bluuebunny/crossref_metadata_2025 huggingface dataset:
Raman and NIR Spectroscopic Methods for Determination of Total Dietary Fiber in Cereal Foods: A Comparative Study
Authors: Archibald D. D. , Kays S. E. , Himmelsbach D. S. , Barton F. E.
Published: October 2003

Partial least-squares regression (PLSR) was used to generate three Raman and three near-infrared reflectance (NIRR) models for the spectroscopic determination of total dietary fiber (TDF) of a wide variety of cereal foods. To allow comparison of the spectral techniques, both analyses used the same sets of samples ( ncal = 63, nval = 63). Six models were optimized by full leave-one-out cross-validation (CV), including a smoothed, a first-, and a second-derivative model for each spectral technique. Both kinds of raw spectral data required correction of interfering baseline and amplitude variations. Derivative preprocessing generally reduced the number of latent variables (LVs) for both spectral types and significantly reduced the CV error of the Raman models. The derivative treatments enhanced the influence of select vibrational-bandwidth-sized features in the Raman data (64–84 cm−1). The Savitzky–Golay derivative calculation method was better for the NIRR data, while the gap-difference method was better for the Raman data, which had a higher level of baseline noise. Raman models required 6 to 9 latent variables while NIRR models required 10 to 14 LVs. The root-mean-squared CV model errors were 2–2.3% TDF for all six models, and the three Raman models had root-mean-squared prediction errors (RMSEPs) in the range 2.8–3.2% TDF, with the best model being generated from second-derivative data. First-derivative data provided the best NIRR model, and for all three NIRR models the RMSEP spanned 2.4–2.9%. For some types of samples, it is suggested that the Raman method is limited by its sampling technique and could be improved with more densely packed, larger-area specimens. The regression vectors of the Raman models seem more easily interpretable than NIRR models. Either spectral method appears capable of acheiving an acceptable level of error; TDF reference method precision was 0.68% TDF, while the product label information had an error of 2.8% TDF relative to the reference.
On-Line Monitoring of Chlorosilane Streams by Raman Spectroscopy
Authors: Lipp Elmer D. , Grosse Ronda L.
Published: October 2003

On-line Raman spectroscopy was used to monitor the composition of methylchlorosilane streams from distillation columns. A spectrometer was assembled that used 532 nm laser light and a fiberoptic probe that could be inserted into corrosive liquid streams. The spectral regions below 800 cm−1 and near 2250 cm−1 contained strong, distinctive bands that were used to identify and quantitate the species of interest. On-line spectra were recorded at 5 min sampling intervals. Several instances were found where large changes in the composition of the columns were observed. Detection limits of 1000 ppm were generally achievable, and, in favorable circumstances, compositional changes of 100 ppm could be detected. Raman spectroscopy gave much better time resolution than current gas chromatography (GC) monitoring and is also projected to have lower capital and maintenance costs.
Investigation of the Subcellular Localization of Zinc Phthalocyanines by Raman Mapping
Authors: Freeman T. L. , Cope S. E. , Stringer M. R. , Cruse-Sawyer J. E. , Brown S. B. , Batchelder D. N. , Birbeck K.
Published: October 2003

Raman mapping has been used to determine the subcellular distribution of two substituted zinc phthalocyanines designed for use as photosensitizers in photodynamic therapy. Each compound was incubated over a range of time periods in two cultured cell lines, and the cells were subsequently formalin-fixed for analysis. Raman spectra were recorded at 1–2 μm steps across the cell, with the use of 782 nm laser excitation in order to minimize absorption by the photosensitizer chromophore and the consequent photodynamic activation of the system. Maps have been formed showing the distribution of the phthalocyanines within the cells. This distribution is seen to depend upon incubation time and the molecular structure of the phthalocyanine. Similar patterns of uptake are observed in both cell lines. Atomic force microscopy has been used to validate the technique used to correct the maps for variations in Raman sampling volume, resulting from inhomogenous cell thickness.
Matrix-Enhanced Calibration Procedure for Multivariate Calibration Models with Near-Infrared Spectra
Authors: Riley Mark R. , Arnold Mark A. , Murhammer David W.
Published: October 2003

A novel method is introduced for developing calibration models for the spectroscopic measurement of chemical concentrations in an aqueous environment. To demonstrate this matrix-enhanced calibration procedure, we developed calibration models to quantitate glucose and glutamine concentrations in an insect cell culture medium that is a complex mixture of more than 20 components, with three components that manifest significant concentration changes. Accurate calibration models were generated for glucose and glutamine by using a calibration data set composed of 60 samples containing the analytes dissolved in an aqueous buffer along with as few as two samples of the analytes dissolved in culture medium. Standard errors of prediction were 1.0 mM for glucose and 0.35 mM for glutamine. The matrix-enhanced method was also applied to culture medium samples collected during the course of a second bioreactor run. Addition of three culture medium samples to a buffer calibration reduced glucose prediction errors from 3.8 mM to 1.0 mM; addition of two culture medium samples reduced glutamine prediction errors from 1.6 mM to 0.76 mM. Results from this study suggest that spectroscopic calibration models can be developed from a relatively simple set of samples provided that some account for variations in the sample matrix.
Detecting and Identifying Spectral Anomalies Using Wavelet Processing
Authors: Stork Chris L. , Veltkamp David J. , Kowalski Bruce R.
Published: October 2003

