bluuebunny/crossref_metadata_2025 huggingface dataset:
Metal Ion Sensors Based on a Luminescent Ruthenium(II) Complex: The Role of Polymer Support in Sensing Properties
Authors: Rowe Heather M. , Xu Wenying , Demas J. N. , DeGraff B. A.
Published: October 2003

Oxygen and copper(II) ion quenching studies were conducted on a model sensor system to elucidate the significant, yet not fully characterized, role of polymer supports in sensor performance. The system consisted of [Ru(Ph2phen)2(4-cyclamCH2(4′-Me)bpy)]Cl2 (Ph2phen = 4,7-diphenyl-1,10-phenanthroline; bpy = 2,2′-bipyridine; cyclam = 1,4,8,11-tetraazacyclotetradecane) as the sensor molecule, copper(II) ions as the quenching analyte, and two polymer supports. One polymer used was a cyclic siloxane cross-linked with a hydrophilic poly(ethylene oxide); the other was a ternary polymer with poly(ethylene oxide), poly(dimethylsiloxane), and 2-hydroxyethylmethacrylate. Both polymers contain a hydrophobic binding region for the sensor molecule and a hydrated hydrophilic region for transport of the ions to the sensor. Luminescence intensity and lifetime measurements show the polymer supports to be equally effective at shielding the sensor molecule from oxygen quenching but not copper(II) ion quenching. Unlike oxygen, the copper(II) ions quench the sensor molecule in solution and in the polymer supports through a combination of static and dynamic quenching. The unquenched excited state lifetimes, bimolecular rate constants, and equilibrium constants are presented, and their differences are interpreted to provide information about the local environment of the sensor molecule immobilized in the polymer supports.
Raman Microscopy and Mapping as a Probe for Photodegradation in Surface Relief Gratings Recorded on Layer-by-Layer Films of Congo Red/Polyelectrolyte
Authors: Constantino C. J. L. , Aroca R. F. , He J.-A. , Zucolotto V. , Li L. , Oliveira O. N. , Kumar J. , Tripathy S. K.
Published: October 2003

Raman microscopy, mapping, and surface-enhanced Raman scattering techniques have been applied to investigate the degradation of Congo Red (CR) in a surface relief grating (SRG) recorded on an electrostatically assembled layer-by-layer film of CR alternated with poly(dimethyl diallylammonium chloride) (PDAC). Photoinduced degradation was suggested by a decrease in the Raman bands assigned to CR with a concomitant increase in the background signal. More degradation was observed in the valleys of the SRG, which corresponded to the most illuminated areas. In a line mapping across the SRG, the Raman intensity of CR bands follows the modulation of the grating, which indicates that photodegradation of CR contributes at least partially to the SRG formation. Surface-enhanced resonance Raman scattering (SERRS) indicates that the phenyl ring groups are located at the film surface. Mapping of the Raman signal over many periods of SRG shows that, within the limits of detection, the chromophores appear to be oriented in much the same way throughout the film. They have no preferred orientation in the peaks and valleys of the SRG after the recording process has been completed.
Towards in situ Raman Microscopy of Single Catalytic Sites
Authors: Fokas Christian , Deckert Volker
Published: October 2003

We describe analytical techniques that allow an observation of heterogeneously catalyzed reactions, close to realistic chemical reaction conditions, with a spatial resolution down to 100 nm. Vibrational spectroscopy and scanning-force microscopy are combined to accomplish this goal. Raman microscopy is used for the investigation of the structural changes during heterogeneous catalytic reaction. This results already in a resolution of 1–2 μm, while in combination with scanning near-field optical microscopy (SNOM), a spatial resolution of even 100 nm has been achieved. Surface-enhanced Raman scattering (SERS) improves the sensitivity of Raman spectroscopy by many orders of magnitude and thus allows the study of a much broader range of reactions. As a model reaction system, the Pd catalyzed hydrogenation of benzene to cyclohexane was chosen. Spectra measured under reactive conditions differ significantly from reference spectra of the reactants and products measured under nonreactive conditions. This is explained by a structural change of the adsorbates on the activated surface but also by the possible formation of reaction intermediates.
Fourier Transform Infrared Microscopic Imaging of an Embedded Paint Cross-Section
Authors: Van Der Weerd J. , Brammer H. , Boon J. J. , Heeren R. M. A.
Published: October 2003

Fourier transform infrared imaging is presented as a new analytical approach in the study of paint cross-sections. Analytical FT-IR reflection imaging provides the spatially resolved acquisition of infrared spectra with a resolution of about 7 μm. The technique reveals detailed information on the organic functional group distribution in the individual layers of embedded paint cross-sections and is used complementary to visual microscopy and scanning electron microscopy/energy dispersed X-ray spectroscopy (SEM-EDX). This method was applied to a paint cross-section of Rembrandt's Portrait of a Standing Man (1639). FT-IR imaging of this cross-section identified and localized different compounds present in the layers of this sample. Identification of these compounds based on their infrared spectra is confirmed by results from art historical and conservation literature. Special attention was given to a discoloration that was observed in large parts of the described painting. This discoloration was clearly visible in the paint cross-section. A hypothesis on the nature of the discolored paint layer is formulated based on the FT-IR imaging results.
Variable Selection for Partial Least-Squares Calibration of Near-Infrared Data from Orthogonally Designed Experiments
Authors: Setarehdan S. Kamaledin , Soraghan John J. , Littlejohn David , Sadler Daran A.
Published: October 2003

