bluuebunny/crossref_metadata_2025 huggingface dataset:
Tomography of Optical Emission Line Intensities of a Radio-Frequency Magnetron Discharge
Authors: Debal F. , Wautelet M. , Dauchot J. P. , Hecq M.
Published: October 2003

An experimental setup for spectroscopic optical tomography of glow discharges is presented. It combines a fiber-optics system with a monochromator coupled to a charge-coupled device (CCD) camera. The light emitted by the discharge is sent to the input of 10 optical fibers through a collimating system. The outputs of these optical fibers are coupled to the entrance slit of a monochromator. The CCD camera is in the output slit. This arrangement allowed us to acquire 10 spectra simultaneously, each being associated with a small zone of the discharge. By translation of the optical fibers, the whole discharge was studied. The data were then analyzed by means of a tomographic reconstruction program in order to obtain the three-dimensional spectroscopic optical tomography, for a large number of lines. This experimental setup was used to deduce the three-dimensional optical emission of various lines of a radio-frequency (rf)-powered magnetron discharge. The discharge deals with an aluminum base alloy cathode, sputtered by Ar. Emission lines corresponding to the cathode (Al: 394.4- and 396.2-nm lines) and the gas discharge (Ar: 763.5 nm-line) were considered. The three-dimensional emission profiles, I( r, Z), of the lines were measured; r is the distance from the center of the cathode, and Z is the distance from the cathode. I( r, Z) profiles are different for the Al and Ar lines. The effects of the electrical power and the pressure were also studied. It was found that the corresponding I( r, Z) profiles behave differently with the pressure. In order to compare the results, I( r, Z) was fitted with an empirical analytical mathematical function, with parameters depending on pressure. At high pressure, the shape of I( r, Z) for the Al line tends towards the shape of the Ar line.
Oxygen Sensors Based on Luminescence Quenching: Interactions of Tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) Chloride and Pyrene with Polymer Supports
Authors: Kneas Kristi A. , Xu Wenying , Demas J. N. , DeGraff B. A.
Published: October 2003

Oxygen quenching of [Ru(Ph2phen)3]Cl2 (Ph2phen = 4,7-diphenyl-1,10-phenanthroline) and pyrene has been studied in a series of polymer networks of Gp-163 (a methacryloxy functional polydimethylsiloxane) co-polymerized with one of several co-monomers: styrene, trimethylsilyl-methylmethacrylate (T3642), vinyl-tris(2-methoxy-ethoxy)silane, or vinyl-tris(trimethylsiloxy)silane. Sensor performance was studied as a function of the polymer composition in order to delineate the important features for satisfactory O2 sensor supports. Quenching behavior was examined as a function of polymer structure, including amount and type of co-monomer. This work shows that the earlier two-domain model is too simplistic. The relative affinities of the different domains for the [Ru(Ph2phen)3]Cl2 and pyrene and the efficacy of the domains for O2 quenching are important; however, subtle changes in microstructure within domains can also strongly affect behavior. In particular, T3642 exhibits excellent structural and good quenching properties with [Ru(Ph2phen)3]Cl2.
Thermal Decomposition Analysis of Spin-Coated Films of Partly Protected Polyvinylphenol with the t-Butoxycarbonyl Group Using Time-Resolved IR
Authors: Tanimura Sachiko , Kumada Teruhiko , Ueyama Akemi , Kobayashi Junji , Kuramoto Kazuo
Published: October 2003

Thermal decomposition of spin-coated films of partly protected polyvinylphenol with the t-butoxycalbonyl ( tBOC-PVP) group has been investigated by monitoring the intensity of the carbonyl stretching peak of the tBOC group by using temperature-variable time-resolved infrared spectroscopy (TR/IR). The temperature programming method has been used for determining the activation energy ( Ea) of the thermal decomposition. We compared the thermal decomposition behavior of tBOC-PVP films with that of the powders and the behavior of a 22% protected tBOC-PVP film with that of a 66% protected tBOC-PVP film. It was found that the Ea of the 22% protected tBOC-PVP film is distinctively higher than the others including the result given from thermogravimetric analysis (TG). In addition, the Ea of the 22% protected tBOC-PVP film increased up to 50 kcal/mol with the decrease of the remaining tBOC group, while the others were constant at 30 kcal/mol. Diglyme, which was used as the solvent in the 22% protected tBOC-PVP film, was residual after the temperature increased above 80 °C, and the reaction velocity of the tBOC group increased in accordance with the generation of the OH group. These results suggest that the OH group, which accelerates the thermal decomposition of tBOC-PVP, is hindered by the residual solvent in the case of the 22% protected tBOC-PVP films.
Stability and Surface Uniformity of Selected Thiol-Coated SERS Surfaces
Authors: Deschaines Timothy O. , Carron Keith T.
Published: October 2003

The use of surface-enhanced Raman scattering (SERS) as an analytical technique continues to grow, but questions about its viability remain. This paper addresses the concern about the long-term stability of the surfaces used with the SERS technique. We have studied the long-term stability of Ag surfaces coated with three different thiol compounds. For this study, we have used 1-propanethiol, 1-do-decanethiol, and p-cresolthiol to coat the Ag surfaces. These surfaces showed long-term stabilities of over a month with minimal surface degradation. In order to mimic a realistic application of SERS, we stored the coated surfaces in a solution of water. Sodium dodecylsulfate (SDS) was added to maintain consistent surface wetting conditions so that reproducible results were obtainable on a day-to-day basis. Spatial heterogeneity of the surfaces and coating was analyzed with a fiber-optic Raman system. The spatial heterogeneity of the surfaces explains the day-to-day variations observed in the detection when the same portion of the surface used for analysis varies from day to day.
Application of Coherent Anti-Stokes Raman Scattering (CARS) Technique to the Detection of NO
Authors: Doerk T. , Ehlbeck J. , Jedamzik R. , Uhlenbusch J. , Höschele J. , Steinwandel J.
Published: October 2003

