bluuebunny/crossref_metadata_2025 huggingface dataset:
IR and EPR Study of the Na Ion-Implanted SiO2/Si System
Authors: Nagai N. , Yamaguchi Y. , Saito R. , Hayashi S. , Kudo M.
Published: October 2003

Na ion-implanted silicon dioxide films are studied by infrared absorption (IR) and electron paramagnetic resonance (EPR) techniques. The samples were treated with sequential HF etchings, and subsequent IR and EPR measurements were made. The spectra are analyzed by principal component analysis (PCA), two-dimensional correlation analysis (2DCA), and effective medium analysis (EMA). The PCA and 2DCA show that a 1000 cm1 band appears in IR spectra in the silicon dioxide films after ion-implantation. And the 2DCA between IR and EPR spectra show that the 1000 cm−1 band is strongly correlated with the E' and/or peroxy radical in depth distribution; therefore, the band can be assigned to radical related Si-O stretching, such as O≡Si· and/or Si-O-O· configurations. The distribution of these configurations in the as-implanted film is also correlated to that of the voids. However, after annealing, the 1000 cm−1 band drastically diminished but the void volume fraction was unchanged and remained in the films. Annealing acted to reconstruct the dangling bonds to Si-O bonding and rearranged the void distribution in the film, but the volume fraction did not change drastically. The results of EMA support the depth distribution of the defects calculated from 2DCA.
Quantitative Investigation of Probabilistic Spectral Processing Methods Using Simulated NMR Data
Authors: Ebbels Timothy M. D. , Lindon John C. , Nicholson Jeremy K.
Published: October 2003

We have investigated the performance of two approaches for Bayesian processing of NMR data: Memsys5—a maximum entropy algorithm—and Massive Inference (MassInf). Spectra were simulated at two different noise levels to assess the algorithms' reconstruction of signals with close doublets, linewidth variation, high dynamic range, variable line shapes, and nonuniform baselines. The resulting reconstructions were analyzed in terms of efficacy of deconvolution, reconstruction of mock data, and accuracy of line positions and integrals. In the majority of the tests performed, the residuals between the simulated input and reconstruction were below the input noise. MassInf showed greater robustness than Memsys5 at rejecting noise peaks in regions where there was genuinely no signal, thus producing more visually impressive noise-suppressed spectra. Doublets with splittings down to 0.7 of the line width were resolved, even at relatively low signal to root mean square (rms) noise ratios (∼10), and large relative intensities (e.g., 10:1). Where multiplets were correctly resolved, both algorithms were accurate in their inferred line positions with errors seldom above 0.2 linewidths. At high signal to rms noise ratios (e.g., 100:1), line integrals were comparable with those obtained by directly integrating the input spectrum. However, the relative performance of the Bayesian algorithms improved as the noise level was increased. Finally, it was found that any curvature of the baseline significantly decreased both of the algorithms' noise suppression abilities as well as increasing their processing time requirements.
Spectrochemical Analysis of Metal Elements Electrodeposited from Water Samples by Laser-Induced Shock Wave Plasma Spectroscopy
Authors: Pardede Marincan , Kurniawan Hendrik , Tjia May On , Ikezawa Kazuhiro , Maruyama Tadashi , Kagawa Kiichiro
Published: October 2003

We have succeeded in applying laser-induced shockwave plasma spectroscopy (LISPS) to the problem of the detection and analysis of metal elements deposited from water samples by means of electrolysis. It is shown that metal elements are generally deposited in the form of a thin film on the electrode surface, while the electrode also conveniently serves as a subtarget for the relatively soft metal film, thereby providing the necessary conditions for the generation of shockwave plasma, which is favorable for highly sensitive spectrochemical analysis. It is shown that the detection sensitivity of this method reaches its highest value at low surrounding air pressure of around 1 torr. The lowest detection limit attained for various metal elements investigated in this experiment varies from around ten to a few tens of ppb. This limit can be readily improved upon by incorporating an optical multichannel analyzer into the detection system. We have thus presented a promising method for the realization of a compact mobile monitoring system for the accurate control of water and soil quality.
New Method of Rapid Luminescence Lifetime Determination Using Square-Wave Excitation
Authors: Chan Sing Po , Fuller Z. J. , Demas J. N. , Ding Fei , DeGraff B. A.
Published: October 2003

A new rapid lifetime determination method (RLD) that uses a rectangular excitation is presented. The information from the exciting, as well as the emitting, portion is used to extract decay parameters for a single exponential decay. The lifetime is computed from the ratio of the integrals of the emission during the excitation period and an equal time interval during the decay (Δ t). The new square-wave RLD method (SWRLD) shows speed similar to the standard RLD method but without the necessity of matching Δ t to the lifetime for precise results. Monte Carlo simulations are used to predict the capabilities of the SWRLD, and the theory is tested with a luminescent terbium complex. The method is particularly applicable to rapid lifetime analysis for high-performance liquid chromatography (HPLC) and for fluorescence microscopy. It lends itself to use with inexpensive square-wave modulated light-emitting diodes (LEDs).
Temperature Measurement of Liquids by Differential Absorption of Two Diode Lasers: Application of Contactless Optical Detection in Isotachophoresis
Authors: Krivtzun V. , Graß B. , Hergenröder R. , Bolshov M. , Niemax K. , Zybin A.
Published: October 2003

