bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of Data Pretreatment and Model Building Methods for the Determination of Glucose from Near-Infrared Single-Beam Spectra
Authors: Ding Qing , Small Gary W. , Arnold Mark A.
Published: October 2003

Near-infrared single-beam spectra are used to build partial least-squares (PLS) calibration models for the determination of glucose in biological matrices. Two different data sets of the same sample constituents are used in this investigation. The glucose samples consist of an aqueous matrix of varied concentrations of bovine serum albumin (BSA) and triacetin. The BSA and triacetin are models for blood proteins and triglycerides, respectively. Due to the effects of intensity variation in the single-beam spectra, calibration models obtained with unprocessed spectra are not as good as those computed with the corresponding spectra in absorbance units. When this intensity variation is reduced through the use of multiplicative signal correction (MSC), a spectral normalization method, or a logarithmic transform, the resulting models are as good as or better than those obtained in the analysis of absorbance spectra. An attempt is made to model the nonlinear relationship between single-beam spectral intensities and glucose concentrations by use of step-wise quadratic PLS (QPLS) models. The QPLS models are found to perform better than linear PLS models in some cases (e.g., with MSC-corrected single-beam spectra). The effect of digital filtering on the calibration models computed with single-beam spectra is also studied. The results obtained with and without filtering are found to be similar in terms of model performance, but the models based on filtered single-beam intensities require fewer latent variables and perform more consistently as a group. A final test is performed to compare the robustness of calibration models computed with single-beam spectra to those based on absorbance spectra. When applied to spectra that lie outside the time span of the calibration data, the models based on single-beam spectra are still competitive with those computed with absorbance spectra.
Raman, IR, and 27Al-MAS-NMR Spectroscopic Studies of Sodium (Hydroxy)Aluminates
Authors: Watling H. R. , Sipos P. M. , Byrne L. , Hefter G. T. , May P. M.
Published: October 2003

A series of solid sodium (hydroxy)aluminates has been prepared from highly caustic aqueous sodium aluminate solutions. The coordination geometry of the aluminum in these compounds was established by 27Al magic angle spinning nuclear magnetic resonance (27Al-MAS-NMR) spectroscopy and was used to identify the Raman and IR vibration frequencies characteristic of tetrahedral (Raman: 440 cm−1; IR: 823 cm−1 and 540 cm−1) and octahedral (Raman: 490–500 cm−1; IR: 728 cm−1) aluminum sites. The vibrational spectra of these solids differ markedly from those observed for concentrated aqueous solutions, and it appears that solid-state vibrational spectra cannot be used to predict the structure of aluminate species existing in solutions.
Inclusion Complexes of N-Benzoyl-d-Leucine and N-Benzoyl-l-Leucine with β-Cyclodextrin by Raman Spectroscopy
Authors: Spivey Robin , Swofford Robert L.
Published: October 2003

We report what is believed to be the first detection of chiral recognition in the inclusion complexes of cyclodextrins by Raman spectroscopy. The spectra of inclusion complexes of N-benzoyl-d-leucine or N-benzoyl-l-leucine with β-cyclodextrin were recorded in the 1500–1800 and 3000–3150 cm−1 regions. These chiral molecules were chosen to provide group frequencies (NH2+ and benzoyl C=O) near the chiral center of the guest as well as COO− and phenyl CH for probing the guest molecule without spectral interference from the vibrational bands of the cyclodextrin host. Frequency shifts and intensity decreases were observed for some Raman bands of N-benzoyl-leucines upon inclusion in the cyclodextrin cavity. In the Raman spectra of the inclusion complex, the frequency shifts were greater for N-benzoyl-d-leucine than for N-benzoyl-l-leucine.
Raman Spectroscopy with a Single-Frequency, High-Power, Broad-Area Laser Diode
Authors: Claps R. , Sabbaghzadeh J. , Fink M.
Published: October 2003

A high-power, broad-area laser diode was used as an incident light source in a Raman spectrometer. The laser was forced to lase in a very narrow frequency range (⩽ 400 MHz) by the use of a Metcalf–Littman arrangement. All side bands and light-emitting diode (LED) modes were suppressed; their intensities are lower than the noise of recorded rotational spectra. The incident wavelength was tuned to coincide with the D1 transition of 85Rb. Due to this choice, the elastically scattered light (Rayleigh component) can be eliminated by a Rb cell in front of the spectrometer. The usefulness of this arrangement is demonstrated for CO2, N2, and air. Because of the suppression of the dominating Rayleigh intensity, this setup is ideally suited for a Fourier transform Raman spectrometer.
Heterogeneity Studies of a Single Particle/Fiber by Using Fourier Transform Infrared Micro-Sampling Photoacoustic Spectroscopy
Authors: Jiang Eric Y.
Published: October 2003

This paper reports the first investigation of the micro-sampling possibility of Fourier transform infrared photoacoustic spectroscopy (FT-IR PAS) in depth profiling of a single particle and a single fiber. The samples studied in this paper include a Bio-Bead™ (150 μm in diameter) coated with commercial strawberry flavor oil, a nylon wire with grease coating, and a piece of natural human hair (60 μm in diameter and 7 mm in length) with gel-coating. Major FT-IR PAS operation modes utilized in depth profiling of heterogeneous/layered macro-samples reported previously, such as (continuous-) rapid-scan, phase-, and nonphase modulation step scans, were used in this study. The software-based digital signal processing (DSP) algorithms for step-scan photoacoustic (fundamental and harmonic) signal modulation/demodulation were employed in the phase modulation experiments. Both modulation frequency variation and photoacoustic signal phase analysis methods were applied to elucidate detailed spectral depth profiling information from the raw data of these micro-samples. The results conclude that FT-IR micro-PAS offers a unique and complementary method in analysis of heterogeneous micro-samples with nondestructive, noncontact, and cost-effective advantages compared with conventional FT-IR micro-transmission/reflection/ATR approaches.
Multichannel Asynchronous Time-Resolving System for a Conventional FT-IR Spectrophotometer
Authors: Masutani K. , Numahata K. , Nishimura K. , Ochiai S. , Nagasaki Y. , Katayama N. , Ozaki Y.
Published: October 2003

