bluuebunny/crossref_metadata_2025 huggingface dataset:
Baseline and in vivo Total Photoluminescence of Endospore Material Using the Parasitoid Wasp C. Congregata
Authors: Anderson J. E. , Webb S. R. , Fischer R. L. , Kester K. M. , Brown B. L.
Published: October 2003

In a laboratory test, total luminescence spectroscopy was used to detect and measure the in vivo presence of a biohazard surrogate, endospores of Bacillus megaterium, within the parasitoid wasp C. congregata (Say) (Hymenoptera:Braconidae). Upon emergence, exposed wasps were allowed to feed on five different concentrations of endospores suspended in 5 mL of honey solution. After 12 h insects were chilled at −80 °C for 5 min to permit capture. Aqueous suspensions were prepared by homogenizing the wasps in 3 mL of deionized water. The total excitation-emission matrix (EEM) was measured for each suspension by using an SLM Series 2 luminescence spectrometer. For wasps exposed to spore concentrations of 3.0 × 102 to 3.0 × 106 colony forming units (CFU)/mL, two intensity maxima were observed. The emission for tryptophan was identified at excitation (Ex) 300 nm and emission (Em) 350 nm. A second emission that resulted from other biological materials including nitroheterocyclic compounds and endospores occurred at Ex 350 nm and Em 420 nm. Changes in the ratio of intensity between the tryptophan and second emission were found to be related to endospore material present in the suspensions at original feeding concentrations of 15 000 to 15 million spores. Intensity ratios for the positive samples equaled 0.9, while the intensity ratios for the control equaled 1.9. One notable difference recorded for the emission spectra was an apparent, but minor, red shift of approximately 5 nm of the second emission when compared against a signature library of pure cultures. Diagnostic information such as this should contribute to methods for the detection and potential identification of biohazard materials with the use of photoluminescence.
Determination of Ultratrace-Level Fluorescent Tracer Concentrations in Environmental Samples Using a Combination of HPLC Separation and Laser-Excited Fluorescence Multiwavelength Emission Detection: Application to Testing of Geothermal Well Brines
Authors: Kleimeyer James A. , Rose Peter E. , Harris Joel M.
Published: October 2003

Lowering the limits of detection for fluorescent tracers in environmental samples can reduce the cost and environmental impact of tracer testing and allow a wider variety of tracer dyes to be used. Detecting dyes in environmental water samples at the sub-part-pertrillion level raises significant challenges in the sensitivity and selectivity of measurement. In the present work, we address this issue by developing a high-sensitivity multiwavelength fluorescence detector for high-performance liquid chromatography (HPLC)-separated samples. The fluorescence flow-cell utilizes fiber-optic coupling of laser excitation and the collected emission, which is dispersed in a short spectrograph and detected with a cooled charge-coupled device (CCD). The HPLC separation step not only resolves the target tracer from fluorescent impurities in the sample but also transfers the dye molecules into a solution of reproducible composition which provides a constant Raman scattering background against which the tracer fluorescence spectrum may be detected. The combination of emission-wavelength and elution-time measurement provides a multidimensional data set that improves selectivity for detecting a tracer. For analysis of the data, partial least-squares modeling is tested, along with two methods that do not require prior knowledge of interfering species: rank annihilation and self-modeling curve resolution. The method is developed and tested on fluorescein standards, and a detection limit for fluorescein of 40 ppq (4.0 × 10−14 g/mL) is predicted. This capability was tested on geothermal well samples, in which ∼40 ppq fluorescein could be detected in the presence of 15-fold greater fluorescence from an unknown interferent.
Simultaneous Fluorimetric Determination of Pteridin Derivatives: Comparison between Synchronous, Partial Least-Squares, and Hybrid Linear Analysis Methods
Authors: Espinosa-Mansilla A. , Durán-Merás I. , Galian R.
Published: October 2003

Several methods are described for the simultaneous determination of binary mixtures of xanthopterin (XAN) and isoxanthopterin (ISO) and of binary mixtures of xanthopterin and biopterin (BIO). The total luminiscence information from each compound has been used to optimize the most adequate analytical signal. A synchronous spectrofluorometric univariate procedure to analyze XAN and ISO is proposed. The procedure is compared with two multivariate procedures based on partial least-squares (PLS-1) and hybrid linear analysis (HLA/XS), by using synchronous spectral data as analytical signals. For the resolution of binary mixtures of XAN and BIO, a comparison between the predictive ability of the multivariate calibration methods, PLS-1 and HLA/XS, on two spectral data sets, excitation and emission spectra, has been performed. The calculation of the net analyte signal (NAS) by the HLA/XS method allows the determination of selectivity and sensitivity in each case. The proposed procedures are validated in the determination of several mixtures of these compounds, and the error values in a test set are reported.
Experimental Investigation of Sodium Emission following Laser Photofragmentation of Different Sodium-Containing Aerosols
Authors: Núñez M. Hidalgo , Omenetto Nicoló
Published: October 2003