A modification of the wavelength modulation diode laser (DL) absorption technique for detection of broad-band molecular absorption lines is proposed. The method based on the detection of differential absorption of two narrow-band DLs at specially selected wavelengths within the molecular absorption band enables the measurement of the temperature changes of a sample. These cause shifts and deformations of the absorption band. The potentials and limitations of the proposed technique are shown using contactless detection of the temperature of isotachophoretic zones on a polymer microchip as an example. A variation in the temperature of an ITP-zone provides a difference in the absorption of two diode laser beams with their wavelengths tuned to the opposite slopes of a broad molecular absorption band of water. The 970 nm absorption band of water was used in this work. The minimum detectable temperature increment of about 0.4 °C is realized in a capillary filled with a typical ITP buffer. The drifts and fluctuations of the base line increase 10–20 fold if a buffer front propagates along the capillary. The propagation of the temperature front was numerically simulated using the tabulated values for heat capacity and electric and thermal conductivity of ITP-buffers and plastic material. The simulated values of temperature variations caused by on/off switching of the capillary current fit very well the experimentally measured ones. It is expected that the sensitivity and temporal resolution of the technique can be improved by modification of the microchip and by use of the strongest absorption band of water at 1.44 μm.
Enhanced Chemical Classification of Raman Images Using Multiresolution Wavelet Transformation
Authors: Cai T. Tony , Zhang Dongmao , Ben–Amotz Dor
Published: October 2003

Multiresolution wavelet transformation (MWT) and block thresholding is used to effectively suppress both background and noise interference while minimally distorting Raman spectral features. The performance of MWT as a spectral pre-processing algorithm is demonstrated using both synthetic spectra and experimental hyper-spectral Raman images with large background and noise components. The results are quantified by comparing correlation coefficients of synthetic spectra with either the same or different backgrounds. The improved chemical imaging performance obtained using MWT is demonstrated by comparing principal component analysis (PCA) channel images and spectral angle mapping (SAM) classified images before and after MWT pre-processing.
Rapid Quantitative Determination of Ciprofloxacin in Pharmaceuticals by Use of Solid-State FT-Raman Spectroscopy
Authors: Skoulika Stavroula G. , Georgiou Constantinos A.
Published: October 2003

FT-Raman spectroscopy based on band intensity or band area measurements was used for the quantitative determination of ciprofloxacin in pharmaceutical solid dosage forms. Univariate calibration was used for quantitative analysis. Bands observed at 1708, 1624, 1548, 1493, 1273, 1253, 1238, 1024, 805, 787, 752, 718, 665, and 638 cm−1 were used. Calibration curves were linear in the concentration range of 3–100% w/w with correlation coefficients of 0.99–0.996 and 0.991–0.9993 for band intensity and band area measurements, respectively. Precision ranged from 0–11 and 0.4–12% relative standard deviation (RSD) (n = 3) for band intensity and band area measurements, respectively, and results were in good agreement with the results obtained by the current United States Pharmacopoeia (USP 24) and National Formulary (NF 19) method. Multivariate calibration was also used for quantitative analysis. Multiple linear regression using the intensities of the 1545 and 1272 cm−1 bands gave results in accordance with those obtained by the current United States Pharmacopoeia (USP 24) and National Formulary (NF 19) method. As measurement takes just 30 s using the analytical readout from a single band, the proposed method can be used to replace tedious and time-consuming methods.
Fiber-Optic System for 77 K Phosphorescence Lifetime Measurements of Polycylic Aromatic Compounds in Shpol'skii Matrices
Authors: Martin Travis L. , Campiglia Andres D.
Published: October 2003

A fiber-optic system is reported for rapid, accurate, and precise 77 K measurements of relatively long phosphorescence lifetimes ( τp = 200 ms). The instrument employs stimulated Raman scattering in connection with a pulsed laser source for sample excitation. Phosphorescence decay waveforms are collected at maximum emission wavelengths with a single channel detection system and the aid of a LabVIEW based in-house program acting as a data acquisition instrument, data storage device, and data interpreter. By means of program looping, up to 20 decays are recorded from a frozen sample in less than 5 min. A cryogenic fiber-optic probe directly frozen into the sample matrix removes the random errors associated with the classic sample freezing procedure and provides excellent reproducibility of measurements. The relative standard deviations of τp measured from several polycyclic aromatic compounds varied between 0 and 4.30%. The simplicity of the experimental procedure, the rather large τ p differences observed from compounds within the same pollutant class, and the analytical figures of merit provide a solid foundation for pursuing low-temperature phosphorescence, time-resolved low-temperature phosphorescence, and low-temperature multidimensional luminescence analysis.
Raman Microscopy Applied to Rechargeable Lithium-Ion Cells-Steps towards in situ Raman Imaging with Increased Optical Efficiency
Authors: Panitz Jan-Christoph , Novák Petr , Haas Otto
Published: October 2003

Important improvements have been made in an in situ Raman cell developed to monitor the processes of lithium intercalation into the carbon and metal oxide materials used in lithium-ion cells. By reducing the electrolyte gap in the cell and changing the optical arrangement, the signal-to-noise ratio could be improved by a factor of about 20. The optimized cell gives optical access to either electrode (anode or cathode) employed in commercial lithium-ion batteries. The optical efficiency is such that Raman maps of electrode surface segments can be recorded under in situ conditions with an acquisition time of about 30 s per spectrum.
On-Line Analysis Using Raman Spectroscopy for Process Control during the Manufacture of Titanium Dioxide
Authors: Clegg Ian M. , Everall Neil J. , King Bert , Melvin Hugh , Norton Colin
Published: October 2003