A coherent anti-Stokes Raman scattering (CARS) setup has been developed to detect contamination of atmospheric nitrogen by nitric oxide (NO). To allow spatially resolved measurements and the possibility of utilizing windows close by the test volume, we chose the folded BOXCARS setup with a CARS lens of focal length 0.5 m and a diameter of 80 mm. A frequency-doubled Nd:YAG laser (= 532 nm; EL = 50 mJ; L = 10 ns; repetition rate, 10 s−1; bandwidth, 0.05 cm−1) serves as pump for a dye laser ( Ep = 25 mJ; EL = 2 mJ; bandwidth, 0.03 cm−1), which is tunable between 585 and 615 nm. Nitric oxide CARS spectra including the first hot band have been measured with high spectral resolution in a temperature range from 300 to 800 K. The detection limit of NO is on the order of 0.25% in nitrogen under atmospheric pressure. With suppression of the nonresonant background in the application of polarization CARS, the detection limit could not be scaled down in a desirable manner. The comparison between measured and calculated CARS spectra of NO in an N2 surrounding confirms the reliability of the energy matrix elements and the Lorentzian width of the type ( p, T = 0.06(298 K/T)0.6 p/ p0 cm−1.
Application of Multivariate Calibration Techniques to Quantitative Analysis of Bandpass-Filtered Fourier Transform Infrared Interferogram Data
Authors: Mattu Mutua J. , Small Gary W. , Arnold Mark A.
Published: October 2003

Multivariate calibration models are developed that allow quantitative analysis of short segments of Fourier transform infrared (FT-IR) interferogram data. Before the interferogram segments are submitted to partial least-squares (PLS) regression analysis, a bandpass digital filter is applied to isolate a narrow range of frequencies that correspond to an absorption band of the target analyte. This adds frequency selectivity to the analysis, thereby overcoming the principal obstacle to the direct use of interferogram data for quantitative analysis. With the optimization of the frequency response function of the filter, as well as the position and length of the interferogram segment employed, calibration models are developed that compare well with those computed with conventional absorbance spectra. This methodology is demonstrated by developing calibration models for determining glucose in an aqueous buffer matrix over the physiologically relevant concentration range of 1–20 mM. Through the use of a time-domain filter designed to isolate the modulated interferogram frequencies corresponding to the glucose C–H combination band at 4400 cm−1, a three-factor PLS calibration model is computed on the basis of interferogram points 601–850. This model is characterized by standard errors of calibration (SEC) and prediction (SEP) of 0.3311 and 0.6950 mM, respectively. The best model obtained in a thorough analysis of the corresponding absorbance spectra was also based on three PLS factors. This model was characterized by values of SEC and SEP of 0.2396 and 0.6115, respectively. In addition to achieving similar calibration and prediction results to the spectral-based model, the interferogram-based method has the advantage of requiring no background measurement of the sample matrix. Furthermore, since the analysis is based on only a 250-point segment of the interferogram, a reduction in the instrumentation and data collection requirements is realized.
Detection of Caries and Composite Resin Restorations by Near-Infrared Raman Spectroscopy
Authors: Hill Wieland , Petrou Verena
Published: October 2003

Near-infrared Raman spectra of sound tooth substance show characteristic bands of its main components hydroxyapatite and collagen, and they are virtually free of luminescence. Spectra of carious tooth substance exhibit, in addition to the Raman bands, broadband luminescence with an intensity similar to that of the Raman scattering. It is assumed that this luminescence is due to microbiological products. Raman spectra of tooth-colored composite resin restorations differ considerably from those of natural tooth substances and can therefore be used for spectroscopic detection of such restorations.
Relations between Mid-Infrared and Near-Infrared Spectra Detected by Analysis of Variance of an Intervariable Data Matrix
Authors: Barros A. S. , Safar M. , Devaux M. F. , Robert P. , Bertrand D. , Rutledge D. N.
Published: October 2003

A mathematical procedure based on the analysis of variance of an intervariable data matrix (AVID) was used to relate wavenumbers and wavelengths between the mid-infrared and near-infrared domains. Initially the method calculates for each sample the product of intensities at all combinations of the frequencies in the two domains. This data matrix is submitted to analysis of variance (ANOVA) based on a classification criterion. This procedure gives a matrix of Fisher F values for all possible combinations of wavenumbers and wavelengths. To remove the masking effect due to a few extremely significant frequencies and to highlight the relations between the frequencies, this matrix of F values was corrected by subtraction of a matrix of independence. The examination of the corrected data matrix allowed the assignment of the most important peaks for the discriminating criterion. This procedure also allows the study of vector profiles, where one spectral domain is examined in relation to a particular frequency in the other domain. The study of vector profiles is a very useful tool to see the relations between the wavenumbers and wavelengths of the two domains under study.
Infrared-Emitting Species Identified in the Combustion of Boron-Based Pyrotechnic Compositions
Authors: Smit Kenneth J. , Hancox Ronald J. , Hatt David J. , Murphy Shane P. , De Yong Leo V.
Published: October 2003