A method of variable selection for use with orthogonally designed calibration data sets, such as factorial or partial factorial designs, is described. The procedure works by assessing the degree of correlation between each X variable (e.g., wavelength) and each Y variable (concentration, composition, etc.). The X variables are then ranked according to the degree of correlation. A forward selection method is then used to determine the optimum number of high-ranked variables to be used for calibration purposes. The algorithm was tested on a data set obtained by near infrared (NIR) spectrometry. Significant improvements in the prediction accuracy of partial least-squares (PLS) models were observed for two of the components in the chemical mixture by using the selected wavelengths in the NIR spectra rather than all the variables in the original spectra or the variables obtained using a spectral-variance-based variable selection method.
Analysis of Aqueous Solutions by Laser-Induced Breakdown Spectroscopy of Ion Exchange Membranes
Authors: Schmidt Norman E. , Goode Scott R.
Published: October 2003

Elemental analysis of solutions can be achieved by concentrating and immobilizing the metal ions into a commercially available ion exchange polymer membrane followed by laser-induced breakdown spectroscopy. Two methods of sample preparation were investigated: filtering the solution through the ion exchange membrane with suction, and placing the membrane in the solution and allowing the ions to equilibrate with the membrane. The membrane was then ablated with the focused energy of a Nd:YAG laser at 1064 nm. The emitted light was collected by an echelle spectrometer through a fiber-optic cable and detected with an intensified charge-coupled device (CCD). Ten different metals, most covered by the Resource Conservation and Recovery Act (RCRA), were studied. The concentrations of barium, cadmium, chromium, cobalt, copper, silver, lead, mercury, nickel, and zinc can be measured simultaneously with limits of detection ranging from 2 μg/mL to 4 ng/mL. The linear range is 2–6 orders of magnitude depending upon the element and sampling method. The major advantages of the technique are the multielement capability and the ease of sample preparation.
Remote Analysis of a Mineral Melt by Laser-Induced Plasma Spectroscopy
Authors: Panne U. , Neuhauser R. E. , Haisch C. , Fink H. , Niessner R.
Published: October 2003

The performance of a customized mobile laser-induced plasma spectroscopy (LIPS) system, based on a Nd:YAG laser for plasma ignition and an echelle spectrometer with an intensified charge-coupled device (CCD) camera, was tested during a field campaign for in situ and on-line process analysis of major constituents in a mineral melt of 1600 °C. After an optimization of the instrumental parameters, such as irradiance, gate width, and delay of the integration time relative to the laser pulse, LIPS allowed the on-line identification of all elements relevant for mineral wool production (i.e., Ti, Fe, Mn, Mg, Ca, Si, Na, and Al) directly from the melt in a rather harsh industrial environment. Validation of the LIPS analysis was performed via manual sampling and X-ray fluorescence (XRF) analysis. A reasonable correlation between the LIPS analysis and the reference analysis was obtained considering the experimental constraints; LIPS demonstrated, however, a superior temporal resolution. The observed differences between LIPS and XRF analysis during load changes of the oven are probably due to unknown processes in or on the melt or rheological effects, which were not detected by bulk reference analysis.
Fourier Transform Infrared Imaging of Nematic Liquid Crystals
Authors: Rafferty Denise Wade , Koenig Jack L. , Magyar Gregory , West John L.
Published: October 2003

Fourier transform infrared spectroscopy is often used to study liquid crystals and liquid crystal systems. In this work, the factors that influence the IR absorbance of nematic liquid crystals and their consequences on FT-IR imaging are examined. In the IR spectrum of E7, ordering in the nematic phase causes a 28.7% reduction in the nitrile band height relative to the isotropic phase, and the combination of ordering and liquid crystal director alignment causes a 65.0% decrease in the nitrile band height. For a phase-separated blend of E7 and 10% NOA65 polymer, the FT-IR images were found to be concentration-based for the polymer-specific carbonyl band and phase/alignment-based, which masked the concentration dependence, for the liquid crystal-specific nitrile band. These findings were exploited to produce an FT-IR image of the isotropic-to-nematic phase transition of neat E7. This transition image emphasizes the dependence of liquid crystal bands on ordering and alignment and the need for caution in the interpretation of FT-IR images of liquid crystals and liquid crystal systems.
Analysis of Thermal Phase Transition via Time-Resolved Infrared Spectra Using Partial Least-Squares Regression Modeling Parameters
Authors: Hasegawa Takeshi , Nishijo Jujiro , Sonoyama Masashi , Nakano Tatsuhiko
Published: October 2003

The thermal phase transition of dl-norleucine (crystalline) has been analyzed via time-resolved Fourier transform infrared (FT-IR) spectroscopy by using a double-scores plot calculated from partial least-squares regression (PLSR). In a previous study, the temperature-dependent spectra collected by time-resolved infrared spectroscopy suggested that another minor thermal phase transition would be present prior to the well-known major transition at ∼118 °C. Eigenvalue analysis by principal component analysis (PCA) suggested, however, that there were four distinguishable signal components, which was not consistent with the evaluation by the absorbance-change plot. In the present study, it has been noticed that a non-systematic response to the temperature increase is involved in the systematic spectral changes. To discriminate the temperature-independent (non-systematic) change from the temperature-related (systematic) changes, two scores of X- and Y-variables in the PLSR modeling have been comparatively used. The new evaluation has readily discriminated a non-systematic factor from basis factors, and the non-systematic factor has been attributed to fringes due to the optical setup used for the measurements.
Comparison of Organic Self-Assembled Monolayers as Modified Substrates for Surface-Enhanced Infrared Absorption Spectroscopy
Authors: Seelenbinder John A. , Brown Chris W.
Published: October 2003