A system based on Raman spectroscopy has been developed for closed-loop control during the manufacture of titanium dioxide (TiO2). Spectra were obtained in the 50 to 700 cm−1 range using excitation at ∼532 nm and a fixed transmission-grating spectrograph coupled to a CCD detector. Quantitation has been achieved by linear interpolation based on the integrated intensity of phonons at 142 and 610 cm−1 due to anatase and rutile phases, respectively. The spectroscopic instrumentation has been integrated with a powder sampling system and installed on four full-scale manufacturing plants. Fiber coupling (up to 100 m) has been employed, and each spectrometer system is multiplexed to three sampling heads. Spectra are corrected for changes in sample temperature, and the systems are designed to be fully automatic and require no user intervention.
Near-Infrared Raman Spectra of Azo Dye Produced by a Nitrogen-Dioxide-Gas-Selective Coloration Reaction in a Porous Glass Chip
Authors: Ueno Yuko , Ajito Katsuhiro , Maruo Yasuko Yamada , Niwa Osamu , Torimitsu Keiichi , Ichino Toshihiro
Published: October 2003

We directly observed azo dye in a porous glass chip by near-infrared (NIR) Raman spectroscopy. We produced the dye by a modified Saltzman reaction by using sulfanilamide (SFA) and N, N-dimethyl-1-naphthylamine (DMNA) as reagents and used it for the selective sensing of atmospheric nitrogen dioxide gas (NO2). The use of NIR laser excitation is particularly advantageous for the direct measurement of azo dye because it avoids the problem of interference from fluorescence. We obtained the 1597 cm−1 band assigned to the phenyl group stretching mode and the 1415 cm−1 band assigned to the azo group stretching mode. The Raman intensity and visible absorption intensity of the peaks of the azo dye in a porous glass chip increased as we increased the exposure time to NO2. This allowed us to monitor the NO2-sensing reaction in a porous glass chip using NIR Raman spectroscopy. Furthermore, we determined the depth profiles of the azo dye concentration in the porous glass chip by confocal NIR Raman spectroscopy and found that they were different in the early and later NO2-exposure stages. This result indicates that the consumption of the NO2-sensing reagents that accompany azo dye production occurs preferentially at the surface to the deeper regions of the porous glass chip.
FT-IR and Raman Spectroscopic Characterization of the Major Oilfield Sulfate Scale Forming Minerals
Authors: Wylde Jonathan J. , Allen Geoffrey C. , Collins Ian R.
Published: October 2003

Sulfate minerals commonly form in the oilfield environment due to secondary recovery operations. Two essential tools for identification of these minerals are Fourier transform infrared (FT-IR) and Raman spectroscopies. In this paper, a comprehensive database of the FT-IR and Raman spectra of these minerals has been composed. The symmetry of the sulfate tetrahedra in the various sulfate molecules has been assigned from observation of the vibrational degeneracy. Force constant calculations show that cation mass and polarizability are the dominant influences upon sulfate symmetry. Studies of the vibrational peak positions have demonstrated a direct relationship between properties of the associated sulfate cation and the positions of both the infrared and Raman v1 and v3 vibrations. The major influences were found to be cation electronegativity, cation mass, and cation ionic radius. These observations were confirmed from force constant calculations. It has been concluded that both FT-IR and Raman spectroscopies are valid techniques for identification of oilfield scale minerals. Raman spectroscopy is particularly useful as it can be applied to aqueous systems and the in situ measurements of scale formation.
Analysis of Noise for Rapid-Scan and Step-Scan Methods of FT-IR Difference Spectroscopy
Authors: Andrews Steven S. , Boxer Steven G.
Published: October 2003

Quantitative vibrational difference spectroscopy of small signals requires techniques that minimize spectral noise. As simple modulation of the sample followed by signal demodulation is often problematic due to interference with the FT-IR Fourier frequencies, alternate methods are necessary. Using vibrational Stark spectroscopy as an example, the DC method involves alternating complete interferogram scans in which a DC electric field is turned on with scans in which the field is turned off. A new synchronized AC method is similar, but the field is switched at every interferogram sampling point. In the step-scan method, a sinusoidal electric field is used and the detector signal is demodulated with a lock-in amplifier at each mirror position. Noise levels for these methods are derived analytically in this paper and compared with experimental values, yielding results that are broadly applicable to FT-IR difference spectroscopy. It was found that the DC method performed the best, although specific experimental factors may favor other methods.
Contribution of ATR/FT-IR Spectroscopy for Studying the in vivo Behavior of Octylmethoxycinnamate (OMC) after Topical Application
Authors: Laugel C. , Nascimento C. Do , Ferrier D. , Marty J. P. , Baillet A.
Published: October 2003