Measurement of infrared emission spectra for boron-based pyrotechnic combustion has enabled the elucidation of a number of boron oxidation products. The raw spectra were corrected for instrument responsivity and atmospheric attenuation for the region 1500 to 3000 cm−1. The alkali metal metaborates and boron oxide (B2O3) were among the principal combustion products depending on which of three different oxidants were used. In addition, thermochemical modeling studies were undertaken on each composition to predict the combustion products. The thermochemical modeling data were qualitatively in agreement with the identified combustion products.
Stress and Structural Images of Microindented Silicon by Raman Microscopy
Authors: Bowden Michael , Gardiner Derek J.
Published: October 2003

The microline focus spectrometer (MiFS) Raman imaging process is described and is used to investigate stress and structure defect patterns in micro-indented single-crystal silicon. Raman intensity, frequency, and bandwidth images are reported with 0.3-μm pixel resolution, which reveal residual compressive stress distributions around the indentation site and areas of tensile stress at the crack tips. A previously unreported annular structural defect region, remote from the indent site, is observed in images where the indenter tip edges are aligned with the 110 direction of the silicon crystal.
Simultaneous FT-Raman Differential Scanning Calorimetry Measurements Using a Low-Cost Fiber-Optic Probe
Authors: Sprunt John C. , Jayasooriya Upali A.
Published: October 2003

A low-cost fiber-optic probe was constructed and used to couple an FT-Raman spectrometer to a differential scanning calorimeter (DSC). The utility of this system is demonstrated by the investigation of the different phases of ammonium nitrate.
High-Temperature, Oxygen-Resistant Molecular Fluorescence Thermometers
Authors: Bai Fenglian , Melton Lynn A.
Published: October 2003

Four strongly emitting fluorescent molecules have been identified as effective liquid-phase thermometers for use at temperatures as high as 175 °C under oxygen-saturated conditions. In each case, the thermometry is based on shifts and/or changes in the shape of the fluorescence emission with temperature. The four molecules and the temperature ranges tested were POPOP [1,4-di(2-(5-phenyloxazoyl)benzene], 25–150 °C; NPO [2-(1-naphthyl)-5-phenyloxazole], 25–173 °C; BTBP [ N,N-bis(2,5-di-tert-butylphenyl)-3,4,9,10-perylene dicarboximide], 25–173 °C; and BPB [benzo(ghi)perylene], 25–171 °C. Six other laser dyes were tested and were found to be unsatisfactory.
Complex Refractive Index Determination for Uniaxial Anisotropy with the Use of Kramers—Kronig Analysis
Authors: Yamamoto Kiyoshi , Ishida Hatsuo
Published: October 2003

Kramers—Kronig analysis of reflection spectra from a single interface with perpendicular ( s) and parallel ( p) polarization has been theoretically studied. The reflection spectra have been simulated from the complex refractive indices based on dispersion theory by using Fresnel equations for an anisotropic material whose optical axis is normal to the surface. The errors in anisotropic complex refractive indices obtained from simulated reflection spectra by Kramers—Kronig analysis have been examined for such techniques as external and total internal reflection spectroscopies.
Determination of Seawater Salinity by Ultraviolet Spectroscopic Measurements
Authors: Noto Vito Di , Mecozzi Mauro
Published: October 2003

A method for the determination of seawater salinity by ultraviolet (UV) spectroscopy is proposed. The effects of single salt concentrations and of salinity on UV absorption in the 190–250-nm range were investigated. These studies revealed that the absorption spectrum of a solution with a given salinity is due mainly, in order, to KBr >MgCl 2>NaCl. The influence of the temperature and salt concentration on UV spectra was studied by using synthetic seawater samples with the salinities ranging from 1 to 50 parts per thousand (%). Results showed that, in the absence of interferences, the most sensitive and reliable conditions for measuring the salinity are at 212 nm and at temperatures in the range of 25–30 °C. Under these conditions this method shows quite linear calibration curves and allows us to perform salinity determinations in seawater solutions at concentrations as low as 4%. Moreover, it requires no sample pretreatment and offers a precision of 0.20%. The proposed method is very simple and rapid for laboratory and on-board analysis. Finally, the interference of organic matter, nitrite, and nitrate species with the salinity determinations was investigated. These studies show that organic matter does not interfere at concentrations of carbon lower than 1 mg/L and at 210 nm. Interferences due to NO− x species can be ignored if these species are dissolved in solution at concentrations lower than ≈0.2 mg/L and the analyses are carried out at wavelengths lower than 212 nm.
Evaluation of Fourier Transform Near-Infrared for the Simultaneous Analysis of Light Alkene Mixtures
Authors: Yalvac E. D. , Seasholtz M. B. , Crouch S. R.
Published: October 2003

A Fourier transform near-infrared (FT-NIR) spectrometer incorporating a fiber-optic-coupled sample cell was used for simultaneous determination of ethylene and monoalkylated light alkenes in liquid mixtures at room temperature and pressure. Ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, and 1-decene were selected for the evaluation. Several additional alkylated alkenes (e.g., 1,1 dialkylated, cis, trans dialkylated, and trialkylated alkenes) were investigated to determine the effects of the molecular structure on this determination. The first overtone of the asymmetric =CH2 stretch of the monoalkylated alkenes was found to be unique for the light alkenes in the NIR region. This region of the spectrum was used for quantitative analysis using classical least-squares (CLS) regression. Ethylene/1-octene mixtures were studied as an example. The concentrations of these alkenes were determined with an error of less than 1% by weight.
Use of He(I) 447.1-nm Line with Forbidden Component for Electron Density Determination in Plasmas
Authors: Mijatović Z. , Kobilarov R. , Djurović S. , Stevanov M.
Published: October 2003

