bluuebunny/crossref_metadata_2025 huggingface dataset:
Behavior of Steel Tube and Confined High Strength Concrete for Concrete-Filled RHS Tubes
Authors: Zhang Sumei , Guo Lanhui , Ye Zaili , Wang Yuyin
Published: May 2005

This paper presents an experimental study of the separated behavior of short ( L/H=3) high strength concrete-filled rectangular hollow section (RHS) tubes concentrically loaded in compression to failure. A total of 50 specimens were tested. Experimental results showed that the concrete strength influenced the failure pattern of the specimen. The height-to-breadth ratio of the rectangular tube (varying from 1.0 to 1.6) had no evident influence on the ultimate bearing capacity of the specimen. Then based on the experimental results, a numerical separation method was successfully used to separate the compressive load carried by the steel tube and the core concrete. The equivalent One-Dimensional nonlinear stress-strain models of the steel and the confined concrete were suggested, which can be used to determine the overall behavior of the high strength concrete-filled RHS tubes. The stress-strain models have been used to numerically analyze the behavior of high strength concrete-filled RHS tubes. The numerical results are compared with the experimental results and they agreed well with each other.
Elastic Stability of Two-Span Continuous Beams under Moving Loads
Authors: Zhang Lei , Tong Gengshu
Published: May 2005

The elastic stability of two span continuous beams has been studied using FEA methods. Two formulae for estimating the critical loads are proposed, one is suitable for two-span beams with one span loaded, while the other is suitable for two-span beams with both spans equally loaded. Two identical concentrated loads symmetrically located about the mid-span of each loaded span were considered in the derivation of both formulae, and the effect of the height of loaded points for doubly symmetric beams was included. The formulae presented are also accurate enough in calculating the critical loads for two-span continuous beams with the mono-symmetric sections used in practice if the point of load application is at or above the shear centre. A linear approximation is suggested for the interaction of two spans when the two spans of the beam are not equally loaded. For a two-span continuous runway girder supporting moving cranes, the minimum critical load and the maximum absolute moment were investigated, some possible combination of wheel forces on beams considered, and approaches to calculating the critical load for each load combination are suggested when the girder has either one or two cranes moving along it.
Optimization of Defense Hole System for Biaxial Loaded Plate with Three Coaxial Holes
Authors: Tahat Montasser , Akour Salih , Habali Saad , Nayfeh Jamal
Published: May 2005

Optimum design of elliptical Defense Hole System (DHS) under biaxial loading in a finite plate with a row of circular holes is presented. Maximum stress reduction is made possible by introducing elliptical auxiliary holes close to the mainmain holes in the areas of low stresses along the principal stress direction. A systematic study is undertaken by using the finite element analysis (FEA) to determine the optimum shape, location and size of the auxiliary defense hole system. These parameters are examined in relation to plate dimensions for a number of plates with different mainmain-hole-diameter to plate-width ratios and different pitch to main-hole-diameter ratios. Maximum stress reductions from 6–18% were achieved. With such reduction in the maximum stress level the improvement in fatigue life of a structural part can be very significant. The FEA results are validated experimentally by applying an enhanced RGB-photoelasticity technique. The photoelasticity experimental results and the FEA results show good agreement.
Rehabilitation of Compression Steel Members Using FRP Pipes Filled with Non-Expansive and Expansive Light-Weight Concrete
Authors: Liu Xiangdong , Nanni Antonio , Silva Pedro F.
Published: May 2005

This paper presents the experimental and analytical evaluation of the feasibility of a proposed fiber reinforced polymer (FRP) retrofit method to strengthen corroded steel columns. This method consists of two steps: (1) wrapping the corroded steel column with an FRP jacket, and (2) filling the jacket with expansive light-weight concrete. Seven steel columns were tested in the laboratory including five strengthened columns with the proposed technique. The first two were used as control units where one was a virgin shape and the second was notched in the center zone to simulate the loss of section due to corrosion. The remaining five were all notched, and confined with FRP composite pipes within the simulated corroded zone and subsequently filled with light-weight concrete. All specimens were axially loaded to failure while strain and displacement readings were measured to demonstrate the feasibility of this repair concept. Test results show that the proposed FRP retrofit method for steel columns can be successfully applied. Furthermore, an analytical model was developed that can predict the load capacity of the FRP retrofitted steel column.
Metastability in Monolayer Films Transferred onto Solid Substrates by the Langmuir-Blodgett Method: IR Evidence for Transfer-Induced Phase Transitions
Authors: Rana Fazale R. , Widayati Suci , Gregory Brian W. , Dluhy Richard A.
Published: May 2005

The rate at which a monomolecular film is deposited onto a solid substrate in the Langmuir-Blodgett process of preparing supported monolayer films influences the final structure of the transferred film. Attenuated total reflectance infrared spectroscopic studies of monolayers transferred to germanium substrates show that the speed at which the substrate is drawn through the air/water interface influences the final conformation in the hydrocarbon chains of amphiphilic film molecules. This transfer-induced effect is especially evident when the monolayer is transferred from the expanded region of surface-pressure-molecular-area isotherms at low surface pressures; the effect is minimized when the film molecules are transferred from condensed phases at high surface pressures. This phenomenon has been observed for both a fatty acid and a phospholipid, which suggests that these conformational changes may occur in a variety of hydrocarbon amphiphiles transferred from the air/water interface. This conformational ordering may be due to a kinetically limited phase transition taking place in the meniscus formed between the solid substrate and aqueous subphase. In addition, the results obtained for both the phospholipid and fatty acid suggest that the structure of the amphiphile may help determine the extent and nature of the transfer-speed-induced structural changes taking place in the monomolecular film.
Identification of Tablet Formulations inside Blister Packages by Near-Infrared Spectroscopy
Authors: Aldridge P. K. , Mushinsky R. F. , Andino M. M. , Evans C. L.
Published: May 2005

