bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemometric Quantitation of the Active Substance (Containing C≡N) in a Pharmaceutical Tablet Using Near-Infrared (NIR) Transmittance and NIR FT-Raman Spectra
Authors: Dyrby M. , Engelsen S. B. , Nørgaard L. , Bruhn M. , Lundsberg-Nielsen L.
Published: October 2003

In this study, near-infrared (NIR) transmittance and Raman spectroscopy chemometric calibrations of the active substance content of a pharmaceutical tablet were developed using partial least-squares regression (PLS). Although the active substance contained the strongly Raman active C≡N functional group, the best results were obtained with NIR transmittance, which highlights the difference between (microscopic) surface sampling and whole tablet diffuse transmittance sampling. The tablets exist in four dosages with only two different concentrations of active substance (5 mg (5.6% w/w), and 10, 15, and 20 mg (8.0% w/w) active substance per tablet). A calibration on all four dosages resulted in a prediction error expressed as the root mean squared error of cross-validation (RMSECV) of 0.30% w/w for the NIR transmittance calibration. The corresponding error when using Raman spectra was 0.56% w/w. Specially prepared calibration batches covering the range 85–115% of the nominal content for each dosage were added to the first sample set, and NIR transmittance calibrations on this set—containing coated as well as uncoated tablets—gave a further reduction in prediction errors to 0.21–0.289% w/w. This corresponds to relative prediction errors (RMSECV/ynom) of 2.6–3.7%. This is a reasonably low error when compared to the error of the chromatographic reference method, which was estimated to 3.5%.
Light Leakage Effects with Different Sample Holder Geometries in Quantitative Near-Infrared Transmission Spectroscopy of Pharmaceutical Tablets
Authors: Sparén Anders , Malm Mattias , Josefson Mats , Folestad Staffan , Johansson Jonas
Published: October 2003

Transmission geometry is becoming an alternative to the conventional reflectance geometry in near-infrared (NIR) spectroscopy of pharmaceuticals. An advantage of transmission NIR is that it samples a volume whereas reflectance NIR merely samples the surface region of solid preparations. This leads to more representative measurements on complex matrices, such as some types of tablets. However, more attention must be paid to sample presentation with respect to light leakage. An investigation of the effects of the light leakage obtained with different sample holder geometries on content calibrations for transmission NIR on tablets was performed. Two different model samples, a composite and a compact tablet, were measured in sample wells in which the diameters and heights were varied according to a multivariate design. This was done in order to simulate a mismatch between the tablet and the sample well. Partial least-squares (PLS) models were built and used to evaluate the significance of the sample well geometry. Liquid chromatography was used as a reference method. As expected, for both types of tablets it was found that a small mismatch in tablet-to-well diameter deteriorated the repeatability of the NIR spectra, although, unexpectedly, this gave the best predictions and more robust models. In all, this indicates that light leakage should not be minimized at calibration, but included as a factor in the multivariate model that spans the future expected variation in light leakage.
Near-Infrared Spectral Analysis of Gas Mixtures
Authors: Van Agthoven Maria A. , Fujisawa Go , Rabbito Philip , Mullins Oliver C.
Published: October 2003

The analysis by near-infrared spectroscopy (NIR) of a series of gas mixtures approximating natural gases is reported. Wide variations of gas pressure and temperature are used in accord with conditions found in various utilitarian gas flow streams. The NIR analysis of CH4 and CO2 composition is found to be straightforward and depends only on compound mass density, but not explicitly on temperature, pressure, or composition. Linearity of the spectra of more complex mixtures is maintained, but the NIR analysis is more complex. Principal component analysis is shown to resolve composition for those gas mixtures.
Effect of Powder Properties on the Intensity of Raman Scattering by Crystalline Solids
Authors: Wang Hsiaoling , Mann Charles K. , Vickers Thomas J.
Published: October 2003

The effect of particle size on Raman intensity has been measured for a number of crystalline solids with a fiber-optic-based Raman spectrometer. Particle sizes ranged from 76 to 605 μm. Materials examined were sodium nitrate, sodium chlorate, sodium bromate, potassium ferrocyanide, potassium ferricyanide, and copper(II) sulfate. Raman intensity was found to decrease with increasing particle size. The factors responsible for this trend are discussed. We conclude that the major factor is diffuse reflectance that enhances the overlap between the excitation and collection beams. The depth of sample contributing to the Raman signal has been examined for both powders and tablets as a function of powder particle size. Materials examined in this study were sodium nitrate, sodium sulfate, sodium chlorate, sodium bromate, potassium ferrocyanide, potassium ferricyanide, and copper(II) sulfate. For nonabsorbing powders, the depth of sample contributing to the signal exceeded 15 mm. The effect of the pressure used in forming tablets on the Raman signal strength and reproducibility has been examined for sodium nitrate. The Raman intensity was found to decrease with increasing pressure until a tablet of constant density was formed. The effect of particle size and particle size mismatch on the sodium nitrate Raman signal in binary mixtures with potassium chloride, potassium bromide, and potassium iodide has been examined. Good reproducibility was found to require matching of component particle sizes.
Fluorescence of the Complexes of 2-Methylnaphthoate and 2-Hydroxypropyl-α-, -β-, and -γ-Cyclodextrins in Aqueous Solution
Authors: Marino Antonio Di , Mendicuti Franscisco
Published: October 2003