An automated method integrating wavelet processing and techniques from multivariate statistical process control (MSPC) is presented, providing a means for the simultaneous localization, detection, and identification of disturbances in spectral data. A defining property of the wavelet transform is its ability to map a one-dimensional chemical spectrum into a two-dimensional function of wavelength and scale. Therefore, unlike the traditional MSPC approach where disturbance detection is carried out in the original wavelength domain by using a single principal component analysis (PCA) model, detection employing wavelet transform processing results in the generation of multiple models within the wavelength-scale domain. Provided that the spectral disturbance can be localized within a subregion of the wavelength-scale domain through an advantageous choice of basis set, the method described allows the identification of the underlying disturbance. The utility of the proposed method in localizing, detecting, and identifying spectral disturbances is demonstrated by using real near-infrared measurements, suggesting its general applicability in spectroscopic monitoring of chemical processes.
Stress Dependence of Infrared-Active Mode of the β-Si3N4 Ceramic Appearing at 1020 cm−1 Measured by Micro-FT-IR Spectroscopy
Authors: Honda Katsuya , Yokoyama Shino , Tanaka Shun-Ichiro
Published: October 2003

The stress dependence of the β-Si3N4 infrared-active band appearing at ∼1020 cm−1 was evaluated by using micro-FT-IR. A four-point-bending jig was built to apply stress to the sample. Two β-Si3N4 ceramics, prepared by pressureless sintering and hot-pressed sintering, were examined. The hot-pressed sample showed a linear relation to applied stress, whereas the pressureless sintered sample showed relatively scattered stress dependence due to the inferior signal-to-noise ratio of the spectra. The stress dependence parameter of the 1020 cm−1 band was evaluated as ∼2 cm−1/GPa.
Characterization of a Fiber-Optic System for the Distributed Measurement of Leakages in Tanks and Pipelines
Authors: Sensfelder E. , Bürck J. , Ache H.-J.
Published: October 2003

A fiber-optic sensor system for the distributed measurement of organic chemicals is presented in this paper. The system uses the technique of optical time-domain reflectometry (OTDR) and a polymerclad optical fiber that is sensitive to nonpolar substances. The location of the chemicals is attained by measuring the time delay between a short laser light pulse entering the fiber and a discrete change in the backscatter signal caused by the enrichment of the analyte in the fiber cladding. Chemical substances enriched in the cladding of the sensor fiber lead to changes in the OTDR response signal, because the light-guiding properties of the fiber are affected through the evanescent wave. The enrichment of an analyte with a higher refractive index than the fiber cladding, for example, will induce a light loss because of mode stripping. This light loss is followed by a step drop in the OTDR response signal. If the analyte penetrating into the fiber cladding absorbs the emitted laser light pulse, a step drop also occurs in the backscatter signal because of the light loss due to the absorption. A fluorescent substance in the fiber cladding leads to a characteristic peak in the OTDR response signal. The intensity of the different signals is correlated with the refractive index and the concentration of the analyte, the interaction length between analyte and sensing fiber, and the temperature, fiber diameter, and bend radius of the fiber.
Spectroscopic Studies of Indigo Carmine Dye in Organized Media
Authors: Roberts Eric L. , Burguieres Sarah , Warner Isiah M.
Published: October 2003

The absorbance and fluorescence properties of indigo carmine (IC) dye have been investigated in various solvents and organized media (β-, γ-, 2-hydroxypropyl-β-, 2,6-Di-O-methyl-β-cyclodextrins and CTAB and Brij-35 surfactants). A long-wavelength (LW) emission for IC dye in solution is reported that results from the long-wavelength excitation energy of the molecule (∼609 nm). This emission for IC dye exhibits significant sensitivity to changes in viscosity and hydrophobicity of the microenvironments of the various organized media and solvents used. Induced circular dichroism (ICD) studies of the dye in 2-hydroxypropyl-β-cyclodextrin indicate an axial inclusion of the molecule along the CD axis of symmetry. The spectral data in organized media are supplemented by photochemical stability and binding studies of the molecule in aqueous solutions of CDs under neutral (pH 7) and basic (pH 12) conditions, at 25°C and 37 °C. These data are used to suggest the suitability of the dye as a molecular probe and as a reagent in the development of a hydroperoxide assay.
Comparison of Prediction- and Correlation-Based Methods to Select the Best Subset of Principal Components for Principal Component Regression and Detect Outlying Objects
Authors: Verdú-Andrés J. , Massart D. L.
Published: October 2003

In the present work the use of prediction and correlation criteria for the best subset selection of principal components for principal component regression is compared. Results for both methodologies are similar, and always equal to or better than those obtained by using top-down principal component regression. In this comparison, the prediction criterion is based on the use of leverage-corrected residuals. In addition, the plot of leave-one-out cross-validated residuals vs. leverage-corrected residuals for the selected model is also proposed as a new graphic tool to detect possible outliers. In a test of the different methodologies, three different data sets have been studied.
Regression Analysis of Microwave Spectra for Temperature-Compensated and Density-Independent Determination of Wheat Moisture Content
Authors: Archibald Douglas D. , Trabelsi Samir , Kraszewski Andrzej W. , Nelson Stuart O.
Published: October 2003

