bluuebunny/crossref_metadata_2025 huggingface dataset:
Set of Secondary Emission Standards for Calibration of the Spectral Responsivity in Emission Spectroscopy
Authors: Gardecki J. A. , Maroncelli M.
Published: October 2003

Technical spectra are reported for a series of six secondary emission standards based on the commercially available fluorophors: tryptophan, α-NPO, tetraphenylbutadiene, coumarin 153, DCM, and LDS 751. These spectra cover the wavelength range between 300 and 800 nm with significant spectral overlap and conform to the requirements of secondary emission standards. Standard emission spectra are determined by averaging the technical spectra obtained from three independently calibrated fluorescence spectrometers. A method for generating the wavelength-dependent correction file by using these standards is outlined. Comparison to the National Bureau of Standards (NBS)-reported quinine sulfate spectrum illustrates the accuracy of both the emission standards and the method of generating a complete emission correction file. With the use of the standards and method reported here, the accuracy of the emission correction is estimated to be better than 10% for the entire wavelength range and significantly better over the wavelength region of a typical spectrum.
Investigation into the Analytical Utility of Plasma Etching in Reactive Glow Discharge Plasmas
Authors: Barshick C. M. , Hess K. R. , Zook A. L. , Steiner R. E. , King F. L.
Published: October 2003

Tetrafluoromethane (CF4, 1.01% by weight) was added to the argon support gas of a hollow cathode glow discharge to investigate the analytical utility of etch atomization. When a conducting copper cathode was analyzed, the sputtering rate (as measured by weight loss) was reduced by a factor of five compared to operation with pure argon. Copper atomic absorbance and copper atomic emission intensity were also reduced by factors of seven and two, respectively. When a nonconducting sample was analyzed, the stainless steel ring that held the sample acted as an auxiliary cathode, supporting the discharge processes. Radical fluoride species formed in this discharge reacted with the nonconducting substrate (silica) to produce volatile SiF4 that spontaneously evolved into the gas phase, carrying with it copper and uranium. This approach is analogous to plasma etching, a well-established technique for semiconductor processing. Atomic emission data were obtained with a pure argon discharge and an argon/CF4 discharge. With the addition of CF4, a 30% enhancement was observed for uranium in glass and a 50% enhancement for copper in glass. Scanning electron microscopy (SEM) was used to support the supposition that etching of the silica matrix on the inner surface of the hollow cathode contributed to this enhancement.
Elemental Analysis of Individual Combinatorial Chemistry Library Members by Energy-Dispersive X-Ray Spectroscopy
Authors: Neilly J. P. , Hochlowski J. E.
Published: October 2003

Elemental analysis of single combinatorial chemistry library members bound to polystyrene beads was studied by energy-dispersive X-ray spectroscopy (EDS) on a scanning electron microscope (SEM). The effects of bead geometry and electron beam exposure time on the elemental analysis results were evaluated. Elemental analysis data were highly variable on round beads, but reliable concentration data could be obtained from flattened beads held in silicon wafer bead holders. The duration of exposure time on flattened beads had no effect on elemental concentration data for the compounds studied. EDS analysis of single beads provided results similar to those obtained by combustion analysis. In summary, elemental analysis of single combinatorial chemistry library members by EDS was shown to be a reliable and fast method of analysis of single beads.
Resonance Raman Spectroscopy at 257 nm Excitation of Normal and Malignant Cultured Breast and Cervical Cells
Authors: Yazdi Youseph , Ramanujam Nirmala , Lotan Reuben , Mitchell Michele Follen , Hittelman Walter , Richards-Kortum Rebecca
Published: October 2003

The sensitivity and selectivity of UV-excited resonance Raman spectroscopy indicate that this technique may be useful in studying certain biochemical changes in cells, especially changes in DNA that occur during the development of cancer. To determine whether this technique can distinguish normal from malignant cells, we have measured UV resonance Raman spectra at 257.26 nm excitation of suspensions of normal and malignant cultured breast and cervical cells. Samples were excited with the use of an intracavity doubled argon-ion laser, and the spectra were recorded with a single grating spectrograph and a liquid nitrogen-cooled charge-coupled device. Cell spectra obtained closely resembled that of DNA, with peaks around 1330, 1480, and 1580 cm−1, due to the nucleotide bases. In addition to these, the uracil base in RNA provides a peak at 1230 cm−1. Strong tryptophan and tyrosine contributions appear in the 1520–1670 cm−1 range. The ratios of Raman spectral peaks 1480/1614 cm−1 and 1480/1540 cm−1, which are sensitive to the concentration of nucleic acids relative to cell proteins, were found to be higher in malignant cells than in normal cells. Normal and malignant cells could also be differentiated by using the ratio at 1330/1480 cm−1. This difference may be the result of decreased hypochromism due to changes in stacking of the purine bases. Changes in relative amounts of RNA may also contribute to this ratio. The results of this pilot study indicate that there may be significant differences in the UV resonance Raman spectra of normal and cancerous cells. These differences may be related to changes in nucleotide/protein concentrations in the cell, as well as changes in the vibrational structure of the nucleic acids associated with the malignant cell phenotype.
Spectral Imaging in a Programmable Array Microscope by Hadamard Transform Fluorescence Spectroscopy
Authors: Hanley Quentin S. , Verveer Peter J. , Jovin Thomas M.
Published: October 2003