A novel multichannel asynchronous time-resolving system with 16 time-resolving channels has been developed for conventional FT-IR spectrophotometers. The system enables measurement at 16 time delays simultaneously. This reduces the measuring time substantially and decreases possible damage of a sample by the stimulus. Moreover, simultaneous time resolving by the multichannel system improves the reliability of the data. As a performance test of the system, application to the study of reorientation dynamics in a ferroelectric liquid crystal is reported.
Forward-Scattering Degenerate Four-Wave Mixing Detection in Micro-Column Liquid Chromatography Using Fused-Silica Capillary Flow Cells
Authors: de Beer Tjipke , Hoornweg Gerard Ph. , Besoo Paul , Brinkman Udo A. Th. , Velthorst Nel H. , Gooijer Cees
Published: October 2003

In order to have as simple a chromatographic setup as possible, laser-based forward scattering degenerate four-wave mixing (F-D4WM) detection is applied directly to fused-silica capillary flow cells that can be used in micro-column liquid chromatography (μLC). Compared to the previously used specially designed flow cells (optimized from an optical point of view), such cylindrically shaped cells have obvious disadvantages such as background scatter and signal beam distortion. However, a laser beam can be focused easily in a fused-silica capillary, yielding a laser-probed volume of less than 100 pL, which is attractive for miniaturized chromatographic systems. Parameters such as capillary dimensions (internal and outer diameters), capillary configuration in relation to eluent flow direction, flow rate, and various background suppression techniques are considered from a theoretical and a practical point of view and subsequently optimized. Interestingly, the direction of the eluent flow is critical; it should be in the plane formed by the two laser beams. μLC/F-D4WM is used to analyze spiked river Rhine water.
Characterization of an Acousto-Optic Tunable Filter and Use in Visible Spectrophotometry
Authors: Bucher Ewa G. , Carnahan Jon W.
Published: October 2003

The use of a paratellurite acousto-optic tunable filter (AOTF) is demonstrated as a monochromator for spectrophotometry. This device operates in the range of 400 to 700 nm with a resolution from 2.5 nm (at 633 nm) to 0.5 nm (at 400 nm). Results of the initial characterizations indicate that behavior follows the theoretical model in terms of frequency/wavelength relationships, dependence of the output wavelength upon the incident radiation angle, and bandpass as a function of wavelength. Initial results of spectroscopic characterizations of permanganate, cobalt(II), holmium(III), praseodymium(III), and neodymium(III) solutions are presented. Placing a polarizer in the light path reduced the amount of stray light reaching the detector. Two types of photomultiplier tubes were used as detectors. The sensitivity of the PMTs varied at different wavelengths, which affected spectral responses and the effects of scattered light.
Adaptive Signal Enhancement of Laser-Induced Breakdown Spectroscopy
Authors: Younan N. H. , Zhang H.
Published: October 2003

A noise reduction technique to analyze laser-induced breakdown spectroscopy spectra is presented in this paper. This technique is an adaptive-type technique for noise minimization. It is based on an improved adaptive line enhancement to effectively increase the signal-to-noise ratio level in spectral data. It requires no a priori knowledge of the signal or of the noise, and it has the capability of on-line implementation. Medium and weak spectra are considered, and a comparison with traditional techniques is made to illustrate the applicability of the foregoing technique.
Simple Near-Infrared Time-Correlated Single Photon Counting Instrument with a Pulsed Diode Laser and Avalanche Photodiode for Time-Resolved Measurements in Scanning Applications
Authors: Zhang Yuling , Soper Steven A. , Middendorf Lyle R. , Wurm John A. , Erdmann Rainer , Wahl Michael
Published: October 2003

A simple apparatus for time-correlated single photon counting (TCSPC) measurements in the near-infrared (near-IR) region for scanning-type applications has been constructed and examined. The apparatus consisted of five major components including a pulsed diode laser source (lasing wavelength = 780 nm; repetition rate 80 MHz; power = 5 mW; pulse width = 150 ps), an integrated microscope, a large-photoactive-area avalanche photodiode (APD), a TCSPC PC-board including the electronics, and a Windows-based software package for accumulating the fluorescence decay profiles. The instrument response function (IRF) of this assembly was found to be 460 ps, which is adequate for measuring lifetimes with τf ⩾ 500 ps. Due to the small size of the device, it also allowed implementation into scanning experiments where lifetimes were measured. To demonstrate this capability, we scanned a three-well microscope slide containing a near-IR dye. The decay profile of the near-IR dye, aluminum 2,3-naphthalocyanine, was collected and analyzed to obtain its lifetime, which was found to be 2.73 ns, in close agreement with the literature value for this particular dye. In addition, a three-dimensional plot showing the decay profiles (time vs. photocounts) and scan position of aluminum 2,3-naphthalocyanine fluorescence was acquired by scanning the microscope head over this three-well glass slide. In the scanning mode, the IRFs as well as the decays of the dyes were found to be very stable. The device demonstrated a concentration detection sensitivity of 0.44 nM; however, the dynamic range was limited due to the slow time constant (passive quenching) associated with the APD.
β-Sheet Recognition by Time-Resolved Fluorescence Spectroscopy
Authors: De Rossi U. , Hermel H.
Published: October 2003