Near-infrared spectroscopy was evaluated as a method for nondestructively discriminating tablets containing an active drug from two placebo tablet formulations inside blister-packaged clinical supplies without removing the tablets from the blind study tablet cards. A custom sampling device was constructed to allow the spectra of individual tablets to be collected. Spectra of 165 tables were acquired over the wavelength range of 400 to 2500 nm. These tablets were of two different sizes and three formulations. The second derivatives of the spectra were calculated and randomly divided into two groups, each containing approximately half the samples. A factor-based library/model was constructed with the use of the second-derivative spectra from one of the groups over the wavelength range from 1600 to 2500 nm. The model was then validated by predicting the identity of the tablets in the remaining group. The identity and formulation of all the tablets were correctly predicted. This model was then used to confirm the identity of thousands of clinical trial samples. Apart from being nondestructive, the NIR method is less labor and time intensive than the previously used TLC assay.
Diffuse Reflectance FT-IR Characterization of Active Sites under Reaction Conditions: The Production of Oxygenates in the CO/H2 Reaction
Authors: Benítez J. J. , Carrizosa I. , Odriozola J. A.
Published: May 2005

The reactivity of a Lu2O3-promoted Rh/Al2O3 catalyst in the CO/H2 reaction is reported. Methane, heavier hydrocarbons, methanol, and ethanol are obtained. In situ DRIFTS has been employed to record the infrared spectra under the actual reaction conditions. The structure of the observed COads DRIFTS bands has been resolved into its components. The production of oxygenates (methanol and ethanol) has been correlated with the results of the deconvolution calculation. Specific sites for the production of methanol and ethanol in the CO/H2 reaction over a Rh,Lu2O3/Al2O3 catalyst are proposed.
High-Voltage Monitor for Measuring Electrical Characteristics of Pulsed Hollow Cathode Discharges
Authors: Moore James H. , Bray C. W. , Griffin S. T. , Mixon P. D. , Williams J. C.
Published: May 2005

A high-voltage monitor has been developed for measuring small signal differences between large voltage waveforms. This device reduces the number of channels needed for a differential measurement from two to one while maximizing the performance of an oscilloscope by removing large common-mode signals present in typical discharge applications.
FT-Raman Study on Charge-Transfer Polyiodide Complexes and Comparison with Resonance Raman Results
Authors: Deplano Paola , Devillanova Francesco A. , Ferraro John R. , Mercuri Maria Laura , Lippolis Vito , Trogu Emanuele F.
Published: May 2005

In resonance Raman (RR) spectroscopy, the laser excitation sources have often been found to be destructive towards polyiodides if compared with the milder conditions under which the Fourier transform Raman (FT-R) technique operates. In fact, our FT-R spectra of some model polyiodides—[(CH3)4N]I5 (I5− bent), [(C2H5)4N]I7, and [(CH3)4N]I9—are significantly different from the literature RR data, give evidence of decomposition of the samples in RR, and are in agreement, respectively, with the I− · 2I2, I3− · 2I2 and (I− · 2I2) · 2I2 descriptions. In addition to the above-cited cases, the FT-R spectra of (Mn(modtc)3]Is (modtc = morpholine carbodithioato) and (moH]I5 (moH = morpholinium) are reported. The crystal structures indicate that in these two compounds the I5 anions can be properly described as I− · 2I2 and I3− · I2, respectively, and FT-R spectra agree well with this formulation. Moreover, the first FT-R spectrum of an I164– anion in [mo2ttl]2I16, ([mo2ttl]2+ = 3,5-di( N-morpholinio)-1,2,4-trithiolane), whose X-ray structure shows a sequence of two I3− … I2 … I− ·I2 (I82–) interacting anions, is reported. A close correlation of the FT-Raman peaks with the molecular species, identified by the interatomic distances, is also observed in this case. Thus, a combination of X-ray structural data and FT-R data can provide a reasonable interpretation of the nature of the acceptor iodine moiety in charge-transfer polyiodide complexes.
Evaluation of Particle Beam Fourier Transform Infrared Spectrometry for the Analysis of Globular Proteins: Conformation of β-Lactoglobulin and Lysozyme
Authors: Turula Vincent E. , de Haseth James A.
Published: May 2005