Several time-integrated and time-resolved experiments have been performed on different sodium-containing dry aerosols in air to investigate the behavior of atomic sodium emission at the yellow doublet after photofragmentation with 193 nm photons provided by an ArF excimer laser. It is shown that sodium chloride, sodium hydroxide, and especially sodium sulfate require different thresholds for the overall process of vaporization, dissociation, and excitation of atomic emission. This can be clearly seen by the experimental fact that (1) the onset of the time-integrated emission signal starts at different laser energies, and (2) the time-resolved shapes of the emission signal during the laser pulse (13 ns) are markedly different in the case of chloride and sulfate aerosols, the former rising faster than the latter. From an analytical point of view, the detection limit for sodium in airborne particles is 0.3 ng of sodium per gram of air (∼ 0.017 ppbv), which is about one order of magnitude better than the detection limit reported by early laser-induced plasma experiments.
FT-NIR Spectroscopic Study of OH Groups in Ethylene-Vinyl Alcohol Copolymer
Authors: Iwamoto Reikichi , Amiya Shigetoshi , Saito Yoichiro , Samura Hideo
Published: October 2003

In the present study we have demonstrated the unique capability of near-infrared/infrared (NIR/IR) spectroscopy to characterize the hydrogen bonding of the OH groups in ethylene-vinyl alcohol copolymer (EVOH). Fourier transform (FT)-NIR/IR spectroscopic measurements were made of EVOHs with ethylene contents of 33, 49, 75, and 89 mole %. A strong and broad absorption at ∼ 4780 cm−1, which is the first combination of the OH stretching and deformation vibrations, is assigned to the aggregated OH groups. The band shows a shoulder at 4970 cm−1 at an ethylene content of 49 mole %, which becomes a distinct peak at a content of 89%. This feature is assigned to the free OH group isolated in the surroundings of the ethylene component. Existence of the free OH group is additionally evidenced by the appearance of sharp absorptions of the OH stretching fundamental at 3027 cm−1 and its first overtone at 7094 cm−1. The relative population of the free OH has been estimated as 0, 0.3, 1.5, and 3.9 mole % for ethylene content of 33, 49, 75, and 89, mole %, respectively.
Application of Fourier Transform Infrared Spectrometry and Chemometrics to Analysis of Polystyrene and Copolymerized Styrene in Ethylene-Styrene Copolymers
Authors: Qin Deru
Published: October 2003

The physical properties of ethylene-styrene (ES) copolymers, like many other copolymers, are determined primarily by copolymer composition. ES copolymers may also contain a small amount of polystyrene. It is important to quantify the copolymerized styrene and polystyrene in ES copolymers. The difficulty associated with this analysis, however, arises from the fact that copolymerized styrene and polystyrene have a similar infrared spectrum. The quantitative analysis of ethylene-styrene copolymers by the Fourier transform infrared (FT-IR) technique, combined with the partial least squares (PLS) method, is described. The use of the PLS method facilitates the analysis. The PLS factors, which are calculated iteratively to maximize the covariance between the independent variable and the dependent variable in PLS, remove the collinearity problem present in the original spectral data, and make this analysis possible. The standard error of calibration (SEC) for 60 samples included in the calibration is 0.19% for polystyrene and 0.48% for copolymerized styrene. The standard error of prediction (SEP) for polystyrene and copolymerized styrene, calculated from 120 samples that were excluded from the calibration, is 0.25 and 0.51%, respectively.
Study of Thermal Melting Behavior of Microbial Polyhydroxyalkanoate Using Two-Dimensional Fourier Transform Infrared Correlation Spectroscopy
Authors: Tian Ge , Wu Qiong , Sun Suqin , Noda Isao , Chen Guo-Qiang
Published: October 2003

The molecular level premelting process of purified biosynthesized polyester poly(hydroxybutyrate-co-hydroxyvalerate) or P(HB-co-HV) (20.4% HV) was investigated by two-dimensional Fourier transform infrared (2D FT-IR) correlation spectroscopy. Intensity variations and band shifts in the characteristic spectral regions for C=O groups (1710–1770 cm−1), C-H groups (2910–3010 cm−1), and C-O-C groups (1220–1310 cm−1) were selected for a detailed study of the thermally induced phase transition of the copolymer. The 2D correlation approach successfully demonstrated that a fully amorphous liquid-like structure was formed following the disappearance of the crystals in the sample, by going through an intermediate state related to the lost conformation of the highly ordered and helical polyester main chain.
Vibrational Spectroscopic Study of l-Phenylalanine: Effect of pH
Authors: Olsztynska S. , Komorowska M. , Vrielynck L. , Dupuy N.
Published: October 2003

Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectra of l-phenylalanine in aqueous solution were recorded in the pH range 0–13. The vibrational molecular spectroscopic study of this amino-acid, a well-known component of human tissue, showed that l-phenylalanine undergoes structural changes under the influence of pH. Characteristic bands of each ionic species were highlighted and the p Ka values were determined from IR measurements by using an intensity ratio method. ATR-FTIR spectroscopy appears to be a powerful tool for obtaining valuable information on the building blocks of proteins and for measuring tissue damage in aqueous environments.
Multinuclear Magnetic Resonance Spectroscopy of Human Healthy and Neoplastic Renal Tissues
Authors: Tosi M. R. , Tugnoli V. , Bottura G. , Lucchi P.
Published: October 2003

