is given. A unique setup based on an FT-IR spectrometer was built to measure this parameter in several couplers. It is observed that the coupling efficiency between the coupled and the direct output arms increases linearly with the interaction length and monotonously with the wavelength in the mid-IR region. A coupling ratio of almost 20% at 10 μm has been achieved with an interaction length of 120 mm, while the conical input beam has a 40° opening angle. A theoretical model connecting the coupling efficiency and the coupler's gap is introduced. A comparison between this model and the observations yields an effective gap value of about 40 nm.
Spectroscopic and Thermoanalytical Characterization of (+)-Fenfluramine Hydrochloride
Authors: Berbenni Vittorio , Marini Amedeo , Bruni Gianna , Bini Marcella , Magnone-Grato Angelo , Villa Marco
Published: May 2005

We have analyzed the vibrational, structural, and thermal properties of a pure enantiomer of fenfluramine. At room temperature the samples, as-received or ground, are in the α-phase, in which hydrogen bonds are formed among adjacent molecules. Evidence of these H bonds is no longer found in samples which have been annealed above a critical temperature. Grain size, sample treatment, or defects influence the temperature range where the H bonds break down; this phenomenon is accompanied by thermal effects such as endothermic peaks or anomalies of heat capacity, and followed by a slow structural rearrangement into a γ-phase. No evidence of hydrogen bonds is found in the water recrystallized fenfluramine, which maintains up to the melting temperature a crystallographic form (β-form) distinct from both α - and γ-phases. It is suggested that “folded” and “extended” fenfluramine molecules are characteristic of the α- and β-phase, respectively.
Time-Resolved Impulse Photoacoustic Measurements by Step-Scan FT-IR Spectrometry
Authors: Budevska Boiana O. , Manning Christopher J.
Published: May 2005

An impulse/response approach for measuring photoacoustic spectra is described. Instead of the usual modulation from either a chopper or an interferometric phase modulation, a radiation pulse is used to generate the photoacoustic (PA) signal at each step of a step-scan FT-IR spectrometer. The signal from the PA cell is recorded as a time-resolved sequence. The time-dependent photoacoustic signal reveals depth-profiling information for solid samples. Examples of time-resolved impulse photoacoustic spectra (TRIPAS) of gas and solid samples are presented.
Use of Fluorescence Spectroscopy in Concentration and Supersaturation Measurements in Citric Acid Solutions
Authors: Yedur Sanjay K. , Berglund Kris A.
Published: May 2005

Measurement of supersaturation is of critical importance in the operation and control of crystallizers. In this work, we report a novel spectroscopic technique to achieve the measurement of concentration and supersaturation in crystallizing solutions. In order to develop a sensor for this measurement, citric acid is chosen as the model solute, and the analytical technique involves fluorescence spectroscopy. Citric acid is a common food-grade compound with a wide range of applications that is exclusively produced by crystallization. The fluorescent properties of a probe, 8-hydroxy-1,3,6-pyrenetrisulfonate (pyranine), are used to provide concentration measurements in aqueous citric acid solutions, thereby providing for supersaturation estimation. The change in the relative emission peak intensities of the probe in different solute concentrations gives an excellent calibration curve for concentration measurements. It is also shown that, although pyranine responds to both its solvent microenvironment and the pH of the solution, it is still possible to measure concentration and supersaturation by using this fluorescence technique.
Raman Investigation of Photopolymerization Reactions of Single Optically Levitated Microparticles
Authors: Esen C. , Kaiser T. , Schweiger G.
Published: May 2005

Raman spectroscopy was used to investigate polymerization reactions in a single micrometer-sized monomer droplet. An Ar+ laser levitated the microparticles and simultaneously excited the Raman scattering. The polymerization reaction was initiated by exposing the monomer droplets to the UV radiation of a mercury arc excitation lamp. The Raman spectrum of the reacting particle was investigated on-line. The results demonstrate that the combination of the technique of optical levitation and Raman spectroscopy allows nondestructive in situ measurements of single particles and is therefore very useful for the study of fundamental processes.
Infrared Study of the Interactions between Poly(Vinyl Pyridines) and Poly(Mono-n-Alkyl Itaconates)
Authors: Velada José L. , Cesteros Luis C. , Katime I.
Published: May 2005