Four parameters of the He(I) 447.1-nm line with a forbidden component were measured. A pulsed arc was used as a plasma source. Electron density in the range (1.9–5.9) 1021 m−3 was measured with a CO2 laser interferometer. On the basis of the comparisons of the obtained results with several theories and empirical formulae for plasma density determination, it is shown that this line could be used for simple but precise electron density measurement, with an error < 10%.
Hyperspectral Raman Line Imaging of an Aluminosilicate Glass
Authors: Jestel Nancy L. , Shaver Jeremy M. , Morris Michael D.
Published: October 2003

An aluminosilicate glass, which is a model for glass formulations used as dental restorations, was examined by hyperspectral Raman line imaging. The data set consisted of more than 30000 spectra, which were analyzed by using factor analysis. Nine score images were constructed from the nine significant factors identified. Three factors represent convolutions of noise, background, and offset. The other six factors represent Raman spectra of different bonding environments of the silicate tetrahedron. Three of those factors contain narrow Raman features. These are associated with a fully polymerized silica network, with a silicate tetrahedron with one nonbridging oxygen, and with an alumina-related inclusion or a silicate tetrahedron with two nonbridging oxygens. The last three significant factors contain broad Raman bands representing continua of slightly different bonding environments of silicate tetrahedra with 0–4 nonbridging oxygens. The score images reveal that the glass, although not homogeneous, has few regions with discrete heterogeneities. The different bonding networks commingle and could be interconnected.
Raman Cross-Section De-Enhancement Phenomenon in the Excitation Profile of the 1347 cm−1 Mode of Nitrobenzene
Authors: Ahmad S. R. , Foster V. G.
Published: October 2003

Absolute values of the Raman scattering cross section of the totally symmetric 1347 cm−1 mode of nitrobenzene (NB) were measured over an excitation wavelength range of 260–520 nm. The data, when fitted to the Albrecht A-term preresonance approximation (AAT-PA) theory, showed the value of the enhancing state for the observed resonance to be 247 nm in wavelength units. This is considered to be in good agreement with the charge-transfer state of NB at about 250 nm. However, a deviation from the theory at around 350 nm, in the form of a de-enhancement in the Raman excitation profile (REP), was observed. This effect could not be adequately explained by invoking an interference phenomenon due to additive and subtractive combinations of the Raman tensors corresponding to the enhancing state and an electronically allowed but dipole-forbidden state, as has been attempted by others for benzene and some metal/ligand complexes. This is primarily because an alternative enhancement, either preceding or following this de-enhancement, has not been observed, which is expected from the formalism based on interference between the polarizability tensors representing the enhancing state and the relevent forbidden state. An explanation based on a competitive intersystem transition process in the vicinity of a forbidden state is presented. The forbidden n, Π* state of NB at about 350 nm is known to undergo rapid triplet-state conversion with high quantum yield. The explanation was supported by the anomalous results on the depolarization ratio of the Raman mode at the vicinity of this forbidden band.
Observation of Picosecond Transient Raman Spectra by Asynchronous Fourier Transform Raman Spectroscopy
Authors: Sakamoto Akira , Okamoto Hiromi , Tasumi Mitsuo
Published: October 2003

Asynchronous Fourier transform (FT) Raman spectroscopy with 100 picosecond time resolution has been developed. A signal-processing assembly required for time-resolved and transient Raman measurements consists of a picosecond Nd:YLF laser system, a gate circuit, and a low-pass filter, and it can be attached to any conventional continuous-scan FT-Raman spectrophotometer. The principle of signal processing employed in this method is almost the same as that of asynchronous pulsed-laser-excited FT-Raman spectroscopy. This method does not require synchronization between Raman excitation by probe laser pulses and sampling by the analog-to-digital converter. Transient Raman spectra have been obtained from the first excited singlet state of three anthracene derivatives in cyclohexane solutions and photoexcited poly( p-phenylenevinylene) [(C6H4CH=CH) n] by using 351 nm light (pulse width ã 70 ps) for photoexcitation and 1053 nm light (pulse width ã 100 ps) for Raman excitation.
Excitation Energy-Dependent Transient Spectral Relaxation of Coumarin 153
Authors: Flory W. C. , Blanchard G. J.
Published: October 2003

We report on the excitation energy-dependent transient spectral response of the polar dye molecule coumarin 153 (C153) in selected solvents. We find that the blue edge of the spontaneous emission spectrum of C153 contains several spectral features and that the relative contribution of these features to the overall response varies with the identity of the solvent and the excitation wavelength. The central result of these data is that the transient spectral response of C153 depends sensitively on the excitation wavelength and that the spectral evolution behavior of this molecule is therefore not related in a simple manner to solvent reorganization dynamics.
Evidence for the Formation of a Benzo[a]phenothiazine/2-Hydroxypropyl-β-Cyclodextrin Inclusion Complex Using a Fluorescence Method*
Authors: Maafi Mounir , Aaron Jean-Jacques , Mahedero Maria Carmen , Salinas Francisco
Published: October 2003