This work aims to evaluate the contribution of ATR/FT-IR spectroscopy as an in vivo analytical tool for following the percutaneous penetration of octylmethoxycinnamate and its possible modifications after light exposure. OMC cis and trans isomers in solution were assessed by liquid chromatographic and ATR/FT-IR validated methods. An in vivo quantification model was built from ATR/FT-IR measurements on the naked skin. This model reveals, suitable for evaluating, the formation of cis-OMC from trans-OMC after sun irradiation. Moreover, the results obtained from trans-OMC testify to the suitability of the method for studying in vivo the degradation and the percutaneous penetration of this molecule. After topical application, the disappearance of OMC over the surface of the skin was studied. Simultaneously, the kinetics of percutaneous penetration were established using the stripping method. Both results are in accordance with previous published works.
High-Temperature Properties of a Low Dielectric Constant Organic Spin-on Glass for Multilevel Interconnects
Authors: Wang C. Y. , Shen Z. X. , Zheng J. Z.
Published: October 2003

In this paper, we report on the thermal properties of a low-dielectric-constant organic spin-on glass, methyl silsesquioxane (MSQ), an important material for semiconductor device fabrication. The compositional and structural changes of this MSQ material, when heated in air and N 2, were investigated in detail with Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric analysis (TGA). MSQ transforms to thermal oxide SiO 2 above 500 °C when heated in air, and it forms oxygen-deficient SiO 2 above 700 °C in N 2. Our results suggest that a cure temperature higher than the current 425 °C is preferred to form films with better cross-linked network structure.
Time-Resolved Reflectance Spectroscopy Applied to the Nondestructive Monitoring of the Internal Optical Properties in Apples
Authors: Cubeddu Rinaldo , D'Andrea Cosimo , Pifferi Antonio , Taroni Paola , Torricelli Alessandro , Valentini Gianluca , Ruiz-Altisent Margarita , Valero Constantino , Ortiz Coral , Dover Colin , Johnson David
Published: October 2003

Time-resolved reflectance has been used for the nondestructive measurement of optical properties in apples. The technique is based on the detection of the temporal dispersion of a short laser pulse injected into the probed medium. The time distribution of re-emitted photons interpreted with a solution of the diffusion equation yields the mean values of the absorption and reduced scattering coefficients of the medium. The proposed technique proved useful for the measurement of the absorption and scattering spectra of different varieties of apples, revealing the spectral shape of chlorophyll. No major variations were observed in the experimental data when the fruit was peeled, showing that the optical properties measured were those of the pulp. With this technique the change in chlorophyll absorption during storage and ripening could be followed. Finally, a compact prototype working at few selected wavelengths was designed and constructed, demonstrating potentialities of the technique for industrial applications.
Quantitative Electron Paramagnetic Resonance: The Importance of Matching the Q-Factor of Standards and Samples
Authors: Blakley Richard L. , Henry Dwight D. , Morgan Walter T. , Clapp William L. , Smith Carr J. , Barr David
Published: October 2003

Electron paramagnetic resonance (EPR) quantification of free radicals from different samples facilitates comparison of free radical concentrations. Stable free radicals, such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), in a suitable solvent (e.g., benzene) can be used as a quantification standard. Free radicals found in samples can be shorter lived than radicals in prepared standards and require stabilizing spin-trapping agents such as N-tert-butyl-α-phenylnitrone (PBN) in an appropriate solvent (e.g., benzene). Analysis in our laboratory showed that free radicals from spin-trapped samples quantified against a standard of TEMPO in benzene displayed large differences among identical samples measured on either a Micro-Now 8300, Micro-Now 8400, or Bruker EMX EPR instrument. The Bruker instrument reported that the typical TEMPO in benzene standard had a Q-factor of ∼4400 while the Q-factor of our PBN-containing samples was ∼2500. (The Q-factor is inversely proportional to the amount of dissipated microwave energy in an EPR cavity.) By placing the TEMPO standard in a PBN/benzene solvent matrix we were able to match the Q-factor of our standards and samples, resulting in each of the three EPR instruments giving the same quantified free radical yields for the samples. This result points out the importance of matching the Q-factor between samples and standards for any quantitative EPR measurement.
Spectroscopic Measurements of Temperature with Uranyl Compounds
Authors: Barabas L. , Gorguinpour C. , Leung A. F. , McCoy J.
Published: October 2003

A new class of fluorescent probes for measuring temperature is described. The intensities of the strong fluorescence bands of uranyl acetate, uranyl nitrate hexahydrate, and uranyl orthophosphate were recorded when the uranyl compound was illuminated with an argon-ion laser operating at 488 nm. The intensity ratio of two fluorescence bands of uranyl acetate at room temperature were determined for five freshly prepared samples and shown to be independent of the intensity of the laser excitation and optical alignment. The intensities of the fluorescence bands lying between 500 and 570 nm were measured at various temperatures ranging from 77 to 295 K. The ratio of the intensities of two fluorescence bands was calculated and shown to vary linearly with temperature. A linear fit provided the slope. The largest positive slope of all the intensity ratios associated with uranyl acetate was 6.02 × 10−3 K−1, that associated with uranyl orthophosphate was 4.68 × 10−3 K−1, and that associated with uranyl nitrate hexahydrate was 1.81 × 10−3 K−1. The potential of uranyl compounds as a new group of temperature probes is discussed.
Interactions of Phosphors in Glucose Glasses for Solid-Matrix Phosphorescence
Authors: Mendonsa Shaun D. , Hurtubise Robert J.
Published: October 2003