High-resolution multinuclear magnetic resonance spectroscopy (MRS) (1H, 13C, and 31P) has been applied for the first time to the study of the biochemical composition of human healthy and neoplastic renal tissues. Thirteen healthy renal tissues, thirteen renal cell carcinomas, and five oncocytomas were examined. From each sample two types of extract were obtained: the water-soluble fraction and the lipid fraction. 1H MRS of aqueous extracts yielded information on renal osmolytes which can be considered markers of physiological renal function. The decrease or the disappearance of these osmolytes and the appearance of glycine in renal cell carcinomas is a hallmark of cancer. The oncocytomas, benign tumors, appear to have a biochemical composition in between healthy and malignant tissue. Further information can be derived from the 13C MR analysis of the lipid fraction: cholesteryl esters, present in high amounts in renal cell carcinomas, are related to the vascularization degree of the tumor. Other correlations between the spectroscopic results and the histopathological data are reported.
Polymer Degradation Study by Factor Analysis of GPC-FT-IR Data
Authors: Schoonover Jon R. , Zhang Shuliang L. , Bridgewater Jon S. , Havrilla George J. , Fletcher Michael A. , Lightfoot J. M.
Published: October 2003

Factor analysis has been performed on gel permeation chromatography (GPC)-Fourier transform infrared (FT-IR) spectroscopic data sets for one control and two artificially aged, multicomponent polymer systems. This approach was utilized to provide insight into degradation chemistry and to obtain component spectra (factors) and their concentration profiles (scores). The results are evaluated in terms of the infrared spectra of the chemical species present, their concentration profiles, and the different aging environments. For the formulation of a poly(ester urethane) with added plasticizer, and stabilizer, the results demonstrate that chain scission and nitration of the poly(ester urethane) are dominant degradation pathways under radiolytic aging conditions. Thermal aging conditions induce some chain scission. In both aging studies, branching is shown not to be a dominant degradation pathway. However, because branching processes produce insoluble cross-linked material, this possibility was not further investigated in this study.
Direct Determination of Metals in Soils and Sediments by Induction Heating-Electrothermal Vaporization (IH-ETV) Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES)
Authors: Rybak Michael E. , Salin Eric D.
Published: October 2003

The application of an induction heating (IH) electrothermal vaporization (ETV) sample introduction arrangement for the determination of As, Cd, Cu, Mn, Pb, and Zn in soils and sediments by inductively coupled plasma-optical emission spectrometry (ICP-OES) is presented. Samples were deposited either directly as a solid or by means of slurry sampling into graphite cups that were then positioned in a radio-frequency (RF)-field and vaporized in a carrier flow of 15% (v/v) SF6-Ar. Four certified reference materials (CRMs) were examined: two soil samples—SRM 2710 and SRM 2711 (NIST); and two marine sediments—MESS-2 and PACS-2 (NRC Canada). In general, sample delivery was simpler and observed signal precision was better with slurry sampling when compared to the analysis of the solid directly, with peak area RSDs ranging from 4–16% ( n = 6). Plots of intensity vs. certified concentration for the four CRMs were linear with log-log slopes of 0.98–1.02 and r2 values ≥ 0.995 for As, Cu, Pb, and Zn. Recoveries of 80–105% were achieved for the above elements in SRM 2711 by using an external standards curve constructed from the 3 remaining CRMs. Aqueous standard solutions were used for the analysis of all 4 CRMs by standard additions, resulting in recoveries ranging from 54–139% (average recovery of (101 ± 15)%) across all six determined elements in all four samples.
Near-Infrared Multispectral Imaging Technique for Visualizing Sequences of Di- and Tripeptides Synthesized by Solid Phase Combinatorial Method
Authors: Alexander Troy , Tran Chieu D.
Published: October 2003

A new method based on the near-infrared (NIR) multispectral imaging technique has been developed for the noninvasive and nondestructive determination of the identity and sequences of amino acid residues in di- and tripeptides. The di- and tripeptides were synthesized on polymer beads (i.e., Rink) using the solid phase peptide synthetic method. The developed method is capable of determining the identity of sequences of the peptides (with and without the Fmoc protecting group) directly on the polymer beads. It can distinguish not only dipeptides from tri-peptides but also peptides with very similar structures (e.g., Rink-Gly-Ala-Ala, Rink-Gly-Ala-Phe, Rink-Gly-Ala-Leu, Rink-Gly-Ala-Val, and Rink-Gly-Ala-Met). More importantly, it is capable of distinguishing peptides with the same amino acid residues but different sequences (e.g., Rink-Gly-Leu-Val from Rink-Gly-Val-Leu).
Coherent Raman Spectroscopic Monitoring of Pulsed Radio Frequency PECVD of Silicon Nitride Thin Films
Authors: Phillips B. J. , Steidley S. D. , Lau L. D. , Rodriguez R. G.
Published: October 2003