The efficacy of the particle beam LC/FT-IR interface, in its development as a tool for the determination of dynamic protein structure from experiments such as HPLC separations and folding/refolding intermediate analysis, is presented here. The particle beam apparatus can be used to desolvate proteins rapidly in preparation of IR measurements. Several experiments have been designed to determine whether the operation of the particle beam apparatus causes alteration to the complex structural features of globular proteins, and whether it produces a solid-state spectrum representative of protein solution structure. It is shown here that the structural integrity of β-lactoglobulin is maintained when nebulized, desolvated from solution, and deposited onto the IR-substrate. Since enzyme activity is dependent upon the maintenance of higher-order structure, a complementary series of spectrophotometric-activity experiments with lysozyme collected from the particle beam were performed to determine the state of the tertiary and quaternary structures. The lysozyme particle beam deposit not only produced a secondary structure estimate similar to that of solution; it also retained its biological activity. It is demonstrated that the particle beam can induce structural changes in proteins with a carrier-liquid concentration gradient; this characteristic is useful for band assignment.
Studies on Spectra/Structure Correlations in Near-Infrared Spectra of Proteins and Polypeptides. Part I: A Marker Band for Hydrogen Bonds
Authors: Liu Yongliang , Cho Rae-Kwang , Sakurai Kaori , Miura Tsuyoshi , Ozaki Yukihiro
Published: May 2005

FT-NIR spectra have been measured for various polypeptides and proteins with different secondary structures to find an NIR marker band for the structure of the proteins and polypeptides. Their FT-IR spectra have also been obtained to assist in the interpretation of the FT-NIR spectra. Comparison between the FT-NIR and FT-IR spectra shows that there is a clear correlation between the frequency of an NIR band near 4855 cm−1, assignable to a combination of amide A and amide II, and that of an IR band near 3300 cm−1 due to amide A for the polypeptides investigated. Therefore, the NIR band (hereafter, we identify it as amide A/II) may be used as a practical indicator for the strength of hydrogen bonds in the amide groups, as in the case of amide A. The frequency of amide A/II changes little with the secondary structure for both the polypeptides and proteins, and thus it is rather difficult to use this band as a marker band of the secondary structure. For the globular proteins such as hemoglobin, albumin, and lysozyme, irrespective of their secondary structure, both amide A/II and amide A appear in similar positions. However, collagen (Type I, Type IV, and Type V) gives them much higher frequencies, suggesting that the hydrogen bonds in collagen are much weaker than those in typical globular proteins. The amide A/II band shows a significant upward shift upon the thermal denaturation of pepsin. This observation indicates that amide A/II can also be used for monitoring the destruction of the hydrogen bonds in the amides induced by the denaturation.
Electrochemical SERS Detection of Chlorinated Hydrocarbons in Aqueous Solutions
Authors: Storey John M. E. , Shelton Robert D. , Barber Tye E. , Wachter Eric A.
Published: May 2005

An in situ method for the determination of trichloroethylene (TCE), perchloroethylene (PCE), chloroform (CHCl3), and carbon tetrachloride (CCl4) in aqueous solution is described. The method is based on ESERS—a combination of electrochemical methods and surface-enhanced Raman scattering (SERS). Electrochemistry prepares the surface of a copper electrode for SERS and concentrates the analyte on the surface. The formation of common reaction products for chloroalkanes and for chloroalkenes prevents unequivocal differentiation within a specific class of chlorinated hydrocarbons. However, spectroscopic selectivity between the chloroalkane and chloroalkene classes is excellent, while differences in electrochemical response provide a secondary means for differentiating analyte class. Sensitivity was found to be: <1 ppm for TCE; 15 ppm for PCE; 15 ppm for CHCl3; and 10 ppm for CCl4. Application of the method to groundwater contaminated with TCE has been demonstrated. In combination with a fiber-optic waveguide, the ESERS technique offers potential for remote detection of chlorinated hydrocarbons in groundwater and remediation process streams.
Dynamic and Solid-Matrix Quenching by Moisture in Solid-Matrix Phosphorescence with Filter Paper
Authors: Chen Jie , Tjioe S. W. , Hurtubise Robert J.
Published: May 2005

The room-temperature solid-matrix phosphorescence intensity ratios behaved very differently than the phosphorescence lifetime ratios for 4-phenylphenol, protonated benzo( f)quinoline, and two tetrols adsorbed on filter paper over a wide range of wt % adsorbed moisture. The changes in phosphorescence intensity ratios and lifetime ratios were related to regions before the monolayer coverage of water and beyond monolayer coverage of water on filter paper. An equation was obtained that describes the changes in the phosphorescence intensity ratio as a function of phosphorescence lifetime ratio and an exponential expression that included the wt % of adsorbed moisture. This equation defined both dynamic and solid-matrix quenching of phosphorescence by adsorbed moisture. The changes in the phosphorescence lifetime ratios were readily related to wt % adsorbed moisture by the use of a dynamic quenching model.
Argon Fluoride Laser-Excited Atomic Fluorescence of Arsenic in a H2/Air Flame and in an Ar ICP
Authors: Hueber D. , Smith B. W. , Madden S. , Winefordner J. D.
Published: May 2005

Laser-excited atomic fluorescence spectrometry (LEAFS) can be an extremely sensitive method of trace analysis. However, some elements, such as As, have strong absorption lines only below 200 nm. Dye laser systems capable of resonance excitation of As are complicated and very expensive. By coincidence, a simple fixed-frequency argon fluoride (ArF) excimer laser produces a broad-band output centered at 193.0–193.2 nm overlapping the As absorption line at 193.7 nm. The use of an ArF excimer laser as a source for LEAFS detection of As in a H2/air flame and an Ar-ICP has been evaluated. Detection limits of about 20 ng/mL were obtained with both atomizers. The limiting noise was laser-induced scatter in both cases. Methods of improving the detection powers are discussed.
Identification of Bromohydrins in Ozonated Waters
Authors: Collette Timothy W. , Richardson Susan D. , Thruston Alfred D.
Published: May 2005