The effect of using self-assembled monolayers to facilitate the physical and chemical adsorption of analytes onto surface-enhanced infrared absorption (SEIRA) gold substrates has been investigated. Self-assembled monolayers of thiopropane, thiohexane, and thiophenol were tested to determine the response for short and medium-size normal alkanes monolayers and aromatic monolayers. The analytes consisted of 4,6-difluoro-nitrobenzene, o-dinitrobenzene, 4,6-dinitro- o-cresol, and tri-nitrobenzene. Spectral results for the self-assembled monolayers were compared to those obtained with an uncoated gold SEIRA surface and with typical transmission spectra of the same test samples. Some enhancement was obtained in all cases; however, the aromatic thiol monolayer produced the largest enhancements, with a maximum increase of 21 fold. As a practical application of the SEIRA technique, a prototype sensor for the detection of trinitrotoluene (TNT) was prepared and tested.
Simple Preparation Method for Silver SERS Substrate by Reduction of AgNO3 on Copper Foil
Authors: Nie Chong-Shi , Feng Zuru
Published: October 2003

A simple new preparation method for silver surface-enhanced Raman scattering (SERS) substrate (Ag/Cu film) was developed by reduction of aqueous Ag+ on copper foil, which is used for making print circuit board. The properties of the substrate were evaluated. The approximate limit of detection (LOD) was measured using 2,2′-bipyridine (bpy) and 1,1′-diethyl-trimethincyanine dye (TMC) as probing compounds. The LOD of bpy and TMC are 1 nanomole and 0.13 nanomole, respectively. The film-to-film reproducibility is comparable to the nitric acid etched silver foil SERS substrate. The surface morphology of the Ag/Cu film was observed by scanning electron micrography. The high SERS sensitivity of the film may be attributed to its special surface structure.
Fourier Transform Infrared, UV-Visible, and X-Ray Diffraction Analyses of Organic Matter in Humin, Humic Acid, and Fulvic Acid Fractions in Soil Exposed to Elevated CO2 and N Fertilization
Authors: Naidja A. , Huang P. M. , Anderson D. W. , Van Kessel C.
Published: October 2003

FT-IR, UV-visible, and X-ray diffraction analyses were used to investigate the nature of organic matter in three fractions of soil humic substances (humin, HU; humic acid, HA; and fulvic acid, FA) extracted at a depth of 0–10 cm from the soil under rye grass ( Lolium perenne) culture. FT-IR and XRD analyses showed that the extracted HAs still contained the clay matrix, but the extracted FAs, which were purified by adsorption-desorption from a macroreticular nonionic resin, were free from the clay mineral constituents. The data obtained in the present study shed more light on the chemical structure of the HU, HA, and FA fractions in the infrared absorption band region of 400–1000 cm−1 where the assignments of bands are still lacking in the literature. The bands characteristic of organic functional groups, especially benzene rings and condensed aromatics, which were masked by the strong bands of the clay matrix in the HU and HA fractions, were clearly shown in the FA fraction, which was free from the clay mineral constituents. While the UV-visible spectra of HAs and FAs were similar, the E465/E665 ratios of HAs were about three times lower than those of FAs. Amounts of carboxyl groups, determined by titration, were about four times higher in the FA than in the HA fraction, which is in agreement with the FT-IR analysis. The HU, HAs, and FAs fractions extracted from the soil under the same culture and exposed to elevated CO2 levels (60 Pa pCO2) under different N fertilizer application rates (100 and 420 kg N/ha) were also studied. The results show that there was no significant change in the spectra of HU, HAs, and FAs extracted from soils exposed to elevated CO2 for 2 years. In contrast, elevated CO2 combined with a high N fertilization rate resulted in a remarkable increase of the acidic OH groups of the FA.
Comparison of an Innovative Nonlinear Algorithm to Classical Least-Squares for Analyzing Open-Path Fourier Transform Infrared Spectra Collected at a Concentrated Swine Production Facility
Authors: Childers Jeffrey W. , Phillips William J. , Thompson Edgar L. , Harris D. Bruce , Kirchgessner David A. , Natschke David F. , Clayton Matthew
Published: October 2003