Quenching of the room-temperature solid-matrix phosphorescence (SMP), near-infrared spectrometry, differential scanning calorimetry, and a polarity probe were used to study interactions of heterocyclic aromatic amines in glucose glasses prepared using crystalline glucose and a glucose melt. A near-infrared spectrometry method was developed to determine the wt % moisture in the glucose glasses. The wt % moisture of the glucose glasses was then related to phosphorescence intensities and lifetime ratios of the heterocyclic aromatic amines. A modified form of the Stern–Volmer equation was used to describe the changes in phosphorescence intensity and lifetime ratios. In other experiments, the glass transition temperatures of the glucose glasses were determined using differential scanning calorimetry. The glass transition temperatures were then correlated to the SMP of the heterocyclic aromatic amines in the glucose glasses. Lastly, the micro-environmental polarities of the glucose glasses were studied using a polarity probe. From these results a model was developed that described the effects of several parameters on the glucose glass matrices. For example, water was able to diffuse through channels in the glucose glasses and cause dynamic quenching of the phosphorescence. Also, the hydrogen bonding network in the glucose glasses was disrupted by water. This resulted in matrix quenching of the phosphorescence signals.
Identification of Chemical Structures from Infrared Spectra by Using Neural Networks
Authors: Tanabe Kazutoshi , Matsumoto Takatoshi , Tamura Tadao , Hiraishi Jiro , Saeki Shinnosuke , Arima Miwako , Ono Chisato , Itoh Shoji , Uesaka Hiroyuki , Tatsugi Yasuhiro , Yatsunami Kazushige , Inaba Tetsuya , Mitsuhashi Michiko , Kohara Shoji , Masago Hisashi , Kaneuchi Fumiko , Jin Chihiro , Ono Shuichiro
Published: October 2003

Structure identification of chemical substances from infrared spectra can be done with various approaches: a theoretical method using quantum chemistry calculations, an inductive method using standard spectral databases of known chemical substances, and an empirical method using rules between spectra and structures. For various reasons, it is difficult to definitively identify structures with these methods. The relationship between structures and infrared spectra is complicated and nonlinear, and for problems with such nonlinear relationships, neural networks are the most powerful tools. In this study, we have evaluated the performance of a neural network system that mimics the methods used by specialists to identify chemical structures from infrared spectra. Neural networks for identifying over 100 functional groups have been trained by using over 10 000 infrared spectral data compiled in the integrated spectral database system (SDBS) constructed in our laboratory. Network structures and training methods have been optimized for a wide range of conditions. It has been demonstrated that with neural networks, various types of functional groups can be identified, but only with an average accuracy of about 80%. The reason that 100% identification accuracy has not been achieved is discussed.
Comparison of Spectral and Interferogram Processing Methods Using Simulated Passive Fourier Transform Infrared Remote Sensing Data
Authors: Shaffer Ronald E. , Combs Roger J.
Published: October 2003

Computer-generated synthetic single-beam spectra and interferograms provide a means of comparing signal processing strategies that are employed with passive Fourier transform infrared (FT-IR) sensors. With the use of appropriate radiance models and spectrometer characteristics, synthetic data are generated for one-, two-, and four-component mixtures of organic vapors (ethanol, methanol, acetone, and methyl ethyl ketone) in two passive FT-IR remote sensing scenarios. The single-beam spectra are processed by using Savitsky–Golay smoothing and first-derivative and second-derivative filters. Interferogram data are processed by Fourier filtering using Gaussian-shaped bandpass digital filters. Pattern recognition is performed with soft independent modeling of class analogy (SIMCA). Quantitative models for the target gas integrated concentration-path-length product are built by using either partial least-squares (PLS) regression or locally weighted regression (LWR). Pattern recognition and calibration models of the filtered spectra or interferograms produced comparable results. Discrimination of target analytes in complex mixtures requires a sufficiently large temperature differential between the infrared background source and analyte cloud. Quantitative analysis is found to be possible only when the temperature of the analyte cloud is stable or known and differs significantly from the background temperature. Net analyte signal (NAS) methods demonstrate that interferogram and spectral processing methods supply identical information for multivariate pattern recognition and calibration.
“Real Time” Raman Studies of Electrospun Fibers
Authors: Stephens J. S. , Frisk S. , Megelski S. , Rabolt J. F. , Chase D. Bruce
Published: October 2003

Raman spectra of as-spun fibers produced through electrospinning have shown that high S/N data can be obtained on 50-μm diameter fibers in relatively short collection times (25 s). Using this same instrumental approach, “real time” Raman spectra of the electrospinning liquid fiber jet at the origin of the jet and 1 cm downstream have been obtained. The results show that “on-line” analysis of the solvent/polymer ratio and spectroscopic measurements of polymer orientation are possible and will lead to a more quantitative understanding of the development of the polymer microstructure during the electrospinning process.
Multiple Band-Pass Filtering Method for Improvement on Prediction Accuracy of Linear Multivariate Analysis
Authors: Qu Jianan Y. , Shao Lan
Published: October 2003

An approach coupling signal processing and partial least-squares regression analysis (PLS) is described in which raw spectral data are processed with a multiple band-pass filter and the filtered spectra are used in a PLS to build a calibration model for the analyte of interest. The multiple band-pass filter is specifically designed for a desired analyte based on the Fourier frequency characteristics of the pure spectrum of the desired analyte and the spectra of the interference background. It maximizes the ratio of signal to background. This combined multiple band-pass filtering and PLS method (MFPLS) was evaluated by determining clinically relevant levels of glucose, urea, ethanol, and acetaminophen in simulated human sera, in which triglyceride was simulated with triacetin; bovine serum albumin and globulin were used to model protein molecules in the serum. The results demonstrate that MFPLS produces better accuracy of prediction than PLS in all instances.
Laser Ablation Inductively Coupled Plasma Mass Spectrometry of Pressed Pellet Surrogates for Pu Materials Disposition
Authors: Borisov Oleg V. , Bannochie Christopher J. , Russo Richard E.
Published: October 2003