In this paper we have performed a spectroscopic study of the polymer–polymer complexes and polymer blends formed by mixing poly-acids [a series of poly(mono- n-alkyl itaconates)], and polybases [poly(2-vinyl pyridine) and poly(4-vinyl pyridine)]. The poly(mono- n-alkyl itaconates) are proton donors and the poly(vinyl pyridines) are good proton-acceptor polymers. Therefore, these pairs of polymers can interact via hydrogen bonding under given conditions. The obtained spectroscopic results point out the existence of hydrogen bonding in the studied systems. In addition to the qualitative hydrogen-bonding evidence observed in the hydroxyl and carbonyl stretching region, the curve-fitting analysis of the characteristic modes of the pyridine groups allows a quantitative study of the specific interactions to be performed.
In situ Study of Photoinduced Orientation in Azopolymers by Time-Dependent Polarization Modulation Infrared Spectroscopy
Authors: Buffeteau Thierry , Pézolet Michel
Published: May 2005

Infrared spectroscopy has been coupled with the polarization modulation technique in order to characterize the molecular orientation in films of azopolymers irradiated in situ with polarized visible light. The results obtained on disperse red 1-containing amorphous azopolymer (pDR1A) demonstrate the high efficiency of polarization modulation infrared linear dichroism to determine quantitatively the time dependence of the orientation function of several chemical groups during the orientation (laser on) and relaxation (laser off) processes. The difference dichroic spectra show that polarized visible light induces a preferential orientation of the azobenzene groups perpendicular to the direction of the polarization of the writing laser. This orientation of the side chains also results in a slight cooperative orientation of the C=O ester groups of the main chain of the polymer. The time dependence of the orientation function shows that the orientation and relaxation processes could be described by a biexponential function involving “fast” and “slow” response modes. The rate constants associated with these modes are the same for the main chain and the side chains of the polymer. Finally, we have observed that the level of orientation and the rate constants of the orientation and relaxation processes depend strongly on the film thickness.
Comparative Study of Some Fiber-Optic Remote Raman Probe Designs. Part II: Tests of Single-Fiber, Lensed, and Flat- and Bevel-Tip Multi-Fiber Probes
Authors: Cooney Thomas F. , Skinner H. Trey , Angel S. M.
Published: May 2005

We compare relative performances of flat-tipped, beveled (two-fiber and six-around-one), and single-lensed focused fiber-optic Raman probes and, where feasible, evaluate the utility of optical filters for reducing fiber background. The sensitivity profile of each probe is determined by measuring the relative intensity of light backscattered off a flat surface as a function of distance from the probe tip. The experimental results are compared with a simple light-cone-overlap model incorporating fiber numerical aperture, fiber and immersion medium refractive indices, separation between excitation and collection fibers, number of fibers, and fiber bevel angle and/or lens focal length. The model and sensitivity profiles are used to interpret the sampling regions for Raman spectra obtained by using each of the probes with a clear, transparent sample (single-crystal sparry calcite), a white, partially transparent sample (acetaminophen tablet), and a set of organic liquids of varying refractive index. The sensitivity of the tested commercial lensed probe drops off symmetrically about the focal point. For both solid samples, the intensity of fiber background follows a profile determined primarily by laser backscattering off the surface, whereas the sample Raman signal follows a profile dependent upon sampling depth.
Transportable Spectrophotometer System for On-Line Classification of Poultry Carcasses
Authors: Chen Yud-Ren , Huffman Roy Winfield , Park Bosoon , Nguyen Minh
Published: May 2005

This paper describes a transportable spectrophotometer system developed for real-time classification of poultry carcasses on-site at slaughter plants. The system measures the spectral reflectance of poultry carcasses in the visible/near-infrared regions (471 to 963.7 nm). An optimal neural network classifier for real-time classification of poultry carcasses into normal, septicemic, and cadaver classes with an average accuracy of 93% was obtained. When the classifier was used to classify the carcasses into two classes, normal and abnormal (septicemic and cadaver), the average accuracy was 97.4%. The percentages of the false positive and the false negative error rates were 2.4 and 2.9%, respectively. This paper also proposes implementing the system at the slaughter plants as a poultry carcass screening system (PCSS). Using two visible/NIR spectrophotometer systems, the PCSS tests both sides of the breast of each bird. With the PCSS, the inspection-passed-bird and inspection-rejected-bird error rates by the spectrophotometer systems would be minimal, and less than 5% of the incoming birds would require further inspection by human inspectors.
Comparative Study of Some Fiber-Optic Remote Raman Probe Designs. Part I: Model for Liquids and Transparent Solids
Authors: Cooney Thomas F. , Skinner H. Trey , Angel S. M.
Published: May 2005