Open-path Fourier transform infrared (OP/FT-IR) spectrometry was used to measure the concentrations of ammonia, methane, and other atmospheric gases at an integrated swine production facility. The concentration-pathlength products of the target gases at this site often exceeded the linear dynamic range of the OP/FT-IR spectrometer. To minimize the effect of this nonlinearity on the accuracy of the reported concentrations, a piecewise, linear classical least-squares (CLS) analysis method, which used a calibration set containing multiple reference spectra for each target gas at concentration-pathlength products that encompassed those found in the field spectra, was used to predict the path-averaged concentrations of the target gases. The predicted concentrations reported by this piecewise, linear CLS method were compared to those predicted by a conventional linear CLS method, which used a calibration set consisting of only one reference spectrum at a single concentration-pathlength product for each target gas, and an innovative nonlinear algorithm (NLA), which performs an iterative fit of the convolved spectral line data from the high-resolution transmission molecular absorption (HITRAN) database to the single-beam field spectra. The conventional, linear CLS method generally under-reported the target gas concentrations relative to those predicted by the piecewise, linear CLS method when the field spectra exhibited concentration-pathlength products larger than those of the reference spectra in the single-level calibration set. In extreme cases, for example, during measurements of methane along the waste lagoon, the concentrations predicted by the conventional CLS methods were more than 30% lower than those predicted by the piecewise, linear CLS method. In contrast, the concentrations of methane predicted by the NLA were, on average, within 4% of those predicted by the piecewise, linear CLS method. For ammonia, however, the concentrations predicted by the NLA were slightly higher than those predicted by the piecewise, linear CLS method at the lower range of observed concentration-pathlength products and slightly lower than those predicted by the piecewise, linear CLS method at the upper range of concentration-pathlength products. The NLA also consistently predicted higher concentrations of nitrous oxide and carbon dioxide relative to that predicted by the piecewise, linear CLS method. Differences in the background spectra and spectral ranges over which the analyses were conducted apparently did not contribute to the differences in the path-averaged concentrations predicted by these two analysis methods.
Fast Monitoring of the Molecular Orientation in Drawn Polymers Using Micro-Raman Spectroscopy
Authors: Voyiatzis George A. , Andrikopoulos Konstantinos S.
Published: October 2003

A new method is proposed for the estimation of the segmental orientation of vinyl or vinylidene polymers of moderate crystallinity by acquisition of only one Raman spectrum at a specific polarization geometry. A highly anisotropic rigid rod or/and resonant Raman-active guest-agent incorporated into a host-polymer can be easily detected at low concentration levels and can be used as an indicator of the molecular orientation of the processed host-polymer. A suitable polarized Raman measurement and the automatic calculation of the ratio of two Raman bands, one sensitive and another roughly nonsensitive to the drawing process, may allow, via an appropriate calibration curve, a continuous on-line molecular orientation monitoring of drawn vinyl and vinylidene polymers during an industrial process. Polymers of common use, like poly(vinyl chloride) (PVC), isotactic polypropylene ( iPP) and poly(vinylidene fluoride) (PVF2), were selected for the application of the methodology in question. Promising results were derived utilizing a new custom-made flexible laser Raman instrumentation bearing a specially designed polarized Raman micro-probe able to accumulate fast-polarized Raman spectra in all backscattering polarization geometries.
Assessment of One- and Two-Photon Excited Luminescence for Directly Measuring O2, pH, Na+, Mg2+, or Ca2+ in Optically Dense and Biologically Relevant Samples
Authors: Baker Gary A. , Munson Chase A. , Bukowski Eric J. , Baker Sheila N. , Bright Frank V.
Published: October 2003

We compare the emission spectra and analytical response profiles of several semiselective luminescent probes that are commonly used to quantify nonfluorescent analytes (ruthenium(II) tris(2,2′-bipyridyl) dication, tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) dication, SNARF®-1, fluorescein, Rhodol Green™, and Sodium™, Magnesium™, and Calcium Green™) when they are excited under one- and two-photon excitation conditions in water, aqueous solutions of dyes or fluorophores, undiluted mouse or human serum, human urine, and mouse whole blood. The results from this work can be summarized as follows. First, in cases where the probes possess ground states that are composed of multiple species in equilibrium (e.g., acid and base forms of a luminophore), the analyte-dependent emission spectra can be significantly different under one- and two-photon excitation conditions due to differences in the relative one- and two-photon cross-sections associated with the individual ground-state species. Second, for those probes that exhibit one- and two-photon dependent emission spectra, an assessment of the analytical response vs. target analyte concentration profiles show that the response dynamic range can be improved by up to 100 fold, but the response sensitivity can decrease by up to 25% for two- vs. one-photon excitation. Third, two-photon excited luminescence provides a means to use these semiselective luminescent probes to quantify nonfluorescent analytes directly within optically dense mixtures, including solutions of dyes, mouse or human serum, human urine, and mouse whole blood. Finally, two-photon excited luminescence allows one to quantify nonfluorescent analytes in a spatially defined manner within complex samples.
New Hybrid Algorithm for Maintaining Multivariate Quantitative Calibrations of a Near-Infrared Spectrometer
Authors: Wehlburg Christine M. , Haaland David M. , Melgaard David K. , Martin Laura E.
Published: October 2003

Our newly developed prediction-augmented classical least-squares/partial least-squares (PACLS/PLS) hybrid algorithm can correct for the presence of unmodeled sources of spectral variation such as instrument drift by explicitly incorporating known or empirically derived information about the unmodeled spectral variation. We have tested the ability of the new hybrid algorithm to maintain a multivariate calibration in the presence of instrument drift using a near-infrared (NIR) spectrometer (7500–11 000 cm−1) to quantitate dilute aqueous solutions containing glucose, ethanol, and urea. The spectral variations required to update the multivariate models for both short- and long-term drift were obtained using a single representative midpoint sample whose spectrum was repeatedly measured during collection of calibration data and during collection of separate validation sample spectra on three subsequent days. The performance of the PACLS/PLS model for maintaining a calibration was compared to PLS with subset recalibration, a method that has previously been applied to maintenance and transfer of calibration. Without drift corrections, both PACLS/PLS and PLS had poor predictive ability on sample spectra collected on subsequent days. Unlike previous maintenance of calibration studies that corrected for long-term drift only, the PACLS/PLS and PLS models demonstrated the best predictive abilities when short-term drift was also corrected. The PACLS/PLS hybrid model outperformed PLS with subset recalibration for near real-time predictions when instrument drift was determined from the repeat samples closest in time to the measurement of the unknown. Near real-time standard errors of prediction (SEPs) for the hybrid model were comparable to the cross-validated SEPs obtained with the original calibration model.
Characterization of Iron Hydroxides in a Weathered Rock Surface by Visible Microspectroscopy
Authors: Nagano Tetsushi , Isobe Hiroshi , Nakashima Satoru , Ashizaki Midori
Published: October 2003