Partial least-squares regression (PLSR) was used to generate wheat moisture content predictive models from eight-frequency microwave attenuation (A) and phase (P) spectra in the 10.36 to 18.0 GHz range, as obtained by a free-space technique with a 10.4 cm thick sample. Spectra ( n = 379) were measured for a set of grain samples that had been treated to span the agriculturally practical ranges of moisture content (M) (10.6 to 19.2% g/gwet), temperature (K) (–1 to 42°C), and bulk density (D) (0.72 to 0.88 g/mL). The sample– property space formed by M, K, and D was used to prune redundant samples and select representative subsets for calibration ( n = 279), cross-validation ( n = 40 segments), and testing ( n = 31). Twelve model types are reported and vary from attenuation or phase alone to the combination of attenuation, phase, temperature, and density (i.e., APKD). For optimization of each PLSR model, the raw spectral, temperature, and density data were preprocessed with variable ratios, mathematical transformations, and/or variable scaling. The lowest moisture prediction errors were for temperature-and density-corrected models with variables AKD or APKD; these produced root-mean-square cross-validation and prediction errors (RMSECV and RMSEP) of 0.19 to 0.20% in moisture content units. The more practical unifrequency models, APK at 15.2 GHz, and AK at 18.0 GHz, yielded RMSECV values of 0.21% and 0.35%, respectively. Addition of temperature to dielectric data always substantially reduced the model error. However, the multiplicative effect of density is well corrected by using the ratio A/P, or partly corrected by using the features in the attenuation spectra. Data trends suggest that dual-frequency PK models might benefit from a wider frequency range, and unifrequency AK models might be better at frequencies higher than 18.0 GHz. The results presented make it possible to evaluate a wide variety of instrumental configurations that might be proposed to suit particular engineering criteria such as measurement accuracy, range of operating conditions, and hardware complexity.
Enzymatic Polymerization of Poly(ε-CL) Containing an Ethyl Glucopyranoside Head Group: An NMR Study
Authors: Bisht Kirpal S. , Gross Richard A. , Cholli Ashok L.
Published: October 2003

The usefulness of the 2D-NMR techniques in the structure determination of the oligo ε-caprolactone ethyl glucopyranoside (oilgo(ε-CL) EGP) conjugate, synthesized by a lipase-catalyzed regioselective reaction, is described. Data from a 13C–13C COSY NMR spectrum of the ethyl glucopyranoside is used for complete and unambiguous assignments of the carbon resonances in the 13C NMR spectrum of the anomeric mixture of EGP. A comparison of the DEPT-135 spectrum of the product oilgo(ε-CL) EGP conjugate with that of the starting material, ethyl glucopyranoside (EGP), led to the conclusion that the lipase-catalyzed ring-opening of ε-CL initiated by a multifunctional initiator, EGP, proceeded in a regioselective fashion. Also, a detailed analysis of the NMR data has allowed determination of the site for lipase-catalyzed ring-opening polymerization of ε-CL. Our study suggests that among the possible four initiation sites in EGP only the hydroxyl group on carbon C-6 took part in the initiation process.
In situ Detection of Adsorbates at Silica/Solution Interfaces by Fourier Transform Infrared Attenuated Total Reflection Spectroscopy Using a Silica-Coated Internal Reflection Element
Authors: Poston Pete E. , Rivera Dion , Uibel Rory , Harris Joel M.
Published: October 2003

A silica-coated ZnSe internal reflection element (IRE) was used to acquire attenuated total reflection (ATR) Fourier transform infrared (FT-IR) spectra of ethyl acetate at an n-heptane/silica surface. A thin silica film was deposited onto the IRE by withdrawing the substrate from a suspension of fumed silica; upon drying, a durable, porous SiO2 layer is formed on the IRE that is stable in contact with aprotic solvents. The layer thickness is targeted to be comparable to the depth of penetration of infrared radiation beyond the IRE/film interface. These films were used to investigate the adsorption of ethyl acetate onto silica from n-heptane. A multidimensional least-squares fit of the spectroscopic data reveals multiple surface-site energies on the silica surface, as reflected in both the solution concentration dependence of ethyl acetate accumulation on the surface and the frequencies of vibrational modes that shift upon adsorption.
Determination of Kenaf (Hibiscus Cannabinus L.) Lignin in Crude Plant Material Using Diffuse Reflectance Infrared Fourier Transform Spectroscopy
Authors: Pappas C. , Tarantilis P. A. , Polissiou M.
Published: October 2003

Hibiscus cannabinus L. (kenaf) is a plant of the Malvaceae family and is a renewable resource for industry. The determination of kenaf lignin in crude plant material of four varieties using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is described. In particular, a linear relationship was established between the peak area at 1506 cm−1 and the lignin content in the plant material. With the use of the DRIFTS method, lignin was found in the bark, wood, and pith of four kenaf varieties at 10.4 to 10.8%, 20.5 to 20.6%, and 14.9 to 15.3% of plant material, respectively.
Extending the Range of Beer's Law in FT-IR Spectrometry. Part II: Theoretical Study of Continuous Apodization Functions
Authors: Zhu Changjiang , Griffiths Peter R.
Published: October 2003