Because ozonation is becoming a popular alternative to chlorination for disinfection of drinking water and little is known about the potential adverse health effects of ozonation disinfection by-products (DBPs), we have sought to identify ozone DBPs, particularly brominated organics, which are of principal concern due to their anticipated toxicity. Using gas chromatography coupled (independently) to low-resolution electron-impact mass spectrometry (LR-EI-MS), high-resolution EI-MS, chemical ionization MS (with 2% ammonia in methane), and Fourier transform infrared spectrometry, we have identified a series of bromohydrins and related compounds detected in extracts of an ozonated natural water sample that was artificially enhanced with bromide. The bromohydrins, which constituted the majority of by-products in the samples we studied, were detected but could not be identified by GC/LR-EI-MS, the technique used almost exclusively for environmental monitoring. A key to identifying the bromohydrins was the manifestation of intramolecular hydrogen bonding in the gas-phase IR spectra. Many of the by-products had two chiral centers, and both diastereomers were present and were separated by GC. In most cases, the IR spectra also permitted us to distinguish between diastereomers. We interpreted the IR and EI-MS spectra of several representative compounds in detail, and gave peak assignments for all that were identified. Molecular mechanics calculations and an experimental determination of the enthalpy change for conversion of free and hydrogen-bound conformers for a representative bromohydrin were used to verify the IR interpretations.
Laser Koehler Epi-Illumination for Raman and Fluorescence Microscopic Imaging
Authors: Pallister David M. , Morris Michael D.
Published: May 2005

A comparison of microscopic Raman images acquired with an optical-fiber critical (Nelson) illumination system, an optical-fiber Koehler laser illumination system, and Koehler laser illumination without an optical fiber demonstrates performance differences between the three illumination methods. Best images are obtained with optical-fiber Koehler illumination.
New Design for Fourier Transform Infrared Vibrational Circular Dichroism Spectrometers
Authors: Chen Gang-Chi , Polavarapu Prasad L. , Weibel Stephen
Published: May 2005

Fourier transform infrared (FT-IR) spectrometers are commonly designed with small-area detectors and tight focusing mirrors. Vibrational circular dichroism (VCD) measurements made with such FT-IR instruments contain polarization artifacts, and VCD measurements on both enantiomers (or one enantiomer and racemic mixture) are required in order to reduce these artifacts. This restriction limits the VCD measurements to only those samples for which both enantiomers (or one enantiomer and racemic mixture) are available. Recently a modified design was reported in the literature where the mirrors between sample and detector were replaced with a BaF2 lens, and a larger-area detector was substituted for the smaller-area counterpart. These modifications successfully alleviated some of the artifact problems. This design, however, is not suitable for polarizing interferometers, where polarizations exiting the interferometer are to be preserved to a high degree of purity. In addition, it is not clear whether the throughput enhancement advantage realized with a larger-area detector completely offsets the disadvantage from increased noise with detector area. Furthermore, BaF2 lenses reduce the broad range routinely available on an FT-IR instrument. Here we report a new design that replaces all the mirrors at the exit port of the interferometer with two KBr lenses and retains the full spectral range (4000–400 cm−1) of mid-infrared FT-IR spectrometers. VCD measurements obtained with small- (1 × 1 mm) and large- (4 × 4 mm) area detectors are found to have similar signal quality.
Infrared Intensities of Liquids XIII: Accurate Optical Constants and Molar Absorption Coefficients between 6500 and 435 cm−1 of Toluene at 25°C, from Spectra Recorded in Several Laboratories
Authors: Bertie John E. , Jones R. Norman , Apelblat Yoram , Keefe C. Dale
Published: May 2005

This paper presents accurate infrared absorption intensities of liquid toluene at 25°C. The accuracy is estimated from the agreement between the intensities measured by different spectroscopists using the same instrument in the same laboratory and also by different spectroscopists in different laboratories using instruments made by different manufacturers. The average agreement between integrated intensities over specific wavenumber ranges is about ±1.8%. The spectra from the different laboratories have been averaged, unweighted, to give intensity spectra of toluene that are presented as the best available. The use of data from different instruments in different laboratories has included the influence of systematic instrumental errors, so that the precision of the intensity data presented should be a better approximation to its accuracy than would be the case from an extensive study by one person on one instrument. The results obtained agree with the only measurements that have been made against a primary standard, the estimated accuracy of which is about 6%. The results are presented as graphs and tables of the molar absorption coefficient spectrum and the real and imaginary refractive index spectra between 6500 and 435 cm−1. The peak heights and the areas under the bands in the imaginary refractive index (i.e., absorption index) and molar absorption coefficient spectra are reported. The absorption index, k(ν˜), and molar absorption coefficient, Em (ν˜), values are believed to be accurate to an average ±2.5% at the peaks of 39 strong, medium, and weak bands and ±1.9% at the peaks of 51 very weak bands below 4100 cm−1. Above 4100 cm−1, 11 very weak bands have an average accuracy of ±1.3%. The baseline k(ν˜) values are accurate to between ±3 and ±10%. The areas under bands or band groups in k(ν˜) and εm (ν˜) spectra are accurate to 2.4% on average, or 1.2% for strong, medium, and weak band groups between 3150 and 775 cm−1 with 0.002 < kmax < 0.112. The real refractive index, n(ν˜), values are believed to be accurate to 0.2%.
Interpretation of Infrared Transmittance Spectra of SiO2 Thin Films
Authors: Kučírková A. , Navrátil K.
Published: May 2005