Fluorescence techniques were employed to study the inclusion complexes of 2-methylnaphthoate (MN) with 2-hydroxypropyl-α-cyclodextrin (αHPCD), 2-hydroxypropyl-β-cyclodextrin (βHPCD), and 2-hydroxypropyl-γ-cyclodextrin (γHPCD). Emission spectra of MN show two vibronic bands whose intensity ratio R is very sensitive to the polarity of the medium. The stoichiometry and formation constants of these complexes were investigated by obtaining R as a function of the cyclodextrin (CD) concentration. Results showed identical stoichiometry (1/1) for the three MN/αHPCD, MN/β-HPCD, and MN/γHPCD complexes. Formation constants at 25 °C were 780 ± 15, 2700 ± 130, and 165 ± 10 M−1, respectively. ΔH0 and ΔS0 were obtained from linear van't Hoff plots. Results reveal that the complexation of MN with αHPCD is enthalpy driven. With βHPCD, both the entropy and enthalpy terms favor the process, whereas the formation of the complex with γHPCD is entropically governed. The extrapolation of R at infinite CD concentration allows us to estimate the effective dielectric constants of the inner CD cavities, which are around 50, but which differ from their counterparts, the naturally occurring α-, β-, and γ-CDs. Fluorescence anisotropy, quencher lifetimes, and average lifetimes can also give additional information about the structure and driving forces accompanying the formation of such complexes.
Two-Photon-Excited Phase-Resolved Fluorescence Spectroscopy
Authors: Bukowski Eric J. , Bright Frank V.
Published: October 2003

We have constructed a new two-photon phase-resolved fluorimeter that can be used to selectively record analyte emission spectra from optically challenging samples (soft drinks, juices, and urine) without sample pretreatment. We demonstrate the use of two-photon-excited phase-resolved fluorescence (TPEPRF) by minimizing hyper-Rayleigh scatter and autofluorescence in real samples. When compared to steady-state two-photon-excited fluorescence, TPEPRF offers an improvement in signal-to-background of one to two orders of magnitude.
Measurements of Urea and Glucose in Aqueous Solutions with Dual-Beam Near-Infrared Fourier Transform Spectroscopy
Authors: Jensen Peter Snoer , Bak Jimmy
Published: October 2003

This study investigates the use of a dual-beam, optical null, FT-IR spectrometer to measure trace organic components in aqueous solutions in the combination band region 5000–4000 cm−1. The spectrometer may be used for both single- and dual-beam measurements, thereby facilitating comparison of these two modes of operation. The concentrations of aqueous solutions of urea and glucose in the ranges 0–40 mg/dL and 0–250 mg/dL, respectively, were determined by principal component regression using both modes. The dual-beam technique eliminated instrumental variations present in the single-beam measurements that must be taken into account when quantifying trace components from single-beam spectra. The data obtained with the dual-beam technique resulted in more stable calibration models based on principal component regression. These calibration models need fewer factors and yield lower prediction errors than those based on traditional single-beam data.
Near-Infrared Transmission Spectroscopy of Aqueous Solutions: Influence of Optical Pathlength on Signal-To-Noise Ratio
Authors: Jensen Peter Snoer , Bak Jimmy
Published: October 2003

The optimal choice of optical pathlength, source intensity, and detector for near-infrared transmission measurements of trace components in aqueous solutions depends on the strong absorption of water. In this study we examine under which experimental circumstances one may increase the pathlength to obtain a measurement with higher signal-to-noise ratio. The noise level of measurements at eight different pathlengths from 0.2 to 2.0 mm of pure water and of 1 g/dL aqueous glucose signals were measured using a Fourier transform near-infrared spectrometer and a variable pathlength transmission cell. The measurements demonstrate that the noise level is determined by the water transmittance. The noise levels in the spectral region from 5000 to 4000 cm−1 show that the optimal pathlength (0.4 mm) is the same for pure water and 1 g/dL aqueous glucose solutions. When detector saturation occurs it is favorable to increase the pathlength instead of attenuating the light source. The obtained results are explained by an analytical model.
On-Line Spectroscopic Characterization of Sodium Cyanide with Nanostructured Gold Surface-Enhanced Raman Spectroscopy Substrates
Authors: Tessier Peter M. , Christesen Steven D. , Ong Kate K. , Clemente Eva M. , Lenhoff Abraham M. , Kaler Eric W. , Velev Orlin D.
Published: October 2003

To implement surface-enhanced Raman spectroscopy as a practical detection method, highly enhancing, stable, and reproducible substrates need to be fabricated in an efficient manner, and their performance in different solution environments should be well characterized. In this work structured porous gold films have been fabricated using colloidal crystals to template gold nanoparticles. These films were integrated into an on-line flow chamber and used to study the effects of pH and other additives on the detection of sodium cyanide. The gold films proved to be highly enhancing and were used to detect cyanide over a wide range of pH values in the concentration range of ∼2 to 200 ppb. The Raman signal intensity could be increased by lowering the pH after the adsorption of cyanide, which was likely due to both a change in the ionization state and a conformational change of the bound molecules. The peak intensity could also be enhanced multifold by treating the substrate with silver nitrate. Cyanide could be removed from the substrates using hydrochloric acid, although this also passivated the structures, and the activity could only be restored partially with tannic acid. These results provide a rational method to optimize the online detection of cyanide in water.
Surface-Enhanced Resonance Raman Spectroscopy Signals from Single Myoglobin Molecules
Authors: Bizzarri Anna Rita , Cannistraro Salvatore
Published: October 2003