In the previous paper in this series, it was shown that deviations from Beer's law caused by limited resolution could be reduced through the application of Norton Beer apodization functions. The side lobes in the instrument line shape (ILS) function introduced by these functions converge quite slowly because of the discontinuities at the maximum optical retardation. It is possible that these side lobes may limit the range of peak absorbance for which linear Beer's law plots are observed. To check on this hypothesis, we have examined the effect of three continuous apodization functions (cosine, Bessel, and sinc squared), on the Beer's law behavior of Lorentzian bands. Despite the much smaller side-lobe amplitude away from the main lobe of the ILS function, the performance of these apodization functions is only slightly better than that of the Norton Beer functions for broad bands. Better adherence to Beer's law for strongly absorbing bands is obtained for spectra measured with a resolution parameter, ρ, of about 0.5.
Evaluation of Ultrasonic Nebulization for the Analysis of Transient Samples: A Theoretical Model and Practical Considerations
Authors: Pack Brian W. , Ray Steven J. , Potyrailo Radislav A. , Hiettje Gary M.
Published: October 2003

Three spray chambers designed for use with ultrasonic nebulization have been evaluated for the introduction of transient samples into an inductively coupled plasma. The spray chambers were (1) a conventional Fassel type, (2) a commercially available CETAC spray chamber, and (3) a novel spray chamber design that was constructed in-house. All have different volumes and modes of central-channel gas introduction, and consequently different washout times. Interestingly, they can all be described by the same model for both their washin and washout times. This model was able to predict the time response of the three spray chambers based upon the convolution of a Gaussian and an exponential curve. In particular, the experimental washout times can be successfully fit to an exponential-decay model that pertains to an ideal mixing chamber. It was found that the washin time (Gaussian response) was limited mainly by the nebulization process itself and partly by dispersion of the sample aerosol as dictated by the length of the desolvation assembly and by the length of tubing that carried the dry aerosol to the plasma source. It was determined that the spray chamber washout time is the factor that limits instrument response and that the desolvation system utilized in the study caused no appreciable peak tailing but did slighty broaden the Gaussian peak width caused by a laminar flow profile and by the nebulization event. The newly designed spray chamber offered washout times that are 1.6 and 5.2 times faster than the CETAC and Fassel spray chambers, respectively. The practical limitations of ultrasonic nebulization for the analysis of transient samples is discussed with a focus on spray-chamber design and based upon the simple model that was developed for the response curves of transient samples.
Direct Measurement of Carbonate Content in Soil Samples by Means of CO Laser Infrared Photoacoustic Spectroscopy
Authors: Dóka Ottó , Bicanic Dane , Szücs Mihály , Lubbers Marcel
Published: October 2003

CO laser infrared (IR) photoacoustic spectroscopy (PAS) at 1801 cm−1 was used to determine the content of carbonate in various soils. The PA signal is linearly proportional to the content of carbonate within the 0–30% (w/w) range; the 2% (w/w) limit of detection (LOD) is adequate for the application in practice.
Emission Spectroscopy: An Excellent Tool for the Infrared Characterization of Textile Fibers
Authors: Friedrich M. , Zahn D. R. T.
Published: October 2003

Infrared emission spectroscopy was applied to characterize various textile fibers not suitable for the usual transmittance measurements. For the emission measurements, the fiber samples were mounted by wrapping them around a resistively heated wire. For spectra evaluation, the instrument response function was determined via reflection and infrared emission measurements at different temperatures of a sample. With knowledge of the instrument response function, single-beam emission spectra can be corrected and become independent of the type of spectrometer or detector. The corrected emission spectra are characteristic for the material and can be collected in a database similar to that for transmission spectra. The usefulness of the method is clearly demonstrated by the spectra of fiber samples.
Photoinduced Anisotropy in a Polymer Doped with Azo Dyes in the Photostationary State Studied by Polarized FT-IR Spectroscopy
Authors: Tawa Keiko , Kamada Kenji , Sakaguchi Toru , Ohta Koji
Published: October 2003

Photoinduced optical anisotropy in poly(methyl methacrylate) (PMMA) films doped with Disperse Orange 3 (DO3, NO2–C6H4–N=N–C6H4–NH2) was investigated by polarized FT-IR spectroscopy. Symmetric (NOs2) and antisymmetric (NOas2) stretching modes of the NO2 group and the C–N stretching mode of C–NH2(C–N) in the infrared absorption spectra of DO3 were found to be useful in order to evaluate the degree of orientation of DO3 molecules in the polymer matrix. Infrared dichroism was observed in the NOs2, NOas2, and C–N bands under the stationary irradiation by visible light. The orientation factors, K( n) Zf ( f = x, y, z, n = trans, cis), determined from the observed dichroism of each isomer in the photostationary state indicate that the p-NO2–C6H4 group is less mobile than the p-NH2–C6H4 group in PMMA during trans- cis- trans isomerization. This dynamic behavior of the DO3 molecules can be interpreted in terms of restriction of rotation within the free volume of PMMA. This study shows that polarized FT-IR spectroscopy is one of the most powerful methods available for the analysis of the physical mechanisms of photoinduced anisotropy.
Nanosecond Time-Resolved Resonance CARS Spectroscopy Using the Scanning Multichannel Technique
Authors: Funk J.-M. , Michelis T. , Eck R. , Materny A.
Published: October 2003