During pulsed plasma enhanced chemical vapor deposition, (PECVD), of silicon nitride thin films, depletion of silane reactant was measured by coherent anti-Stokes Raman scattering, (CARS), spectroscopy as a function of radio frequency pulse width, peak power, and delay time after the rf pulse. The results were correlated with “goodness of deposition parameters” including film thickness, deposition rate, and N-H and Si-H film content. The pulse width and peak power affected the plasma similarly, as silane depletion, film thickness, and rate of film growth all increased with both pulse width and peak power for a 10 Hz repetition rate. The CARS measured silane depletion also increased proportionally with pulse width for short rf pulses but not for long ones. Although the film properties changed with both power and pulse width, there were differences in the effects. A decreasing SiH/NH ratio resulted from increasing peak power, but increases in pulse width lead to an increasing ratio in some cases. The delay studies showed the CARS-measured silane depletion was higher 2 ms after the rf pulse had ended than 0.5 ms within the pulse. This result was accounted for by the flow rate, shower head design, and placement of the focus of the laser beams. Based on the results of the CARS-measured silane depletion as a function of pulse width and delay time, it is evident that the reactants move in a segregated-flow with a significant proportion of the velocity component directed toward the lower electrode, at least for the conditions of this experiment. Thus differences noted between pulsed and continuous PECVD processing likely depend largely on the transit time of the molecules in the plasma region.
General Expression for the Voigt Function That is of Special Interest for Applied Spectroscopy
Authors: Di Rocco H. O. , Iriarte D. I. , Pomarico J.
Published: October 2003

The purpose of this work is twofold. First we obtain a series expansion for the Voigt function that is valid for all values of the dimensionless parameter a (a measure of the ratio between the Lorentzian and Gaussian widths). Furthermore, the resulting coefficients are independent of the generalized coordinate b (the wavelength measured in units of the Gaussian width). In the second place, we fit an experimental “shaped bell” curve to a Voigt profile using certain theoretical restrictions that relate the maximum height and the full width at half-maximum.
Robust Calibration with Respect to Background Variation
Authors: Mittermayr C. R. , Tan H. W. , Brown S. D.
Published: October 2003

The application of linear regression on wavelet coefficients for robust calibration of spectral data with highly variable background was successfully demonstrated with synthetic and real data. A Monte Carlo study was made to investigate the performance of the methods in both the cases where the background variation in the prediction set was the same as in the calibration set and where the variation was different. Multivariate linear regression on wavelet coefficients proved to be competitive in the first case and superior in the second case with respect to partial least squares (PLS) calibration. Results on real near-infrared (NIR) data confirmed the simulation study. As a study of regression on wavelet coefficients, this is the first application study of regression on wavelet coefficients that shows how the wavelet's property of vanishing moments can be used for reducing the effects of varying background. As a background correction method, the proposed approach avoided errors introduced in the estimation process. In addition, the strategy proposed here can be applied to data collected by various other analytical techniques as well.
Chemometric Evaluation of Synchronous Scan Fluorescence Spectroscopy for the Determination of Regulatory Conformance and Usage History of Insulation Oils
Authors: Bessant Conrad , Ritchie Laurie , Saini Selwayan , Pahlavanpour Bruce , Wilson Gordon
Published: October 2003

This paper describes the evaluation of synchronous scan fluorescence spectroscopy as a means of determining key characteristics of mineral insulating oils that are used in electrical apparatus around the world. Characteristics of interest to commercial operators include regulatory conformance, the history of the oil (whether it has been used or not), and, ideally, the identity and manufacturer of the oil. The oils analyzed in this study are highly relevant to real applications as they were acquired from actual high voltage power transformers operated in the United Kingdom (UK) or from stocks intended for future use in transformers. A small number of foreign oils that do not conform to UK regulations were also analysed. Principal components analysis (PCA) is used to evaluate the usefulness of the information contained in the acquired fluorescence spectra. This reveals that oils from different manufacturers can exhibit different types of spectra and that it may be possible to determine the identity of an oil from its spectral characteristics. It is also found that the spectra can be used to determine whether or not an oil has been used and whether it meets British regulatory standards. It is concluded that synchronous scanning fluorescence spectroscopy, combined with appropriate chemometrics, could provide the basis for a rapid screening test, capable of indicating whether or not a particular new or used transformer oil is suitable for initial use or continued use in high voltage equipment.
Optical Characterization of Polymeric Films by a New Methodological Approach
Authors: Mormile P. , Petti L. , Immirzi B. , Malinconico M. , De Luca V. , Manera C.
Published: October 2003

A simple method for evaluating polymeric films to be employed in the agricultural field is proposed. The method consists of optical characterization (spectral analysis) and numerical elaboration of the experimental data on the basis of a theoretical model, in order to predict the optical behavior of organic materials, which determines the temperature variations inside a physical system. Results for new biodegradable materials for mulching and soil solarization are presented and compared with the traditional materials. Our work demonstrates the validity of the proposed methodological approach and confirms the potential of the considered materials for use in agriculture.
Fluorescent Fiber-Optic Sensor Arrays Probed Utilizing Evanescent Fiber-Fiber Coupling
Authors: Prince Barry J. , Kaltcheva Nadejda T. , Schwabacher Alan W. , Geissinger Peter
Published: October 2003