A cyanine dye is used for the determination of β-sheet protein structures above the critical protein aggregation concentration through a bathochromic shift of the longwavelength absorption band. Simultaneously the fluorescence quantum yield of the dye increases strongly in the presence of β-sheet protein as compared to aqueous solution. Results from fluorescence lifetime experiments exhibit a short component (100 ps) of the dye in aqueous solution, which increases to about 1800 ps in protein-containing solutions. In contrast to absorption properties, the values of fluorescence lifetime and fluorescence intensity also depend on protein concentration and can be used not only to determine the protein structure but also to roughly estimate the concentration of the protein. Due to the protein-induced formation of H-aggregates, the absorption, the fluorescence intensity, and the amplitude of the fluorescence lifetime depend on time delay between sample preparation and measurement.
Enhancement of 5,10,15,20-Tetra(m-Hydroxyphenyl)Chlorin Fluorescence Emission by Inclusion in Natural and Modified Cyclodextrins
Authors: Demore Delphine , Kasselouri Athena , Bourdon Olivier , Blais Jocelyne , Mahuzier Georges , Prognon Patrice
Published: October 2003

Fluorescence properties of 5,10,15,20-tetra( m-hydroxyphenyl)chlorin ( m-THPC), a sensitizer used in photodynamic therapy (PDT), were studied in the presence of three native cyclodextrins (CDs) -α, -β, and γ-CD—and two modified cyclodextrins—heptakis (2,6-di- O-methyl) β-CD (Me-β-CD) and heptakis (2- O-hydroxy-propyl) β-CD (HP-β-CD). The CDs studied have been shown to undergo the formation of an inclusion complex with m-THPC, leading to a large enhancement (up to 300 times) of m-THPC fluorescence intensity depending on the CD used. Stoichiometry and association constants have been determined on the basis of the variation of fluorescence intensity. A 1:2 stoichiometry has been found for m-THPC complexes with γ-CD, Me-β-CD, and HP-β-CD. Association constants as high as K = 9.5 × 108 M−2 in the case of m-THPC/2Me-β-CD and K = 2.7 × 109 M−2 in the case of m-THPC/ 2HP-β-CD complex were determined, whereas a lower value ( K = 2.4 × 104 M−2) was found in the case of m-THPC/2γ-CD. Because of the highest fluorescence enhancement (a factor of about 300) observed with Me-β-CD, this compound would be the most suitable to improve the detection of m-THPC in further pharmacokinetics and biodistribution studies.
Adsorption and Ordering of Resorcinare Layers on Planar and Colloidal Gold and the Influence of Surface Modification: A SERS and IRRAS Study
Authors: Nissink J. Willem M. , van der Maas John H.
Published: October 2003

Near-infrared surface-enhanced Raman spectroscopy and infrared reflection-absorption spectroscopy have been applied to investigate adsorption and ordering processes of resorcinarene cavitands at interfaces. Colloidal gold was applied in the case of NIR-Raman measurements, and planar gold substrates were used for reflection spectroscopy. Selected cavitands substituted on their upper rim with different functionalities were employed as probe molecules. An assignment of vibrational bands is presented. Interactions between probe molecules and substrates are present in all cases. From Raman measurements, it is difficult to deduce an orientation of the probe molecule adsorbed onto the gold particle, as the selection rules for SERS cannot be applied straightforwardly. Furthermore, an orientation depends on a proper assignment of vibrational bands. Infrared spectroscopy shows that the orientation of the resorcinarene molecules deposited on a planar gold or gold/monolayer interface is influenced by the underlying substrate. The directing effect, however, does not extend into the adjoining bulk of the sample layer.
Analysis of Odorous Vapor Exhaled from Rubber by Surface-Enhanced Raman Scattering
Authors: Hill Wieland , Wehling Bernhard , Klockow Dieter
Published: October 2003

Vulcanized rubber evolves an evil-smelling gas for months after contact with the fumigant methyl bromide. The analysis of the gas by surface-enhanced Raman scattering (SERS) shows that it contains traces of a thiomethyl compound, which was identified as methyl mercaptane. The SERS method can be used to determine gas-phase concentrations of methyl mercaptane in the low ppbv range by analyzing the velocity of adsorption. The investigated example demonstrates the capability of SERS for the detection and identification of very low gas concentrations of substances that are adsorbed irreversibly at silver surfaces.
Fourier Transform Raman Spectra of Linear Low-Density Polyethylene and Prediction of Their Density by Multivariate Data Analysis
Authors: Sano K. , Shimoyama M. , Ohgane M. , Higashiyama H. , Watari M. , Tomo M. , Ninomiya T. , Ozaki Y.
Published: October 2003