We have developed models describing the sensitivity and sampling volume of various remote fiber-optic Raman probes—single-fiber, lensed, dual-fiber beveled-tip, dual-fiber flat-tipped, and multi-fiber flat-tipped. The models assume clear samples and incorporate radii, separation, bevel angle, and numerical aperture of the fibers; overlap geometry of illumination and excitation light cones; and refractive index of immersion medium. For the Raman spectra of solid samples in air, single-fiber and lensed probes are predicted to yield the highest Raman signal. Beveled probes should provide greater Raman signal strength than do flat-tipped probes because beveled probes can collect light from a restricted volume closer to the probe end. Although multiple collection fibers improve Raman signal strength, progressively distant concentric fiber rings contribute less and sample material further from the probe.
Investigation of Vapor Condensation in Graphite Furnace Atomic Absorption Spectrometry by the Shadow Spectral Digital Imaging Technique
Authors: Hughes Dianne M. , Chakrabarti Chuni L. , Goltz Douglas M. , Sturgeon Ralph E. , Grégoire D. Conrad
Published: May 2005

Condensation of vapors of gold (analyte) and matrices of various chemical modifiers and compounds in graphite furnace atomic absorption spectrometry was investigated by using the shadow spectral digital imaging technique with a charge-coupled device camera. Spatial and temporal nonuniformity in the light scattering was observed, and these effects were attributed to the formation of condensed-phase particles during the processes of high-temperature vaporization and atomization. The materials investigated were Au, MgCl2, NaCl, (NH4)2HPO4, La(NO3)3, and a mixture Pd and Mg(NO3)2. The nonuniform distributions of the condensed-phase particle clouds were attributed to the gas-flow patterns that developed in the graphite tube furnace during heating, as well as the steep temperature gradients that developed along the longitudinal axis of the end-heated graphite tube of the Massmann-type graphite furnace. Differences observed with fast and slow rates of heating were related to thermal expansion of gas and diffusion effects. Use of either a graphite platform or a low argon purge gas flow during the high-temperature heating of the graphite furnace was found to reduce condensation of matrix vapor and to improve accuracy of continuum source background correction.
Minimization of Noise in Spectral Data
Authors: Iwata Tetsuo , Koshoubu Jun
Published: May 2005

We have developed a novel noise-minimization method that is applicable to all kinds of spectral data, which introduces little distortion in the signal waveform. It is based on the singular value decomposition of a matrix and is an advanced version of the conventional method for minimizing the background noise from a line spectrum, the details of which we reported in a previous paper [Appl. Spectrosc. 48, 1453 (1994).]. In order to cope with a continuum spectrum, we have calculated a difference spectrum between an observed spectrum and a smoothed one. After minimizing noise components from the difference spectrum by the use of the previous method, we add it to the smoothed spectrum. We also propose a method for reducing the computation time by introducing a data-division technique. Noise minimization for an infrared absorption spectrum of polystyrene is shown.
New Approach to Quantitative Analysis of Two-Component Polymer Systems by Infrared Spectroscopy
Authors: Cole K. C. , Thomas Y. , Pellerin E. , Dumoulin M. M. , Paroli R. M.
Published: May 2005