Optical-fiber sensors that use fluorescent probes located in the fiber cladding are of great interest for monitoring physical and chemical properties in their environment. The interrogation of a fluorophore with a short laser pulse propagating through the fiber core allows for the measurement of the location of the fluorophore by measuring the time delay between the exciting pulse and the returning fluorescence pulse. The spatial resolution of such an array of fluorescent sensors is limited since a minimum separation of the fluorophores is required to resolve returning light pulses. For many applications a closer spacing of sensor regions is desirable, particularly for fibers prepared by using our recently introduced one-dimensional combinatorial chemistry method [A. W. Schwabacher et al., J. Am. Chem. Soc. 121, 8669 (1999)]. This method allows for efficient preparation of large, diverse, and densely packed linear arrays of sensors. We demonstrate that by using a second fiber as an optical delay line, the minimum spacing between adjacent sensor regions can be well below the fluorescence lifetime limit. Since the coupling between the two fibers is evanescent, the attenuation of the excitation pulse is low, making long arrays of sensor regions feasible. Moreover, we identify the conditions that allow for the optical readout of long arrays of sensors.
Quantifying the Optical Properties and Chromophore Concentrations of Turbid Media by Chemometric Analysis of Hyperspectral Diffuse Reflectance Data Collected Using a Fourier Interferometric Imaging System
Authors: Pham Tuan H. , Eker Charlotta , Durkin Anthony , Tromberg Bruce J. , Andersson-Engels Stefan
Published: October 2003

A non-contact Fourier transform interferometric imaging system was used to collect hyperspectral images of the steady-state diffuse reflectance from a point source in turbid media for the spectral range of 550–850 nm. Steady-state diffuse reflectance profiles were generated from the hyperspectral images, and partial least-squares (PLS) regression was performed on the diffuse reflectance profiles to quantify absorption (μ a) and reduced scattering (μ' s) properties of turbid media. The feasibility of using PLS regression to predict optical properties was examined for two different sets of spatially-resolved diffuse reflectance data. One set of data was collected from 40 turbid phantoms, while the second set was generated by convolving Monte Carlo simulations with the instrument response of the imaging system. Study results show that PLS prediction of μ a and μ' s was accurate to within ±8% and ±5%, respectively, when the model was trained on turbid phantom data. Moreover, PLS prediction of optical properties was considerably faster and more efficient than direct least-squares fitting of spatially-resolved profiles. When the PLS model was trained on Monte Carlo simulated data and subsequently used to predict μ a and μ' s from the diffuse reflectance of turbid phantom, the percent accuracies degraded to ± 12% and ± 5%, respectively. These accuracy values are applicable to homogenous, semi-infinite turbid phantoms with optical property ranges comparable to tissues.
Surface Plasmon Resonance Spectroscopy of Dielectric Coated Gold and Silver Films on Supporting Metal Layers: Reflectivity Formulas in the Kretschmann Formalism
Authors: Roy D.
Published: October 2003

In surface plasmon resonance (SPR) studies of thin films, a binder metal (Cr, W, or Ti) is often used to support the SPR-active gold or silver substrate on a glass prism. The optical response of the SPR device is affected by such binder layers, and in the analysis of experimental data, it is necessary to account for these effects. The present report examines the theoretical considerations for SPR spectroscopy involving these types of supported substrates. It is shown that usually, the binder effects are weak in the neighborhood of the resonance angle. In the same region, the SPR plot exhibits an approximately Lorentzian behavior and is characterized here by extending the previously known Kretschmann formalism to a five-phase system. The calculations lead to a set of analytical formulas, indicating the limiting factors of the binder metal and expressing the reflectivity of the multilayer structure in terms of the thickness and dielectric function of the sample layer. In addition, these formulas explicitly show how the characteristic features of SPR plots are governed by certain experimental variables. The calculations provide a relatively simple framework for analyzing the results of SPR studies that focus primarily on resonance angle measurements.
Improved IRRAS Apparatus for Studies of Aqueous Monolayer Films: Determination of the Orientation of Each Chain in a Fatty-Acid Homogeneous Ceramide 2
Authors: Flach Carol R. , Xu Zhi , Bi Xiaohong , Brauner Joseph W. , Mendelsohn Richard
Published: October 2003

The performance of a new accessory for measuring IR reflection-absorption (IRRAS) spectra at various angles of incidence from monolayer films of lipids is demonstrated. The device is comprised of an external variable angle reflectance accessory and a self-contained computer-controlled unit for varying the angle of incidence, both units being coupled to a custom-designed Langmuir trough. This combination provides for excellent experimental precision and reduction of interference from H2O vapor in the 1500–1800 cm−1 spectral region. A set of ∼20 s- and p-polarized IRRAS spectra over a range of angles of incidence from 25° to 70° may be acquired from a single monolayer film in ∼3 h. The performance of the device is demonstrated for two lipids as follows. First, the instrument precision is demonstrated through determination of the orientation of each of the chains in a fatty acid homogeneous ceramide 2 derivative. Interestingly, the orientation (tilt angles from the bilayer normal) of the individual chains differ, as determined from an isotopically-labeled derivative where the fatty acid chain is perdeuterated. The fatty acid chain is tilted at 24° from the normal to the bilayer, while the base chain is tilted at 18°. As a control, the average tilt angle for both ceramide 2 acyl chains has been determined from a fully proteated derivative to be 20°. The precision of the derived tilt angle varies from ∼1–3°. Second, the reduction of interference from water vapor in the 1500–1800 cm−1 is demonstrated for sn-2–13C=O-1,2 distearoylphosphatidylcholine, where spectra from the individual C=O bonds in the molecule are readily detected with good signal/noise and signal/water vapor ratios. The device provides a major advance in the determination of chain orientation by IRRAS and will facilitate the determination of functional group orientation.
Prediction of Molecular Properties with Mid-Infrared Spectra and Interferograms
Authors: Collette Timothy W.
Published: October 2003