We report the use of a thin-film transistor (TFT) twisted nematic liquid crystal spatial light modulator (SLM) for Hadamard transform two-dimensional spectral imaging in a fluorescence microscope. The liquid crystal SLM placed in the primary image plane of the microscope generates a set of spatial encoding masks defined by a cyclic S-matrix. The light passing through the mask is relayed by anamorphic optics to the entrance of an imaging spectrograph and detected with a charge-coupled device (CCD) camera. The SLM allows for the convenient generation of arbitrary masks without moving parts. The Hadamard transform approach transmits up to 50% of the light from the image field for multichannel detection, but is subject to transmission losses in the SLM. The system allows the convenient acquisition of two-dimensional spectral images. We characterized and tested many of the parameters controlling both spatial and spectral resolution, and demonstrated the system in the analysis of both naturally fluorescing and stained biological samples.
Evaluating Bulk-to-Surface Partitioning of Erucamide in LLDPE Films Using FT-IR Microspectroscopy
Authors: Joshi Nitin B. , Hirt Douglas E.
Published: October 2003

The objective of this research is to experimentally characterize the spatial distribution of an additive across the thickness of a single-layer polymer film. Concentration-distribution data are then used to quantify the amount of additive that diffuses from the bulk of the film to the film surfaces as a function of time. These results are important because a film's surface property, such as coefficient of friction, depends on the additive surface concentration. The concentration profiles of an erucamide slip agent in linear low-density polyethylene (LLDPE) films were measured with Fourier transform infrared microspectroscopy. This paper describes in detail the procedures used to microtome specimens and map the concentration profiles for the erucamide-LLDPE system. Data show that the additive concentration profile is uniform across the thickness of the film immediately after it has been formed. After aging at 60 °C for 4.5 h (not yet to equilibrium), approximately 40% of the additive accumulates at the film surfaces.
Dynamic Infrared Spectroscopy in Tension and Shear
Authors: Chase D. B. , Ikeda R. M.
Published: October 2003

The utility of polarized infrared spectroscopy for the study of polymeric systems undergoing dynamic deformation has been established by several groups following the pioneering work of Noda and Marcott. All previous studies have utilized tensile deformation, and tensile experiments are complicated by sample thinning. One must also rely on the assumption of transverse isotropy to determine the three elements of the dynamic absorption tensor. An alternative approach involves the use of shear rather than tensile deformation. Experimentally, two different shear geometries are readily achievable. In one, the IR beam is passed normal to the shear plane and the polarizers must be set at ±45° to the flow direction. Since no sample thinning is involved with no net flow of material in or out of the sampling volume, the trace of the dynamic absorption matrix must be zero, and all three elements of the dynamic absorption tensor can be obtained in a single experiment. In the second geometry, the IR beam is passed parallel to the shear plane. In this configuration, the optical signals are modulated at twice the deformation frequency, and the magnitude of the dynamic dichroism scales with the square of the shear strain. Since the shear strains are usually quite small, severe sensitivity problems can arise with this second configuration.
Improvement in Data Acquisition for a Step-Scan Fourier Transform Spectrometer
Authors: Chin Thou-Long , Lin King-Chuen
Published: October 2003

We have designed a controller circuit to be incorporated into a commercial step-scan Fourier transform spectrometer (Bruker IFS 88 FTS). Alternatively, time-resolved data may be acquired with a transient digitizer provided by the user. We have demonstrated the versatility of the controller with a Lecroy 9450A transient digitizer as the recorder in the time-resolved emission detection of the CH radical populated in the A2Δ state and in the absorption measurement of the ambient air. The controller, which may be conveniently coupled to any data acquisition system, makes the use of the FTS more flexible and less expensive.
Infrared Reflection-Absorption Study of Ordering and Hydrogen Bonding within Chiral and Nonchiral Self-Assembled Monolayers on Gold
Authors: Nissink J. W. M. , van der Maas J. H.
Published: October 2003

Ordering processes in chiral and racemic monolayers of three phenylalanyl-substituted ω-thiol alkanoic acids on gold have been investigated with the use of infrared reflection absorption spectroscopy. For chiral molecules, packing is influenced by both hydrogen-bonding interactions between the end groups at the air/monolayer interface and the length of the spacer chain within the monolayer. Results for a mixed monolayer of octadecylmercaptane and phenylalanyl-substituted ω-thiol docosanoic acid indicate that formation of large islands of either one of the compounds can be excluded. For a racemic monolayer of phenylalanyl-substituted ω-thiol undecanoic acid, a dense, yet unregular, packing is observed.
FT-IR Spectroscopic Study on Basicity of Alumina with Adsorption of Boric Acid Trimethyl Ester
Authors: Liu Jianke , Ying Pinliang , Xin Qin , Li Can
Published: October 2003

Surface basicity of alumina and modified alumina has been studied by FT-IR spectroscopy using boric acid trimethyl ester (BATE) as the probe molecule. The surface basic sites on alumina can be probed by the adsorption of BATE and coadsorption of BATE and CO2. BATE is found to interact with both types of basic sites on alumina: basic hydroxyls and surface oxygen anions. A general interaction model of BATE with basic sites on metal oxide is proposed.
Surface-Enhanced Fluorescence on SiO2-Coated Silver Island Films
Authors: Tarcha Peter J. , Desaja-Gonzalez J. , Rodriguez-Llorente S. , Aroca R.
Published: October 2003