A new treatment is proposed for quantitative analysis of two-component polymer systems by infrared spectroscopy. Like much previous work, it is based on a ratio involving two peaks in the same spectrum. The relationship between such a ratio and the concentration of a given polymer is inherently nonlinear. It is shown that this nonlinearity can be well described by a simple equation derived from the laws of optical transmission. This equation has the form χ1 = m1 + m2 R/(1 + m3 R), where χ1 is the weight fraction of polymer 1, the mi are adjustable coefficients, and the ratio R is equal to Aa/( Aa + Ab). The quantities Aa and Ab are the absorbances (peak heights or areas) at two frequencies a and b of which the first is associated mainly with polymer 1 and the second with polymer 2. This equation has been applied to various peak combinations in spectra of miscible blends of poly(phenylene ether) with polystyrene (both mid-IR and near-IR data) and immiscible blends of polypropylene with polyethylene (mid-IR data). It is shown that the equation is valid in all cases, covering the full concentration range from 0 to 100% even when the peaks used for the analysis involve absorption by both polymers. It is therefore believed to be of broad general usefulness for the analysis of polymer blends and copolymers.
Liquid Crystal Tunable Filter Raman Chemical Imaging
Authors: Morris Hannah R. , Hoyt Clifford C. , Miller Peter , Treado Patrick J.
Published: May 2005

A Lyot-type liquid crystal tunable filter (LCTF) suitable for high-definition Raman chemical imaging has been developed. The LCTF has been incorporated into an efficient Raman imaging system that provides significant performance advantages relative to any previous approach to Raman microscopy. The LCTF and associated optical path is physically compact, which accommodates integration of the LCTF within an infinity-corrected optical microscope. The LCTF simultaneously provides diffraction-limited spatial resolution and 7.6-cm-1 spectral bandpass across the full free spectral range of the imaging spectrometer. The LCTF Raman microscope successfully integrates, in a facile manner, the utility of optical microscopy and the analytical capabilities of Raman spectroscopy. In this paper the LCTF Raman imaging system is described in detail, as well as results of initial studies of polymer and corrosion product model systems.
High-Pressure On-Line Photolysis with NMR Detection
Authors: Yonker C. R. , Wallen S. L.
Published: May 2005

The investigation of the photoreversible fulgide Aberchrome-540 as a function of pressure and temperature with the use of nuclear magnetic resonance (NMR) detection is described. This technique demonstrates the novel combination of high-pressure NMR and laser photolysis with the use of fiber optics for the conversion of the fulgide on-line in the instrument. Investigation of the photolysis of Aberchrome-540 to 2.0 kbar and 120 °C is reported. Extension of this technique should allow the investigation of photoinitiated reaction kinetics and equilibria as a function of pressure and temperature with simultaneous structure characterization by NMR.
Fourier Self-Deconvolution: Parameter Determination and Analytical Band Shapes
Authors: Rahmelow Kim , Hübner Wigand
Published: May 2005

On the basis of general theories of Fourier self-deconvolution and curve fitting, an objective procedure to obtain the deconvolution parameters halfwidth, σ, and breaking point, L, is described. In the curve fitting routine, the analytical accessible line shape functions, derived for different apodization functions, are used to simulate the deconvoluted spectra. The fully automated deconvolution program was applied to the IR spectra of the amide I band of dry protein films to determine the secondary structure content.
TO-LO Splitting in Infrared Spectra of Thin Films
Authors: Yamamoto Kiyoshi , Masui Akio
Published: May 2005

The importance of transverse optic-longitudinal optic (TO-LO) splitting in the interpretation of infrared spectra of thin films is experimentally presented. When infrared spectra are observed at oblique angles of incidence, the shifts in peak position and/or the changes in peak shape may be due to TO-LO splitting. Before one assigns the optical behavior to surface phenomena such as molecular orientation, proper care must be employed. The proposed technique includes optical calculation to extract surface phenomena from TO-LO splitting in the spectra, and it is applied to reflection absorption spectra of perfluoropolyether.
Genetic Regression as a Calibration Technique for Solid-Phase Extraction of Dithizone-Metal Chelates
Authors: Paradkar Rajesh P. , Williams Ronald R.
Published: May 2005

The application of genetic regression (GR) to reflectance spectra of a solid-phase colorimetric extraction for the determination of Hg(II) is demonstrated. GR is a technique that combines wavelengths that optimize linear regression using a genetic algorithm. Solid polystyrene (PS) beads with a molecular weight distribution of 125,000–250,000 were impregnated with Hg(II)-dithizonate, filtered, allowed to dry, and packed in quartz cuvettes, and their reflectance spectra were collected. Quantitation with the use of normal calibration methods could not be achieved because of baseline fluctuations which originate in sample packing, presentation to the spectrometer, and particle size. Results indicate that GR can easily compensate for these baseline fluctuations and provide excellent calibrations.
Low-Temperature Electrothermal Vaporization of 8-Hydroxyquinolinate Complex for Determination of Trace Vanadium by ICP-AES
Authors: Tao Shiquan , Kumamaru Takahiro
Published: May 2005