Fourier transform Raman spectra have been measured for pellets of sixteen kinds of linear low-density polyethylene (LLDPE) with short branches and one kind of PE without any branch. Before we tried chemometrics analysis, the Raman spectra of LLDPE were investigated by comparing them with the spectrum of PE in order to explore the effects of the branches on the Raman spectra. Partial least-squares (PLS) regression was applied to the Raman spectra in the 1600–600 cm−1 region after multiplicative scatter correction (MSC) to propose a calibration model that predicts the density of LLDPE. The correlation coefficient was calculated to be 0.968, and the root mean square error of cross validation (RMSECV) was found to be 0.0018 g/cm3. The loadings plot of regression coefficients for the calibration model shows that, not only a sharp upward peak at 1417 cm−1 corresponding to the CH2 bending mode reflecting the crystallinity, but also a broad downward peak near 1308 cm−1 corresponding to the amorphous board band of LLDPE plays a key role in the prediction of their density. The chemometrics study has deepened the analysis of the Raman spectra of LLDPE. For example, the detailed analysis of the principal component weight loadings plots has elucidated the existence of bands due to the CH3 groups of branches and those arising from amorphous parts of LLDPE that are almost missing or hidden by other intense bands. In other words, the chemometrics analysis has enhanced spectral resolution.
Signal-to-Noise Ratio of FT-IR CO Gas Spectra
Authors: Bak J. , Clausen S.
Published: October 2003

The minimum amount of a gaseous compound which can be detected and quantified with Fourier transform infrared (FT-IR) spectrometers depends on the signal-to-noise ratio (SNR) of the measured gas spectra. In order to use low-resolution FT-IR spectrometers to measure combustion gases like CO and CO2 in emission and transmission spectrometry, an investigation of the SNR in CO gas spectra as a function of spectral resolution has been carried out. We present a method to (1) determine experimentally the SNR at constant throughput, (2) determine the SNR on the basis of measured noise levels and Hitran simulated signals, and (3) determine the SNR of CO from high to low spectral resolutions related to the molecular linewidth and vibrational-rotational lines spacing. In addition, SNR values representing different spectral resolutions but scaled to equal measurement times were compared. It was found that the SNR was at a local minimum at a spectral resolution of 4 cm−1. As a result of the investigations, we suggest that the specific spectral resolution which smears out the vibrational-rotational line structure of the smaller molecules should be considered to be low (4 cm−1 for CO).
Shock Excitation and Cooling Stage in the Laser Plasma Induced by a Q-Switched Nd:YAG Laser at Low Pressures
Authors: Budi Wahyu Setia , Suyanto Hery , Kurniawan Hendrik , Tjia May On , Kagawa Kiichiro
Published: October 2003

An experimental study has been carried out on the dynamical process taking place in the secondary plasma generated by a Q-switched Nd:YAG laser (80 mJ, 8 ns) on a copper target at reduced pressure. Accurate dynamical characterization of the cross-sectional view of the plasma has been made possible by the unique combination of a plasma confinement configuration and the time-resolved measurement technique. In addition to reaffirming the role of the blast-wave mechanism in the generation of secondary plasma, an analysis of the time-resolved spatial distributions of emission intensities and the time-resolved spatial distributions of temperature was made. As a result, the occurrence of two-stage emission processes, the “shock excitation stage” and “cooling stage,” has been proved. For instance, at 2 Torr it is shown that the emission process is initiated by a brief shock excitation process (∼ 1 μs) and followed by a longer cooling process (∼ 3 μs). The experimental results concerning the characteristics of the plasma can be well understood by considering the two-stage processes.
Detection of Styrene Impurities in Phenylacetylene by Resonance-Enhanced Multiphoton Ionization Time-of-Flight Mass Spectrometry
Authors: Tzeng W. B. , Narayanan K. , Lin J. L.
Published: October 2003

Three commercially available phenylacetylene samples were studied by using resonance-enhanced multiphoton ionization (REMPI) time-of-flight mass spectrometry. Analyses of the observed mass peaks and the resulting optical spectra show that all these samples contain styrene impurities. The observed spectral features have been successfully assigned on the basis of comparison with the results from our ab initio calculations and experimental data available in the literature. The present studies demonstrate the feasibility of the REMPI technique coupled with mass analysis to obtain unambiguous spectral information for a sample mixture containing many components.
In situ Detection of Chromate Using Photoacoustic Spectroscopy
Authors: Foster Nancy S. , Amonette James E. , Autrey S. Tom
Published: October 2003

Pulsed-laser photoacoustic spectroscopy (LPAS) can be used to non-destructively assay aqueous Cr(VI) concentrations at trace levels. The technique involves the absorption of light pulses at 371 nm by Cr(VI) species (predominately chromate and bichromate). The absorbed energy is subsequently released in the form of heat generating a local pressure wave that is detected by an ultrasonic transducer. Because the total absorptivity of a Cr(VI) solution depends on the mixture of Cr(VI) species present and, thus, is strongly correlated with pH, a simple working expression relating solution absorbance to pH was developed, and molar absorptivities for several Cr(VI) species are reported. The detection limit for Cr(VI), which is effectively determined by the absorptivity of water, is reported to be 1 ng mL−1 at pH 6. Detection limits near 0.3 ng mL−1 would be expected for solutions at pH 8 and above, where the absorptivities of Cr(VI) species are greater. The nondestructive nature of this technique makes in situ studies of trace-level Cr(VI) chemistry in small volumes possible. We show how the technique can be used to study, in essentially real time, the thermodynamics and kinetics of Cr(VI) sorption by hematite (α-Fe2O3) powder, and the effect of competing ions, such as phosphate, on these properties.
Quantitative Multiwavelength Constituent Measurements Using Single-Wavelength Photon Time-of-Flight Correction
Authors: Leonardi Lorenzo , Burns David H.
Published: October 2003