The inclusion complex of benzo[ a]-12H-phenothiazine (BPHT) and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) was investigated in an aqueous solution containing 1% ethanol. It was found that the fluorescence emission intensity of the complexed fluorophore is six times larger than that of un complexed species and 1.5 times higher than that in pure ethanol. BPHT forms a 1:1 complex when included in the HP-β-CD. An association constant of the complex of 100±20 M−1 was calculated by using the Benesi–Hildebrand treatment of fluorescence emission data. A discussion based on AM1 semiempirical calculation of BPHT geometry indicates that the inclusion of BPHT in HP-β-CD is partially achieved, probably by the hydrophobic aromatic moiety of the molecule.
Effects of Water Loading on the Fluorescein/Anti-Fluorescein Antibody System in Aerosol-OT Reverse Micelles Formed in n-Heptane
Authors: Lundgren Jeffrey S. , Watkins A. Neal , Bright Frank V.
Published: October 2003

We report on the behavior of monoclonal 4-4-20 mouse anti-fluorescein antibodies sequestered within aerosol-OT (AOT) reverse micelles formed in liquid n-heptane as a function of water loading ( R). Our data suggest that the fluorescein binding site structure is unaffected by R. However, we note that there is a region, at intermediate R values, where the fluorescein apparently binds even more strongly to the monoclonal anti-fluorescein antibodies compared to the native antibody in solution. These results are qualitatively explained in terms of the Ruckenstein–Karpe model, which is based on charge disproportionation and redistribution within the reverse micelle. The results demonstrate that R, within an AOT reverse micelle, influences the apparent anti-fluorescein affinity.
Fiber-Optic Sensor for Aromatic Compounds in Water Based on Solid-Phase Microextraction and Ultraviolet Evanescent Wave Absorption Spectroscopy
Authors: Merschman Sheila A. , Tilotta David C.
Published: October 2003

A method is described for the determination of aromatic contaminants in water samples that combines solid-phase microextraction and ultraviolet evanescent wave absorption (UV-EWA) spectroscopy. In this method, the aromatic compounds are partitioned from a 10 mL sample of water into the polymer cladding of a 10 cm length of UV-transmitting fiber. The aromatics are then detected directly in the cladding by EWA spectroscopy. The time required for four BTEX compounds to reach concentration equilibrium between the aqueous phase and the cladding ranges from 12 to 80 min, although we show that quantitative determinations can be accomplished in 30 min. Detection limits for these compounds range from 1 to 18 ppm, with relative standard deviations from 3 to 17%. Finally, preliminary work demonstrates that natural water matrices pose no significant matrix effects and that this method shows promise in determining the total aromatic concentrations of water samples contaminated with gasoline.
Chemical Sensors Based on Surface-Modified Sol-Gel-Coated Infrared Waveguides
Authors: Han Ling , Niemczyk Thomas M. , Lu Yunfeng , Lopez Gabriel P.
Published: October 2003

Attenuated total reflectance sampling, or waveguide sampling, is commonly used to obtain infrared spectra of aqueous solutions. The detection limits achieved for the determination of organic analytes in aqueous solutions using waveguide sampling are limited by the strong water absorption features and relatively small effective sample thickness due to the short penetration depth of the evanescent wave into the sample. Sol-gel processing has been used to produce a porous silica film on the surface of an infrared waveguide. The surface of the sol-gel film was modified with a silanizing reagent to produce a hydrophobic surface. The resulting waveguide was used to obtain infrared spectra from samples of benzonitrile in water. The benzonitrile spectral features obtained with the modified waveguide are enhanced by more than a factor of 103 when compared with those obtained with an unmodified waveguide.
Infrared ATR Spectroscopy of Substrates in Aqueous Solution Using Cryoenrichment and its Application in Enzyme-Activity Assays
Authors: Fujii Toshiko , Miyahara Yuji
Published: October 2003

Assays of enzyme activity in aqueous solutions were carried out with the use of the cryoenrichment method for infrared spectroscopy. A calibration method that used partial least-squares (PLS) for the measurement of enzyme activity was investigated. In this method, the enzyme activity was estimated by measuring the change in the concentration of a substrate or a product based on enzyme catalysis using the cryoenrichment method for infrared spectroscopy. The correlation coefficients between the activity levels of lactate dehydrogenase, amylase, and creatine kinase and the concentration changes of the substrate or the product were over 0.93. However, the correlation coefficient for alkaline phosphatase was only 0.78. Our findings from this study confirm that enzyme activity can be measured by infrared spectroscopy.
New Window Function for Very Short Acquisition Times
Authors: Spencer Lynne R. , Traficante Daniel D.
Published: October 2003

An apodization function, the sinc-TRAF function (S-TRAF), has been developed for application to exponentially decaying data sets where the acquisition times ( AT) is less than or equal to one time constant, T2. For heavily truncated time-domain signals, S-TRAF is able to remove sinc ripple with only minor losses in linewidth (LW) and signal-to-noise ratio (S/N). Ripple removal achieved with the application of S-TRAF rivals that observed from use of the “ultimate ripple-free resolution enhancement” function (URFRE) for AT as low as 0.3 T2*. S-TRAF maintains LW and S/N better than URFRE for all acquisition times examined.
Evaluation of a System for Generating Quantitatively Accurate Vapor-Phase Infrared Reference Spectra
Authors: Richardson Robert L. , Griffiths Peter R.
Published: October 2003