The extremely large cross-section available from metallic surface enhancement has been exploited to investigate the Raman spectrum of heme myoglobin adsorbed on silver colloidal nanoparticles at very low concentrations. The study has been performed on particles both in solution and immobilized onto a polymer-coated glass surface. In both the cases, we have observed striking temporal fluctuations in the surface-enhanced resonance Raman spectroscopy (SERRS) spectra collected at short times. A statistical analysis of the temporal intensity fluctuations and of the associated correlations of the Raman signals has allowed us to verify that the single molecule limit is approached. The possible connections of these fluctuations with the entanglement of the biomolecule within the local minima of its rough energy landscape is discussed.
FT-IR Imaging of Patterned Photocrosslinkable Poly(Vinyl Cinnamate)
Authors: Rafferty Denise Wade , Koenig Jack L. , Magyar Gregory , West John L.
Published: October 2003

The use of photocrosslinkable polymers and photomasks was proposed as a means of reducing the number of raw materials necessary to create a chemical sensor array. To test this hypothesis, poly(vinyl cinnamate) was crosslinked to various degrees with the use of a photomask, exposed to a binary solvent vapor of benzonitrile and dimethyl formamide, and examined by FT-IR imaging. The results illustrate that FT-IR imaging is effective for visualizing the patterning of the crosslink density of a polymer film as well as the temporal and spatial sorption patterns of different solvent vapors. The FT-IR images show that the decrease in sorption capacity with crosslink density is solvent-specific, which suggests that photocrosslinkable polymers can be used to reduce the number of raw materials needed to create a chemical sensor array. The potential disadvantage of using glassy polymers as chemical sensors is also demonstrated by the temporal FT-IR images of solvent desorption.
Symmetrically Tapered <30-μm-thick Quasi-Planar Germanium Waveguides as Chemical Sensors for Microanalysis
Authors: Vongsvivut Jitraporn , Shilov Sergey V. , Ekgasit Sanong , Braiman Mark S.
Published: October 2003

Symmetrically tapered planar IR waveguides have been fabricated by starting with a ZnS coated concave piece of single-crystal Ge, embedding it in an epoxide resin as a supporting substrate, and then grinding and polishing a planar surface until the thickness at the taper minimum is <30 μm. Such tapering is expected to enhance a waveguide's sensitivity as an evanescent wave sensor by maximizing the amount of evanescent wave energy present at the thinnest part of the waveguide. As predicted by theory, the surface sensitivity, i.e., the absorbance signal per molecule in contact with the sensing region, increases with decreasing thickness of the tapered region even while the total energy throughput decreases. The signal-to-noise ratio obtained depends very strongly on the quality of the polished surfaces of the waveguides. The surface sensitivity is superior to that obtained with a commercial Ge attenuated total reflection (ATR) accessory for several types of sample, including thin films (<10 ng) and small volumes (<1 μL) of volatile solvents. By using the waveguides, light-induced structural changes in the protein bacteriorhodopsin were observable using samples as small as ∼50 pmol (∼1 μg). In addition, the waveguide sensors can reveal the surface compositions on a single human hair, pointing to their promise as a tool for forensic fiber analysis.
Near-Infrared Compositional Analysis of Gas and Condensate Reservoir Fluids at Elevated Pressures and Temperatures
Authors: Fujisawa Go , Van Agthoven Maria A. , Jenet Fredrick , Rabbito Philip A. , Mullins Oliver C.
Published: October 2003

The near-infrared spectroscopic (NIR) analysis of several fluid mixtures approximating natural gases or condensates is reported. Spectra were measured under wide variations of pressure and temperature in accord with conditions found in various gas or condensate reservoirs. Some restrictions simulating currently feasible hardware specifications were placed on spectral data before they were used for analysis. We employed principal components regression (PCR) on inverted Beer's Law for compositional analysis. The result shows that it is feasible to conduct an in situ compositional analysis in the reservoir environment. In fact, this algorithm is currently being utilized successfully with an optical spectrometer operating down-hole in oil wells.
Absorptivity of Carbon Dioxide and Molecular Oxygen at 193 nm at High Temperatures up to 1600 °C
Authors: Rice Steven F. , Hanush Russell G.
Published: October 2003

The absorptivity of CO2 and O2 at 193 nm over the temperature range of 900–1600 °C is reported. The data were collected in a flow-type tube furnace using an ArF excimer laser at the light source. CO2 was mixed at 5% by volume in N2 and O2 was examined at 5% and 10%. The internal transmittance of a 1-meter externally heated absorption cell was measured. The results establish a value for the absorptivity, α, for CO2 ranging as high as 2.35 × 10−19 cm2/molecule at 1600 °C. For O2, the absorptivity is 1.81 × 10−19 cm2/molecule at 1600 °C. The results partially agree with those reported in the literature recently by others at 1000 °C and 193 nm and extend those data to higher temperatures; however, the agreement is far from exact. The results are inconsistent with the higher temperature, 1500–2500 °C, values inferred by others from indirect measurements for these two species.
Development and Evaluation of a Polarization-Division Interferometer with Cube Corner Mirrors
Authors: Polavarapu Prasad L. , Bose Pranati K. , Rilling Allan J. , Buijs Henry , Roy Jean Rene
Published: October 2003