A method to correct for spectral variations in multiwavelength responses using a photon time-of-flight measurement was investigated. A new approach is described where near-infrared spectra of various absorbing and scattering solutions are corrected for nonlinear variations in the measured attenuation. The spectral attenuation measured in a sample is related to the concentration of the analyte as well as the scattering from the medium. The dependence of the detected attenuation on the absorption and scattering at a single wavelength can be described by the steady-state diffusion approximation. With the use of the steady-state diffusion approximation, single-wavelength correction methodologies for multiwavelength responses were developed to refine constituent estimates in a scattering medium. The single-wavelength corrections examined the use of multiwavelength responses ratioed to the absorption and scattering determined at a single wavelength to reduce the scattering influence in the detected attenuations. The single-wavelength correction method improved constituent estimates in a variable medium. The correction utilized the absorption and scattering determined from processed time-resolved photon distributions at a single wavelength. Partial least-squares (PLS) regression was used to obtain constituent absorption estimates from diffuse transmittance spectra of turbid samples. A 70% improvement over PLS-processed spectra was obtained with a combined single-wavelength absorption and scattering correction. In comparison to steady-state multiwavelength correction methods such as wavelength normalization, derivative spectroscopy, and multiplicative signal correction, the results demonstrate a significant improvement in estimates of the dye concentration. Results suggest a practical method to correct for scatter variations in multiwavelength responses for routine spectroscopic chemical analysis of turbid samples.
Representative Layer Theory for Diffuse Reflectance
Authors: Dahm Donald J. , Dahm Kevin D.
Published: October 2003

The fractions of light absorbed by and remitted from samples consisting of different numbers of plane parallel layers can be related with the use of statistical equations. The fractions of incident light absorbed ( A), remitted ( R), and transmitted ( T) by a sample of any thickness can be related by an absorption/remission function, A( R,T):

A( R,T) = [(1 - R)2 - T2]/ R = (2 - A - 2 R) A/ R = 2 A0/ R0.

Being independent of sample thickness, this function is a material property in the same sense as is the linear absorption coefficient in transmission spectroscopy. The absorption and remission coefficients for the samples are obtained by extrapolating the measured absorption and remission fractions for real layers to the fraction absorbed ( A0) and remitted ( R0) by a hypothetical layer of infinitesimal thickness. A sample of particulate solids can be modeled as a series of layers, each of which is representative of the sample as a whole. In order for the layer to be representative of the properties of the individual particles of which it is comprised, it should nowhere be more than a single particle thick, and should have the same void fraction as the sample; further, the volume fraction and cross-sectional surface area fraction of each particle type in the layer should be identical to its volume fraction and surface area fraction in the sample as a whole. At lower absorption levels, the contribution of a particle of a particular type to the absorption of a sample is approximately weighted in proportion to its volume fraction, while its contribution to remission is approximately weighted in proportion to the fraction of cross-sectional surface area that the particle type makes up in the representative layer.
Novel Use of a Static Modification of Two-Dimensional Correlation Analysis. Part I: Comparison of the Secondary Structure Sensitivity of Electronic Circular Dichroism, FT-IR, and Raman Spectra of Proteins
Authors: Pancoska Petr , Kubelka Jan , Keiderling Timothy A.
Published: October 2003

A modification of Noda's algorithm that allows for calculation of two-dimensional (2D) correlation maps is presented as a method for analysis of a series of (static) spectra of proteins. In this approach, fractional secondary structure was used as the perturbation to generate the 2D correlation. The functional dependence of the spectral intensities on secondary structure is approximated by an even-order polynomial fit to the protein spectra at each spectral frequency. These functions are used to calculate the 2D correlation and disrelation maps, and their regression coefficients are used to weight the results to minimize artifacts. Electronic circular dichroism (ECD), Fourier transform infrared (FT-IR) (amide I and II regions), and Raman spectra of up to 22 proteins are used in the study. Spectral regions identified by the α-helix- and β-sheet-based 2D correlation maps are in agreement with established interpretation of ECD and FT-IR spectra in terms of secondary structure and provide insight into secondary structure assignment for a broad range of Raman bands. Comparison of our functional fit method, specifically designed to identify synchronous correlations, with Noda's Fourier transform-based method, which generates asynchronous maps as well, is discussed.
Novel Use of a Static Modification of Two-Dimensional Correlation Analysis. Part II: Hetero-Spectral Correlations of Protein Raman, FT-IR, and Circular Dichroism Spectra
Authors: Kubelka Jan , Pancoska Petr , Keiderling Timothy A.
Published: October 2003

The two-dimensional (2D) static correlation model developed in the previous paper is here extended to hetero-spectral applications for the correlation of spectral features arising from two separate techniques. The calculational method is detailed, and examples are given of Raman vs. circular dichroism (CD) (electronic) and Raman vs. Fourier transform infrared (FT-IR) 2D correlation and disrelation maps with fractional secondary structures used as the perturbation. This approach allows use of well-established secondary structure assignments of spectral features in one technique to interpret structurally less clearly assigned bands, particularly for β-turns, or possibly misassigned bands in other spectra via their calculated 2D correlations.
In situ Analysis of a High-Temperature Cure Reaction in Real Time Using Modulated Fiber-Optic FT-Raman Spectroscopy
Authors: Aust Jeffrey F. , Cooper John B. , Wise Kent L. , Jensen Brian J.
Published: October 2003