We report on an experimental setup which has been developed to perform efficient nanosecond time-resolved coherent anti-Stokes Raman scattering (CARS) experiments using either the scanning CARS or the broadband CARS technique. A special electronic device has been constructed that allows the CARS probing laser system to be triggered with a variable delay after the excitation pulse of a nitrogen laser and furthermore prevents any temporal drifts of the nitrogen laser emission. The acquisition of the broadband CARS spectra is based on the recently developed scanning multichannel technique, which is applied in the present paper to CARS spectroscopy. Several examples of ground- and excited-state CARS spectra are shown to demonstrate the performance of the setup and to point out the benefits and limitations of the various measurement techniques. Moreover, we present CARS spectroscopic investigations of triplet relaxation processes in order to illustrate the feasibility of the designed spectrometer for nanosecond time-resolved CARS experiments.
Infrared Titration of Aqueous Glycine
Authors: Max Jean-Joseph , Trudel Michel , Chapados Camille
Published: October 2003

The infrared (IR) spectra of glycine in aqueous solutions were obtained in the pH range 0.2 to 14 in order to determine the ionic distribution of the molecule as a function of pH by factor analysis (FA). After subtraction of the water bands, FA was used to separate the spectra of each ionic species and determine their real abundance. The p Ka values were retrieved from the volumetric titration as a function of pH and were used to obtain the theoretical abundance of each ionic species as a function of pH. These distribution curves were compared with the distribution curves obtained from IR. The agreement between the two curves was good. The following species were observed for glycine in water: the cation (pH 0 to 5); the zwitterion (pH 0 to 12.5); and the anion (pH 7 to 14).
Subtraction of the Water Spectra from the Infrared Spectrum of Saline Solutions
Authors: Max Jean-Joseph , Trudel Michel , Chapados Camille
Published: October 2003

The infrared (IR) spectrum of a sample in a saline solution cannot be retrieved adequately when the spectrum of pure water is subtracted. Some water bands remain in the spectrum. The retrieved spectrum is good only when the spectrum of NaCl in water at the right concentration is subtracted. However, when the concentration of the salt is unknown, it is still possible to obtain a good spectrum of the sample free of water. This is done by subtracting from the original spectrum a fraction of two eigenspectra of water: one for pure water and one for NaCl solvated water. The fraction of the eigenspectra is determined with the 2100 and 3300 cm−1 bands. The effectiveness of the method is illustrated with a solution of sodium monochloroacetate in a saline solution.
Structure of Dihydrogen Phosphate Ion Aggregates by Raman-Monitored Serial Dilution
Authors: Shaver Jeremy M. , Christensen Kenneth A. , Pezzuti Jerilyn A. , Morris Michael D.
Published: October 2003

The aggregation of dihydrogen phosphate ion has been studied by Raman spectroscopy during serial dilution of highly concentrated (>5 M) solutions. Factor analysis has been used to recover monomer and aggregate spectra from families of 600–2000 spectra obtained during dilution to about 0.1 M. Spectra of the free aquated dihydrogen phosphate ion and its dimer, trimer, and tetramer have been obtained. There is some evidence for the existence of longer chain aggregates. The serial dilution procedure has been verified by dilution of 2.3 M glycine solution. Only spectra of monomer and dimer ions are recovered. For the well-understood glycine system, the band positions and intensities and the dimerization concentration-dependence are in agreement with previously reported values.
Surface-Enhanced Raman Spectroscopy of Lipids on Silver Microprobes
Authors: Weldon Millicent K. , Zhelyaskov Valentin R. , Morris Michael D.
Published: October 2003

The surface-enhanced Raman scattering (SERS) spectra of model sebaceous gland secretions and their bacterially generated fatty acids are described. Long-chain fatty acids, their parent triglycerides, and long-chain hydrocarbons have characteristic SERS signatures that make them readily resolvable in heterogeneous mixtures. Silicon-substrate silver microprobes are shown to be useful for studying the spatial distribution of lipids and their corresponding fatty acids in nanoflow rate systems.
Infrared Absorption Enhancement at Silver Colloidal Particles
Authors: Kang So Young , Jeon Il Cheol , Kim Kwan
Published: October 2003

Infrared absorption enhancement is observed as occurring at silver colloidal particles spread on an infrared transparent substrate. Its applicability to qualitative analysis was tested by comparing the transmission spectra of 9,10-anthraquinone (AQ) on a KRS-5 plate with and without silver colloidal particles. The largest enhancement factor observed was about 100, and the detection limit for AQ appeared to be less than 10 ng/cm2. The scanning electron micrograph indicated that the colloidal silver film consisted of irregularly shaped islands. AQ does not possess a functional group reactive to silver, so that the infrared absorption enhancement could be assumed to occur through the long-range electromagnetic enhancement mechanism.
High-Precision Determination of Size, Refractive Index, and Dispersion of Single Microparticles from Morphology-Dependent Resonances in Optical Processes
Authors: Popp J. , Lankers M. , Trunk M. , Hartmann I. , Urlaub E. , Kiefer W.
Published: October 2003