We have investigated optical properties of thermally grown SiO2 layers within the thickness range 150 to 500 nm. The complex dielectric constant ε(ν˜) can be represented by six Lorentz-Gauss oscillators, which allow us to determine the optical constants of SiO2 films by fitting IR transmittance spectra. The spectra of ε(ν˜), unlike transmittance, are not affected by the multiple reflections at the film/air and film/substrate interfaces. Changes of optical constants for different thicknesses can be attributed to changes of physical properties of the film. We compare dielectric functions of samples oxidized at different conditions and discuss the influence of thickness and surface preparation of the substrate. We also compare our results with the dielectric function of bulk vitreous silica.
Atomic Emission Spectra of Xenon, Krypton, and Neon: Spectra from 200 to 900 nm by Sealed Inductively Coupled Plasma/Atomic Emission Spectroscopy
Authors: Jacksier Tracey , Barnes Ramon M.
Published: May 2005

The emission spectra of pure xenon, krypton, and neon are reported over the spectral range of 200 to 900 nm from an enclosed inductively coupled plasma discharge operated at atmospheric pressure and 350 W.
Nonlinear Modeling of Chromium Tanning Solution Using Artificial Neural Networks
Authors: Marjoniemi M.
Published: May 2005

In this article artificial neural networks (ANNs) are applied for multivariate calibration using spectroscopic data and for generation of quantitative estimates of the concentrations of a component (chromium) in solutions. Neural networks are capable of handling nonlinear relationships. Absorbance is nonlinearly dependent on concentration, especially in the case of wide concentration ranges and multicomponent solutions. In addition to the aforementioned reasons, nonlinearities are also caused by aging and by differences in pH and in the temperatures of the chromium-tanning solutions to be modeled. The sigmoid output function was used in the hidden layer to perform nonlinear fitting. The results are compared with the results obtained with principal component regression (PCR) and partial least-squares regression (PLS) methods.
Analysis of Some Errors in the Calculation of Orientation Functions for Polymers from Infrared Dichroism Measurements
Authors: Myers Craig W. , Cooper Stuart L.
Published: May 2005

Infrared dichroism is an important means of characterizing polymer orientation (via the orientation function) which relies upon spectra obtained with polarized infrared radiation. A quantitative analysis is presented here for three different types of errors in the analysis of orientation via this method. First, the importance of accounting for the conformer distribution within a monomer unit is considered with respect to an example polymer, poly(ethylene oxide). Second, the effects of imperfect polarizer operation (“leakage”) are considered in detail for high-precision polarization optics. It is found that polarizer leakage results in at most ∼4% error in the orientation function at reasonable values for measured absorbances and relatively high frequencies (∼3000 cm−1). Third, since it is common practice to make certain assumptions regarding transition moment angles in the course of calculating orientation functions, an assessment is made of the effects on the orientation function of erroneously choosing the angle value. The likelihood of adversely affecting the orientation function is found to be lowest near 0° and 90°, increasing steeply as one approaches the magic angle (54.7°) from either direction.
Multicomponent Assay for Blood Substrates in Human Plasma by Mid-Infrared Spectroscopy and its Evaluation for Clinical Analysis
Authors: Heise H. M. , Marbach R. , Koschinsky Th. , Gries F. A.
Published: May 2005

An analytical multicomponent method for the blood substrates total protein, glucose, total cholesterol, triglycerides, and urea in human EDTA plasma by FT-IR spectroscopy is described. The spectra were obtained with the use of the attenuated total reflection technique. Partial least-squares was applied for multivariate calibration over optimized spectral ranges. The mean-square prediction errors for the population of 126 plasma samples of different patients calculated by cross-validation are in the range of clinical acceptance. Within an error variance analysis, the contributions of the reference method and the spectrometric measurement to the average (root mean square) prediction error have been estimated for each substrate, giving evidence of the limitations of the spectrometric method. The problem of the biocompatibility of the plasma has been investigated, and the protein adsorption onto the ATR crystal can be reduced to a constant and tolerable level by appropriate cleaning and rinsing. The potential for further improvement is discussed.
Principal Component Regression for Mixture Resolution in Control Analysis by UV-Visible Spectrophotometry
Authors: Blanco M. , Coello J. , Iturriaga H. , Maspoch S. , Redon M.
Published: May 2005

The potential of principal component regression (PCR) for mixture resolution by UV-visible spectrophotometry was assessed. For this purpose, a set of binary mixtures with Gaussian bands was simulated, and the influence of spectral overlap on the precision of quantification was studied. Likewise, the results obtained in the resolution of a mixture of components with extensively overlapped spectra were investigated in terms of spectral noise and the criterion used to select the optimal number of principal components. The model was validated by cross-validation, and the number of significant principal components was determined on the basis of four different criteria. Three types of noise were considered: intrinsic instrumental noise, which was modeled from experimental data provided by an HP 8452A diode array spectrophotometer; constant baseline shifts; and baseline drift. Introducing artificial baseline alterations in some samples of the calibration matrix was found to increase the reliability of the proposed method in routine analysis. The method was applied to the analysis of mixtures of Ti, AI, and Fe by resolving the spectra of their 8-hydroxyquinoline complexes previously extracted into chloroform.
Spectroscopy of p-Methoxybenzoic Acid: An AM1 and ab Initio Study
Authors: Palafox M. Alcolea , Gil M. , Núñez J. L.
Published: May 2005