We have built infrared spectroscopy-based partial least-squares (PLS) models for molecular polarizabilities with the use of a 97-member training set and a 59-member independent prediction set. These 156 compounds span a very wide range of chemical structures. Our goal was to use this well-defined chemical property to test the breadth of application of a method whose end use is aimed at predicting poorly defined, environmentally important properties and activity parameters (e.g., microbial transformation rate constants). Separate models were built by using gas-phase mid-infrared spectra and, alternatively, their Fourier transformations (i.e., interferograms). The optimum spectrum- and interferogram-based models produced approximately the same error (root mean square deviation divided by the parameter value range) for the independent prediction set, 9.53 and 9.92%, respectively. With spectrum-based models, we found that deresolving the spectra from a point spacing of 6 cm−1 to about 40 cm−1 produced much lower error (under leave-one-out cross-validation) when all 156 compounds were included, but much higher error when a model was built by using a structurally narrow subset of the compounds (namely, 38 alkanes). Qualitative interpretation of the first PLS weight-loading vector from the spectrum-based model provided important information on the relationship between chemical structure and molecular polarizability.
Temperature-Dependent FT-IR Spectroscopy Study of Silver 1,9-Nonanedithiolate
Authors: Choi Hyouk Jin , Han Sang Woo , Lee Seung Joon , Kim Kwan
Published: October 2003

The structure and thermal behavior of silver 1,9-nonanedithiolate (AgNDT) is investigated by means of diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and elemental analysis. The XRD data suggests that AgNDT has a layered structure but with poor registry between layers. The poor registry seems to be associated with the deficiency of Ag by 20% in binding to the available sulfur atoms. DRIFT spectral data nonetheless indicates that the carbon chains take nearly all-trans conformation. The temperature-dependent DRIFT spectral data suggests that AgNDT should degrade at >530 K without any thermodynamic phase transition, in agreement with the TGA and DSC analysis. The finding that AgNDT does not exhibit liquid-crystalline behavior upon melting is attributed to the formation of two Ag-S bonds (as α,ω-dithiolate) in AgNDT, even though each Ag atom is trigonally bonded to sulfur, as in silver monothiolate (AgSR).
Investigation into the Effect of Instrumental Parameters in Two-Dimensional Correlation Spectrometry
Authors: Berry R. James , Ozaki Yukihiro
Published: October 2003

Two-dimensional correlation spectroscopy (2D-COS) has been of increasing interest in recent years. It is known that baseline variations, spectral shifts, and other phenomena can change the 2D-COS spectra. However, little attention has been placed upon what, if any, effects changing the instrumental parameters may have. We will show that some instrumental parameters such as resolution and acquisition time make significant contributions to the 2D-COS spectrum, and parameters such as apodization function and zero-filling make minor contributions. Gain makes no significant contribution to conventional 2D-COS. Type of phase correction and gain makes no significant contribution to conventional 2D-COS but can change the phase angle 2D-COS spectra.
Near-Infrared Raman Spectroscopy for in vivo Detection of Cervical Precancers
Authors: Utzinger Urs , Heintzelman Douglas L. , Mahadevan-Jansen Anita , Malpica Anais , Follen Michele , Richards-Kortum Rebecca
Published: October 2003

This study evaluates the potential of near-infrared Raman spectroscopy for in vivo detection of squamous dysplasia, a precursor to cervical cancer. A pilot clinical trial was carried out at three clinical sites. Raman spectra were measured from one colposcopically normal and one abnormal area of the cervix. These sites were then biopsied and submitted for routine histologic analysis. Twentyfour evaluable measurements were made in vivo in 13 patients. Cervical tissue Raman spectra contain peaks in the vicinity of 1070, 1180, 1195, 1210, 1245, 1330, 1400, 1454, 1505, 1555, 1656, and 1760 cm−1. The ratio of intensities at 1454 to 1656 cm−1 is greater for squamous dysplasia than all other tissue types, while the ratio of intensities at 1330 to 1454 cm−1 is lower for samples with squamous dysplasia than all other tissue types. A simple algorithm based on these two intensity ratios separates high-grade squamous dysplasia from all others, misclassifying only one sample. Spectra measured in vivo resemble those measured in vitro. Cervical epithelial cells may contribute to tissue spectra at 1330 cm−1, a region associated with DNA. In contrast, epithelial cells probably do not contribute to tissue spectra at 1454 cm−1, a region associated with collagen and phospholipids.
Elemental Analysis Using NMR: Simultaneous Determination of Aluminum and Sodium in Zeolite a Using Low-Field NMR
Authors: Guihéneuf Thierry M. , Simeral Larry S.
Published: October 2003

The standard methods for elemental analysis of aluminum and sodium in zeolites typically require significant sample and reagent preparation before the final titrimetric or atomic spectroscopic measurement. Low-resolution, bench top nuclear magnetic resonance (NMR) has shown important applications for rapid quantitative analysis of hydrogen and/or fluorine containing materials without sample preparation in the food, chemical, and polymer industries. Here we demonstrate the determination of aluminum and sodium in zeolite A without sample preparation by using multinuclear, low-field NMR. The simultaneous determination of aluminum and sodium can be performed in under five minutes with a precision of ∼ 1% relative. The method, calibration, data collection, and significant other applications are discussed.
Raman Spectroscopy and Genetic Algorithms for the Classification of Wood Types
Authors: Lavine B. K. , Davidson C. E. , Moores A. J. , Griffiths P. R.
Published: October 2003