Analyzing morphology-dependent resonances observed in optical processes, like Raman scattering or fluorescence emission from single microparticles, allows an exact determination of size, refractive index, and optical dispersion. The main feature of the method discussed here is an exact Mie calculation combined with an optimization program. The results obtained from a gradient-trapped emulsion particle and those from an optically levitated droplet are discussed to show the advantages of the method. It is further demonstrated that only by a precise analysis of the observed morphology-dependent resonances is it possible to describe the droplet evolution.
Single-Shot Multiwavelength Imaging of Laser Plumes
Authors: Nelson Matthew P. , Bell Wendy C. , McLester Michael L. , Myrick M. L.
Published: October 2003

A novel optical approach to single-shot chemical imaging with high spectroscopic resolution is described with the use of a prototype dimension-reduction fiber-optic array. Images are focused onto a 30 × 20 array of hexagonally packed 250 μm o.d. f/2 optical fibers that are drawn into a 600 × 1 distal array with specific ordering. The 600 × 1 side of the array is imaged with an f/2 spectrograph equipped with a holographic grating and a charge-coupled device (CCD) camera for spectral analysis. Software is used to extract the spatial/spectral information contained in the CCD images and de-convolute them into wavelength-specific reconstructed images or position-specific spectra that span a 190 nm wavelength space. “White light” zero-order images and first-order spectroscopic images of laser plumes have been reconstructed to illustrate proof-of-principle. Index Headings: Fiber optics; Chemical imaging; Spectroscopic imaging; Charged-coupled device (CCD); Laser-induced breakdown spectroscopy (LIBS).
Fluorescent Enzymatic Probes Suitable for Two-Photon Excitation
Authors: Overway Kenneth S. , Lytle Fred E.
Published: October 2003

Several common aminopeptidase probes are examined for the strength of two-photon excited fluorescence. The fluorophores 4-methoxy-β-naphthylamine and 7-amino-4-methylcoumarin have limits of detection of 930 pM and 200 pM, respectively. The coumarin derivative is shown to have a two-photon cross section at 590 nm, which is exceptionally large for an aromatic amine. Spectral data for this compound also indicate that excitation near 690 nm should permit quantitation at concentrations as low as 40 pM.
Hybrid Photomultiplier: Its Characterization and Application as a Wide-Dynamic-Range Photon Detector
Authors: Alfano Angelo J.
Published: October 2003

The hybrid photomultiplier (HPMT) is commercially available in proximity- and electrostatically focused versions, and both contain a photocathode and a PIN-diode substrate. This recent addition to the family of photon detectors offers good timing characteristics, reasonable gain, excellent pulse height distribution, and a wide dynamic range. This report provides details on the wiring and characterization of a typical electrostatically focused production device for gain, impulse response, and pulse height and pulse integral linearity. A gain of 1.8 × 103 was obtained at less than the maximum high-voltage bias. The impulse response rise time was 1.0 ns and the fall time was 0.9 ns. The full width at half-maximum (FWHM) of the impulse response was 4.3 ns at 160 V reverse diode bias. The pulse height was linear up to 4.45 × 104 photoelectrons, and the pulse integral was linear up to the maximum tested (2.23 × 105 photoelectrons). The HPMT is not damaged by light levels that are three orders of magnitude beyond the range of linear response for a conventional PMT. Therefore, the HPMT can be directly implemented in spectroscopic applications that previously required elaborate gating schemes to protect a detector from a large optical flash that preceeds a weak subsequent optical event of interest.
Spatially Resolved Temperature Determination of an Air/Acetylene Flame Using the Two-Step Laser-Enhanced Ionization Technique
Authors: Ke Chin-Bin , Lin King-Chuen
Published: October 2003

We have demonstrated a two-step laser-enhanced ionization (LEI) technique to be potentially useful in measuring a spatially resolved temperature in an atmospheric air/acetylene flame. As a complement to the existing optical methods, LEI detection shares the advantages of extremely high sensitivity and the capability of achieving a high spatial resolution, confined to the dual-beam intersection area of 1 mm × 1 mm. A theoretical model was developed to precisely extract the temperature information from the obtained two-step LEI signal. The physical parameters required in the experiment include simply the relative values of the LEI signals, associated with the fine-structure doublets of a selected thermometric species, and their corresponding laser energies. The subsequent treatment is also convenient without the need to know the absolute energy of the incident laser beam and to accurately calibrate the detection system. Al and Ga were selected as the thermometric species. The resultant radial and axial temperature mappings are consistent with each other and are also comparable with those reported by other optical methods.
Partial Least-Squares Modeling of Near-Infrared Reflectance Data for Noninvasive in Vivo Determination of Deep-Tissue pH
Authors: Zhang Songbiao , Soller Babs R. , Micheels Ronald H.
Published: October 2003