Fluorescence is one of the molecular spectroscopic properties that is enhanced by placing the molecule on the rough surface of a coinage metal. The surface-enhanced fluorescence (SEF) can be directly observed in steady-state fluorescence experiments. The observations are the results of a delicate balance between the enhanced emission and the quenching due to energy transfer to nonradiative surface plasmons. In the present report, SiO2-coated silver films were fabricated at varying dielectric thickness. The surface of the films was analyzed with the use of atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). AFM confirms the surface roughness and XPS analysis indicates that the SiO2 coverage was successful. SEF and SERS (surface-enhanced Raman scattering) were observed on active 6, 10, and 14 nm silver films coated with SiO2. Similar results were obtained with a 6 nm silver film coated with 6 nm SiO. The SEF work was carried out on fluorescent molecules with different quantum yield, and the typical enhancement factor obtained for the fluorescent signal was approximately 10. Both the SiO2 and SiO overlayers provide stable surfaces with well-defined hydrophilic properties. Such stable constructions have applicability towards the advancement of SERS and SEF as routine analytical techniques in bio- and chemical sensors.
Trace Metal Detection by Laser-Induced Breakdown Spectroscopy
Authors: Vander Wal Randall L. , Ticich Thomas M. , West Joseph R. , Householder Paul A.
Published: October 2003

Laser-induced breakdown spectroscopy (LIBS) has been widely pursued for trace elemental determination in gases, solids, and liquids. Application to liquids has proved problematic due to high spatial confinement of the LIBS plasma and rapid quenching of the excited-state emission. This work presents an alternative approach to trace metal determination in liquids in which 1.0 mL of liquid is deposited onto a carbon planchet and then evaporated, thus transforming the liquid analysis to a solid surface analysis. Using optimized excitation and detection conditions, we have identified spectral regions for sensitive detection of 15 metals (Mg, Al, Si, Ca, Ti, Cr, Fe, Co, Ni, Cu, Zn, As, Cd, Hg, Pb). The limit of detection (LOD) for the technique ranged from 10 ppb to 10 ppm for these elements. A 100 ppb LOD represents detection of 130 picograms of metal (approximately 2 picomoles) in a single measurement calculated from the laser spot size on the sample. Scanning electron microscopy (SEM) images and energy-dispersive X-ray (EDX) spectra of the samples provide insight into the observed reproducibility and linearity of the technique for several of the metals studied.
Simple Transient Extension Chamber to Permit Full Mass Scans with Electrothermal Vaporization Inductively Coupled Plasma Mass Spectrometry
Authors: Langer Delony , Holcombe James A.
Published: October 2003

The design for an in-line transient extension (TEx) chamber was developed to provide a simple means of lengthening an electrothermal vaporizer (ETV) signal for the purpose of obtaining a full mass scan from a single ETV firing with inductively coupled plasma mass spectrometry (ICP-MS) detection. The TEx chamber is simply a flask (e.g., 100–500 mL) with a mated joint allowing the ETV-generated aerosol to enter the chamber in a pulse and exit the chamber exponentially diluted. Characterization of the TEx chamber was completed with the use of the following metals: Ba, Be, Ce, Co, In, Mg, Pb, Th, and Tl. A decrease in peak area of 20 ± 4% was witnessed when the TEx chamber was put in-line between the ETV and the ICP-MS for all metals tested. Comparison of the peak areas obtained with and without the addition of 10 μL of 100 ppm NaCl to the sample without the TEx chamber in-line resulted in increases from 8 to 40%, depending on the metal. Repetition of the experiment with the TEx chamber in line showed no appreciable difference in results. This outcome indicates that dilution in the TEx chamber does not influence the behavior (i.e., enhancement effect) of the carrier. Interrupting the carrier gas flow for up to 2 min after the TEx chamber was “loaded” with the aerosol caused decreases in peak area from 25 to 35%, depending on the length of time the sample was held in the chamber. This result is most likely due to settling/loss of the aerosol particles in the chamber. Addition of 10 μL of 100 ppm NaCl to the sample showed a decrease in peak area of 30-43% when the sample was held for up to 2 min in the chamber, slightly higher than when no NaCl was present. A comparison of full mass scans taken with a concentric nebulizer and the ETV with an in-line TEx chamber using identical data collection rates and times showed that the TEx chamber can be used successfully as a method for both qualitative and quantitative identification of trace elements in an unknown solution. Detection limits for the nine metals tested with the TEx chamber in line are given.
Fundamentals of Calibration Transfer through Procrustes Analysis
Authors: Anderson Chad E. , Kalivas John H.
Published: October 2003

In analytical chemistry, it is necessary to form instrument-dependent calibration models. Problems such as instrument drift, repair, or use of a new instrument create a need for recalibration. Since recalibration can require considerable costs and cause time delays, methods for calibration transfer have been developed. This paper shows that many of these approaches are based on the statistical procedure known as Procrustes analysis (PA). Transfer by PA methods is shown to involve translation (mean-centering), rotation, and stretching of instrument responses. This study investigates the ability of different forms of PA to transfer near-infrared spectra measured on two different instruments. Spectroscopic interpretations of translation, rotation, and stretching are provided. It is found for the data sets investigated that unconstrained forms of PA generally produce better results. It is also shown that translation is the key step for transformation of spectra and may often be all that is required.
Characterization of Dendrimers by X-Ray Photoelectron Spectroscopy
Authors: Demathieu Caroline , Chehimi Mohamed M. , Lipskier Jean-François , Caminade Anne-Marie , Majoral Jean-Pierre
Published: October 2003