A trace amount of vanadium was vaporized as 8-hydroxyquinolinate complex by using a low-temperature tungsten boat furnace for sample introduction in ICP-AES. Experimental results suggest that vanadium was vaporized as vanadium(III) 8-hydroxyquinolinate complex. Vanadium(V) and vanadium(IV) were reduced in the heating process before vaporization. The operating conditions were optimized, and the effects of foreign ions were investigated. The existence of tin(II) ion in sample solution was found to enhance the emission intensity of vanadium, improve the precision of the proposed method, and also suppress the interferences from other foreign ions. The detection limit in the presence of 5 μg tin(II) was determined to be 4 pg, and in the absence of tin(II), 7 pg, of vanadium. Sub-μg L−1 levels of vanadium in sample solution could be determined by the proposed method. The precisions in relative standard deviation (% RSD) for 100 pg of vanadium under the same conditions described above were 1.9% and 4.1%, respectively. The contents of vanadium in some standard steel and rock samples determined by the proposed method were in good agreement with their certified values.
Mid-Infrared Sources Using Dye Lasers in KTiOAsO4 and LiIO3
Authors: Kung A. H. , Fei Suli , Strauss H. L.
Published: May 2005

A coherent infrared source tunable from 3.4 to 5.3 μm has been constructed by difference-frequency mixing of the second harmonic of a Q-switched Nd:YAG laser and a pulsed dye laser using the new crystal KTiOAsO4 (KTA). A peak power of >50 kW and pulse energy of >250 μJ are measured at 4.4 μm. The results are compared with mixing in LiIO3. For a low-power Nd:YAG laser that produces 200 mJ of 532-nm radiation, the infrared power is similar for the two crystals. For high-power YAG lasers, calculation shows that commercial KTA crystals can produce over 10 mJ of IR power in the absence of absorption loss. The laser damage threshold of KTA at 532 nm is determined to be 300 ± 30 MW/cm2. Both the maximum IR power and the damage threshold are several times higher for KTA than for LiIO3. A simple frequency calibration method is described.
Myoglobin Oxygen Saturation Measured Independently of Hemoglobin in Scattering Media by Optical Reflectance Spectroscopy
Authors: Arakaki Lorilee S. L. , Kushmerick Martin J. , Burns David H.
Published: May 2005

Partial least-squares (PLS) and second-derivative preprocessing were used to obtain estimates of myoglobin oxygen fractional saturation from diffuse reflectance spectra of solutions containing myoglobin, hemoglobin, and a scatterer. A computer model and solutions in vitro were used to simulate several physiological situations. The maximum standard error (SE) was 0.082 for these trials; myoglobin fractional saturation varies between 0 and 1. These results show that a statistical approach can differentiate two highly overlapping absorbance peaks in the presence of diffuse scatter. A robust PLS model was created by using a calibration set with a range of scattering coefficients and concentrations of hemoglobin. Second derivatives of the spectra were less affected by changes in scattering coefficients than were the original spectra. A linear scaling of PLS estimates produced accurate myoglobin saturations from in vitro prediction set spectra that had scattering and absorption coefficients both within and beyond the range represented by the calibration set. Preliminary estimates of myoglobin fractional saturation from spectra acquired from the rat hind limb suggest that this calibration set is appropriate for use in vivo.
Multivariate Raman Imaging of Simulated and “Real World” Glass-Reinforced Composites
Authors: Stellman Christopher M. , Booksh Karl S. , Myrick Michael L.
Published: May 2005

A Raman imaging system has been used to investigate chemical and physical homogeneity in interstices of glass-reinforced composites. A protocol for monitoring chemical and physical spatial variations via multivariate statistics has been developed with the use of a simulated composite which provides a well-defined system of known chemical composition and curing conditions. Finally, a preliminary study of a “real world” glass-reinforced composite is presented.
Recent Developments in Raman Optical Activity of Biopolymers
Authors: Barron L. D. , Hecht L. , Bell A. F. , Wilson G.
Published: May 2005