Noninvasive monitoring of deep-tissue pH has been demonstrated with the use of near-infrared spectroscopic measurements and the partial least-squares (PLS) multivariate calibration technique. The near-infrared reflectance spectra (700 to 1100 nm) of the teres major muscle in five New Zealand rabbits were obtained in vivo, along with reference pH values in the muscle measured by microelectrodes. The muscle pH was varied by controlling the blood supply to the muscle. PLS analysis with cross-validation techniques, along with several data preprocessing methods, was used to relate the tissue pH to spectra. When multi-subject PLS calibration models were used to predict a new independent subject, a subject-dependent offset was observed. Several strategies for minimizing the subject-dependent offset were discussed. With a baseline subtraction procedure, the subject-dependent offset was minimized to less than 0.1 pH units while the average standard error of prediction (SEP) was close to 0.05 pH units. This result suggests that it is possible to build a single robust calibration model for all new independent subjects. Tissue chemistry during ischemia (blood flow reduction) is different from the chemistry of reperfusion (blood flow restoration), and it was found that separate calibration models permit more accurate prediction of pH.
Direct Visualization of Secretion from Single Bovine Adrenal Chromaffin Cells by Laser-Induced Native Fluorescence Imaging Microscopy
Authors: Tong Wei , Yeung Edward S.
Published: October 2003

Direct visualization of the secretion process of individual bovine adrenal chromaffin cells was achieved with laser-induced native fluorescence imaging microscopy. By monitoring the native fluorescence of catecholamines excited by the 275 nm laser line with an intensified charge-coupled-device (CCD) camera, we obtained good temporal and spatial resolution simultaneously without using additional fluorescent probes. Large variations were found among individual cells in terms of the amounts of catecholamines secreted and the rates of secretion. Different regions of a cell also behave differently during the secretion process. However, the degree of this local heterogeneity is smaller than in neurons and neuralgia. The influence of deep-ultraviolet (UV) laser excitation on cells is also discussed. This quantitative imaging technique provides a useful noninvasive approach for the study of dynamic cellular changes and the understanding of the molecular mechanisms of secretory processes.
Solid-Matrix Fluorescence and Phosphorescence Detection and Characterization of Benzo[a]pyrene–DNA Adducts with Whatman No. 1 and Whatman 1PS Filter Paper
Authors: Tjioe S. Wey , Hurtubise Robert J.
Published: October 2003

Benzo[ a]pyrene (B[a]P) is a potential carcinogen and mutagen, and it has been studied very extensively. In humans, B[a]P can be metabolized and becomes chemically bonded to DNA. A variety of methods are needed for the characterization of B[a]P–DNA adducts because of the structural complexity of the adducts. In this work, several solid-matrix luminescence methods were developed for the characterization of the B[a]P-DNA adducts. Both solid-matrix fluorescence and solid-matrix phosphorescence could be obtained from the adducts on Whatman No. 1 and Whatman 1PS filter paper at nanogram levels. Thallium nitrate proved to be an effective heavy atom in enhancing the solid-matrix phosphorescence of the adducts. By selective excitation of the phosphorescence of the adducts, it was possible to excite different forms of the adducts. With moisture quenching of the solid-matrix phosphorescence of the B[a]P-DNA adducts, it was feasible to selectively detect quasi-intercalated adducts. With Whatman 1PS filter paper, a unique method was developed for the solid-matrix fluorescence detection of adducts externally bound to DNA by the hydrophobic interaction of the adducts with the 1PS paper.
High-Resolution, Time-Resolved Spectra of Indium and Aluminum Atoms, Fluorides, Chlorides, and Oxides in a Graphite Tube Furnace
Authors: Shepard Michael R. , Jones Bradley T. , Butcher David J.
Published: October 2003

High-resolution (4.4 pm), time-resolved (every 0.2 s during the atomization step) spectra of indium and aluminum atoms and molecules (InF, InCl, AlF, AlCl) were obtained in a graphite tube furnace with the use of a xenon arc lamp for excitation and a linear photodiode array detector. The spectra of indium fluoride, aluminum fluoride, and aluminum chloride were shown to be composed of several vibrational bands making up the (0, 0) sequence, while the indium chloride spectrum included vibrational progressions as well. For indium fuoride and aluminum fluoride, the diatomic molecule appeared temporally earlier than atoms of the metal. Spectra of reagents used to produce indium fluoride and aluminum fluoride were similar to previous spectra in the literature that were assigned to In2O and Al2O, respectively. The spectral overlap of the absorption band for aluminum chloride (261.44 nm) with a lead absorption line (261.42 nm) is discussed with respect to its implications for background correction for graphite furnace atomic absorption spectrometry.
Laser-Induced Breakdown Spectroscopy for Polymer Identification
Authors: Sattmann R. , Mönch I. , Krause H. , Noll R. , Couris S. , Hatziapostolou A. , Mavromanolakis A. , Fotakis C. , Larrauri E. , Miguel R.
Published: October 2003

Laser-induced breakdown spectroscopy has been applied to polymer samples in order to investigate the possibility of using this method for the identification of different materials. The plasma emission spectra of high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyvinyl chloride (PVC), polyethylene terephthalate (PET), and polypropylene (PP) have been studied. Spectral features have been measured—for example, the 725.7 nm chlorine line, the 486.13 mm Hβ line, and the 247.86 nm carbon line—whose evaluation with neural networks permits identification accuracies between 90 and 100%, depending on polymer type.
Identification of Modified Starches Using Infrared Spectroscopy and Artificial Neural Network Processing
Authors: Dolmatova Ludmila , Ruckebusch Cyril , Dupuy Nathalie , Huvenne Jean-Pierre , Legrand Pierre
Published: October 2003