The vibrational spectrum of a high-temperature (330 °C) polymerization reaction was successfully monitored in real time with the use of a modulated fiber-optic Fourier transform (FT)-Raman spectrometer. A phenylethynyl-terminated monomer was cured, and spectral evidence for two different reaction products was acquired. The products are a conjugated polyene chain and a cyclized trimer. This is the first report describing the use of FT-Raman spectroscopy to monitor a high temperature (>250 °C) reaction in real time.
Application of Temperature-Programmed Diffuse Reflectance Infrared Fourier Transform Spectroscopy to the Study of the Thermal Evolution of the Species Present in a Reacted Selective Catalytic Reduction V2O5 /TiO2 Catalyst
Authors: Centeno Miguel Angel , Carrizosa Ignacio , Odriozola José Antonio
Published: October 2003

Temperature-programmed diffuse reflectance infrared Fourier transform spectroscopy (TPDRIFTS) has been used to characterize a reacted selective catalytic reduction (SCR) vanadia/titania catalyst. At room temperature the reacted catalyst presents ammonium ions adsorbed on the surface. On heating under N2 flow, a surface redox reaction takes place; ammonium ions are oxidized to bridged nitrosyls species, while V5+ = O groups are reduced to V3+. Reduction of V5+ species to V3+ ions occurs at lower temperatures than those observed in conventional TPR processes under H2 atmospheres. At higher temperatures, bridged nitrosyls species become monodentate, first in an angular configuration and then in a linear one. Previous data on the SCR reaction let us propose that they are desorbed from the surface as gaseous N2O.
Prediction of the pH in Wood by Diffuse Reflectance Infrared Fourier Transform Spectroscopy
Authors: Pappas C. , Rodis P. , Tarantilis P. A. , Polissiou M.
Published: October 2003

The diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) spectrum of the peeled wood of kenaf ( Hibiscus cannabinus L.), cotton ( Gossypium barbadense), and pine ( Pinus brutia) revealed three broad absorptions in the region of 1800–1540 cm−1. The deconvolution of spectra in this region revealed the existence of 10 major peaks contributing to that spectrum in the aforementioned region. The absorption peaks at 1710 and 1608 cm−1 have been assigned to carboxylic (–COOH) and carboxylate (–COO−) groups, respectively. Since their relative size is pH dependent, the ratio of their area was used as a pH indicator. A linear relationship was then established between that ratio and the amount of acid need to bring the pH of the wood to 3, as it is measured by the pH determination of a water extract of the wood. This is the pH at which the wood is processed during manufacturing of chipboards.
Photothermal FT-IR Spectroscopy: A Step towards FT-IR Microscopy at a Resolution Better Than the Diffraction Limit
Authors: Hammiche A. , Pollock H. M. , Reading M. , Claybourn M. , Turner P. H. , Jewkes K.
Published: October 2003

We have used a miniaturized Wollaston wire resistive thermometer as a probe to record infrared absorption spectra of polymeric samples by detecting photothermally induced temperature fluctuations at the sample surface. This method opens the way to absorption Fourier transform infrared spectroscopy/microscopy with a spatial resolution that is no longer diffraction limited, but is determined instead by the size of the contact between probe and sample. At present, this is on the order of a few hundred nanometers. The thermal probe, of a type used in scanning thermal microscopy and microthermal analysis, allows us to detect the photothermal response of a specimen exposed to the beam of a Fourier transform infrared spectrometer and heated thereby. The signal from this probe measures the resulting temperature fluctuations, and thus provides an interferogram which replaces the interferogram normally obtained by means of direct detection of the IR transmitted by a sample.
Snapshot Absorption Spectroscopy
Authors: Homan B. E. , Vanderhoff J. A.
Published: October 2003

Experimental improvements have been made in the UV-visible absorption spectroscopy technique applied to propellant flame diagnostics. The two-dimensional feature of an intensified charge-coupled device (CCD) detector was used to simultaneously record multiple, spatially distinct absorption spectra over a region of 0.35 cm. Temporal resolution has been increased to 1 ms by pulsing a simmering xenon arc lamp. The resulting increase in the light intensity by 30 to 70 times over the nonpulsed output provides the necessary light flux to achieve single-pulse, multiple absorption spectra. Species with low concentrations can be measured with the inclusion of multiple-pass optics to increase the effective pathlength through the combustion region. Due to broadband UV-visible absorption observed in propellant flame spectra, typically only 20% of the incident light is transmitted. However, inclusion of a neutral-density filter during the measurement of the incident intensity I0 allows the dynamic range of the detector to be effectively increased by a factor of 5. With these improvements, temperature and OH and NO concentration maps, with 1 ms temporal resolution, have been determined with two different propellant flames.
Dehydroxylation and the Vibrational Spectroscopy of Aluminum (Oxo)Hydroxides Using Infrared Emission Spectroscopy. Part III: Diaspore
Authors: Frost Ray L. , Kloprogge J. Theo , Russell Shane C. , Szetu Jennifer
Published: October 2003

Dehydroxylation of diaspore has been followed by a combination of differential thermal analysis (DTA) and infrared emission spectroscopy (IES). The DTA endotherm of diaspore is not simple, and two inflections are observed at 505 and 531 °C. Dehydroxylation shows that diaspore loses 15% of its weight upon dehydroxylation. The Mn-substituted diaspore shows major endotherms at 620 and 649 °C with a broad endotherm at 539 °C. Infrared absorption bands of diaspore were observed at 3365, 3284, and 3095 cm−1 in the hydroxyl stretching region and at 911, 755, 706, 668, 649, 570, and 544 cm−1 in the low-frequency region. Infrared emission bands were observed at 3239 and 2958 cm−1 in the hydroxyl stretching region. Low-frequency infrared emission bands in agreement with the absorption bands were observed at around 916, 752, 706, 668, 649, 570, and 544 cm−1. The variation of intensity of the hydroxyl stretching frequencies with temperature follows a pattern similar to that for the DTA curves.
Bent Silica Fiber Evanescent Absorption Sensors for Near-Infrared Spectroscopy
Authors: Littlejohn David , Lucas Donald , Han Ling
Published: October 2003