The use of cube corner mirrors in conventional Fourier transform infrared (FT-IR) spectrometers has led to increased stability and enhanced signal-to-noise ratio. Polarization-division interferometers for the mid- and far-infrared regions, however, were based on either the Martin–Puplett design, which utilizes roof-top mirrors, or the Michelson interferometer design, which utilizes the plane mirrors. In this paper, we report the development of a polarization-division interferometer with cube corner mirrors. In this design, two different wire-grid beamsplitters are used for the division and recombination of polarized light. The performance of this new instrument has been evaluated by measuring the linear dichroism of oriented films and the circular dichroism of isotropic samples. This development facilitates the adaptation of commonly used FT-IR spectrometers with cube corner mirrors for polarization-division configuration.
Raman Mapping Study of Compatibilized and Uncompatibilized Polymer Blends of Nylon 12 and Polyethylene
Authors: Sato Harumi , Sasao Shigehiro , Matsukawa Kimihiro , Kita Yasuo , Ikeda Teruki , Tashiro Hideo , Ozaki Yukihiro
Published: October 2003

Raman mapping images have been obtained for compatibilized and uncompatibilized polymer blends in films of Nylon 12 and high density polyethylene (HDPE) (blend ratios were 20/80, 50/50, and 80/20). A total of 400 Raman spectra were measured for each sample with areas of 100 μm2 and in step sizes of 0.5 μm (for 20 × 20 probe spots). To develop the Raman mapping images, the intensity ratio of two bands, a band at 1635 cm−1 due to Nylon 12 (amide I mode) and that at 1296 cm−1 arising from both HDPE and Nylon 12 (CH2 twisting) is used. The Raman mapping images of the uncompatibilized polymer blends show a clear “sea-island” structure while those of the compatibilized polymer blends exhibit a compatibilized structure. The Raman mapping images enable simultaneous exploration of the morphology and molecular structure of the blends. We have also developed a Raman mapping image that represents the variation of crystallinity in the uncompatibilized film.
Automated Detection of Chemical Vapors by Pattern Recognition Analysis of Passive Multispectral Infrared Remote Sensing Imaging Data
Authors: Zhang Lin , Small Gary W.
Published: October 2003

Pattern recognition methods are developed for the automated interpretation of passive multispectral imaging data collected from an airborne platform. Through the use of an infrared line scanner equipped with 14 spectral bandpass filters, passive infrared images are collected of an ammonia plant within a nitrogen fertilizer facility. Piecewise linear discriminant analysis is used to implement an automated algorithm for the detection of scene pixels that correspond to chemical vapor signatures. A separate classifier is used to detect the presence of hot carbon dioxide (CO2) within the images. In the assembly of training and prediction data for the development of both classifiers, the K-means clustering algorithm is used together with knowledge of the site to assign pixels to the plume/nonplume and CO2/non-CO2 categories. The effects of temperature variation within the imaged scene are removed from the data through the use of an algorithm for separating the contributions of temperature and emissivity to the Planck equation. Averaged across four data runs containing a total of 3.5 million pixels, the resulting discriminants are observed to detect approximately 91% of the plume pixels while achieving a false detection rate of less than 0.01%. The corresponding performance criteria for the CO2 classifier are a successful detection of approximately 94% of the pixels with a CO2 signature and a false detection rate of less than 0.7%. The robustness of the CO2 classifier is further enhanced through the adoption of a probability-based classification rule.
Combinatorial Study of Zeolites in Catalyzing the Acylation of Benzene via Laser-Induced Fluorescence Imaging
Authors: Su Hui , Yeung Edward S.
Published: October 2003

Laser-induced fluorescence imaging (LIFI) has been developed into a high-throughput screening (HTS) technique for heterogeneous catalysis. A laser beam is focused into a sheet parallel to the surface of the solid catalyst. Fluorescence from selected gaseous products formed immediately above the surface is imaged by a charge-coupled device (CCD) camera. Here, in situ LIFI was used to simultaneously screen the catalytic properties of a 15-member library consisting of mordenites (MOR), ferrierites (FER), ZSM-5 (MFI), zeolite γ-(gamma) (FAU), and beta zeolites (BEA) with various Si/Al ratios in the acylation of benzene with phthalic anhydride. Only beta zeolites were found to be active in this reaction over the temperature range of 190 to 340 °C. Substantial deactivation of beta zeolites was observed within less than one minute at higher temperature and the degree of deactivation varied with reaction temperature and the composition of the reactant mixture, as well as the Si/Al ratio of the beta zeolites. The deactivated beta zeolites can be regenerated partially by heating in a flow of oxygen. Up to 80% recovery of the catalytic activity was obtained. Similar recovery was observed after several deactivation–regeneration cycles.
Spectroscopic Studies of Cyclodextrin Complexes with 2,5-Bis-(4-Methylphenyl)Oxazole
Authors: Yarabe H. Hyacinthe , Agbaria Rezik A. , Rugutt Joseph K. , McCarroll Matthew E. , Gooden Robert A. , Werner T. C. , Warner Isiah M.
Published: October 2003

The complexation of γ-cyclodextrins (γ-CDs) with the guest molecule 2,5-bis-(4-methylphenyl)oxazole (MPPO) has been studied by use of fluorescence spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and dynamic light scattering (DLS). The changes in the 1H NMR aromatic signals of MPPO in aqueous γ-CD provide evidence of complexation and inclusion. DLS was used to confirm the existence of a distribution of the aggregates in the nanometer range. Excimer fluorescence was pronounced in the presence of γ-CD. The evidence of the existence of two species was shown through fluorescence lifetime data. The emission intensities of the steady state fluorescence and the fluorescence anisotropies of the linear aggregates revealed a phase transition temperature of 60 °C.
Infrared Spectroscopic Evidence for the Ice Formation Mechanisms Active in Aerosol Flow Tubes
Authors: Hung Hui-Ming , Martin Scot T.
Published: October 2003