The vibrational spectra of p-methoxybenzoic acid (anisic acid) were calculated and compared with the experimental spectra. All measured bands in the IR and Raman spectra were interpreted in terms of calculated vibrations from the AM1 and 4–21G* methods, and their frequencies were correlated. Several scale coefficients were used to improve the theoretical spectra. The optimum geometric parameters were also computed with the AM1 semiempirical method and with the 4–21G* ab initio procedure.
Development of a Multiwavelength Thermal Lens Spectrophotometer Based on an Acousto-Optic Tunable Filter as a Polychromator
Authors: Tran Chieu D. , Furlan Ricardo J. , Lu Jian
Published: May 2005

Instrumentation development of a novel multiwavelength thermal lens spectrophotometer which has the capability of achieving truly multiwavelength excitation is described. The spectrophotometer is based on a new concept by which the sample is excited by multiwavelength excitation beams simultaneously, not sequentially as in previously reported multiwavelength thermal lens apparatus. This was accomplished by use of the acousto-optic tunable filter (AOTF) as a polychromator. Specifically, four different rf signals were simultaneously applied to the filter to enable it to diffract incident multiline laser light into a beam which contained four different wavelengths. This multiwavelength beam was then used to excite the sample, and the corresponding thermal lens signal was measured by a He-Ne probe laser. Compared with other multiwavelength thermal lens instruments, this all-solid-state thermal lens spectrophotometer has advantages that include its ability to simultaneously analyze multicomponent samples in microsecond times scale, without the need for any prior sample preparation. With this apparatus and with the use of a 12-mW multiwavelength excitation beam, the limit of detection for four-component (lanthanide ions) samples is estimated to be 10−6 cm−1, which is similar to the detection limit obtained for one-component samples with the use of a single-wavelength system.
Matrix-Isolation Infrared Spectroscopy of Organic Phosphates
Authors: George Lisa , Sankaran K. , Viswanathan K. S. , Mathews C. K.
Published: May 2005

Matrix-isolation infrared spectra of trimethyl phosphate (TMP), triethyl phosphate (TEP), and tri- n-butyl phosphate (TBP), in argon and nitrogen matrices, are reported for the first time. The peak widths of the sharpest features in our matrix-isolated spectra are typically 2 cm−1, compared with peak widths of 40 cm−1 seen in liquids for these compounds. Comparison with the vapor-phase spectrum of TMP reported earlier indicates that TMP is trapped in two different conformations in these matrices. Similar spectra were also obtained for TEP. Our matrix-isolated spectra indicate that the intramolecular hydrogen bonding (which is believed to be responsible for the lowering of the P=O frequency in the C3, conformer relative to the C3 conformer in these compounds) is stronger in TEP than in TMP. In the case of TBP, the peak widths were larger (8–10 cm−1) than those obtained for TMP and TEP. This observation is probably due to a distribution of conformers that may be trapped in the matrix, as a result of the increased alkyl chain length in TBP.
Generalized Gans—Gill Method for Smoothing and Differentiation of Composite Profiles in Practice
Authors: Rzhevskii Alexander M. , Mardilovich Peter P.
Published: May 2005

A comparison has been made of the effectiveness of smoothing and differentiating Savitzky-Golay filters in terms of the minimization of total error criterion. The advantages of multipassing filters based on quartic/quintic (for smoothing) and cubic/quartic (for differentiation) polynomials have been proved. A generalized method is proposed for the choice of polynomial length, for both smoothing and differentiating filters, in the fine-structure analysis of composite spectra. This method follows the suggestion of P. Gans and G. B. Gill to locate an inflection point on the curve of variance of residuals between observed and smoothed spectra with respect to the polynomial length of the filter applied. A block diagram of the computer program is shown for optimum choice of polynomial lengths, and an example of its application in the analysis of the fine structure of an experimental multiplet band system is demonstrated.
Infrared Intensities of Liquids XIV: Accurate Optical Constants and Molar Absorption Coefficients between 4800 and 450 cm−1 of Chlorobenzene at 25°C from Spectra Recorded in Several Laboratories
Authors: Bertie John E. , Jones R. Norman , Apelblat Yoram
Published: May 2005

Accurate infrared absorption intensities of liquid chlorobenzene at 25°C are presented. Their accuracy was estimated from the agreement between the intensities measured by different spectroscopists using different instruments in different laboratories and by different spectroscopists using the same instrument in the same laboratory. The spectra from different spectroscopists have been averaged, unweighted, to give intensity spectra of chlorobenzene that are presented as the best available. The results are presented as graphs and tables of the molar absorption coefficient, Em (ν˜), and the real and imaginary refractive indices, n(ν˜) and k(ν˜), between 4800 and 450 cm−1. The peak heights and the areas under the bands in the absorption index (imaginary refractive index) spectrum are reported, as are areas under the molar absorption coefficient spectrum. Absorption index, k(ν˜), and molar absorption coefficient, Em (ν˜), values are believed accurate to an average ±2.4% at the peaks of bands with kmax > 0.002 and ±3.3% at the peaks of bands with kmax < 0.002. In the baseline k(ν˜) is accurate to ∼ ±5% above 3000 cm−1 and ∼ ±2.5% below 3000 cm−1. The areas under bands in k(ν˜) and Em (ν˜) spectra for which kmax > 0.002 are accurate to ±1.3% on average. The real refractive index, n(ν˜), values are believed to be accurate to ±0.2%.
Elemental Speciation Measurements with Electrospray Mass Spectrometry: An Assessment
Authors: Agnes George R. , Stewart Ian I. , Horlick Gary
Published: May 2005