Silica optical fibers have been modified to improve their sensitivity as evanescent wave sensors for liquids. A section of fiber is stripped of its cladding and bent or coiled, which significantly increases the evanescent wave interaction with the surrounding environment. The effect of sensor shape, solute concentration, refractive index, and temperature on the sensor response is discussed.
Instrument-to-Instrument Transfer of Raman Spectra
Authors: Mann Charles K. , Vickers Thomas J.
Published: October 2003

A procedure has been developed to permit recalculation of a Raman spectrum that has been taken on a source spectrometer to allow its quantitative use with data taken from a target system. The procedure is based on accurate characterization of both the source and target spectral abscissas by means of a neon spectrum that is recorded at the time the Raman measurements are made. Corrections are made for wavelength-dependent behavior of both systems, for differences in dispersion for the two systems, and for variation in the number, spacing, and size of the detector elements. An example is presented in which the fingerprint and CH regions of the Raman spectrum of cyclohexane are transferred from higher to lower resolution context.
Single-Frame Chemical Imaging: Dimension Reduction Fiber-Optic Array Improvements and Application to Laser-Induced Breakdown Spectroscopy
Authors: Nelson Matthew P. , Myrick M. L.
Published: October 2003

A single-frame approach to chemical imaging with high spectroscopic resolution is described that makes use of a second-generation dimension-reduction fiber-optic array. Laser-induced plume images are focused onto a 17 × 32 rectangular array of square close-packed 25 μm cross-sectional f/2 optical fibers that are drawn into a 544 × 1 distal array with serpentine ordering. The 544 × 1 side of the array is imaged with an f/2 spectrograph equipped with a holographic grating and a gated intensified charge-coupled device (ICCD) camera for spectral analysis. Software is used to extract the spatial/spectral information contained in the ICCD images and de-convolute them into wavelength-specific univariate reconstructed images or position-specific spectra that span an 86 nm wavelength space. Temporal resolution is provided by imaging sequential laser plumes with varying time delays after each laser pulse on the gated intensifier.
Comparison of Three Methods to Improve Adherence of Thin Gold Films to Glass Substrates and Their Effect on the SERS Response
Authors: Mosier-Boss Pamela A. , Lieberman Steven H.
Published: October 2003

Vapor-deposited Ag and Au films exhibit high surface-enhanced Raman scattering (SERS) sensitivity. With thin metal films, SERS spectra can be obtained by using a “backside” configuration in which the laser light is focused through the substrate onto the metal film/liquid (or gas) interface. Use of the “backside” configuration is particularly advantageous for obtaining SERS spectra of aqueous samples. Because excitation occurs only at the metal/film/liquid interface, both attenuation of the signal by water and fluorescence interference are minimized. However, noble metals, such as Ag and Au, do not adhere well to glass substrates, and significant exposure to water damages the films. In this paper, three methods of adhering Au to glass and their effect on the SERS response are examined. The methods include the use of a buffer metal between the SERS-active metal film and the glass substrate; the use of (3-mercaptopropyl)trimethoxysilane (MCTMS); and the use of organometallic paints. Of the methods examined, the best film adherence and SERS response was obtained by using MCTMS to bind the metal film to a chemically etched glass slide.
Raman Microscopy Study of Cafarsite
Authors: Kloprogge J. Theo , Frost Ray L.
Published: October 2003

Normal, polarized, and cross-polarized Raman spectra of a single crystal of cafarsite, Ca8(Ti, Fe, Mn)6–7(AsO3)12·4H2O, from Binntal (Switzerland) are reported. Comparison with known metal oxides was used to achieve assignments of the observed bands. Differences between the polarized and cross-polarized spectra helped to identify the symmetric and asymmetric modes. The bands at 258, 319, 721, and 763 cm−1 are assigned to the ν4(E), ν2(A1), ν3(E), and ν1 arsenite modes after comparison to AsF3. The bands at 204, 437, and 620 cm−1 are assigned to the asymmetric Fe(2)–O modes, while the bands at 232, 288, 464, and 506 cm−1 are the symmetric ones. The two bands at 837 and 880 cm−1 are ascribed to the symmetric and asymmetric Fe(1)–O modes, respectively. The Ti–O modes are assigned to the bands at 204 and 648 cm−1 (asymmetric) and to 319, 390, and 802 cm−1 (symmetric). Bands at 288 and 587 cm−1 represent the symmetric and asymmetric modes, respectively, of the Ca–O bonds. On the basis of the Raman spectra, no distinction can be made between the two crystallographic Ca sites. Also no difference can be made between the two crystallographic Mn sites in cafarsite. Mn–O bands are observed at 335, 437 (asymmetric), 464, 506, and 601 cm−1 (symmetric).
Reduction of Indicator Leaching from Doped Sol-Gels by Attachment of Macromolecular Carriers
Authors: Skrdla Peter J. , Saavedra S. Scott , Armstrong Neal R.
Published: October 2003