Recent advances in Raman optical activity (ROA) instrumentation are outlined which have enhanced significantly the quality of vibrational ROA spectra of biopolymers in aqueous solution. Peptides, proteins, carbohydrates, glycoproteins, and nucleic acids now provide excellent ROA spectra which contain detailed information about solution structure. ROA spectra can be measured just as easily in D2O as in H2O solution, and, as illustrated for bovine serum albumin and concanavalin A, a comparison of the two can be highly informative. In addition to signatures of extended secondary structure, protein ROA spectra also contain signatures related to loops and turns which are valuable for studying tertiary structure and dynamics, exemplified here by a comparison of the ROA spectra of reduced lysozyme and unordered poly-L-lysine, by the ROA spectra of acid molten globule α-lactalbumin at different temperatures, which reveal a native-like tertiary fold, and by changes in the ROA spectrum of native lysozyme on binding to a saccharide inhibitor. Carbohydrate ROA spectra contain signatures of all the central features of their stereochemistry and, as shown by a comparison of laminaribiose with laminarin, can also probe extended secondary structure in polysaccharides. Results on a glycoprotein, orosomucoid, suggest that ROA can provide information about both the protein and the carbohydrate components. Preliminary results on nucleic acids are outlined with the ROA spectra of Poly(rA)·Poly(rU) and Poly(rI)·Poly(rC) shown as examples.
Vibrational Circular Dichroism of Proline-Containing Oligopeptides
Authors: Miyazawa Mitsuhiro , Inouye Katsuhiko , Hayakawa Tadao , Kyogoku Yoshimasa , Sugeta Hiromu
Published: May 2005

Vibrational circular dichroism (VCD) and infrared absorption spectra in the amide A region of blocked oligopeptides containing proline have been obtained in apolar organic solvents in order to clarify the characteristic VCD for the intramolecularly hydrogen-bonded NH stretching involved in the turn structures of peptide chains as well as the intermolecularly hydrogen-bonded NH stretching in associated molecules. The γ-turn with the intramolecularly hydrogen-bonded C7 conformation exhibits a characteristic positive VCD band at about 3330 cm−1 in dilute solutions of Piv-Pro-NHMe and Ac-Pro-NHMe. The intramolecularly hydrogen-bonded NH stretching in the type II β-turn with C10 conformation gives rise to a positive VCD band at 3345 cm−1 for Piv-Pro-Gly-NHMe. The Gly NH group of Piv-Pro-Gly-OMe and Ac-Pro-Gly-OMe in dilute solutions assumes C7C5 conformation stabilized by a bifurcated three-center intramolecular hydrogen bond and exhibits a positive VCD band near 3300 cm−1 at a lower frequency than the intermolecularly hydrogen-bonded band. All the peptides studied give a characteristic negative—positive bisignate couplet from the high wavenumber side for the intermolecularly hydrogen-bonded NH stretching band at high concentrations.
Ultraviolet Photodissociation of Gas-Phase Alcohols, Amines, and Nitroalkanes
Authors: Ross Philip L. , Van Bramer Scott E. , Johnston Murray V.
Published: May 2005

The 193-nm photochemistry of alcohols, amines, and nitroalkanes in the C3-C6 size range is presented. The photolysis products are photoionized with coherent vacuum ultraviolet radiation and analyzed by time-of-flight mass spectrometry. For alcohols and amines, C-C bond dissociation competes with dissociations involving the heteroatom (C-O, O-H, C-N, N-H). Dissociation of the α(C-C) bond is preferred over other locations. Dissociation of a C-C bond is suppressed when a methyl radical would be produced. This behavior is similar to that observed for other substituted alkanes. Nitroalkanes exhibit both C-N and N-O bond dissociation pathways. Their low bond energies cause a substantial amount of internal energy to be partitioned among the primary photodissociation products. Under collision-free conditions, the alkyl radicals produced from these molecules undergo extensive secondary fragmentation. If the photodissociation step is performed in a free jet expansion, collisional cooling stabilizes the primary products and allows large species, such as intact pentyl and hexyl radicals, to be detected.
Interconvertibility of Electronic and Vibrational Circular Dichroism Spectra of Proteins: A Test of Principle Using Neural Network Mapping
Authors: Pancoska Petr , Janota Vit , Keiderling Timothy A.
Published: May 2005

Electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) are compared with respect to their interconvertibility for protein structural studies. ECD and amide I' VCD spectra of 28 proteins were used with a backpropagation projection neural network with one hidden layer to develop a mapping between the two spectral types. After the network converged, the number of neurons in the hidden layer was optimized by principal component analysis of the synaptic weights of the pilot network topology with redundant hidden neurons. Actual prediction of one spectrum from the other for individual proteins was tested by retraining these networks with 28 reduced training sets having one protein systematically left out. Comparison of network-predicted spectra with experimental ones is used to identify those spectral features which are unique in each method. Similarly, the VCD spectra of 23 proteins measured in both D2O and H2O in the amide I region were mapped onto each other with the use of the same type of neural network calculation. The results show that the effects of partial deuteration on the VCD spectra band shape are predictable from the H2O spectra. An analysis of the synaptic weights of the optimized networks was performed which allowed identification of the linear and nonlinear parts of the obtained mappings. Insight into the details of how the neural networks encode and process the spectroscopic information is derived from a spectral representation of these weight matrices.
Observation of Vibrational Circular Dichroism for Overtone Transitions with Commercially Available CD Spectrometers
Authors: Abbate Sergio , Longhi Giovanna , Givens John W. , Boiadjiev Stefan E. , Lightner David A. , Moscowitz Albert
Published: May 2005

It is demonstrated that some commercially available circular dichroism spectrometers can be used to gather vibrational circular dichroism data associated with overtone transitions. By way of specific example, the circular dichroism spectra of neat S−(−)−limonene and R-(+)-limonene are measured in the region 800–600 nm. The observed spectral features correspond to the overtone bands Δ v = 5 and 6 for CH-stretching motions. A discussion of the data is also given.
Effect of Day-To-Day Noise on UV-Visible Spectrophotometric Control Analyses of Mixtures by Principal Component Regression
Authors: Blanco Marcelo , Coello Jordi , Iturriaga Hortensia , Maspoch Santiago , Alaoui-Ismaili Smail
Published: May 2005

It is demonstrated that noise in UV spectral recordings obtained by using a diode array UV-visible spectrophotometer on different days may conform to a defined pattern. Such structured noise leads to the acceptance, as significant, of components containing noise alone, in calibrations by principal component regression (PCR)—which impedes the detection of outliers at the unknown sample prediction stage and considerably diminishes the potential of this methodology for control analyses. As shown in this paper, the effect of the noise structure can be substantially decreased by recording the spectra for the calibration samples on different days. Also, a procedure for distinguishing between correct samples and outliers is proposed. The procedure fits the distribution of the squared residuals of the absorbances for the calibration samples to an exponential function and uses a 99.9% probability as the acceptable limit. It was applied to analysis of ketoprofen and methylparaben mixtures.
Quantitative Comparison of Experimental Infrared and Raman Optical Activity Spectra
Authors: Qu Xinhua , Lee Eunah , Yu Gu-Sheng , Freedman Teresa B. , Nafie Laurence A.
Published: May 2005

Infrared vibrational circular dichroism (VCD) and vibrational Raman optical activity (ROA) have been measured and compared quantitatively over the frequency range from 835 to 1345 cm−1 for trans-pinane, cis-pinane, α-pinene, and β-pinene. For these molecules in this region of spectral overlap between VCD and ROA, the average ratio of VCD or ROA to its parent vibrational intensity favors ROA by a factor of two to three. Several vibrational modes in each molecule yield both large VCD and large ROA, while several other modes show little propensity toward significant VCD or ROA intensity. Beyond this general property of a few strongly chiral and strongly achiral vibrational modes, little additional correlation between VCD and ROA intensity is found. This quantitative compilation of VCD, infrared, ROA, and Raman intensities provides an experimental basis for computational intensity studies of VCD, ROA, and their theoretical comparison.
Imaging with Extrinsic Raman Labels
Authors: Sijtsema Nanna M. , Duindam Johannes J. , Puppels Gerwin J. , Otto Cees , Greve Jan
Published: May 2005

