bluuebunny/crossref_metadata_2025 huggingface dataset:
Geographic Classification of Extra Virgin Olive Oils from the Eastern Mediterranean by Chemometric Analysis of Visible and Near-Infrared Spectroscopic Data
Authors: Downey Gerard , McIntyre Peter , Davies Antony N.
Published: October 2003

Visible and near-infrared reflectance spectra have been examined for their ability to classify extra virgin olive oils from the eastern Mediterranean on the basis of their geographic origin. Classification strategies investigated were partial least-squares regression, factorial discriminant analysis, and k-nearest neighbors analysis. Discriminant models were developed and evaluated using spectral data in the visible (400–750 nm), near-infrared (1100–2498 nm), and combined (400–2498 nm) wavelength ranges. A variety of data pretreatments was applied. Best results were obtained using factorial discriminant analysis on raw spectral data over the combined wavelength range; a correct classification rate of 93.9% was obtained on a prediction sample set. Though the overall sample set was limited in numbers, these results demonstrate the potential of near-infrared spectroscopy to classify extra virgin olive oils on the basis of their geographic origin.
On the Normalization Method in Two-Dimensional Correlation Spectra When Concentration is Used as a Perturbation Parameter
Authors: Yu Z. W. , Noda I.
Published: October 2003

Data pretreatment is of importance in two-dimensional (2D) correlation analysis when composition is used as a perturbation parameter. For composition-oriented studies, different normalization methods based on both external parameters (i.e., concentration) and internal parameters (i.e., absorbance from individual components) have been compared. It was found that when there is no overlapping between absorption bands of interest, no normalization is needed for data pretreatment. When overlapped bands must be used for 2D correlation analysis, the mean-centered normalization method could be used to obtain correct signs in synchronous spectra for a transformation process in the specific form of A → kC. The intensity of the 2D spectrum, however, may not accurately reflect quantitative information of the overall extent of spectral intensity variation observed during experiments.
Two-Dimensional Correlation Analysis in Application to a Kinetic Model of Parallel Reactions
Authors: Chin Thou-Long , Lin King-Chuen
Published: October 2003

By applying generalized two-dimensional (2D) correlation analysis as reported by Noda, we have systematically studied a kinetic model of parallel reactions. Given the related rate constants and absorption coefficients, the correlation between reactant and products are analyzed. The reactant–reactant, reactant–product, and product–product pairs are found to be synchronously correlated, and their intensities increase with increase of the rate constant and the absorption coefficient. On the other hand, only the reactant–product pairs show in the asynchronous spectra. Their intensities also depend proportionally on the rate constant and the absorption coefficient. The influence of signal-to-noise ratio (S/N) and overlapped spectra are further discussed. The resulting synchronous and asynchronous correlation spectra for the kinetic model appear to be weakly influenced by poor quality of the signal when the reference spectrum is set at zero. The ratio of asynchronous to synchronous correlation intensity yields a coherence spectrum. This spectrum remains a constant intensity for all the correlated peaks, being free from the influence of rate constant and absorption coefficient as well as being weakly disturbed by a small S/N ratio. It also provides a way to evaluate the extent of spectral overlap between two peaks. The coherence spectrum is useful to characterize the type of parallel reactions.
Effective Normalization Method for Sample-Position-Dependence Effect in Photoacoustic Spectrometry
Authors: Shen Jun , Zhou Jianqin , Hu Cheng , Zhao Jianhua
Published: October 2003

Sample position dependence effect in photoacoustic (PA) spectrometry has been reported by several scientists. This effect must be taken into account in a PA application that requires a quantitative theoretical treatment. In this work, we experimentally investigated PA signal magnitude varying with sample-to-window distance in an MTEC Model 300 Photoacoustic Detector, which has a fixed empty (gas) volume in addition to the sample-to-window-distance-dependent gas volume. An operative method was introduced to obtain the coefficient, which considered the sample-to-window distance and the additional gas volume. With this coefficient, the one-dimensional PA model, developed by Aamodt, Murphy, and Parker, can be employed to quantitatively process PA experimental data, no matter what the sample-to-window distance is. Quantitative measurements of thermal effusivities of two samples were performed to prove this effective normalization method.
Determination of the Resolution of a Multichannel Raman Spectrometer Using Fourier Transform Raman Spectra
Authors: Bowie Bryan T. , Griffiths Peter R.
Published: October 2003