Interest in quantifying processes of ice formation in the atmosphere has led to the recent development of new laboratory techniques, including an aerosol flow tube (AFT) reactor employed for the study of the ice nucleation kinetics of suspended submicrometer aqueous particles. The AFT technique employs an infrared (IR) beam along the flow tube axis. Spectral changes between 700 and 6000 cm−1 indicate the formation of ice at sufficiently cool temperatures. Apparent freezing temperatures are determined as a function of condensed-phase mole fraction composition. A typical aqueous chemical system is (NH4)2SO4/H2O. The mole fraction composition of the condensed-phase of this aerosol is determined by the ratio of the integrated spectroscopic bands for H2O and SO42–. A key uncertainty in the AFT-IR technique is the freezing mechanism, and knowledge of the mechanism is essential to estimate homogeneous nucleation rates ( J, cm−3 s−1) from observed apparent freezing temperatures. The current work provides observational and modeling spectral evidence, based upon changes in the scattering component of the recorded IR extinction spectra with temperature, that observed ice freezing events at warmer temperatures arise from the following mechanism: relatively few particles in the aerosol freeze (e.g., 1 in 106) and this primary event is followed by rapid scavenging of water vapor to grow the few ice particles into large ice particles observed in the IR spectra. Correspondingly, the remaining aqueous particles partially evaporate. In contrast, the spectral evidence provides support that a modified mechanism is operative at cooler temperatures: the ice freezing event consists of the freezing of a much larger fraction of the particles (e.g., 1 in 10) accompanied by a much less important vapor-phase mass transfer event.
Diffuse Reflectance Studies of Edible Fats
Authors: Ghosh N. , Datta A. , Gupta P. K.
Published: October 2003

Light scattering properties of ghee (a form of clarified butter) and vanaspati (partially hydrogenated vegetable oil) have been investigated in order to explore the use of optical techniques for detection of adulteration of vanaspati in ghee. Significant differences in the diffuse reflectance spectra of ghee and vanaspati were observed. The estimates for the reduced scattering coefficient (μs′) and the absorption coefficient (μa) for ghee and vanaspati were also obtained from integrating sphere measurements. These suggest that the differences in the diffuse reflectance spectra of ghee and vanaspati are primarily due to the differences in their absorption characteristics in the spectral range of 400 to 550 nm. Further, the results obtained show that the ratio of diffuse reflectance at 460 nm to that at 410 nm could be used to detect adulteration of vanaspati in ghee.
Improvement of a Standard-Free Method for Near-Infrared Calibration Transfer
Authors: Tan Huwei , Sum Stephen T. , Brown Steven D.
Published: October 2003

Previously, a standard-free method using the finite impulse response (FIR) filter was successfully employed to transfer the NIR spectra of caustic brines, analgesics, and terpolymer resins. This paper carries the FIR transfer method one step further, leading to an improved algorithm that makes the transfer more robust and general by avoiding transfer artifacts in the filtered spectra. Investigations of the theoretical aspects and application examples of diffuse reflectance NIR datasets show that in comparison with our previous version the improved method is much easier to use and gives artifact-free transferred spectra. The improved method also compares favorably with other current signal correction methods for calibration transfer. With the additional advantage of not requiring a subset of standards to be measured on main and remote instruments, the proposed method is a very useful alternative for calibration transfer.
Extinction Coefficient Determination of Polymeric Materials and Their Use in the Optical Characterization of Infrared Microscopes: A Preliminary Investigation into Quantitative Infrared Microspectroscopy
Authors: Tisinger Louis G. , Sommer André J.
Published: October 2003

A comparison of infrared spectra collected in both a macro sample configuration and on a microscope accessory was conducted. The results of this comparison demonstrated that as the microscope aperture was reduced, absorbance values increased for a given polymer film by as much as 33% as compared to the same data collected in the corresponding macro experiment. A detailed evaluation of the optical pathlength for both the micro and macro configurations was conducted. Results of this evaluation and that of detector non-linearity showed that the latter effect was most problematic. During the course of the investigation the average angle of light traversing through the objective was determined for several infrared microscopes. Further analysis indicated that changing the aperture size of the microscope can have significant influence on the absorbance values obtained. In addition, extinction coefficients of poly(methyl methacrylate), polystyrene, poly(vinyl acetate), polycarbonate, and poly(ethylene terephthalate) were determined using macro FT-IR spectroscopy.
Depth Profiling of the Degree of Cure during the Photopolymerization of Acrylates Studied by Real-Time FT-IR Attenuated Total Reflection Spectroscopy
Authors: Scherzer Tom
Published: October 2003

Real-time Fourier transform infrared attenuated total reflection (FT-IR/ATR) spectroscopy was used to study the depth profile of the conversion during photopolymerization reactions. The method is based on the UV irradiation of coatings of different thicknesses on the ATR crystal. Due to the finite depth of penetration of the infrared probe signal into the sample, conversion is analyzed only in a narrow layer at the bottom of the coating. The method was used to characterize the effect of photo-initiators on the depth of cure in acrylate coatings. The self-screening of a strongly absorbing morpholino ketone photo-initiator and the photobleaching of a bisacylphosphine oxide initiator are demonstrated. Moreover, depth profiling studies on the filter effect of UV absorbers and on the influence of pigmentation in white-pigmented systems will be reported.
Composition Determination of Multicomponent Organic Aerosols by On-Line FT-IR Spectroscopy
Authors: DeForest Cindy L. , Qian Jun , Miller Roger E.
Published: October 2003