In order to nondestructively characterize chemical forms of ferric hydroxides in weathered rock, charge-coupled device type visible microspectroscopy was applied to brown stains produced in weathered granite surfaces. The combination of visible microspectra and color parameters ( a* and b*) was effective in examining chemical forms of ferric hydroxides in the analytical area. Color parameters in an a*– b* diagram of the brown stains, mostly lying between goethite and ferrihydrite trends, indicated that the brown stains contain ferrihydrite or hematite in addition to goethite. Similarity of the visible microspectra of the brown stains and their first derivatives to those of goethite or ferrihydrite suggests that goethite and/or ferrihydrite are the main weathering products of the granite. Occurrence of ferrihydrite as well as goethite in the brown stains implies that crystallization of ferrihydrite to goethite might be hindered during the granite weathering. This fact suggests the possibility of toxic metal retention in ferrihydrite by its long-term persistence during water–rock interactions at the earth's surface.
Neon Inductively Coupled Plasma for Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry
Authors: Petibon Caroline M. , Longerich Henry P. , Horn Ingo , Tubrett Mike N.
Published: October 2003

The use of a neon inductively coupled plasma (Ne ICP) in place of an argon inductively coupled plasma (Ar ICP) for laser ablation microprobe-inductively coupled plasma-mass spectrometry (LAM-ICP-MS) is demonstrated. Gas blank mass spectra were obtained comparing the signals obtained with an Ar ICP with the Ne ICP. Sensitivity (signal/concentration) data were also obtained for a number of analytes using solid reference materials. The sensitivity data is complicated by significant changes in optimum Ne ICP parameters (especially nebulizer gas flow) for analytes of varying mass. The sensitivity of the Ne ICP is in general also lower than that obtained for the Ar ICP. The potential for the Ne ICP to reduce the formation of argides, both in the background and from sample induced interferences, is demonstrated. Clearly shown is the reduction of the interferences of 63Cu40Ar and 65Cu40Ar on 103Rh and 105Pd in a Cu2S sample, as well as the reduction of the interferences of 58Ni40Ar and 60Ni40Ar on 98Ru and 100Ru in a NiS sample.
Stress Mapping in Silicon: Advantages of Using a Raman Spectrometer with a Single Dispersive Stage
Authors: Bonera E. , Fanciulli M. , Batchelder D. N.
Published: October 2003

Stress is a major concern in microelectronic circuit production and Raman spectroscopy has proved to be an outstanding method for mapping it in silicon. In the literature, a configuration with two or three spectral dispersive stages is usually employed. By using a Raman spectrometer with a single dispersive stage, however, it is possible to have higher collection efficiency, resulting in fast acquisition and high stability of the system. Although the nominal spectral resolution of such a system is approximately 2 cm−1, we have found that the sensitivity to stress is less than 50 MPa, comparable to other systems with more dispersive stages. For low stress values, less than 100 MPa, the Raman measurements can be affected by the patterning of the sample itself, especially if laser plasma lines are used for spectral calibration. It will be shown that the use of a Raman microscope with a single dispersive stage, enabling simultaneous collection of Stokes and anti-Stokes components, provides a feedback for the reliability of the experiment.
Effect on Noise of Intensity-Axis Correction of Spectra Recorded with Charge-Coupled Device Detectors
Authors: Jones Jay Pendell , Wambles Ronald E. , Mann Charles K. , Vickers Thomas J.
Published: October 2003

We have examined the effect of intensity-axis correction on noise in white light spectra recorded with charge-coupled device (CCD) detectors. Measurements were made with five detectors in Raman spectrometers. Detectors were both liquid-nitrogen and thermoelectrically cooled devices and one room temperature device. Both random and pattern noise have been considered. We used cross-correlation of noise sets to provide an indicator of a fixed pattern in the spectra and an assessment of the efficacy of the correction procedure in removing this pattern. For four of the five detectors intensity-axis correction provided a significant improvement in signal-to-noise ratio. Correction was particularly important for measurements made with lower-cost CCD detectors of the kind proposed for process control instruments.
Control of Teflon AF 2400 Permeability in a Liquid-Core Waveguide by an Ultra-Thin Crosslinked Polyamide Coating
Authors: Inya-Agha Obianuju , Stewart Shona , Veriotti Tincuta , Bruening Merlin L. , Morris Michael D.
Published: October 2003