Successful Pu disposition by immobilization in glass or ceramic form requires accurate and precise knowledge of impurity amounts. Analysis of Pu material by conventional liquid nebulization requires dissolution, which is difficult due to the refractory nature of the samples. Laser ablation is a suitable sampling technique for direct analysis of solids. This paper demonstrates the procedures that were established for PuO2 analysis using laser ablation inductively coupled plasma mass spectrometer (ICP-MS). Pressed pellets prepared from CeO2 were used to simulate PuO2. Effects of laser conditions, sample preparation, and matrix composition, specifically mass of a matrix element and color, on the analyses of CeO2, Bi2O3, and PtO2 based pressed pellets were examined. Influence of mixing/grinding time on particle sizes, sample homogeneity, and ablation efficiency were investigated. Laser conditions that produce stoichiometric sampling were examined.
Temporal Gating for the Optimization of Laser-Induced Breakdown Spectroscopy Detection and Analysis of Toxic Metals
Authors: Fisher Brian T. , Johnsen Howard A. , Buckley Steven G. , Hahn David W.
Published: October 2003

Optimal temporal gating for laser-induced breakdown spectroscopy (LIBS) analysis was investigated for a select group of toxic metals, namely the Resource Conservation and Recovery Act (RCRA) metals arsenic, beryllium, cadmium, chromium, lead, and mercury. The differing rates of decay between the continuum plasma emission and the atomic emission were used as a means to maximize the signal-to-noise ratio of the atomic emission lines for these six metal species. Detection windows were investigated corresponding to delay times from 2 to 50 μs following the plasma-initiating laser pulse. For the current experimental conditions, it is concluded that the relatively short delay time of 12 μs is optimal for the detection of arsenic, beryllium, cadmium, and mercury, while a longer delay time of 50 μs is optimal for the detection of chromium and lead. The reduced atomic emission intensity at relatively long delay times is compensated for by the use of long detector gate widths. Estimated detection limits are reported for the six metal species based on the optimized temporal gating and ensemble averaging of multiple laser pulses, and the implications for simultaneous metals monitoring are discussed.
Fiber-Optic Evanescent-Wave Absorption Copper(II) Sensor Based on Sol-Gel-Derived Organofunctionalized Silica Cladding
Authors: Yeh Ta-Chuan , Tien Pei , Chau Lai-Kwan
Published: October 2003

A fiber-optic evanescent-wave absorption sensor was constructed on the basis of an organofunctionalized silica cladding. The cladding material was prepared by the sol-gel processing of an organofunctional silicon alkoxide, which contains a propyl-ethylenediamine triacetate (PEDTA) group. The PEDTA group can chelate with a Cu(II) ion to form a colored complex. Because of the large formation constant of the complexation reaction, a kinetic approach was used to quantify the Cu(II) content in samples. The sensor has a dynamic range of 0.5–100 ppm and a detection limit of 56 ppb. The measurement of the Cu(II) content in a scattering medium has also been demonstrated.
Rugged Fiber-Optic Raman Probe for Process Monitoring Applications
Authors: Niemelä Pentti , Suhonen Janne
Published: October 2003

We report on the development of a simple, rugged fiber-optic probe for process Raman measurements, in which laser line rejection is based on an absorptive longpass filter made from a direct bandgap CdTe semiconductor. The probe can be used with a fixed wavelength laser at 830 nm, and Raman spectra can be recorded down to 200 cm−1 from the laser line. The filter thickness can be adjusted for final turning of the filter edge, as the edge slope is almost independent of thickness in the range 0.1 to 1 mm. Other properties of the probe, such as its signal-to-noise ratio and signal-to-background ratio, are shown to compare well with those of a state-of-the-art probe based on holographic notch filter techniques.
Method for Measuring Cellular Optical Absorption and Scattering Evaluated Using Dilute Cell Suspension Phantoms
Authors: Sefkow A. , Bree M. , MyCek M.-A.
Published: October 2003

The opal glass method (OGM) is a standard technique used by the ocean optics community to measure the spectral absorption coefficients of algal suspensions. We present and evaluate this method for its potential application to measurements of the inherent optical properties (optical absorption and scattering coefficients) of dilute mammalian cell suspensions, as an alternative to the integrating sphere method. In a series of controlled experiments on absorbing and scattering phantoms (Evans blue dye and polystyrene spheres 1–20 μm in diameter), separation of absorption and scattering was possible with less than 20% error in absorption coefficient estimates for particles with major scattering components in the size range of 2–5 μm.
Infrared Spectroscopic Studies of Major Cellular Components. Part II: The Effect of Hydration on the Spectra of Nucleic Acids
Authors: Pevsner Alex , Diem Max
Published: October 2003