A new approach is reported for determining the composition of multicomponent organic aerosols using FT-IR spectroscopy. In this study, laboratory-generated aerosol particles are thermally evaporated and the resulting vapor is immediately analyzed using FT-IR spectroscopy. The composition of the aerosol is determined by fitting the vapor spectrum to a linear combination of reference spectra of the individual components. Application of the method to the detection of polycyclic aromatic hydrocarbons, changes in aerosol composition, and analysis of diesel fuel is demonstrated.
Resonance Raman Scattering from Single Levitated Microparticles
Authors: Laucks Mary L. , Zheng Feng , Davis E. James
Published: October 2003

Measurements of resonance Raman scattering from single crystalline (or amorphous) particles suspended in an electrodynamic balance have been made for inorganic and organic microparticles, potassium permanganate (KMnO4) and p-nitrosodimethylaniline ( p-NDMA), respectively. The microparticle dimensions were in the range 10–50 μm. The particles were obtained by evaporating aqueous solution droplets of KMnO4 and p-NDMA (0.01 M concentration) and potassium nitrate or sodium nitrate (1.0 M concentration) added as a nonresonance Raman standard or reference. Resonance Raman spectra were obtained using laser illumination at wavelengths of 514.5 and 488.0 nm. For MnO−4 particles at a laser wavelength of 514.5 nm, the fundamental symmetric stretch mode (ν1) and up to four overtones were observed. In addition, the antisymmetric stretch mode (ν3) and the combination mode (ν1 + ν3) could be seen. In p-NDMA particles, the phenyl-nitroso deformation mode (ν1) and the symmetric benzene ring-stretching mode (ν3) were observed using 488.0 nm laser radiation, but no overtones were distinguishable. As a measure of the morphological variability between particles, the ratio of the intensity of ν1 to the intensity of the largest nitrate ion (Raman) peak (normalized by the concentrations) was determined for each spectrum. This enhancement ratio or reference ratio was of order 100 and varied by 27% for 12 KMnO4 particles with 514.5 nm illumination, by 39% for 10 KMnO4 particles at 488.0 nm, and by 16% for 14 p-NDMA particles at 488.0 nm. Resonance Raman spectra obtained for KMnO4 particles before and after deliquescence indicated that photolysis occurred in the presence of water.
On-Line Detection of Vapor-Phase Copper Species by Plasma-Excited Atomic Absorption Spectroscopy
Authors: Oikari Risto , Botti Laura , Hernberg Rolf
Published: October 2003

An on-line toxic metal analyzer based on direct current plasma-excited atomic absorption spectroscopy was previously developed for detection of cadmium and lead species in combustion exhaust gases. In the present work the applicability of the analyzer for detection of copper species in industrial processes was investigated. The detection limit was found to be 0.17 mg/m3. Theoretical calculations showed that the detection sensitivity could be improved one order of magnitude by optimizing the background correction. Further improvement in detection sensitivity is predicted using tunable diode laser spectroscopy.
Identification of Outliers in Hyperspectral Raman Image Data by Nearest Neighbor Comparison
Authors: Behrend Caleb J. , Tarnowski Catherine P. , Morris Michael D.
Published: October 2003

A new algorithm for removal of cosmic spikes from hyperspectral Raman image data sets is presented. Spectra in a 3 × 3 pixel neighborhood are used to identify outlier-contaminated data points in the central pixel of that neighborhood. A preliminary despiking of the neighboring spectra is performed by median filtering. Correlations between the central pixel spectrum and its despiked neighbors are calculated, and the most highly correlated spectrum is used to identify outliers. Spike-contaminated data are replaced using results of polynomial interpolation. Because the neighborhood contains spectra obtained in three different frames, even large multi-pixel spikes are identified. Spatial, spectral, and temporal variation in signal is used to accurately identify outliers without the acquisition of any spectra other than those needed to generate the image itself. Sharp boundaries between regions of high chemical contrast do not interfere with outlier identification.
Comparison of Wavelets and Smoothing for Denoising Spectra for Two-Dimensional Correlation Spectroscopy
Authors: Berry R. James , Ozaki Yukihiro
Published: October 2003

Noise can be severely detrimental to two-dimensional correlation spectroscopy (2D-COS), even at levels as low as 2%. In order to circumvent this problem, spectra must be as free as possible from noise. However, this is not always feasible within the confines of some experiments. Smoothing has been previously used to pretreat the data to reduce noise for 2D-COS. We will show that denoising using wavelets is more beneficial than smoothing and eigenvector reconstruction. The effect of noise is shown on data with 1, 2, and 5% synthetic noise added and then processed with wavelet filtering, smoothing, and eigenvector reconstruction. Lastly, the relative benefits of both smoothing and wavelet filtering on near infrared (NIR) spectra of raw milk are compared.
Using an Expectation—Maximization Algorithm to Obtain Dielectric Relaxation-Time Spectra of Aqueous Montmorillonite Clay Suspensions
Authors: Bialkowski Stephen E. , Dudley Lynn , Or Dani
Published: October 2003