The resolution of a grating polychromator for Raman spectroscopy has been simulated by measuring spectra on a Fourier transform (FT) Raman spectrometer and selecting the FT of the apodization function so that the instrument line shape function mimics the triangular spectral slit function of the polychromator. To this end, FT-Raman spectra measured with a nominal resolution of 0.5 cm−1 were modified through the application of sinc2 apodization functions of various widths to simulate spectra measured on a polychromator at lower resolution. The success of this approach was validated using the 1085 cm−1 band of calcite. When the modified FT-Raman spectra were compared with spectra measured on a grating polychromator equipped with slits of widths 100 and 150 μm, the resolution of the polychromator was estimated to be 6.3 and 7.8 cm−1, respectively. This conclusion was verified experimentally by measuring the separation of two bands in the Raman spectrum of BaSO4 at ∼460 cm−1
Automatic Correction of Continuum Background in Laser-Induced Breakdown and Raman Spectrometry
Authors: Gornushkin I. B. , Eagan P. E. , Novikov A. B. , Smith B. W. , Winefordner J. D.
Published: October 2003

The goal of this work was the development and evaluation of an algorithm for the approximation and automatic subtraction of continuum backgrounds in laser-induced breakdown and Raman spectra. The background correction algorithm was applied to simple and complex spectra and its effect on identification accuracy was studied. Linear correlation was used for the identification of plastic samples using both laser-induced breakdown and Raman spectra. For both techniques, the algorithm successfully eliminated continuum background without compromising spectral integrity. A significant improvement in the percentage of correct plastic identifications was observed for Raman spectra. The approach should be applicable to a wide range of background correction problems in atomic and molecular spectroscopy.
Fluorescence Energy Transfer between Fluorescein Label and DNA Intercalators to Detect Nucleic Acids Hybridization in Homogeneous Media
Authors: Talavera Eva M. , Bermejo Ruperto , Crovetto Luis , Orte Angel , Alvarez-Pez Jose M.
Published: October 2003

A general approach to detecting nucleic acid sequences in homogeneous media by means of steady-state fluorescence measurements is proposed. The methodology combines the use of a fluorescence-labeled single-strand DNA model probe, the complementary single-strand DNA target, and a DNA intercalator. The probe was fluorescein labeled to a spacer arm at the N4 position of the cytosine amino groups in polyribocytidylic acid (5′), poly(C), which acts as a model DNA probe. The complementary strand was polyriboinosinic acid (5′), poly(I), as a model of the target, and the energy transfer acceptor was an intercalator, either ethidium bromide or ethidium homodimer. In previous papers we have shown that the fluorescence intensity of the fluorescein label decreases when labeled poly(C) hybridizes with poly(I), and this fluorescence quenching can be used to detect DNA hybridization or renaturation in homogeneous media. In this paper we demonstrate that fluorescence resonance energy transfer (FRET) between fluorescein labeled to poly(C) and an intercalator agent takes place when single-stranded poly(C) hybridizes with poly(I), and we show how the fluorescence energy transfer further decreases the steady-state fluorescence intensity of the label, thus increasing the detection limit of the method. The main aim of this work was to develop a truly homogeneous detection system for specific nucleic acid hybridization in solution using steady-state fluorescence and FRET, but with the advantage of only having to label the probe with the energy donor since the energy acceptor is intercalated spontaneously. Moreover, the site label is not critical and can be labeled randomly in the DNA strand. Thus, the method is simpler than those published previously based on FRET. The experiments were carried out in both direct and competitive formats.
Optical and Mass Spectrometric Study of the Pyrolysis Gas of Wood Particles
Authors: Brackmann Christian , Aldén Marcus , Bengtsson Per-Erik , Davidsson Kent O. , Pettersson Jan B. C.
Published: October 2003

A detailed experimental investigation has been made of the pyrolysis—the first step in biomass combustion—of single birchwood particles. In addition to mass spectrometric and gravimetric analysis, the pyrolysis volatiles were characterized by different optical techniques. Absorption measurements showed a nearly featureless absorption in the ultraviolet spectral region with a continuously stronger absorption for shorter wavelengths. Using different excitation wavelengths, laser-induced fluorescence measurements revealed generally broad spectra in the spectral region from 300–500 nm, which are characteristic spectral signatures for larger hydrocarbons. The optical data were monitored at different times in the pyrolysis process of the particles and compared with the results from the mass spectrometric and gravimetric analysis. The sensitivity of the optical techniques for differentiation between specific molecules was rather low, although formaldehyde could be observed both in absorption and fluorescence spectra. Laser-induced fluorescence measurements were also made for two-dimensional visualization of the pyrolysis volatiles emitted from heated birchwood particles, indicating much higher flows along the fiber direction than across.
Fourier Transform Raman Spectrometry for the Quantitative Analysis of Oil Content and Humidity in Olives
Authors: Muik Barbara , Lendl Bernhard , Molina-Díaz Antonio , Ayora-Cañada Maria José
Published: October 2003