In the last few years Teflon AF has emerged as the leading material for implementing waveguiding with an aqueous core because of its low refractive index (nD = 1.29). This low index should make it possible for very low limits of detection to be achieved in Teflon AF as a result of the ability to excite with laser light over an increased area. Detection limits have remained high, however, due in part to the porosity of the material. In this communication we report a significant reduction in the permeability of Teflon AF 2400 capillary walls with the deposition and subsequent treatment of polyelectrolyte multilayers. Alternating layers of polycations and polyanions on a bare Teflon AF surface are sufficient to reduce its permeability to small molecules such as methanol and benzene. Crosslinking and deprotonation of these multilayers further reduces permeability to less than 10% of the permeability value through uncoated TAF. As a consequence, detection limits are reduced. Evidence of these results is presented with gas chromatography-mass spectrometry (GC/MS) and Raman spectroscopic measurements.
Fourier Transform Infrared Microspectroscopy as a Tool to Differentiate Nitzschia Closterium and Nitzschia longissima
Authors: Vardy Suzanne , Uwins Phillipa
Published: October 2003

Nitzschia closterium and Nitzschia longissima are two species of diatom that are extremely difficult to differentiate using light microscopy. This paper details an investigation into the use of FT-IR microscopy combined with discriminant analysis to differentiate between these species. Spectra were taken from unidentified samples and classified against a training set using either Mahalanobis distances or principal component analysis combined with canonical discriminant analysis. Unidentified samples were classified with a 100% accuracy using both mathematical techniques.
Quantitative Determination of Epoxidized Soybean Oil Using Near-Infrared Spectroscopy and Multivariate Calibration
Authors: Parreira Thais F. , Ferreira Márcia M. C. , Sales Henrique J. S. , De Almeida Wanderson B.
Published: October 2003

The quality of epoxidized soybean oil (ESO), industrially used as a plasticizer and heat stabilizer for PVC films, is given by the degree of epoxidation (EI), the number of double bonds expressed as the iodine index (II), and the water percentage in the final product. In this work, near-infrared (NIR) spectra recorded off line at the chemical industry during the epoxidation process, combined with the multivariate regression method partial least squares (PLS), was used for the quantification of EI, II, and water percentage in the ESO. The water levels were determined by the Karl Fischer titration. The content of iodine was determined by iodometry. The epoxide index was obtained by the hydrogen bromide reaction with the epoxide ring. On average, 50 samples were used to model each analyte and 10 were used for external validation. The results, expressed in terms of the statistical parameters RPD (ratio of standard deviation of experimental concentrations to the standard deviation of the residuals) and RER (ratio error range), were excellent for the EI (26.02 and 80.70, respectively). For the water % and II, the obtained results were fairly good. Good correlations between predicted and real concentrations were attained (0.984, 0.966 and 0.974 for water %, II, and EI, respectively). It is shown in this work that the use of NIRS combined with chemometric methods are of great importance, especially for industrial purposes.
Combined Application of Imaging Methods for the Characterization of a Polymer Blend
Authors: Gupper A. , Wilhelm P. , Schmied M. , Kazarian S. G. , Chan K. L. A. , Reußner J.
Published: October 2003

Morphological studies were performed on a polymer blend, used as a friction bearing, consisting of polyamide 6.6 (80%), poly-(tetrafluoroethylene) (18%), and silicone oil (2%). Raman imaging, FT-IR imaging, scanning electron microscopy with energy-dispersive X-ray spectrometry, and microthermal analysis determined the distribution of poly(tetrafluoroethylene) clusters in the polyamide matrix. Each characterization method allows qualitative identification of the main components and provides information about cluster size and distribution. It is proved that poly(tetrafluoroethylene) clusters of 10 to 30 μm are randomly distributed in a polyamide matrix and that silicone oil can be found at the cluster matrix interface. The good agreement that was obtained in our investigations indicates high reliability of the results since all applied methods are based on different chemical and physical properties. This combined approach revealed information about the morphology of the blend for a better understanding of its working principle and enhanced knowledge for its processing. A comparison of the different methods employed in this study highlights their advantages and limitations for polymer analyses.
New Approach to Generalized Two-Dimensional Correlation Spectroscopy. 1: Combination of Principal Component Analysis and Two-Dimensional Correlation Spectroscopy
Authors: Jung Young Mee , Shin Hyeon Suk , Kim Seung Bin , Noda Isao
Published: October 2003

The direct combination of chemometrics and two-dimensional (2D) correlation spectroscopy is considered. The use of a reconstructed data matrix based on the significant scores and loading vectors obtained from the principal component analysis (PCA) of raw spectral data is proposed as a method to improve the data quality for 2D correlation analysis. The synthetic noisy spectra were analyzed to explore the novel possibility of the use of PCA-reconstructed spectra, which are highly noise suppressed. 2D correlation analysis of this reconstructed data matrix, instead of the raw data matrix, can significantly reduce the contribution of the noise component to the resulting 2D correlation spectra.
Characterization of Transition Temperatures of a Langmuir—Blodgett Film of Poly(tert-butyl Methacrylate) by Two-Dimensional Correlation Spectroscopy and Principal Component Analysis
Authors: Jung Young Mee , Shin Hyeon Suk , Czarnik-Matusewicz Boguslawa , Noda Isao , Kim Seung Bin
Published: October 2003