A series of P=S-containing dendrimers (starburst macromolecules) were characterized by X-ray photoelectron spectroscopy (XPS). This technique is a unique tool for the identification of specific groups from these starbursts such as P=S, aromatic rings, C–O, and C=O. Surface elemental and chemical composition is found to be generally in agreement with the expected stoichiometric formula.
FT-IR Spectroscopy for the in-Flame Study of a 15 MW Dual Fuel Gas/Oil Burner
Authors: Colson Guy , De Ruyck Jacques
Published: October 2003

An FT-IR (Fourier transform infrared) analyzer has been configured for combustion research and allows the simultaneous quantification of CO, CO2, CH4, C2H6, C2H2, C2H4, NO, and N2O concentrations in the flame of natural gas burners. The calibration has been carried out by the multivariate PLS1 algorithm, with calculated standard spectra. For the multivariate CO/CO2 model, special attention has been given to nonlinear effects caused by interference in the 2210–2250 cm−1 region. For this model, two methods of calculating mixture spectra and their influence on prediction parameters are evaluated. Furthermore, the sensitivity of the CO/CO2 model for N2O interference has been tested. The presented results show that conclusions drawn from statistical prediction parameters should be treated cautiously in models that have to deal with spectral interference.
Estimation of Middle Distillate Fuel Properties by FT-IR
Authors: Fodor G. E. , Mason R. A. , Hutzler S. A.
Published: October 2003

As an alternative to established laboratory protocols, partial least-squares (PLS) regression models based on Fourier transform infrared (FT-IR) spectra were developed for the rapid and simultaneous determination of several middle distillate fuel properties. Requiring less than 2 mL of sample, the PLS models use a single wavelength range of baseline-uncorrected FT-IR spectra. Several preprocessing parameters were investigated, including mean-centering of the raw spectra and mean-centering of first- and second-difference spectra. In addition, modification to the calibration parameters included varying the number of cross-validation rotation samples from 5 to 50, applying a baseline correction to the spectra, and using restricted wavelength regions. In order to obtain an accurate estimate of the prediction error, we applied the method provided by Faber and Kowalski [Appl. Spectrosc. 51, 660 (1997)] that corrects for the measurement error in the reference values. On the basis of this work, the following middle distillate fuel properties may be confidently estimated by FT-IR: gravity, API°; density, g/mL; kinematic viscosity, cSt, 40 °C; boiling point at 50% recovery, °C; cetane index; carbon, wt %; hydrogen, wt %; carbon-to-hydrogen ratio, C/H; net heat of combustion, MJ/Kg (or BTU/lb); monocyclic aromatics, wt %; dicyclic aromatics, wt %; polycyclic aromatics, wt %; and total aromatics, wt %. Estimation of several other properties is also possible where reduced precision is acceptable.
Anisotropic Optical Constants of Bacteriorhodopsin in the Mid-Infrared: Consequence on the Determination of α-Helix Orientation
Authors: Blaudez D. , Boucher F. , Buffeteau T. , Desbat B. , Grandbois M. , Salesse C.
Published: October 2003

In this paper, we present the first determination of the anisotropic optical constants of a protein (bacteriorhodopsin or bR) monolayer in the mid-infrared range. This procedure has allowed us to calculate a mean tilt angle of the α-helices' axis with respect to the normal of the surface. Using these optical constants, we have been able to reproduce the polarized attenuated total reflection (ATR) spectra of a bR monolayer deposited on a germanium crystal. On the other hand, the optical constants have to be modified to reproduce the polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) spectrum of a bR monolayer spread at the air/water interface. This modification of the optical constants indicates that the α helices are more tilted when the bR monolayer is spread on the water surface than when it is deposited onto a dry solid substrate.
Raman Performance Characteristics of Teflon®-AF 2400 Liquid-Core Optical-Fiber Sample Cells
Authors: Altkorn Robert , Koev Ilia , Pelletier Michael J.
Published: October 2003

Several properties of Teflon®-AF liquid-core optical-fiber (LCOF) sample cells relevant to their utility in analytical Raman spectroscopy have been investigated. These include the nature and extent of cladding-related background and its effect on signal-to-noise ratio, and the dependence of intensity enhancement on LCOF length, core diameter, excitation wavelength, and scattering wavelength. Significant improvements in signal-to-noise ratio relative to conventional sampling techniques were demonstrated in LCOFs filled with dilute (6 × 10−2 M and 6 × 10−4 M) aqueous solutions of phenylalanine. A maximum intensity enhancement factor of approximately 120 was measured by using 50 μm i.d. LCOFs filled with methanol and 532 nm excitation. Enhancement in 785 nm-excited spectra was found to vary with Raman shift in a manner consistent with self-absorption by high-overtone vibrational bands in the core liquid.
Direct Comparison of Near-Infrared Absorbance Spectroscopy with Raman Scattering Spectroscopy for the Quantitative Analysis of Xylene Isomer Mixtures
Authors: Gresham Christopher A. , Gilmore Daniel A. , Denton M. Bonner
Published: October 2003