The authentication of food is a very important issue both for the consumers and for the food industry with respect to all levels of the food chain from raw materials to finished products. Corn starch can be used in a wide variety of food preparation as bakery cream fillings, sauce, or dry mixes. There are many modifications of the corn starch in connection with its use in the agrofood industry. This paper describes a novel approach to the classification of modified starches and the recognition of their modifications by artificial neural network (ANN) processing of attenuated total reflection Fourier transform spectroscopy (ATR/FT-IR) spectra. Using the self-organizing artificial neural network of the Kohonen type, we can obtain natural groupings of similarly modified samples on a two-dimensional plane. Such mapping provides the expert with the possibility of analyzing the distribution of samples and predicting modifications of unknown samples by using their relative position with respect to existing clusters. On the basis of the available information in the infrared spectra, a feedforward artificial neural network, trained with the intensities of the derivative infrared spectra as input and the starch modifications as output, allows the user to identify modified starches presented as prediction samples.
Quality Analysis for Least-Squares Transformation of Unevenly Spaced Interferograms
Authors: Weidner H. , Peale R. E.
Published: October 2003

A least-squares method of transforming interferograms into spectra is compared with the traditional fast Fourier transform (FFT) for varying degree of point-spacing unevenness. A Gaussian distribution is assumed for the deviations from even spacing. FFT gives inferior spectra quality above a critical unevenness, which decreases as more interferograms are averaged.
Assessing the Validity of Near-Infrared Monochromator Calibrations over Time
Authors: Bouveresse Eric , Casolino Chiara , Massart Désiré-Luc
Published: October 2003

A procedure to check the validity of near-infrared calibration models over time is proposed. Validation samples are analyzed at regular time intervals by both near-infrared and reference methods in order to check the validity of the near-infrared calibration model. When an invalid situation is detected, a stable polystyrene standard is measured, to determine whether this invalid situation is due to fluctuations of the instrumental response of the near-infrared spectrometer or not. A first method based on simulating simple instrumental differences enables one to correct those simple differences with only the polystyrene standard. It is shown that such an approach can correct most of the simple instrumental differences without the use of standardization procedures. However, when the invalid situation is due to more complex instrumental differences, standardization must be applied. This procedure is applied to simulated and real near-infrared data sets.
Signal Detection for Data Sets with a Signal-To-Noise Ratio of 1 or Less with the Use of a Moving Product Filter
Authors: Schulze H. G. , Greek L. S. , Barbosa C. J. , Blades M. W. , Turner R. F. B.
Published: October 2003

We report on a method to reduce background noise and amplify signals in data sets with low signal-to-noise ratios (SNRs). This method consists of taking a data set with mean 0 and normalized with respect to absolute value, adding 1 to all values to adjust the mean to 1, and then applying a moving product (MP) to the transformed data set (similar to the application of a moving average or 0-order Savitzky–Golay filtering). A data point in the presence of a signal raises the probability of that data point having a value >1, while the absence of a signal increases the probability of that data point having a value < 1. If the autocorrelation lag of the signal is larger than the autocorrelation lag of the associated noise, the use of an MP with window comparable to that of the signal width (i.e., 2–3 times the signal standard deviation) will tend to reduce the values of data points where no signal is present and similarly amplify data points where signal is present. Signal amplification, often to a considerable degree, is gained at the cost of signal distortion. We have used this method on simulated data sets with SNRs of 1, 0.5, and 0.33, and obtained signal-to-background noise ratio (SBNR) enhancements in excess of 100 times. We have also applied this procedure to low SNR measured Raman spectra, and we discuss our findings and their implications. This method is expected to be useful in the detection of weak signals buried in strong background noise.
Time-Resolved Laser-Induced Fluorescence as a Unique Tool for Low-Level Uranium Speciation
Authors: Moulin Christophe , Laszak Ivan , Moulin Valérie , Tondre Christian
Published: October 2003

Time-resolved laser-induced fluorescence is a unique method for direct uranium speciation at low level in the framework of environmental studies. By varying pH and uranium concentration in the absence of carbonate ions and at fixed ionic strength, it was possible, together with free uranyl UO22+, to identify spectrally and temporally all the uranium-hydroxo complexes, namely, UO2OH+, UO2(OH)2, UO2(OH)3−, (UO2)2(OH)22+, (UO2)3(OH)5+, and (UO2)3(OH)7−.
Investigations of Radical Polymerization and Copolymerization Reactions in Optically Levitated Microdroplets by Simultaneous Raman Spectroscopy, Mie Scattering, and Radiation Pressure Measurements
Authors: Musick J. , Popp J. , Trunk M. , Kiefer W.
Published: October 2003

The combination of the optical levitation technique with Raman spectroscopy, elastic (Mie) scattering, and radiation pressure measurements enables in situ and real-time investigation of polymerization and copolymerization processes in single microdroplets. The time-dependent evolution of the polymerization and copolymerization reactions of styrene/unsaturated polyester resin (UP-resin) is characterized by observing the educt and product signals in the Raman spectra. The size, the refractive index, and the wavelength dependence of the refractive index of the optically levitated microparticle are determined from the position of the morphology-dependent resonances observed in Raman spectra, in elastic light scattering, and in radiation pressure measurements. This additional information about droplet properties as a function of time allows a better understanding of the entire reaction process within the microdroplet.