Infrared absorption spectra of DNA and RNA as dry, lyophilized powders in KBr pellets, as hydrated KBr pellets, and in solution phase are reported. We find the symmetric and antisymmetric stretching vibrations of the phosphate linkage, νs(PO2−) and νas(PO2−), to be very sensitive to hydration, as intensity changes as well as frequency shifts are observed. An increase in water content causes DNA to undergo a structural transition form A-form to B-form. This observation leads us to believe that the frequency shifts are associated mostly with the conformational change, whereas the increase in intensities may be due to an increase in the local dielectric in the vicinity of the polar and solvent exposed phosphate groups. A similar effect was reported recently for the amide groups of proteins. The structure of RNA is less sensitive to hydration, and only the phophodiester stretching vibrations are affected by hydration. The solution transmission and ATR spectra of DNA and RNA solution are also compared and found to be identical to one another in the 950–1300 cm−1 frequency region. Furthermore, solution spectra resemble the fully hydrated solid-phase spectra.
Raman Spectroscopy Determination of the Thermoplastic Content within Epoxy Resin-Copolyethersulfone Blends
Authors: Van Overbeke E. , Devaux J. , Legras R. , Carter J. T. , McGrail P. T. , Carlier V.
Published: October 2003

The possibility of using Raman spectroscopy to determine the local thermoplastic content within blends of epoxy resins and copolyethersulfone was studied. The required calibration of the Raman data is presented here. It was obtained by multivariate methods and was based on homogeneous samples of known content in amine-ended thermoplastic (expressed in weight %). Blends cured with two types of diamine curing agents were separately studied, the curing agents being the methylene bis(2,6-diethylaniline) (MDEA) and the 4,4′-diaminodiphenylsulfone (DDS). Partial least-squares (PLS) regressions with external validation were performed. With MDEA, root mean square error of prediction (RMSEP) values at validation were 3.2, 3.7, and 3.0% (depending on the spectral pre-treatment and on the wavenumber selection). RMSEP values were 2.4 or 3.0% with DDS (depending on the wavenumber selection). The applicability of the calibrations to blends containing chlorine-ended copolyethersulfone is discussed. Results obtained with small or large Raman confocal holes are also compared.
New DRIFTS Cell Design for the Simultaneous Acquisition of IR Spectra and Kinetic Data Using On-Line Product Analysis
Authors: Schubert M. M. , Häring T. P. , Bräth G. , Gasteiger H. A. , Behm R. J.
Published: October 2003

A new design for a DRIFTS (diffuse reflectance infrared Fourier transform spectrometry) cell for in situ studies in heterogeneous catalysis is presented, which allows for improved reaction control (i.e., gas flow, temperature, minimized background conversion) and for precise kinetic measurements via on-line gas analysis by a tandem-arranged gas chromatograph. Specifically, the very low background activity of the cell itself for CO and H2 oxidation makes it possible to study the preferential CO oxidation in H2-rich gases (PROX) at relevant reaction temperatures (150–350 °C) and reactant concentrations (≤1 kPa CO and O2). Comparison with results obtained in a quartz tube reactor shows excellent agreement with the reaction rates obtained in the DRIFTS cell. The improved performance of the new DRIFTS cell design is demonstrated by examining the influence of CO2 on the PROX reaction over a Au/Fe2O3 catalyst. The addition of CO2 to idealized reformate (varying CO and O2 partial pressures, 75 kPa H2, balance N2) significantly reduces both the CO oxidation rate and the selectivity of the PROX reaction on Au/α-Fe2O3 and strongly affects the frequency of the C–O stretch vibration of adsorbed CO due to CO2 coadsorption.
Multiple Filtering Strategy for the Automated Detection of Ethanol by Passive Fourier Transform Infrared Spectrometry
Authors: Idwasi Patrick O. , Small Gary W. , Combs Roger J. , Knapp Robert B. , Kroutil Robert T.
Published: October 2003

Digital filtering methods are evaluated for use in the automated detection of ethanol from passive Fourier transform infrared (FT-IR) data collected during laboratory and open-air remote sensing experiments. In applications in which analyte signals are overwhelmed by the overlapping signals of an interference, the use of multiple digital filters is observed to improve the sensitivity of the analyte detection. The detection strategy is based on the application of bandpass digital filters to short segments of the interferogram data collected by the FT-IR spectrometer. To implement the automated detection of a target analyte, the filtered interferogram segments are supplied as input to piecewise linear discriminant analysis. Through the use of a set of training data, discriminants are computed that can subsequently be applied to detect the presence of the analyte in an automated manner. This research focuses on the detection of ethanol vapor in the presence of an ammonia interference. A two-filter detection strategy based on the use of separate ethanol and ammonia filters is compared to an approach based on a single ethanol filter. Bandpass parameters of the digital filters and the interferogram segment location are optimized through the use of laboratory data in which ethanol and ammonia vapors are generated in a gas cell and viewed against various infrared background radiances. The filter and segment parameters obtained through this optimization are subsequently tested with field remote sensing data collected when the spectrometer is allowed to view ethanol and ammonia plumes generated from a heated stack. The two-filter strategy is found to outperform the single-filter approach with both the laboratory and field data in situations in which the ammonia interference dominates the ethanol signature.
Calibration Transfer of Chemometric Models Based on Process Nuclear Magnetic Resonance Spectroscopy
Authors: Gislason Jason , Chan Hing , Sardashti Maziar
Published: October 2003