External reflection FT-IR spectra of a Langmuir–Blodgett (LB) film of poly( tert-butyl methacrylate) (PtBMA) were measured at temperatures ranging from 26 to 136 °C. The glass transition temperature ( Tg) was determined from a two-dimensional (2D) mapping of the first derivative spectra of absorbance values against temperature over the wavenumber range 1100–1300 cm−1, which contains spectral features that are very sensitive to conformational changes. This mapping provides a surprisingly simple and direct method for detecting the value of Tg. The glass transition temperature determined from the 2D map was approximately 84 °C. Another transition at 103 °C, corresponding to the glass transition temperature of bulk PtBMA, was also detected from the 2D map. Principal component analysis (PCA) was employed to analyze the temperature-dependent FT-IR spectra. The glass transition temperatures (80 °C; 100 °C) of the PtBMA LB film determined by the score plot of PCA are consistent with those determined by the 2D map. Additionally, the loading vectors of PCA were found to give valuable insight into the molecular-level phenomena associated with the glass transition process. To gain more details about the polymer chain mobility, two-dimensional (2D) correlation analysis was performed on two sets of FT-IR spectra collected above and below Tg. In the synchronous 2D correlation spectrum obtained below the glass transition temperature (26–66 °C), the observation that the strongest intensity change occurs at 1137 cm−1 indicates that the reorganization of the bending mode of the bbC–C–O and bbC–C=O bonds connected to the backbone (bb) chain and coupled to the C–O stretching mode of the tert-butoxy group is potentially the mechanism underlying the β-transition. This result is in good agreement with the presence of a transition (β-transition) at approximately 43 °C obtained from the band around at 1137 cm−1 in the 2D mapping data.
Challenges in Interpreting Vibrational Sum Frequency Spectra: Deconvoluting Spectral Features as Demonstrated in the Calcium Fluoride—Water—Sodium Dodecylsulfate System
Authors: Moore Fred G. , Becraft Kevin A. , Richmond Geraldine L.
Published: October 2003

Vibrational sum frequency spectroscopy is used to examine the CaF2/H2O interface and the CaF2/D2O interface upon adsorption of the anionic surfactant sodium dodecylsulfate (SDS) onto the CaF2 surface. Proper interpretation of the results from this coherent spectroscopic technique requires a meticulous understanding of the interferences that result between sharp CH stretching modes, broad OH stretching modes, and the nonresonant background. The reported studies demonstrate the appropriate spectral analysis procedure required for a correct interpretation of spectra of this type and the errors that can result from a more simplistic but commonly used analysis procedure.
R-Line Luminescence from Trace Amounts of Cr3+ in Aluminum Oxide and its Dependence on Sample Hydration
Authors: Zuo Chen , Jagodzinski Paul W.
Published: October 2003

The R-line luminescence is observed in the Raman spectra of α- and γ-Al2O3 with chromium concentrations of less than 1 ppm. The same signals were previously used to monitor the setting reaction of dental cements. With laser excitation <690 nm, the R-line luminescence can be observed in the optical spectra of most commercial products containing α-Al2O3. It is found that the intensities of R-line signals are related to the degree of hydration of the α-Al2O3 sample, which can be explained by the formation of additional octahedral sites for Cr3+ near the sample surface involving oxygen atoms from the Al2O3 matrix and from absorbed water molecules.
Microchannel Thin Layer Chromatography with in situ Plate Scanning Micro-DRIFTS Detection Using Plain and Polybutadiene Modified Zirconia Stationary Phases
Authors: Musial Beata A. , Sommer André J. , Danielson Neil D.
Published: October 2003

Thin layer chromatography (TLC) of various dyes is compared in microchannels packed with either bare zirconia (normal phase) or polybutadiene (PBD) modified zirconia (reversed phase). In situ micro-diffuse reflectance infrared Fourier transform spectroscopy (μDRIFTS) of the analyte spots is possible due to the low absorption background of both plain and PBD zirconia. An instrument coupling μDRIFTS with a motorized stage that could profile the microchannel TLC plate is developed. The retention order of anthracene and pyrene probes as a function of percent acetonitrile are generally as expected on PBD zirconia but opposite for plain zirconia. Impurities in technical grade methylene blue can be determined after TLC separation on plain zirconia. The separation and infrared identification of various dyes such as dichlorofluorescein and rhodamine B on PBD zirconia is improved using a mobile phase with an additive such as phosphate or dihexylamine that prevents band streaking.
Tools to Rapidly Produce and Screen Biodegradable Polymer and Sol-Gel-Derived Xerogel Formulations
Authors: Cho Eun Jeong , Tao Zunyu , Tang Ying , Tehan Elizabeth C. , Bright Frank V. , Hicks Wesley L. , Gardella Joseph A. , Hard Robert
Published: October 2003

A new method to rapidly produce and screen biodegradable polymer- and xerogel-based formulations is described. The approach is based on a high-speed pin printer and imaging with an epi-fluorescence microscope/charge-coupled device detector. By using this approach we can produce and screen over 600 formulations/h and rapidly identify lead formulations and/or compositions that are the most useful for the development of biodegradable devices or (bio)sensors.
FT-IR Imaging of the Thermal Oxidation of Polyisoprene (PI) Rubber at High Temperature
Authors: Li Gui-Yang , Koenig J. L.
Published: October 2003