A static delivery system for generating infrared vapor-phase reference spectra has been constructed and validated for liquid analytes with polarities up to that of methanol. Several important factors that determine the accuracy of these mixtures have been identified. These include thorough degassing of the liquid analyte, maintenance of water content inside the system below a predetermined value, isolation of the pure analyte vapor before inlet of the fill gas to avoid back-flow of vapor, forced mixing to overcome the effect of excessively slow diffusional mixing of the analyte vapor and fill gas, and measurement within the linear Beer's law range for the resolution and apodization employed. To maintain Beer's law linearity, it is vital to eliminate the effect of a nonlinear response of the mercury cadmium telluride detector. In this paper, the procedure developed to ensure quantitative accuracy from statically generated gas mixtures is described. The effect of detector response linearity on photometric accuracy is discussed, along with a method of empirically correcting for this nonlinear response. The accuracy of vapor-phase samples made by this approach has been validated by comparison to the spectra of certified standards and found to be within 2% of the certified value.
Exploration of a Helium Inductively Coupled Plasma/Mattauch—Herzog Mass Spectrometer for Simultaneous Multielement Analysis
Authors: Nam Sang-Ho , Montaser Akbar , Cromwell Evan F.
Published: October 2003

A helium inductively coupled plasma (He ICP) was coupled with a low-resolution Mattauch–Herzog mass spectrometer (MHMS) for simultaneous ion detection. The potentials and limitations of the system were explored for the introduction of aqueous samples and for laser ablation sampling of solid materials including aluminum alloy, brass, fused ore, and glass standard reference materials. Compared to the data obtained with an Ar ICP on the same instrument, the detection limits were approximately 10 and 100 times worse for samples in solid and solution forms, respectively, partly due to the presence of a strong secondary discharge for the He ICP used with this instrument. In general, the ICP detection limits measured with the MHMS were 10–1000 times inferior to the data obtained with a quadrupole-based instrument.
Comparison of Two Different Approaches toward Model Transferability in NIR Spectroscopy
Authors: Swierenga H. , Haanstra W. G. , De Weijer A. P. , Buydens L. M. C.
Published: October 2003

Recently, efficient methods have become available to transfer a multivariate calibration model from one instrument to another. Two categories can be distinguished: improvement of the robustness of the calibration model by, for example, a proper data preprocessing; and adaptation of the calibration model by, for example, (piecewise) direct standardization. In direct standardization, a subset from the calibration set should be measured on both instruments. Usually, however, the calibration samples cannot be measured on both instruments. When data preprocessing is applied to the transfer of multivariate calibration models, there is no need for remeasurement of a subset on both instruments. In this paper, both categories are compared for the determination of the component concentrations in a ternary mixture of methanol, ethanol, and 1-propanol using NIR spectroscopy. The calibration models obtained on one instrument are transferred to other NIR instruments. It has been found that the results of proper data preprocessing are comparable with the results obtained by direct standardization when the models are transferred over three NIR instruments.
On-Line Determination of Reaction Completion in a Closed-Loop Hydrogenator Using NIR Spectroscopy
Authors: Ward Howard W. , Sekulic S. Sonja , Wheeler Michael J. , Taber Geraldine , Urbanski Frank J. , Sistare Frank E. , Norris Timothy , Aldridge Paul K.
Published: October 2003

An on-line near-infrared (NIR) spectroscopic method has been developed to determine in situ the endpoint of a bulk pharmaceutical hydrogenation reaction in a loop hydrogenator. This hydrogenation employs a 5% palladium-on-carbon catalyst with tetrahydrofuran (THF) as the reaction solvent. The traditional test for monitoring the endpoint of the hydrogenation is a gas chromatographic procedure that requires an estimated 60 min from the time a sample is taken to the point where the analysis results become available. The use of NIR spectroscopy in an on-line mode of operation allows spectra to be collected every 2 min and thereby significantly improves response time and result availability. The need for obtaining results in “real time” stems from the creation of undesired side products if the reaction is allowed to continue past the optimal endpoint. If the reaction is not stopped before these side products reach a level of approximately 0.8% (wt/wt), the batch requires additional purification at considerable time and cost. A partial least-squares model was constructed, validated, and successfully used to determine the endpoint of subsequent batches.
Raman and NIR Spectroscopic Methods for Determination of Total Dietary Fiber in Cereal Foods: Utilizing Model Differences
Authors: Archibald D. D. , Kays S. E. , Himmelsbach D. S. , Barton F. E.
Published: October 2003

This work evaluates the complementarity in the predictive ability of three Raman and three near-infrared reflectance (NIRR) partial least-squares regression (PLSR) models for total dietary fiber (TDF) determinations of a diverse set of ground cereal food products. For each spectral type (R or N), models had previously been developed from smoothed (D0), first-derivative (D1), or second-derivative (D2) spectral data. The NIRR and Raman models tend to have very different sets of outliers and uncorrelated errors in TDF determination. For a single spectral type, the prediction errors of various preprocessing methods are partially complementary. The samples are very diverse in terms of composition, but the main problem groups were narrowed to high-fat, high-bran, and high-germ samples, as well as and those containing synthetic fiber additives. Raman models perform better on the high-fat samples, while NIRR models perform better with high-bran and high-synthetic samples. Raman models were better able to accommodate a wheat germ sample, even though this sample type was poorly represented by the calibration set. Two methods are presented for utilizing the complementarity of the spectral and processing techniques: one involves simple averaging of predictions and the other involves avoidance of outliers by using statistics generated from the sample spectrum to choose the best model(s) for determination of the TDF value. The single best model (N-D1) has a root-mean-squared prediction error of 2.4% TDF. The best model of prediction averages yields an error of 1.9% (combining N-D0, N-D1, N-D2, R-D0, and R-D1). An error of 1.9% was also obtained by choosing a single prediction from the six models by using statistics to avoid outliers. With the selection of the best three models and averaging their predictions, an error of 1.5% was achieved.
Raman Analysis of Chemical Reactions Resulting from the Collision of Micrometer-Sized Particles
Authors: Aardahl Christopher L. , Widmann John F. , Davis E. James
Published: October 2003