In order to overcome instrument problems associated with moving parts, such as optical misalignment and/or mechanical breakdown, we have developed two solid-state (no moving parts) spectrometers suitable for many industrial process monitoring applications. The first instrument utilizes near-infrared absorbance spectroscopy with a 1024-element platinum-silicide linear photodiode array detector, and the other employs Raman scattering spectroscopy with a 1024 × 1024 element charge-coupled device (CCD) detector. In order to demonstrate the utility of solid-state instrumentation for industrial process monitoring analysis, both instruments were used for the simultaneous quantitative analysis of individual components of xylene isomer mixtures. The xylene isomer mixture samples prepared for this study contained approximately 75–86, 0.6–5, and 0.1–14% w/v ortho-, meta-, and para-xylene, respectively, to reflect compositions of xylene raw materials used by specialty chemical manufacturers. Each spectroscopic system provides a means for fast (seconds), nondestructive data acquisition with no sample preparation. With the use of the chemometric data treatment of partial least-squares (PLS) regression, the absolute accuracies at 95% confidence for each isomer were found to be ±0.05, ±0.12, and ±0.09% w/v with near-infrared spectroscopy and ±0.08, ±0.04, and ±0.07% w/v with Raman spectroscopy for ortho-, meta-, and para-xylene, respectively.
Effect of Laser Heating on the Local Temperature and Composition in Raman Spectroscopy: A Study of Ba(NO3)2 and BaO2 Decomposition
Authors: Xie Shuibo , Rosynek Michael P. , Lunsford Jack H.
Published: October 2003

The effect of laser heating on the local concentration of a white Ba(NO3)2 or BaO2 sample in a stationary in situ Raman cell, as determined by Raman spectroscopy, was addressed in this study. The decomposition of Ba(NO3)2 and crystalline BaO2, both supported on MgO, was followed as a function of the temperature of the cell with the use of Raman spectroscopy and product analysis by gas chromatography. At a laser power level of 25 mW and with the sample at 580°C, the decomposition curves were offset by about 3°C, rather than by a temperature difference of more than 15°C that might be expected from laser heating. Diffusion of NO3- and O22- ions from the surrounding region into the 100 mu m-size spot heated by the laser apparently compensates for the loss of materials at the higher temperature. As a consequence, for in situ catalytic studies, the concentrations determined by Raman spectroscopy may be more representative of the sample than one might expect from the local temperature.
In situ Characterization of a Graphite Electrode in a Secondary Lithium-Ion Battery Using Raman Microscopy
Authors: Panitz J.-C. , Joho F. , Novák P.
Published: October 2003

A Raman microscopy study of lithium intercalation into the graphite electrode of a lithium-ion battery is presented. An in situ spectro-electrochemical cell was designed for direct observation of the electrode/electrolyte interface. The performance of this cell is discussed in terms of the results of a calibration experiment performed at a single defined point on the electrode surface. The electrode was made of TIMREX SFG 44 synthetic graphite with polyvinylidene fluoride binder. The electrolyte was lithium perchlorate, LiClO4, dissolved in a mixture of ethylene carbonate and dimethyl carbonate. In the region of the carbonyl stretching vibrational modes of the electrolyte components, changes in the band profile have been observed. At electrode potentials negative to 180 mV vs. Li/Li+, a new band evolved at about 1850 cm−1. This band has tentatively been assigned to a complex between lithium ions and decomposition products of the ethylene carbonate electrolyte component. The maximum intensity of this new band is observed at 5 mV vs. Li/Li+; its intensity decreases with increasing potential upon lithium de-intercalation. Raman mapping of the graphite electrode under potentiostatic conditions indicates that lithium intercalation does not proceed homogeneously over the graphite electrode surface at a potential of 200 mV vs. Li/Li+. An additional Raman mapping study was performed under galvanostatic conditions. With this method, the presence of “blind spots” on the electrode surface can be detected. These points lag behind in the process of lithium intercalation. Furthermore, information on changes in the carbon component of the electrode can be inferred from these measurements.
Quantitation of Sulfur Oxyanions in Industrial Metal Refining Solutions with Dispersive and Fourier Transform Raman Spectroscopy
Authors: Schmidt K. J. , Zhang S. L. , Michaelian K. H. , Webb M. A. , Loppnow G. R.
Published: October 2003

Fourier transform (FT)-Raman and dispersive, visible excitation Raman spectra are reported for standard solutions and highly colored industrial metal refining solutions containing sulfur oxyanions, primarily sulfate and sulfamate. Good-quality spectra are obtained for both standard and industrial solutions. However, quantitation of both sulfur oxyanion concentrations is complicated by self-absorption effects. In the FT-Raman spectra, self-absorption of the incident laser beam yields an exponential correlation between Raman peak intensity, directly proportional to the apparent sulfate concentration, and the actual sulfate concentration. An internal standard, dispersive Raman spectroscopy, and excitation at 647 nm were used in an attempt to apply a self-absorption correction for absorption of the incident laser beam by ratioing the relative Raman intensities of the standard and species of interest. This approach improves the accuracy for sulfate and sulfamate determination to ±6.1% and ±3.4%, respectively. This study represents the most detailed characterization presented so far of the errors expected in quantitative Raman spectroscopy of industrial solutions. These results suggest that Raman spectroscopy is a uniquely powerful technique for the qualitative and quantitative characterization of industrial metal refining solutions.
Rapid Method for Simulating Gas Spectra Using Reversed PCR Temperature Calibration Models Based on Hitran Data
Authors: Bak Jimmy
Published: October 2003