Electrospray mass spectrometry (ES-MS) is shown to be suited for the direct determination of ionic species in solution. Examples used in this investigation of ES-MS for elemental speciation determinations included several inorganic ionic species of chlorine, iodine, sulfur, and iron. These species were differentiated on the basis of differences in the molecular form and/or the oxidation state of the analyte ion. The inorganic complexes of silver-cyanide and iron-fluoride were also measured in this assessment. Finally it is shown that ES-MS is applicable to the determination of organometallic compounds. While ES-MS is not an ideal speciation technique, there is considerable evidence to indicate that ES-MS can become an invaluable tool with which species distributions in a wide range of sample types may be probed.
Elemental Mass Spectroscopy of Remote Surfaces from Laser-Induced Plasmas
Authors: De Young R. J. , Situ W.
Published: May 2005

The elemental mass analysis of laser-produced ions from Al, Cu, Ge, Ag, and a lunar simulant target when irradiated by a 400-mJ, 8-ns, Nd: YAG laser at 1 × 109 W/cm2 is reported. Ions traveled down a 11.1-m evacuated tube to an ion-trap 1-m time-of-flight (TOF) mass spectrometer where an elemental mass spectrum was recorded. The amount of target material removed per laser pulse and the ionization fraction were also measured. The ion spatial distribution was measured at 11.1-m distance and found to be near a fourth-power cosine distribution. These results indicate the ability to mass analyze a surface over a distance of many kilometers for lunar and asteroid surface elemental mass analysis by a remote satellite or lunar rover.
Simultaneous Measurement of Ion Ratios by Inductively Coupled Plasma-Mass Spectrometry with a Twin-Quadrupole Instrument
Authors: Warren Arnold R. , Allen Lloyd A. , Pang Ho-Ming , Houk R. S. , Janghorbani Morteza
Published: May 2005

The ion beam from the inductively coupled plasma (ICP) is split into two parts by a device comprised of two electrostatic analyzers in a back-to-back arrangement. Each ion beam is then monitored by a separate quadrupole mass analyzer and electron multiplier. Thus, ion ratios can be measured simultaneously without scanning. Isotope ratios for copper are measured with a precision of 0.14% relative standard deviation (RSD). Internal standard ratios for Co+/La+ are measured with a precision of 1% RSD. Ion signals in the two channels are highly correlated, and the magnitude of flicker noise is reduced in the resulting ratios. Bias in the measured isotope ratios is substantial but can be corrected by calibration.
Use of Molecular Microspectroscopy to Characterize Pigment-Loaded Polypropylene Single Fibers
Authors: Bouffard S. P. , Sommer A. J. , Katon J. E. , Godber S.
Published: May 2005

Molecular microspectroscopy was used to characterize different pigments loaded into polypropylene fibers. Single-fiber analysis by infrared, visible, and Raman microspectroscopies proved to be quite complementary for identification and quantitation of these materials. Infrared microspectroscopy was effective not only for identification of pigments loaded into the fibers, but also for quantitation of concentration levels at 1% (w/w) and greater. Visible microspectroscopy was effective for quantitation of pigment levels between the range of 0.1 and 1% (w/w). However, it may not be successful for positive identification of most pigments. Raman microspectroscopy was an effective technique for pigment identification and quantitation over all examined concentration levels provided that the sample showed no signs of fluorescence or heating effects. Quantitation for all techniques gave correlation coefficient values of 0.99+ and relative standard deviations typically ranging from 5 to 20%.
Determination of Nicotine by Surface-Enhanced Raman Scattering (SERS)
Authors: Barber Tye E. , List Matthew S. , Haas John W. , Wachter Eric A.
Published: May 2005

The analytical application of surface-enhanced Raman spectroscopy (SERS) to the determination of nicotine is demonstrated. A simple spectroelectrochemical method using a copper or silver electrode as the SERS substrate has been developed, consisting of three steps: polishing a working electrode to a mirror finish; roughening the electrode in an electrolyte solution; and, finally, depositing the nicotine analyte onto the roughened electrode after immersion in a sample solution. During the reduction cycle, a large enhancement in nicotine Raman scattering is observed at the electrode surface. The intensity of the SERS signal on a silver electrode is linear with concentration from 10 to 900 ppb, with an estimated detection limit of 7 ppb. The total analysis time per sample is approximately five minutes. This procedure has been used to analyze the extract from a cigarette side-stream smoke sample (environmental tobacco smoke); the SERS results agree well with those of conventional gas chromatographic analysis.
Use of Differential Thermal Lensing to Study Two-Photon Absorption in Solutions
Authors: Kozich V. P. , Marcano A. , Hernández F. E. , Castillo J.
Published: May 2005