The thermal aging of PI rubber in hot air (140 °C) has been studied using the FT-IR imaging technique. From the analysis of the FT-IR images of the absorbance of the carbonyl (C=O) groups, it was found that the most significant thermal oxidation occurred at the surface of the rubber with a decreasing gradient of oxidation from the surface to the interior of the system. The hydroxyl (OH) groups followed the same pattern as the carbonyl groups. The C=C double bonds decreased from the interior of rubber to the surface, demonstrating the existence of a highly cross-linked oxidative coating, which functions as a protective layer blocking further invasion of the oxygen. The depth of the oxidation coating was constant at approximately 160 μm and the most significant oxidation layer was ∼90 μm after 10 h oxidation. Based on the FT-IR images as a function of time, the oxidation process is interpreted and classified in terms of four time periods: an induction period, a rapid oxidation period, a slow oxidation period, and a diffusion-forbidden period. Both the thickness of the oxidation coating and the degree of oxidation at different depths show that the oxidation process is auto-catalytic and the induction period is approximately two hours.
Quantitative Analysis of Epoxy Resin Cure Reaction: A Study by Near-Infrared Spectroscopy
Authors: Billaud C. , Vandeuren M. , Legras R. , Carlier V.
Published: October 2003

Near-infrared spectroscopy was used to quantify the cure reaction of 4,4′-methylene- bis-(2,6-diethylaniline) (MDEA)–epoxy resins (E/A = 1.4) carried out at 72 and 160 °C. The absorption bands of the functional groups of interest in MDEA–epoxy resins are assigned according to the literature. A new assignment at 6580 cm−1 is also proposed for the secondary amine: it was supported by a synthesized model compound. Two different spectrum treatments were proposed. The first one is based only on a normalization at 4610–4620 cm−1, while the second one needs the subtraction of the normalized spectrum of a post-cure sample. To follow the curing process, amines and epoxy were studied at the same time in the combination and the overtone regions. The results are compared. In the combination region, quantitative results are obtained from absorbance measurements, while in the overtone region spectrum decompositions and area measurements are necessary. Complementary and reliable information are so obtained and allow us to calculate conversions of epoxide and amine I and concentrations in amine II, amine III, hydoxyl groups, and ether links. Kinetics are also established. The curing process mechanism is at last discussed for both curing temperatures.
Use of Entropy Minimization for the Preconditioning of Large Spectroscopic Data Arrays: Application to in Situ FT-IR Studies from the Unmodified Homogeneous Rhodium Catalyzed Hydroformylation Reaction
Authors: Chen Li , Garland Marc
Published: October 2003

In situ spectroscopic measurements are fairly common in homogeneous catalysis. However, although it is easy to accumulate vast amounts of data, their appropriate analysis becomes a critical issue. Accordingly, we have developed a simple-to-implement but numerically sophisticated tool. Let A denote a matrix of absorbance data, n denote the number of preliminary spectra obtained from the stepwise addition of reagents, k denote the number of sequential reaction spectra, and v the spectroscopic channels. Then the preconditioning problem can be stated as [Formula: see text]. A single experiment results in (1) a set of n “pure” component reference spectra and (2) a set of k preconditioned reaction spectra where the reagents have been optimally subtracted. Entropy minimization is examined as a means of achieving both objectives. The developed algorithm was applied to a set of FT-IR spectra obtained from a complex transition-metal homogeneous catalyzed organic synthesis. Excellent reference spectra and excellent preconditioned reaction spectra were readily obtained. In addition, the absorbance of the products in the preconditioned spectra was compared to the absorbance obtained after manual user-defined subtraction. Comparable results were obtained. The present approach is clearly useful for the automated numerical treatment of very large sequential spectroscopic data arrays arising from in situ kinetic studies. Extension to related types of problems in the chemical sciences and to other spectroscopic methods such as NMR are obvious.
Spectroscopic Study of Ultrashort Pulse Laser-Breakdown Plasmas in Air
Authors: Martin F. , Mawassi R. , Vidal F. , Gallimberti I. , Comtois D. , Pépin H. , Kieffer J. C. , Mercure H. P.
Published: October 2003

Time-resolved visible spectroscopy of plasmas produced by laser breakdown of air using femtosecond Nd laser pulses (50–300 mJ, 500 fs) reveals features not observed with nanosecond laser pulses. Emission is initially dominated by molecular lines, specifically the second positive system of N2 and the first negative system of N2+. This is followed by continuum emission with a growth time of ∼3 ns and a decay time of ∼30 ns. Atomic lines of N and O emerge from the decay of the continuum and last up to 1 μs; only faint ionization lines are observed. Several of the atomic lines are initially strongly broadened, narrowing over a period of 100 ns.
Determination of the Information Depth and Sample Size for the Analysis of Pharmaceutical Materials Using Reflectance Near-Infrared Microscopy
Authors: Clarke Fiona C. , Hammond Stephen V. , Jee Roger D. , Moffat Anthony C.
Published: October 2003

The depth near-infrared (NIR) radiation penetrates into a sample during spectral acquisitions in NIR reflectance microscopy was investigated for pharmaceutical materials. Cellulose and its derivatives are widely used as excipients for pharmaceuticals and hence, were the basis for this study. The evaluation of the depth of sample contributing to the measured reflected radiation (information depth) was achieved using varying thicknesses of cellulose placed on top of a substrate. Analyzing the change in the absorption profile of the substrate showed the relationship between thickness and absorption to be exponential. The information depth was evaluated using the point where the substrate signal was reduced by 50%, termed the DP50 value. The DP50 value ranged from 39 to 61 μm at ∼1675 nm, but was found to have an exponential relationship with wavelength. Longer wavelengths had less penetration into the sample; at 2380 nm the DP50 was ∼27 μm but this increased to ∼180 μm at 1100 nm. The sample size was determined using the information depth and an approximate model for the contributing sample volume. Sample size was found to be within the range of 0.03–418 μg of sample per NIR spectrum depending on the wavelength used.