This paper establishes the protocol for calibration transfer of partial least-squares (PLS) regression models between process nuclear magnetic resonance (NMR) spectrometers. The ability to transfer calibration models between instruments allows the addition of new instruments and the upgrade of old instruments with little financial or manpower investment. It will also allow development of calibration for an on-line system on a lab system, which will require less manpower and no down time for the on-line measurements. This capability will result in great cost savings for a production facility where even a minor interruption in the plant operations would result in great loss of production and loss of income.
Polarization Modulation Fourier Transform Infrared Spectroscopy with Digital Signal Processing: Comparison of Vibrational Circular Dichroism Methods
Authors: Hilario Jovencio , Drapcho David , Curbelo Raul , Keiderling Timothy A.
Published: October 2003

Digital signal processing (DSP) has been implemented in a step-scan FT-IR spectrometer in a modification that enables processing of high-frequency polarization modulation signals. In this work, direct comparison is made between vibrational circular dichroism (VCD) spectra measured on the same instrument, with the same samples, under the same conditions, using this new DSP method and a conventional rapid-scan technique (employing a lock-in amplifier for demodulation). In this initial test, both techniques generated high-quality VCD for solution phase, rigid chiral molecules such α-pinene and camphor. Noise and reproducibility of known spectral features, as well as enhancing signal measurability and discrimination, were used as criteria for the selection of optimal DSP measurement parameters. Both DSP and rapid-scan VCD methods produced qualitatively reasonable spectra for biologically related molecules such as poly-γ-benzyl-L-glutamate, poly-L-proline, and duplex RNA homopolymer. In most cases, the DSP method had a slight signal-to-noise advantage based on standard deviations of the noise trace data over the rapid-scan measurement, but the final results did depend on the details of the data collection and the phase correction methods inherent in both methods.
Detection of Gaseous and Particulate Fluorides by Laser-Induced Breakdown Spectroscopy
Authors: Tran Michael , Smith Benjamin W. , Hahn David W. , Winefordner James D.
Published: October 2003

Laser-induced breakdown spectroscopy (LIBS) was evaluated for the detection of gaseous and particulate fluorides in air and other gas mixtures. Analytical figures of merit were compared in pure air, pure He, air-He mixtures, and air with a He sheath flow. Particulate samples were also collected on filters and subsequently detected. It was demonstrated that SF6 is a suitable surrogate for calibration and optimization for the detection of HF in air. For gaseous F in air, limits of detection obtained were 40 mg/m3 for the direct measurement in air and 5 mg/m3 when the air sample was sheathed in He. For particulate F in air, limits of detection were 9 mg/m3 for direct measurement in air and 0.5 mg/m3 using He sheath flow. When the particulates were preconcentrated by collection on a filter and subsequently analyzed, the limit of detection for F was improved to 5 μg/m3 for a 10-min sampling time at 10 L/min flow rate using subsequent LIBS measurements in pure He.
Continuous Monitoring of Toxic Metals in Gas Flows Using Direct-Current Plasma Excited Atomic Absorption Spectroscopy
Authors: Oikari Risto , Häyrinen Ville , Parviainen Tomi , Hernberg Rolf
Published: October 2003

A measurement apparatus employing direct current (dc) plasma excited atomic absorption spectroscopy was developed and demonstrated for continuous measurement of toxic metals in process gases. Process gas is continuously sampled along a heated sample line. Metal compounds contained in the gas are thermally decomposed by mixing the gas with a plasma jet produced with a dc nitrogen plasma torch. Transmission of monochromatic light is measured through the gas jet, and absorbance caused by metal atoms is distinguished from the background by means of the Zeeman effect. The metal concentration in the sample gas is calculated from the measured absorbance with the known dilution and decomposition factors taken into account. The detection limits of the current prototype are 0.04 mg/m3 for cadmium and 0.4 mg/m3 for lead. The measurement accuracy is better than 20%, and the maximum measurement rate is about 100 values per minute. The instrument was designed to withstand wet, corrosive, and particulate-laden flue gases at temperatures up to 1100 °C. The instrument can also be used, after minor modification, for measurements at pressurized conditions. The performance of the instrument was demonstrated in connection with a real fluidized bed combustor.
Real-Time Measurement of Combustion Generated Particles with Photofragmentation-Fluorescence
Authors: Damm Christopher J. , Lucas Donald , Sawyer Robert F. , Koshland Catherine P.
Published: October 2003

Excimer laser fragmentation-fluorescence spectroscopy (ELFFS) is a viable technique for real-time monitoring of carbonaceous particles in combustion exhausts. The exhaust from a single-cylinder two-stroke engine is diluted and diverted into the laser interrogation region, resulting in a particle concentration of approximately 1 × 107/cm3. Light from a 193 nm ArF laser photofragments the particles and then produces fluorescence from the atomic carbon fragments at 248 nm, CH fragments at 431 nm, and C2 fragments at 468 nm. The atomic carbon fluorescence signal is proportional to the number concentration of particles in the laser interrogation region. The 100-shot (1 s) detection limit for particles in the exhaust is 1 mg/m3, expressed as a mass concentration of particulate matter. Interferences from carbon monoxide and carbon dioxide are negligible. The relative fluorescence yield at 248 nm is four times greater from particles than from the gas phase hydrocarbons present in the exhaust. This high yield suggests that the gas phase hydrocarbon interference would not be problematic for measurements of diesel exhaust, where the ratio of particulate carbon to gas phase hydrocarbon is high.