Determination of relaxation-time distributions from dielectric spectra of complex impedance or dielectric permittivity remains a challenge. This problem is one of a wider class of ill-posed inverse problems where the measurement is a superposition or convolution of functions containing the sought-after information. An expectation–maximization (EM) algorithm is shown to be useful for obtaining dielectric relaxation-time distributions from impedance data. This algorithm is stable and converges to realistic relaxation-time spectra without the need for constraints or initial values. The implementation used herein updates expectations in an iterative multiplication step. The models and basic assumptions of impedance spectroscopy are outlined in the first part of this paper. Frequency-dependent impedance measurements are obtained for calibration samples and saturated montmorillonite clays. The EM algorithm is subsequently used to determine the dielectric relaxation times. The dielectric relaxation-time spectra allow facile interpretation of otherwise complicated impedance.
FT-NIR Spectroscopic Analysis of Nitrogen in Cotton Leaves
Authors: Riley Mark R. , Cánaves Loreto C.
Published: October 2003

Near-infrared spectroscopy was evaluated as a means to quantify the nitrogen content in fresh cotton leaves ( Gossypium hirsutum L. var. Delta Pine 90) subjected to a factorial design experiment of varying nitrogen and water applications. Absorbance spectra were collected in the 10 000–4000 cm−1 (1000–2500 nm) region from fresh cotton leaves over a two month portion of the growing season. Total nitrogen content was quantified by a wet chemistry Kjeldahl method for validation purposes. Partial least-squares regression analysis, using an automated grid search method, selected the spectral region 6041 to 5651 cm−1 (1650–1770 nm) for analysis based on having the lowest standard error of prediction of total nitrogen content. This region includes protein spectral features. Nitrogen predictions resulted in a correlation coefficient of 0.83, and a standard error of prediction of 0.29% for nitrogen levels ranging from 3.1 to 5.2% total nitrogen. This approach has promise for providing rapid plant chemical analyses for cotton crop fertilization management purposes.
Fluorescence Quenching Investigation of the Complexes of Dibenzofuran with Natural Cyclodextrins
Authors: Rodríguez Pablo , Sánchez Miguel , Isasi José Ramón , González-Gaitano Gustavo
Published: October 2003

The steady-state fluorescence of dibenzofuran (DBF) in aqueous solution is quenched in the presence of natural cyclodextrins (CDs), α, β, and γ-CD. The decrease in the fluorescence is static in nature for all the macrocycles and follows as a result of the formation of inclusion complexes of dominant 1:1 stoichiometry. With γ-CD, excimer emission is detected at high CD concentrations due to the formation of a complex of 2:2 stoichiometry, DBF2:γ-CD2. The binding constants have been determined from the fluorescence intensities through the analysis of the F0/ F vs. [CD] plots, resulting in a stronger association for β-CD. The thermodynamic parameters of the binding, enthalpy and entropy, have been calculated from the temperature dependence of the formation constants. The different trend displayed by α-CD, in both the absorption and fluorescence spectra, seems to be related to a shallow inclusion of DBF, stabilized by hydrogen bonding between the oxygen atom of the furan ring and the hydroxyl groups of CD.
Solvatochromic Probe Behavior within Binary Room-Temperature Ionic Liquid 1-Butyl-3-Methyl Imidazolium Hexafluorophosphate plus Ethanol Solutions
Authors: Fletcher Kristin A. , Pandey Siddharth
Published: October 2003

Room-temperature ionic liquids (RTILs) have shown tremendous promise as replacements for the toxic and volatile organic solvents used in many applications. Depending on a particular application, addition of a “green” cosolvent can very easily modify/alter the physicochemical properties of the RTILs in a favorable fashion. Solvatochromic probe behavior within binary RTIL 1-butyl-3-methyl imidazolium hexafluorophosphate (BMIMPF6) + ethanol solutions are investigated using four popular probes, pyrene, 1-pyrenecarboxaldehyde, 1,3- bis-(1-pyrenyl)propane, and Reichardt's betaine dye. A simplified preferential solvation model based on the weighted mole-fraction probe response shows that the pyrene cybotactic region is rich in BMIMPF6 in comparison to the bulk composition. However, 1-pyrenecarboxaldehyde and 1,3- bis-(1-pyrenyl)propane solvation environments clearly indicate a cybotactic region dominated by ethanol. Reichardt's betaine dye shows absorbance maxima lower than that observed in either of the two neat components, BMIMPF6 or ethanol. This probe is well known to manifest the hydrogen-bond-donating (HBD) ability of the solvent system. HBD ability also depends on the dipolarity/polarizability of the solvent system. Ethanol has a higher HBD ability but lower dipolarity/polarizability than BMIMPF6. As the mole fraction of ethanol is increased, the increase in the HBD ability of the binary BMIMPF6 + ethanol solution is manifested through the unusual Reichardt's dye response.
Thermal Lensing in Extended Samples
Authors: Marcano A. O. , Rodriguez L. , Melikechi N.
Published: October 2003

We report on a novel pump-probe thermal-lens method for the measurement of absorption in extended samples using nearly collimated continuous wave (CW) and low-power probe and pump beams. We report the measurement of the absorption of a column of distilled water up to 2 meters thick. The method allows the determination of the absorption with sensitivities up to 10−10 W cm−1 in materials with photothermal parameters similar to distilled water.
Application of Maximum Likelihood Principal Components Regression to Fluorescence Emission Spectra
Authors: Schreyer Suzanne K. , Bidinosti Michael , Wentzell Peter D.
Published: October 2003