A computer program was produced to make rapid simulations of CO gas spectra at a spectral resolution of 1 cm−1 and at temperatures ranging from 295 to 845 K and concentrations from 5 to 400 mg/m3. The program is based on loadings and scores from three principal component regression (PCR) temperature calibration models. Three sets of 12 Hitran-simulated high-density spectra, each set spanning the entire temperature range at constant concentrations (50, 150, and 300 mg/m3), were used as calibration spectra in the PCR temperature models. All the spectra were convoluted with a sinc-squared instrumental line-shape function and reduced in the number of data points prior to PCR modeling. The simulated spectra, calculated on the basis of the PCR model parameters, were next scaled by using the areas of the spectra to represent the input concentration. The program simulates spectra very rapidly, ∼ 7 ms, which includes saving the simulated spectrum counting 962 data points to the hard disk. This is an improvement in computational speed of a factor of more than 103 compared to performing all the calculations from scratch. The actual program can be used to simulate CO spectra representing a uniform slab of gas at various temperatures, concentrations, and pathlengths. The gain in speed of the calculations of the spectra is based on the fact that the PCR models include mathematical pretreatments and compress the data effectively.
Two-Dimensional Correlation Spectroscopy: Effect of Normalization of the Dynamic Spectra
Authors: Czarnecki Mirosław A.
Published: October 2003

Simulation studies have demonstrated that linear nonselective intensity variations coupled with nonlinear selective intensity changes may develop new features in two-dimensional (2D) correlation spectra. Some types of linear nonselective intensity changes are hardly seen in the normal and synchronous 2D correlation spectrum. In contrast, they may develop quite strong features in the companion asynchronous spectrum, especially if the selective intensity variations for different bands have similar response functions. The simplest way of removing this effect is normalization of the dynamic spectra prior to 2D correlation analysis. This operation can be easily performed if we know the relationship between the perturbation and the nonspecific intensity variations. Otherwise, one has to employ an “internal reference” for normalization of the experimental spectra. The “internal reference” means the band that does not selectively change in its intensity under given perturbation. Fourier transform near-infrared (FT-NIR) measurements of octan-1-ol in CCl4 revealed a strong correlation between the concentration and the integrated intensity of the second overtone of the v(C–H) band. Also a strong correlation was found between the integrated intensity of the same band and the temperature-induced density changes of pure octan-1-ol. Thus, in the NIR region the second overtone of the v(C–H) band can be successfully applied for normalization of both the concentration and temperature-perturbed spectra of numerous organic samples. The most complicated situation appears for a rheo-optical experiment involving pronounced deformation, where any simple normalization of the experimental spectra cannot be applied. In this instance, knowledge of the exact relationship between the strain and the sample thickness is required.
Plastic Deformation of Polyethylene Studied by Infrared Dichroism
Authors: Elkoun Said , Seguela Roland , Depecker Christophe
Published: October 2003

Infrared dichroism measurements have been carried out to investigate the plastic deformation mechanisms of homogeneous and heterogeneous ethylene copolymers issued from the metallocene and the Ziegler–Natta catalyses, respectively. The two copolymers having the same density display significantly different plastic behavior that should result from different mechanisms of crystal slip. Such mechanisms are analyzed on the basis of the main crystal slip systems (100)[001] and (010)[001] having the higher shear compliances. Attention is focused on the Schmid factor, S, of the slip planes, which is the ratio of the resolved shear stress acting on each slip plane to the applied tensile stress. From the orientation functions of the three crystallographic axes of the orthorhombic unit cell, the Schmid factor of the two slip systems is determined as a function of plastic strain. The heterogeneous copolymer exhibits somewhat higher data for the (010)[001] slip, which suggest a preferred activation of this system during the yielding stage. In contrast, the homogeneous copolymer displays close values for the two slip systems, indicating that plastic flow is more likely governed by a combined activation of the two slip systems, and with eventual cross slip owing to the common [001] slip direction.
In-Line Near-Infrared Monitoring of Polymer Processing. Part I: Process/Monitor Interface Development
Authors: Reshadat Ramin , Desa Stella , Joseph Sibichen , Mehra Mithilesh , Stoev Nikolay , Balke Stephen T.
Published: October 2003

Near-infrared in-line monitoring of polymer processing means using a fiber-optic-assisted spectrometer to obtain spectra of the polymer melt flowing through commonly used processing equipment (an extruder). Conditions in the extruder are typically 200 °C and 20 MPa. This paper shows the design of interfaces between the spectrometer and the molten polymer. Three designs are shown, each permitting monitoring at a different location in the process: a melt-at-die interface, a melt-in-barrel interface, and a strand interface. These designs are for monitoring just before the extruder exit, in the main barrel of the extruder, and after the product exits from the extruder as a strand, respectively. All these interfaces protect the inserted fiber-optic probe from the harsh environment within the extruder while permitting easy replacement of a probe without interrupting the process. This latter characteristic is very important because it permits easy probe repair as well as the use of other types of probes (for monitoring color or particles, for example) to be used during a run. Examples of near-infrared spectra obtained with each of the interfaces used with an immiscible blend of polyethylene and polypropylene are shown. Large differences in the spectra demonstrate that the design of the interface will affect multivariate analysis directed at composition prediction. Subsequent papers are directed at using the melt-at-die interface for composition prediction and accounting for nonlinear relationships between absorbance and concentration.
Chemical Microstructure of Cortical Bone Probed by Raman Transects
Authors: Timlin Jerilyn A. , Carden Angela , Morris Michael D.
Published: October 2003