In two separate examples we demonstrate the use of extrinsic Raman scattering probes for imaging of biological samples. First, the distribution of cholesterol in a rat eye lens is determined with the use of the Raman scattered light from filipin, a molecule which binds specifically to cholesterol. The protein distribution in the same eye lens was obtained by using the 1450-cm-1 CH2 and CH3 bending modes as an intrinsic marker for protein. It appears that the cholesterol is concentrated in the membranes of the eye lens fibers, whereas the protein is distributed more evenly. Second, we demonstrate that phenotyping of lymphocytes can be done by using the Raman scattering of (antibody-coated) polystyrene spheres. The lymphocyte population was also fluorescently labeled with anti-CD4-FITC to demonstrate that Raman and fluorescence labeling can be used simultaneously. Finally, we discuss the potential advantages and disadvantages of using Raman labels.
Binding of Pyrene to Cyclodextrin Polymers
Authors: Werner T. C. , Colwell Karen , Agbaria Rezik A. , Warner Isiah M.
Published: May 2005

Polymers containing the three cyclodextrin (CD) molecules, α-CD, β-CD, and γ-CD, linked by epichlorohydrin (α-CDP, β-CDP, and γ-CDP) are highly water-soluble polydisperse mixtures containing CD units joined by repeating glyceryl linkers [-(CH2-CHOH-CH2-) n]. The average n value is 12-15, and gel filtration chromatography analysis indicates that the two major polymer components have molecular weights (MWs) of <2000 (1 CD/polymer chain) and 9-10,000 (4-5 CDs/polymer chain). We have used fluorescence properties to study the binding of pyrene to the three commercially available CDPs and to dialyzed samples of the CDPs, in which the low-MW (<2000, CDPL) and high-MW (9-10,000, CDPH) components have been separated. The pyrene emission I/III ratios for the three polymers are larger and exhibit a smaller range than the I/III ratios for the CD monomers. Moreover, the I/III ratio for the dialyzed polymers, β-CDPL and β-CDPH, are, within error, the same as that for β-CDP. It has been previously shown that additives, such as pentafluoropropanol (PFP), cause a dramatic decrease in the pyrene I/III ratio in the presence of β-CD. No effect on the pyrene I/III ratio is observed when these additives are added in the presence of the CDPs. The pyrene fluorescence decays in the presence of all three native polymers and the dialyzed β-CDPs are quite similar but different from the pyrene fluorescence decays in the presence of the three CD monomers. Moreover, the pyrene lifetimes show much greater dependence on iodide quencher concentration in the presence of CDPs than in the presence of β-CD and γ-CD. These data suggest that pyrene exists in a more exposed and hydrophilic environment when bound to the CDPs than that observed with the CDs. The agreement of the results for pyrene in the presence of β-CDP, β-CDPH, and β-CDPL would seem to rule out significant cooperative binding from two CD units on a single chain, which has previously been suggested. We conclude that pyrene binding to the CDPs may be largely noninclusional, involving considerable participation of the glyceryl linker units.
Interaction of Fulvic Acids with Al(III) Studied by Self-Modeling Curve Resolution of Second-Derivative Synchronous Fluorescence Spectra
Authors: Da Silva Joaquim C. G. Esteves , Machado Adélio A. S. C.
Published: May 2005

The interaction of Al(III) with two samples of fulvic acids (fua), extracted from materials present in a pinewood soil (fua2 from the upper soil horizon, or leaf litter, and fua3 from lower soil horizons), was followed by synchronous fluorescence (SyF) spectroscopy at pH 4. The variations observed in the inverted second-derivative spectral data were analyzed by SIMPLISMA, a self-modeling curve resolution technique. Three binding sites were detected for each fua sample, and their spectra and SyF intensity profiles were obtained. Conditional stability constants for coordination of one binding site of each fua and Al(III) were obtained (log values): fua2, 5.65(15); fua3, 4.64(2). The experimental and data analysis methodologies were validated by analysis of data obtained for salicylic acid under the same conditions. The log value found for its conditional stability constant for Al(III) coordination at pH 4 was 4.34(15).