Raman spectroscopy and pattern recognition techniques are used to develop a potential method to characterize wood by type. The test data consists of 98 Raman spectra of temperate softwoods and hardwoods, and Brazilian and Honduran tropical woods. A genetic algorithm (GA) is used to extract features (i.e., line intensities at specific wavelengths) characteristic of the Raman profile of each wood-type. The spectral features identified by the pattern recognition GA allow the wood samples to cluster by type in a plot of the two largest principal components of the data. Because principal components maximize variance, the bulk of the information encoded by these spectral features is about differences between wood types. The predictive ability of the descriptors identified by the pattern recognition GA and the principal component map associated with them is validated using an external prediction set consisting of tropical woods and temperate hard and softwoods.
Raman Spectroscopic Analysis of Fertilizers and Plant Tissue for Perchlorate
Authors: Williams Ted L. , Martin Robert B. , Collette Timothy W.
Published: October 2003

Raman spectroscopy, without the need for prior chromatographic separation, was used for qualitative and quantitative analysis of 59 samples of fertilizers for perchlorate (ClO4−). These primarily lawn and garden products had no known link to Chile saltpeter, which is known to contain perchlorate. Perchlorate contamination is emerging as an important environmental issue since its discovery in water resources that are widely used for drinking, crop irrigation, and recreation in the Western U.S. Approximately 90% of the 32 fertilizer samples acquired between November 1998 and January 1999 contained perchlorate, and of these, the level was typically high (500–8000 mg/kg). However, only two of the 27 fertilizer samples acquired from June 1999 to May 2000 contained perchlorate and at a lower level than previously observed (i.e., ∼ 250–350 mg/kg). Raman spectroscopy was also applied to the qualitative identification of perchlorate in extracts of lettuce that had been grown in a greenhouse using irrigation water spiked (at 10 ppm) with perchlorate. Generally, with a fertilizer extract, detection limits were ∼ 50 ppm for perchlorate with short spectral acquisition times (∼5 min). Quantitation was typically accurate to within 2 to 14%, with an average %CV (coefficient of variation) of 6.3 among replicate runs. We compare Raman spectroscopy to ion chromatography, which is the currently recommended method for perchlorate analysis.
Spectroscopic Analysis of Pigments and Binding Media of Polychromes by the Combination of Optical Laser-Based and Vibrational Techniques
Authors: Castillejo M. , Martín M. , Oujja M. , Silva D. , Torres R. , Domingo C. , García-Ramos J. V. , Sánchez-Cortés S.
Published: October 2003

Four spectroscopic techniques, Fourier transform Raman (FTR), Fourier transform infrared (FT-IR), laser-induced breakdown spectroscopy (LIBS), and laser-induced fluorescence (LIF), are employed to characterize the pigment and binding media composition of polychromes. Raman spectra allow the assignment of the main pigments; these are α-HgS (vermilion), 2PbCO3·Pb(OH)2 (lead white), As2S3 (orpiment), Pb3O4 (lead red), and amorphous Carbon. The IR spectra can readily identify the pigment 2PbCO3·Pb(OH)2, the binder CaSO4·2H2O (gypsum) and, in combination with the Raman results, the presence of organic constituents of the binding media such as aliphatic esters, free acids, carbohydrates, and amides. The elemental analysis provided by LIBS corresponds to the pigments identified by the previous techniques and shows in addition the presence of some Hg, Fe, and Pb containing components. The presence of a Hg derivative in some of the sampled areas is supported by the LIF analysis; the fluorescence spectrum is mainly assigned to the binding media with the spectral intensity and shape modified to some extent by the contribution of pigments. In some of the samples studied, a peak assigned to α-HgS is observed. The effect of low intensity KrF laser irradiation of the samples is examined; the combined observations point toward a laser cleaning effect except in the areas that contain the pigment 2PbCO3·Pb(OH)2.
Comparison of Acousto-Optic and Liquid Crystal Tunable Filters for Laser-Induced Breakdown Spectroscopy
Authors: Stratis Dimitra N. , Eland Kristine L. , Carter J. Chance , Tomlinson Samuel J. , Angel S. Michael
Published: October 2003

In this paper, we report the first time-resolved laser-induced plasma images acquired using a liquid crystal tunable filter (LCTF). We also compare the use of LCTFs and acousto-optic tunable filters (AOTFs) for time-resolved plasma imaging applications in terms of resolution, out-of-band rejection, and image quality. Application of tunable filter technologies to plasma imaging is unlike other spectroscopic imaging methods because of the intense and spectrally broad background generated by a laser-induced plasma. High quality images of the distribution of atomic emission within a laser-induced plasma can be achieved using both AOTFs and LCTFs. However, additional filters are needed for rejection of wavelengths outside the tuning ranges of the devices. Both devices exhibited superior resolution in the lower working range of the filters (∼500 nm) with the LCTF exhibiting superior spectral resolution to the AOTF.
Single-Molecule Spectroscopy and Fluorescence Correlation Spectroscopy of the Lateral Transport of the T3 Promoter Primer at a Chemical Interface
Authors: Wirth Mary J. , Swinton Derrick J.
Published: October 2003