A method for the direct and fast determination of oil content and humidity in olives using Fourier transform Raman spectrometry is reported. The only sample preparation step required was crushing of the olives using a hammer mill. The crushed olives were placed in a dedicated sample cup, which was rotated excentrically to the horizontal laser beam during spectrum acquisition. This allowed us to sample an increased volume and thus compensate for sample inhomogeneities. In this way the reproducibility of Raman spectra taken from crushed olives was significantly improved. Partial least-squares (PLS) regression was used for the chemometric evaluation of the Raman spectra. Standard errors of prediction for the validation set of 0.81% for oil content (in the range 19.68–35.71%) and 1.54% for humidity (in the range 29.23–51.49%), both expressed as weight percentage referred to fresh matter, were obtained.
Pore Structure and Sorption Properties of Silica Aerogels Studied by Magnetic Resonance Imaging and Pulsed-Field Gradient Spectroscopy
Authors: Gregory D. M. , Botto R. E.
Published: October 2003

Magnetic resonance imaging (MRI) has provided direct visualization of gaseous xenon and methane in the void spaces of aerogels, offering unique information and insights into the pore structure and molecular diffusivities of occluded sorbates. Nuclear magnetic resonance (NMR) pulsed-field gradient (PFG) techniques were used to characterize exchange and diffusive motion of sorbed xenon gas at equilibrium. PFG measurements showed evidence of anisotropic diffusion; nominal self-diffusivity coefficients of xenon on the order of D = 10−7 m2/s were determined. Based on a mathematical relationship for the restricted diffusion of gases in confined environments, an expression for estimating the mean free path was derived, from which the average pore size could be obtained from the extrapolated value of the diffusion coefficient to low xenon pressures.
Ligand Distributions in Agarose Particles as Determined by Confocal Raman Spectroscopy and Confocal Scanning Laser Microscopy
Authors: Larsson Mina , Lindgren Jan , Ljunglöf Anders , Knuuttila Karl-Gustav
Published: October 2003

Confocal Raman spectroscopy and confocal scanning laser microscopy have been used to analyze ligand distributions within individual chromatographic adsorbent particles. Three different types of particles have been investigated. The first type was synthesized to have a uniform distribution of allyl groups, whereas the two others were designed to have a surface layer of sulphopropyl groups and cores containing allyl groups and dextran, respectively. With confocal Raman spectroscopy it was possible to follow the distribution of both the surface layer and the interior. The distribution of sulphopropyl groups was evaluated with both confocal scanning laser microscopy and confocal Raman spectroscopy, whereas the distributions of allyl groups and dextran were evaluated only with the latter method. The results from the confocal measurements showed the expected result with a uniform distribution of allyl groups in the first type of particle and surface layers of sulphopropyl groups and cores with dextran or allyl groups for the two others.
On-the-Fly Fluorescence Lifetime Detection of Humic Substances in Capillary Electrophoresis
Authors: Hewitt Joseph D. , McGown Linda B.
Published: October 2003

On-the-fly fluorescence lifetime detection was investigated as a tool for studying humic substances in capillary zone electrophoresis (CZE). Humic substances are complex, heterogeneous mixtures of natural products that tend to migrate in a single, broad CZE peak. The intrinsic fluorescence lifetime of five humic substances from the International Humic Substances Society (IHSS) was monitored using excitation at 488 or 364 nm to produce intensity-lifetime electropherograms for each of the substances. Each frequency-domain lifetime measurement, collected at sub-second intervals during the CZE run, contains the equivalent of a complete decay profile. Lifetime analysis of each decay profile was used to construct a lifetime-resolved electropherogram for each lifetime component, from which the variation in relative intensity contributions of each lifetime across the broad CZE peak could be determined. Absorption spectra, fluorescence excitation–emission spectra, and lifetime profiles of batch solutions of the samples were determined as well. It was found that, whereas absorption and fluorescence spectral characteristics tended to discriminate between humic acids and fulvic acids, the batch solution lifetime profiles discriminated instead between samples from different sources, regardless of fraction. On-the-fly lifetime detection provided a more detailed view of the fluorescence decay of the samples, including greater resolution of lifetimes for two of the fulvic acids and greater discrimination among samples based on lifetime profiles across the CZE peaks.
Carbon-Thirteen Cross-Polarization Magic Angle Spinning Nuclear Magnetic Resonance and Fourier Transform Infrared Studies of Thermally Modified Wood Exposed to Brown and Soft Rot Fungi
Authors: Sivonen Hanne , Nuopponen Mari , Maunu Sirkka L. , Sundholm Franciska , Vuorinen Tapani
Published: October 2003