Raman transects, microspectra taken at equal intervals along a line, are used to explore the microstructure of human cortical bone. Transects of 50 spectra taken at 2.5 μm intervals across an osteon show spatial differences in local mineral and protein composition as different physiological structures are traversed. Differences in mineral composition are seen near the rim of an osteon and further out in the lamellae. The blood vessel wall, primarily composed of collagen and elastin, is detected inside the Haversian canal. Factor analysis is used to explore the data set and reveals differences in mineral composition. Factor analysis also yields one bone matrix component, an osteoidal tissue component, and one blood vessel protein component. The 4 cm−1 spectral resolution and 2.5 μm spatial sampling facilitate the development of univariate metrics for bone development and health. Band integration is performed for important marker bands including phosphate v1 at 960 cm−1, monohydrogen phosphate v1 at 1003 cm−1, B-type carbonate v1 at ∼ 1070 cm−1, collagen CH2 wag at ∼ 1450 cm−1, and collagen amide I at ∼ 1650 cm−1. Mineral-to-matrix ratio, phosphate-to-monohydrogen phosphate ratio, and carbonate-to-phosphate ratio are calculated from these measured areas.
Surface-Enhanced Raman Scattering of Biological Molecules on Metal Colloid II: Effects of Aggregation of Gold Colloid and Comparison of Effects of pH of Glycine Solutions between Gold and Silver Colloids
Authors: Dou Xiaoming , Jung Young Mee , Cao Zhuang-Qi , Ozaki Yukihiro
Published: October 2003

As the second paper of a series of our studies on surface-enhanced Raman scattering (SERS) of biological molecules on metal colloid, this paper reports effects of aggregation of gold colloid on the SERS intensity of glycine (Gly) in aqueous solutions and comparison of effects of pH of the Gly solutions between gold and silver colloids. In order to investigate the relation between the SERS effect and colloidal aggregation, we have developed a spectroscopic system by which we can measure simultaneously time-resolved SERS spectra and a time-dependent intensity change in a surface plasmon absorption of a metal colloid system. By use of this instrument we monitored time-dependent intensity changes in the SERS signals and in an absorption band at 802 nm of Gly on gold colloid at pH 3.9 and 6.0. For both pH values, the intensities of the SERS and the absorption band change in concert with each other at the emergence of the SERS effect. The intensity changes in the SERS signals are rather slow for the solution of pH 6.0 while rapid for that of pH 3.9. The coagulation proceeds slowly near the isoelectric point of Gly, whereas the rapid coagulation happens in the acidic region. SERS spectra of Gly adsorbed on silver colloid were measured at various pH values, and it was found that, in sharp contrast to the gold colloid system, which we reported in our previous paper, the SERS intensity of Gly on the silver colloid decreases markedly at pH 2.0 where most of Gly in the solution has a COOH group instead of a COO− group. It seems that the coagulation of the silver colloid particles does not occur very much below p K1 (2.35) because the COOH groups do not interact strongly with the positively charged silver particles.
Surface-Enhanced Infrared Absorption Spectrometry of p-Nitrothiophenol and its Disulfide
Authors: Merklin Gregory T. , He Lin-Tao , Griffiths Peter R.
Published: October 2003

The surface-enhanced infrared spectrometry of p-nitrothiophenol and its disulfide on silver films has been investigated by using deposition from solution, from self-assembled monolayers, and from the vapor phase using a direct-deposition gas chromatography/infrared (GC-IR) interface. In solution, the thiophenol oxidizes to form the disulfide, which then adsorbs to the silver film. If a silver film is deposited on top of a layer of the disulfide, the resulting spectrum is strongly different from that seen with a silver under-layer, more closely resembling the spectrum obtained from the self-assembled monolayer. When a GC-IR interface is used, the presence of the enhancement appears to be correlated with temperature-dependent chemisorption.
Quantitative Determination of Fenthion in Pesticide Formulations by FT-Raman Spectroscopy
Authors: Skoulika Stavroula G. , Georgiou Constantinos A. , Polissiou Moschos G.
Published: October 2003

The Raman spectrum of the organophosphorus pesticide fenthion is presented, and a novel Fourier transform (FT)-Raman method for the quantitative determination of fenthion in pesticide formulations is proposed. Calibration curves based on Raman intensity and band area at 2951, 1065, 661, and 604 cm−1 were linear (correlation coefficients: 0.991–0.998) in the concentration range of 0.4–4.36 M. Detection limits ranged between 0.14 to 0.36 M and precision from 0.4 to 6.8% relative standard deviation (RSD) ( n = 4). Spectra normalization against the 802 cm−1 cyclohexane band proved to be effective in minimizing the effect of excitation intensity fluctuations and sample positioning changes in calibration data, resulting in improved long-term stability of the calibration curves. Results obtained during the analysis of the Lebaycid formulation compare well with those obtained by the gas chromatography (GC) reference method. The proposed FT-Raman method is fast, simple, and safe, avoids sample pretreatment, and minimizes handling of toxic samples.
LDA-Guided Search Engine for the Nonsubjective Analysis of Infrared Microscopic Maps
Authors: Mansfield James R. , McIntosh Laura M. , Crowson A. Neil , Mantsch Henry H. , Jackson Michael
Published: October 2003