The chemical reaction between two micrometer-sized particles has been studied with the use of Raman spectroscopy. Charged particles of Na2CO3 and (NH4)2SO4 were generated with the use of a vibrating orifice aerosol generator fitted with an inductive charging plate. Two particles, one of each substance and of opposite polarity, were held apart by the dc electric field of an electrodynamic balance (EDB) and then brought together by manipulating the dc potential to permit Coloumbic forces to dominate. Raman spectra taken of the particle aggregate show that chemical reaction did not occur when dry particles were combined, but subsequent exposure of the aggregate to water vapor induced a chemical reaction that resulted in the formation of Na2SO4. The Raman data are presented, and the reaction mechanism and products are discussed.
Raman Spectroscopic Identification of Fibrous Natural Zeolites
Authors: Wopenka Brigitte , Freeman John J. , Nikischer Tony
Published: October 2003

Laser Raman microprobe spectra of the natrolite group of zeolites (fibrous hydrous network aluminosilicates) can be used to unambiguously distinguish among the six members of this group, which is difficult by visual, microscopic, and X-ray diffraction methods. The natrolite group of zeolites includes the following minerals: natrolite (Na2Al2Si3O10·2H2O), scolecite (CaAl2Si3O10·3H2O), mesolite (Na2Ca2Al6Si9O30·8H2O), thomsonite (NaCa2Al5Si5O20·6H2O), gonnardite (Na2CaAl4Si6O20·7H2O), and edingtonite (BaAl2Si3O10·4H2O). Accurate locations of peak maxima are given, and complete Raman spectra (from 100 to 4000 Δcm−1) are shown for each mineral. The individual members of this structurally very similar group of minerals can be identified on the basis of the exact Raman peak positions of the two strongest bands near 440 and 535 Δcm−1, the number and positions of weaker bands, and the difference in the dependence of peak intensities upon beam polarization direction. However, the minerals can be especially easily identified on the basis of their strikingly different Raman spectral patterns in the O–H stretching region (3000–3700 Δcm−1). The number and width of peaks in this spectral region correlate with the three different types of framework structures that occur among the natrolite group minerals.
Time-Resolved Laser-Induced Breakdown Spectroscopy: Application for Qualitative and Quantitative Detection of Fluorine, Chlorine, Sulfur, and Carbon in Air
Authors: Dudragne L. , Adam Ph. , Amouroux J.
Published: October 2003

Detection limits for the main heteroatoms in pollutants and chemical agents have been determined in atmospheric conditions with the use of the time-resolved laser-induced breakdown spectroscopy (TRELIBS) method. This method presents many advantages for detection in hazardous or corrosive gas mixtures where sampling systems are not usable. Moreover, low concentrations of fluorine, chlorine, sulfur, and carbon can be measured with short analysis times. Currently, concentration limits are close to 10–50 ppm (w/w) for F, Cl, and C atoms, while presently only 1500 ppm (w/w) limits are reached for S. These measurements are obtained with an analysis time of under 20 s.
Recovery of Variable Loadings and Eigenvalues Directly from Fourier Compressed Ion Mobility Spectra
Authors: de B. Harrington Peter , Hu Lijuan
Published: October 2003

A discrete sine transform (DST) method has been devised for the Fourier compression of ion mobility spectra. The DST allows the calculation of eigenvalues with correct scale directly from the compressed data. A novel procedure for transforming the variable loadings from Fourier to native domains has been devised. For the first time, data may be interpreted in their native domain without decompression of the entire data set. This achievement is significant because results generated from the analysis of compressed data had been restricted to an abstract mathematical form. Methodology to convert these abstract results to a form that is understandable by analytical chemists is presented. This capability has important applications to the analysis of large data sets and embedded data processing under the constraints of miniaturized instrumentation. Five sets of evaluation data were obtained from vapor samples of formamide, 1-pentanol, and a mixture of two chemical warfare simulants (DIMP and DMMP) with a handheld ion mobility spectrometer (IMS). These data sets were compressed by 90% or more and reconstructed with 1% or less relative error. IMS instruments can generate thousands of spectra per hour. MATLAB functions for the DST, the inverse DST, and the two-dimensional DST are furnished in the Appendix.
Hyperspectral Raman Line Imaging of Syndiotactic Polystyrene Crystallinity
Authors: Zhang Shuliang L. , Pezzuti Jerilyn A. , Morris Michael D. , Appadwedula Aruna , Hsiung Chang-Meng , Leugers M. Anne , Bank David
Published: October 2003

The crystallinity of syndiotactic polystyrene (sPS) is studied by hyperspectral Raman line imaging. Images of a 140 × 1200 μm region of an sPS test piece containing 39 200 pixels/image were generated from spectra taken over the wavenumber interval between 300 and 875 cm−1. The spectral region includes the moderate-intensity crystallinity-sensitive bands in the 770 800 cm−1 region, as well as other useful but weaker marker bands. Factor analysis was used to extract structure information from the set of spectra. Four non-noise factors were extracted; two were assigned to crystalline and amorphous sPS and the other two to background. Score images of the crystalline and amorphous sPS factors were used to visualize distribution of those species. The results were compared to the integrated Raman intensity image for the 773 cm−1 band of crystalline sPS.
Imaging of Semicrystalline Polymers and Polymer Blends by FT-IR Microspectroscopy
Authors: Kressler Jörg , Schäfer Rüdiger , Thomann Ralf
Published: October 2003