The application of maximum likelihood multivariate calibration methods to the fluorescence emission spectra of mixtures of acenaphthylene, naphthalene, and phenanthrene in acetonitrile is described. Maximum likelihood principal components regression (MLPCR) takes into account the measurement error structure in the spectral data in constructing the calibration model. Measurement errors for the fluorescence spectra are shown to exhibit both a heteroscedastic and correlated noise structure. MLPCR is compared with principal components regression (PCR) and partial least-squares regression (PLS). The application of MLPCR reduces the prediction errors by about a factor of two over PCR and PLS when a pooled estimate of the measurement error covariance matrix is employed. However, when only the heteroscedascity is incorporated into MLPCR, no improvement in results is observed, indicating the importance of accounting for correlated measurement errors.
Sub-Doppler Spectral Resolution and Improved Sensitivity in a Cesium Resonance Fluorescence Imaging Monochromator
Authors: Pixley Nathan C. , Correll Tiffany L. , Pappas D. , Smith Benjamin W. , Winefordner James D.
Published: October 2003

Improvements in spectral resolution and sensitivity of a cesium based resonance fluorescence imaging monochromator (RFIM) are described. Alignment of the two lasers used in the excitation scheme in a co-propagating geometry have resulted in a detector spectral bandpass (270 MHz) that is narrower than the Doppler broadened profile (380 MHz) of cesium vapor at room temperature. Improvements in the experimental design, namely the addition of an image intensifier and cooled charge-coupled device (CCD) camera, have resulted in increased sensitivity; we report a limit of detection of 108 photons per pixel limited by image intensifier noise. Images of the cesium D2 line emission (852.12 nm) from a cesium hollow cathode lamp were compared to an argon emission line (4Sº1/2 → 4P3/2) at 852.14 nm from a silver/argon hollow cathode lamp as a demonstration of the spectral resolution. The ability of the RFIM to discriminate between photons exciting the F = 4 vs. F = 3 ground state hyperfine level (a frequency difference of 9.2 GHz) of the cesium 62S1/2 state was also investigated to further demonstrate the spectral selectivity. The potential use of the described RFIM for chemical imaging applications is discussed.
Using a Wavelength-Modulated Quantum Cascade Laser to Measure NO Concentrations in the Parts-per-Billion Range for Vehicle Emissions Certification
Authors: Weber W. H. , Remillard J. T. , Chase R. E. , Richert J. F. , Capasso F. , Gmachl C. , Hutchinson A. L. , Sivco D. L. , Baillargeon J. N. , Cho A. Y.
Published: October 2003

Measurements of NO concentrations at sub-ppm levels in vehicle exhaust are needed for emissions certification of future ultra-low emission vehicles. We demonstrate a wavelength-modulation, laser-based, NO detection system suitable for this purpose. A quantum cascade distributed feedback laser (QC-DFB) operating continuous wave (cw) at ∼100 K is frequency modulated at f = 10 kHz and locked to the center of a transition at ∼1921 cm−1 in the fundamental band of NO. The demodulated signal at 2 f of the beam passing through the sample cell directly measures the NO concentration. The cell is a multipass Herriott-type with a 100-m path length. Doppler broadening, pressure broadening, and unresolved Λ doubling combine to yield a pressure for optimum sensitivity of 100 torr and a modulation amplitude of ∼600 MHz. A flowing gas system is used to avoid problems with adsorption and desorption of NO from the cell walls. The reduced pressure eliminates interference from other gas species. Detection of NO concentrations in the few parts-per-billion (ppb) range is demonstrated in diluted exhaust-gas bag samples collected in the vehicle certification process.
Novel Application of a Disposable Optical Film to the Analysis of Bacterial Strains: A Chemometric Classification of Mid-Infrared Spectra
Authors: Mossoba M. M. , Khambaty F. M. , Fry F. S.
Published: October 2003

A microporous polyethylene disposable optical film (DOF) that is mostly transparent to infrared light was used to characterize bacterial strains by Fourier transform infrared (FT-IR) spectroscopy for subsequent classification by principal components analysis (PCA) and hierarchical cluster analysis (HCA). Developing a methodology with a disposable infrared substrate is desirable for the FT-IR measurement of pathogenic bacteria. The bacteria studied were Escherichia coli HB101, E. coli ATCC 43888, a wild-type E. coli, and one strain each of Pseudomonas aeruginosa, Bacillus cereus, and Listeria innocua. The cultures were harvested by centrifugation and the wet cells (5 mg) were placed onto DOF and dried under vacuum at room temperature for one hour. For each strain, four replicates were prepared and measured on each of six different days in order to investigate the possible sources of variance in the sampling procedure. PCA obtained for second derivative, mean-centered spectra for selected frequency ranges (1312–1339, 1026–1061, and 903–930 cm−1) explained over 98.1% of the total variability using the first three principal components. The scores plots exhibited six tight clusters of 24 points each (4 replicates × 6 days). Out of a total of 144 spectra, one outlier was found. The dendrograms resulting from HCA (centroid linkage method) correctly clustered all 143 remaining samples. The analysis provided excellent discrimination between the different species and, more significantly, between the different E. coli strains. This work demonstrates the potential of this procedure for the rapid, repeatable, and precise classification of bacteria, with minimum sample preparation, in food safety laboratories.