Acquisition of large data sets from human tissues by infrared (IR) microscopy is now routine. However, processing such large data sets, which may contain more than 10 000 spectra, provides an enormous challenge. Overcoming this challenge and developing nonsubjective methods for the analysis of IR microscopic results remain the major hurdle to developing clinically useful applications. A three-step pattern recognition strategy based upon linear discriminant analysis has been developed for use as a search engine for tissue characterization. The three-step strategy includes a genetic algorithm-guided data reduction step, a classification step based upon linear discriminant analysis, and a final step in which the discriminant coefficients are converted into a visually appealing, nonsubjective representation of the distribution of each class throughout the tissue section. The application of this search engine in the characterization of tumor-bearing skin is demonstrated.
Fundamental Properties of Aerosols Produced in Helium by a Direct Injection Nebulizer
Authors: McLean John A. , Huff Rebecca A. , Montaser Akbar
Published: October 2003

Fundamental properties of aerosol produced in helium by a direct injection nebulizer (DIN) are determined on a whole-field and spatially resolved basis by using optical patternation and phase-Doppler particle analysis, respectively. The spray structure realized with argon requires a helium gas flow rate higher than the rate for argon. The helium-generated aerosol generally exhibits larger droplet sizes and volume flux, lower mean droplet velocities, and lower droplet number densities than aerosols produced with argon. These findings collectively suggest that helium plasmas should be cooled by the aerosol to a greater extent than argon plasmas.
Relevance of the Luminosity-Resolving Power Product for Spectroscopic Imaging
Authors: Matveev O. I. , Smith B. W. , Omenetto N. , Winefordner J. D.
Published: October 2003

The luminosity-resolving power products of several different types of modern spectrometric imaging and nonimaging systems have been compared. It is shown that if a narrow-band signal is detected in the presence of strong, spectrally continuous background, the luminosity-resolving power product is the critical figure of merit controlling the potential signal-to-noise ratio. Within a spectral resolving power range of 105–109, the signal-to-noise ratio that can be attained by atomic vapor detectors and filters, and by resonance ionization detectors in particular, can be 2–3 orders of magnitude higher than that for the best traditional spectroscopic approaches.
Neutral and Ionic Emission in Q-Switched Nd:YAG Laser-Induced Shock Wave Plasma
Authors: Budi Wahyu Setia , Baskoro Winardi Tjahyo , Pardede Marincan , Kurniawan Hendrik , Tjia May On , Kagawa Kiichiro
Published: October 2003

Excitation mechanisms for copper and zinc atoms as well as their ionic species in the Q-switched (Q-sw) Nd:YAG laser-induced shock wave plasma have been investigated with a time-gated optical multichannel analyzer (OMA) system for various experimental conditions. It is demonstrated that the shock excitation process is the main mechanism responsible for the emission spectra for laser energy ranging from 8 to 86 mJ and surrounding air pressure from 2 to 50 Torr. At air pressure below 2 Torr, collision-induced excitation appears to take over and becomes the operative mechanism. In all cases, the neutral emission dominates over the ionic emission, leading to a high signal-to-background ratio, which tends to decrease, however, at higher laser energy and air pressure.
Optical UV Derivative Spectroscopy for Monitoring Gaseous Emissions
Authors: Vogt F. , Klocke U. , Rebstock K. , Schmidtke G. , Wander V. , Tacke M.
Published: October 2003

UV derivative spectroscopy is investigated for its potential in online control of various processes. One typical application is emission monitoring of several pollutants such as SO2, NO, NO2, NH3, and aromatic hydrocarbons. The proposed method gains selectivity and sensitivity by using the first and second derivative of the transmission spectrum with respect to wavelength. These derivatives are generated in an optical manner and are compared empirically for the first time with the known numerical derivative spectroscopy and conventional transmission spectroscopy. The generation of the optical derivatives is discussed. For demonstration of the feasibility, laboratory monitoring results are reported. With the use of a sample pathlength of 10 cm with this optical method, detection limits are determined to be 4 ppm, compared to 11 ppm with numerically calculated signals and 20 ppm obtained by using the transmission only. Typically a time resolution of below three minutes is achieved. Emphasis is also laid on the treatment of an observed nonlinearity by means of chemometric calibration and evaluation algorithms such as principal component regression (PCR) and partial least-squares (PLS).
Determination of Parts-per-Trillion Levels of Chlorate, Bromate, and Iodate by Electrospray Ionization/High-Field Asymmetric Waveform Ion Mobility Spectrometry/Mass Spectrometry
Authors: Barnett David A. , Guevremont Roger , Purves Randy W.
Published: October 2003

An electrospray ionization (ESI) source was used to transfer oxoanions (XO3−) of nitrogen, chlorine, bromine, and iodine to the gas phase for analysis by a combination of high-field asymmetric waveform ion mobility spectrometry (FAIMS) and mass spectrometry. The combination of ESI with FAIMS and mass spectrometry (ESI-FAIMS-MS) yields mass spectra that are virtually free of common spectral interferences. The unique separation and focusing properties of the FAIMS analyzer improved signal-to-background ratios (S/B) for all these analytes by 3–4 orders of magnitude compared with conventional ESI-MS and produced parts-per-trillion (pptr) detection limits for ClO3−, BrO3−, and IO3− in methanolic solution.