Fluorescence correlation spectroscopy reveals that an oligonucleotide, the T3 promoter primer, undergoes only lateral diffusion when adsorbed to the interface of water and silica chemically modified with a hydrocarbon. The autocorrelation decay fits well to the model of simple diffusion, reporting a diffusion coefficient of 1.8 × 10−6 cm2/s. Single-molecule resolution of bursts for the T3 promoter primer reveals that rare, strong adsorption punctuates the lateral diffusion. Removal of the strong adsorption events from the data set, followed by autocorrelation, shows the actual diffusion coefficient to be 2.8 × 10−6 cm2/s, which is comparable to other oligonucleotides of the same size at the same interface. The single-molecule measurements show that average duration of strong adsorption is 0.2 s, and the average fraction of strongly adsorbed molecules is 10% of the molecules at the interface. While single-molecule spectroscopy reveals a process not evident in fluorescence correlation spectroscopy, the precision of the parameters describing strong adsorption is limited by the statistics of small numbers. Fluorescence correlation spectroscopy is suited to observing a much larger number of events, which is needed for high precision. The two methods are complementary: single-molecule spectroscopy gives estimates of the chemical parameters needed for design of the fluorescence correlation spectroscopy, achieving precise measurements with an accurate interpretation.
Polycondensation Reaction of Bis(Hydroxyethylterephthalate)—Self Modeling Curve Resolution Analysis of On-Line ATR/FT-IR Spectra
Authors: Šašić Slobodan , Amari Toru , Siesler Heinz W. , Ozaki Yukihiro
Published: October 2003

This study presents a thorough qualitative-quantitative analysis by self-modeling curve resolution (SMCR) methods of ATR/FT-IR spectra of the polycondensation reaction of bis(hydroxyethylterephthalate) (BHET) that yields poly(ethyleneterephthalate) (PET) as a final product. We used five different SMCR methods to extract pure-component spectra and concentration profiles. All the results obtained by these five methods are compared. It is shown that particular attention should be given to the scaling of the data. The spectral profiles of the species are obtained through the pure variables determined. Because of the appearance of negative absorbances, the spectra are subjected to the alternating least-square procedure. Rank analysis of the mean centered data shows that the IR spectra of the system in the reaction vessel are predominantly determined by those of BHET and PET, but that a small amount of ethylene glycol (EG), which was evacuated from the reaction vessel, also contributes to the spectra.
Classification of Document Papers by Infrared Spectroscopy and Multivariate Statistical Techniques
Authors: Kher Ashwini , Mulholland Mary , Reedy Brian , Maynard Philip
Published: October 2003

Infrared (IR) spectra of different varieties of document papers were collected with the use of attenuated total reflectance (ATR, 4000-650 cm−1, eight paper varieties) and diffuse reflectance (DRIFTS, 9000-2500 cm−1, six paper varieties) techniques. The spectral data were classified by the application of soft independent modeling of class analogies (SIMCA), using principal components analysis (PCA) to estimate the distance of separation between the different classes of paper samples and discriminant analysis (DA) to obtain a probabilistic classification. The use of DA on spectral data needed a preliminary data reduction step, either by PCA-decomposition of spectra or the selection of discrete spectral features having maximum discriminating ability. The aim of this research was to evaluate these data-reduction techniques and compare the discriminating power of these two spectral techniques (DRIFTS and ATR) by the application of PCA and DA. The use of PCA scores as DA variables provided the best resolution (100% correct classification) for the DRIFTS spectra, while PCA on the ATR spectra resulted in the best discrimination, separating 67.86% paper pairs completely with the use of cross-validation. The results of this study reemphasize that infrared spectroscopy coupled with multivariate statistical methods of analysis could provide a powerful discriminating tool for the forensic questioned document examiner.
Implementation of Locally Weighted Regression to Maintain Calibrations on FT-NIR Analyzers for Industrial Processes
Authors: Chang Shih-Ying , Baughman Ernie H. , McIntosh Bruce C.
Published: October 2003

The maintenance of multivariate models used with on-line near-infrared analyzers often consumes significant resources after installation. This paper presents a proposed calibration strategy based on a locally weighted regression (LWR) model with an extended library and its test results on two industrial data sets. The LWR method uses combined spectral and chemical space for distance, which was modified from Wang et al.'s proposed distance measurements, and linear weightings as well as principal component regression (PCR) analysis. The addition of new sample spectra to adapt process changes or to correct for prediction variations is also proposed. Although the maintenance of predictions within performance specifications was the original goal for the proposed strategy, the LWR approach with extended libraries also provides significant accuracy improvement. The root mean squared error of prediction (RMSEP) for the first concentration property in data set 1 from the LWR model on an extended library is 47% better than the one from a global PCR model. The RMSEP for the second concentration in set 1 is 14% better. On the other hand, global models based on the corresponding extended libraries, which were used by the LWR model, do not show any significant performance improvement. The improvement for the physical property of set 2 is 61%, which may be due to the more clustered sample distribution and the nonlinear relationship between the property and spectral response. Current implementations also show that the LWR model provides a convenient platform to include new samples that were collected after installation to adapt process or sample changes.