It has been demonstrated that Fourier transform infrared (FT-IR) microspectroscopy can be used to study different types of spherulites of poly(vinylidene fluoride) formed by different crystal modifications. Because of selective IR bands of the α and the γ modification, respectively, it is possible to map the crystalline morphology by FT-IR microspectroscopy. Thus the different types of spherulites can be assigned unambiguously to different crystal modifications. It is also possible to map the morphology of phase-separated blends of isotactic polypropylene and syndiotactic polypropylene. There are selective IR bands in the crystalline state as well as in the melt. This characteristic allows for observation of the phase morphology of blends containing isotactic and syndiotactic polypropylene directly in the melt even though the blends appear completely transparent in the light microscope. This capability demonstrates the advantage of FT-IR microspectroscopy compared to light microscopy, which is restricted to samples with differences in the refractive index, which is not given for blends of isotactic and syndiotactic polypropylene above the melting point.
Raman Spectroscopy of the Kaolinite Hydroxyls at 77 K
Authors: Johansson Ursula , Frost Ray L. , Forsling Willis , Kloprogge J. Theo
Published: October 2003

Raman spectroscopy of two types of kaolinites has been obtained at liquid nitrogen temperature (77 K) with the use of a Raman microprobe and a thermal stage. The Raman spectrum is characterized by the combination of the frequencies of the inner hydroxyl and the inner surface hydroxyl groups. The inner hydroxyl frequency is reduced, and the outer hydroxyl frequencies move to higher frequencies upon cooling to 77 K. The inner hydroxyl frequency shifts from 3620 cm−1 at 298 K to 3615 cm−1 at 77 K. The two in-phase inner surface hydroxyl frequencies move from 3684 and 3689 cm−1 at 298 K to 3690 and 3699 cm−1 at 77 K. The two out-of-phase vibrations shift from 3650 and 3668 cm−1 to 3656 and 3675 cm−1. The bandwidth of the inner hydroxyl frequency decreases from 3.7 to 2.1 cm−1 at 77 K. The bandwidth of the inner surface hydroxyl frequency ( v1) increases upon cooling from 17.4 to 19.2 cm−1. It is proposed that the increased resolution at low temperature enabled an additional inner surface hydroxyl frequency to be observed.
Field Test of a Novel Microlaser-Based Probe for in situ Fluorescence Sensing of Soil Contamination
Authors: Bloch Jonathan , Johnson Bernadette , Newbury Nathan , Germaine Jack , Hemond Harry , Sinfield Joe
Published: October 2003

The use of lasers to induce fluorescence in environmental contaminants such as fuels offers the potential for real-time, in situ chemical characterization in a variety of environmental media. This paper describes the first reported use of a passively Q-switched, fiber-coupled microlaser in situ for fuel-contamination characterization in subsurface soil. A 266 nm microlaser-based probe mounted in a cone penetrometer was tested at an area contaminated by both aviation and heating fuels. By examining the spectral and temporal fluorescence characteristics as the probe was pushed into soil, we identified BTEX compounds, as well as moderate-weight and heavy aromatic hydrocarbons, and were able to map an underground contamination plume in real time. Specifically, BTEX compounds were identified by their unique fluorescence signatures (wavelengths less than approximately 315 nm and lifetimes less than 7 to 10 ns) and by comparison with extensive laboratory studies of BTEX and fuel-contaminated soils. These tests demonstrate that the microlaser-based probe offers the potential for in situ, real-time characterization of soils and groundwater in a compact, inexpensive package.
Luminescence Lifetime Quenching of a Ruthenium(II) Polypyridyl Dye for Optical Sensing of Carbon Dioxide
Authors: Marazuela María D. , Moreno-Bondi María C. , Orellana Guillermo
Published: October 2003

Carbon dioxide in gaseous samples can be measured in the 3.5 × 10-4 to 0.1 MPa partial pressure range with the use of a fiber-optic luminescent sensor operated in the time-correlated single photon counting (TC-SPC) detection mode. The sensitive tip is fabricated with tris[2-(2-pyrazinyl)thiazole]ruthenium(II) electrostatically immobilized onto carboxymethyl-Sephadex gel. The photoexcited dye is dynamically quenched by hydrogenphthalate generated upon permeation through silicone and dissolution of CO2 into the indicator gel phase containing phthalate buffer of pH 7.3. The nonlinear response of the optical indicator is shown to obey the calculated complex relationship between its emission lifetime and the PCO2. Luminescence decays (293 > τ > 173 ns) of the polymer-supported indicator are strictly exponential in the 0–100% CO2 range. Relative standard deviation values ( n = 7) of 1.9, 1.2, and 1.7% have been measured for 0.0044, 0.023, and 0.092 MPa CO2 in argon, respectively; almost twice as much were obtained when the sensor was operated in the emission intensity mode. The temperature effect (6.1 ns K-1) on the sensitive membrane and (linear) cross-sensitivity to oxygen are discussed as well. The working principle put forward allows one to monitor CO2 using the same optoelectronic instrumentation already well developed for phase-sensitive luminescence optosensing of O2 with pH-independent Ru(II) indicators.