The extent of leaching of indicator dyes of varying molecular mass, following encapsulation into hydrated sol-gel monoliths prepared from tetramethylorthosilicate (TMOS), was investigated. Dye modification of a water-soluble phthalocyanine with poly(ethylene glycol) side chains (2000 MW) reduced leaching relative to the unmodified dye, but significant losses were still observed. Monoliths doped with fluorescein modified with dextrans of higher molecular weight were investigated in an attempt to determine the minimum size necessary for dye retention. In comparison to monoliths doped with unmodified fluorescein, attachment to a dextran carrier significantly decreased the extent of dye leaching. However, even a 70 000 MW carrier was not sufficient to prevent some loss of dye. In contrast, no leaching of myoglobin (18 000 MW) occurred, which shows that when the entrapped molecule has a organized tertiary structure, diffusion within the pores is eliminated. Malachite green and its dextran conjugate were used to examine the effect of electrostatic interactions on leaching. Minimal loss of both the dye and the conjugate was observed, which indicates that when a favorable interaction between the dye and sol-gel matrix exists, attachment to a macromolecular carrier may not be necessary to prevent leaching.
Comparison of Solvent Elimination Systems for the Analysis of Dyes and Pesticides by High-Performance Liquid Chromatography Fourier Transform Infrared Spectrometry
Authors: Jones Joanna C. , Littlejohn David , Griffiths Peter R.
Published: October 2003

Two systems have been compared for the on-line production of infrared spectra of compounds separated by high-performance liquid chromatography (HPLC). System 1 had a thermospray interface to evaporate the mobile-phase solvents and deposit the solutes onto a moving stainless steel belt, for direct analysis by reflection–absorption IR spectrometry. In system 2, the column effluent was split 1:6 and pumped through an ultrasonic nebulizer. The spray was desolvated at reduced pressure in a heated transfer tube and the solutes deposited onto a ZnSe window for direct analysis by transmission IR spectrometry. When system 1 was used for the analysis of reactive dyes, eluent containing ammonium acetate caused a large background spectrum, as a film of unknown composition was formed on the surface of the stainless steel belt. An alternative procedure, without ammonium acetate, was developed with a mixed-mode column containing C18 and cation exchange particles, but variable retention times were obtained. System 2 could be used satisfactorily with eluents containing ammonium acetate, and it produced dye spectra of better resolution than those obtained with system 1. When the dyes were examined under a microscope, the material on the ZnSe window was more uniform and more evenly distributed on a narrower track than were the deposits on the stainless steel belt. Consequently, the peak shape of the IR chromatograms was better with system 2, and a lower detection limit was achieved for reactive blue 74 (9 ng). When mixtures of the pesticides metolcarb and carbofuran were analyzed, a thermospray temperature of 196 °C was required to desolvate the effluent from the HPLC column in system 1. At this temperature, thermal degradation of the pesticides occurred, and no spectrum was recorded from the belt surface. However, with system 2, deposition of the pesticides was achieved at 90 °C, without degradation, and IR spectra/chromatograms were obtained. Overall, the study showed that the infrared chromatograph (IRC) was the more efficient and flexible interface for HPLC Fourier transform infrared (FT-IR) spectrometry.
Errors and Artifacts in Time-Resolved Step-Scan FT-IR Spectroscopy
Authors: Rödig C. , Siebert F.
Published: October 2003

Several sources of errors leading to distortions in time-resolved step-scan Fourier transform infrared (FT-IR) measurements are described, and their effect on difference spectra and time traces is discussed. Fluctuations of the movable interferometer mirror as well as interference of the power line frequency are shown to be able to cause oscillations in the time traces of absorbance changes obtained by step-scan measurements. It is demonstrated that absorbance changes of the sample and thermal IR signals due to heating of the sample by laser excitation both contribute to the IR intensity changes at a fixed sampling position. Therefore, intensity variations of the laser pulses used to drive the sample reaction can cause considerable fluctuations of the time-dependent IR signals and, thereby, introduce multiplicative noise into the difference spectra. Means to correct these errors are proposed for some cases.
Surface-Enhanced Raman Scattering Detection of Amphetamine and Methamphetamine by Modification with 2-Mercaptonicotinic Acid
Authors: Sulk Roberta A. , Corcoran Robert C. , Carron Keith T.
Published: October 2003

We have demonstrated the use of surface-enhanced Raman scattering (SERS) spectroscopy for the detection of the phenylalkylamines amphetamine and methamphetamine. This work can be viewed as the first phase of development toward a one-step drug detection method with a selective reactive coating on a SERS substrate. This work involves a fairly complicated coupling reaction prior to surface derivatization. Future efforts will be directed at creating a reactive coating directly on the surface. The amines were derivatized by a coupling reaction with 2-mercaptonicotinic acid (2-MNA) with the use of dicyclohexylcarbodiimide (DCC) as the coupling reagent to form the amide compounds AMNA [ N-(1-methyl-2-phenylethyl)-2-mercaptopyridine-3-carboxamide] and MMNA [ N-methyl- N-(1-methyl-2-phenylethyl)-2-mercaptopyridine-3-carboxamide]. The amides were qualitatively identified from SERS spectra. Quantification of the amides was accomplished by adding the internal standard pentachlorothiophenol (PCTP) and measuring the intensity of Raman bands of the analyte relative to a Raman band of the internal standard. Calibration curves were plotted of the relative peak intensity ratios as a function of analyte concentration. Detection limits of 19 ppm and 17 ppm were found for amphetamine/2-MNA (AMNA) amide and methamphetamine/2-MNA (MMNA) amide, respectively.