The thermal lensing technique is applied to study two-photon absorption of dye molecules in organic solutions. With the use of a differential two-cell thermal lens spectrometer, the contribution due to one-photon absorption by solvent molecules is suppressed. Observed power dependence of the thermal lensing signal confirms the two-photon character of the absorption process.
Application of Laser Ablation-ICPMS to the Spatially Resolved Micro-Analysis of Biological Tissue
Authors: Wang S. , Brown R. , Gray D. J.
Published: May 2005

Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) has been applied as a method to determine elemental distribution in biological tissue specimens, providing spatial resolution down to 30 μm with the use of an infrared laser beam. Instrument operating parameters such as the laser energy and “dry plasma” tuning have been optimized to provide the high sensitivity and stability required for this type of analysis. In this work, “natural” internal standards (e.g., calcium and magnesium) have been investigated in an effort to establish and minimize the influence of signal variation associated with the instrumentation and the density of the samples themselves. Specimens studied include fish scales (for “elemental tagging”), rat kidney cross sections, and pig femur (to examine variation in the chemistry of the blood/bone interface).
Stability and Sensitivity Enhancement Using ETV-ICPMS
Authors: Gray D. J. , Wang S. , Brown R.
Published: May 2005

The interfacing of an electrothermal vaporization (ETV) unit to an inductively coupled plasma mass spectrometer (ICPMS) produces a powerful system for ultra-low-level compositional analysis of micro-volume samples, as well as decreasing some of the molecular interferences inherent in a conventional-nebulization ICPMS. Some problems still remain with this technique in respect to signal variation, sample heating profiles, and instrument tuning parameters. Advances are presented concerning the instrumental conditions necessary for lowering signal variation. These include optimization of “dry-plasma” tuning of the spectrometer lens stack, furnace cooling/heating, and tube mounting. Novel ways of enhancing sensitivity by multiple deposition, preconcentration, and chemical modification have been investigated with particular emphasis on uranium and radium determination.
Secondary Structure Estimation of Proteins Using the Amide III Region of Fourier Transform Infrared Spectroscopy: Application to Analyze Calcium-Binding-Induced Structural Changes in Calsequestrin
Authors: Fu Fen-Ni , Deoliveira Daniel B. , Trumble William R. , Sarkar Hemanta K. , Singh Bal Ram
Published: May 2005

A Fourier transform infrared spectroscopic method has been developed to analyze protein secondary structure by employing the amide III spectral region (1350–1200 cm−1)· Benefits of using the amide III region have been shown to be substantial. The interference from the water vibration (∼1640 cm−1) in the amide I region can be avoided when one is using the amide III band; furthermore, the amide III region also presents a more characterized spectral feature which provides easily resolved and better defined bands for quantitative analysis. Estimates of secondary structure are accomplished with the use of Fourier self-deconvolution, second derivatization, and curve-fitting on original protein spectra. The secondary structure frequency windows (α-helix, 1328–1289 cm−1; unordered, 1288–1256 cm−1; and β-sheets, 1255–1224 cm−1) have been obtained, and estimates of secondary structural contents are consistent with X-ray crystallography data for model proteins and parallel results obtained with the use of the amide I region. We have further applied the analysis to the structural change of calsequestrin upon Ca2+ binding. Treatment of calsequestrin with 1 mM Ca2+ results in the formation of crystalline aggregates accompanied by a 10% increase in α-helical structure, which is consistent with previous results obtained by Raman spectroscopy. Thus the amide III region of protein IR spectra appears to be a valuable tool in estimating individual protein secondary structural contents.
Experimental Determination of Line Strengths for Selected Carbon Monoxide and Carbon Dioxide Absorption Lines at Temperatures between 295 and 1250 K
Authors: Medvecz Patrick J. , Nichols Kenneth M.
Published: May 2005

Fourier transform infrared absorption spectroscopy has been used for the determination of the line strengths of 41 CO and CO2 absorption lines at temperatures between 295 and 1250 K. The CO vibrational-rotational lines were from the P branch of the fundamental absorption band (2150–1950 cm−1) while the CO2 vibrational-rotational lines were from the far wing of the R branch of the v3 fundamental band (2395–2380 cm−1). The intensities of the lines were measured from absorption spectra recorded in a high-temperature gas cell containing known concentrations of CO/CO2/N2 gas mixtures at atmospheric pressure. Absorption spectra were recorded through the cell with the use of a moderate-resolution Fourier transform infrared spectrometer. The absorption spectra were mathematically corrected for distortions resulting from the finite resolution of the spectrometer and for peak overlap. Line strength measurements were made from the corrected peaks by using the Bouguer-Lambert law and assuming a Lorenztian line profile. The experimentally obtained line strengths were evaluated (1) by statistical calculations, (2) by consideration of the validity of the Bouguer-Lambert assumption for these data, (3) by comparison with existing room-temperature and high-temperature data, and (4) by comparison with theoretical calculations. For CO, the statistical analysis suggests that the reported values have an uncertainty of ±10–12%, which is similar to the observed discrepancies with other reported values at room temperature. At high temperatures, the difference between these data and previously reported data and theoretical predictions is less than 10%. For CO2, the statistical uncertainty associated with the line strength calculations is less than 5%, which is also the approximate level of agreement with existing room-temperature data. For lines with m indicies of 65–89, at high temperatures, the values reported in this work agree within 5 to 10% of theoretical calculations.