Thermally modified wood has many technically interesting properties, such as increased dimensional stability, low equilibrium moisture content, and enhanced biological and weather resistance. This paper describes solid-state nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopic studies on the decay of heat-treated and untreated pine ( Pinus sylvestris) by brown ( Poria placenta) and soft rot fungi. Both techniques combined with multivariate data analysis proved to be powerful tools for the study of wood degradation by fungi. When untreated pine was exposed to brown or soft rot fungi, a drastic decay of the cell wall polysaccharides was observed. Brown rot fungus degraded mainly hemicelluloses while soft rot fungus attacked cellulose more extensively. The aromatic region of 13C cross-polarization magic angle spinning (CPMAS) NMR spectra revealed that the structure of lignin was also altered. New carboxylic structures were formed as a consequence of the decay. The increased biological resistance of pine wood heat-treated at >220 °C was observed in the 13C CPMAS NMR and IR spectra.
Structural Change of Water with Solutes and Temperature up to 100 °C in Aqueous Solutions as Revealed by Attenuated Total Reflectance Infrared Spectroscopy
Authors: Masuda Kaori , Haramaki Taishiro , Nakashima Satoru , Habert Bertrand , Martinez Isabelle , Kashiwabara Seiichi
Published: October 2003

The attenuated total reflectance infrared (ATR-IR) spectra of several aqueous solutions have been measured by using a newly developed heatable rod-type ATR cell. The OH stretching bands showed systematic change with increasing solute concentrations and these changes can be explained by four different OH components based on curve-fitting results. NaCl solutions show longer H-bond distance character, while carbonate solutions present shorter ones. The Na2CO3 1 M solution conserves this shorter H-bond nature up to 100 °C. On the other hand, the loose nature of NaCl solutions becomes less pronounced at higher temperatures because of the dissociation of pure water clusters. These in situ observations of water structures are generally in agreement with the expected nature of fluids within the earth.
Fourier Transform Infrared Attenuated Total Reflection and Transmission Spectra Studied by Dispersion Analysis
Authors: Macdonald Steven A. , Bureau Bruno
Published: October 2003

Fourier transform infrared transmission (FT-IR) and attenuated total reflection (ATR) spectra of water–ethanol mixtures are recorded and reconstructed thanks to a causal dispersion analysis technique. As expected, the Beer's law technique is an empirical approximate method that cannot account for complex spectral features. On the other hand, a rigorous analysis performed by using the theoretical optical paths for both experimental techniques and Gaussian dispersion analysis (GDA) allows the dielectric functions of the pure liquids to be calculated. Simulations of the whole mid-infrared spectra in the range 500–4000 cm−1 match the experimental data very well, whatever the water–ethanol mixtures. This method is a powerful tool to quantify such model mixtures and more generally could be the first step toward software for assistance to the FT-IR spectrum analysis.
Simulation on Wavelength-Dependent Complex Refractive Index of Liquids Obtained by Phase Retrieval from Reflectance Dip Due to Surface Plasmon Resonance
Authors: Saarinen Jarkko J. , Peiponen Kai-Erik , Vartiainen Erik M.
Published: October 2003

A method for the calculation of the wavelength-dependent complex refractive index of absorbing liquid from reflectance in the vicinity of surface plasmon resonance (SPR) is presented. The calculation is based on the maximum entropy method (MEM). As an example, phase retrieval from a simulated SPR reflectance of a red colored liquid solution is carried out. It is proposed that MEM can be applied to wavelength-dependent complex refractive index assessment from reflectance of absorbing liquids in SPR measurement in wavelength scanning mode.
Improved Methods for Performing Multivariate Analysis and Deriving Background Spectra in Atmospheric Open-Path FT-IR Monitoring
Authors: Hong Daewoong , Cho Seogyeon
Published: October 2003

Open-path Fourier transform infrared spectrometry (OP/FT-IR) may improve the temporal and spatial resolution in air pollutant measurements compared to conventional sampling methods. However, a successful OP/FT-IR operation requires an experienced analyst to resolve chemical interference as well as to derive a suitable background spectrum. The present study aims at developing a systematic method of handling the OP/FT-IR derived spectra for the measurement of photochemical oxidants and volatile organic compounds (VOCs) in urban areas. A classical least-squares (CLS) method, the most frequently used regression method in OP/FT-IR, is modified to constrain all the analyzed chemical species concentrations within a physically reasonable range. This new CLS method, named constrained CLS, may save the effort of predetermining the chemical species to be analyzed. A new background spectrum generation method is also introduced to more efficiently handle chemical interferences. Finally, CLS is shown to be prone to propagating errors in the case that a few data points contain a significant amount of error. The L1-norm minimization method reduces this error propagation to considerably increase the stability compared to CLS. The presently developed analysis software based on these approaches is compared with the other conventional CLS method using an artificially made single-beam spectrum as well as a field single-beam spectrum.
Assessment of Pareto Calibration, Stability, and Wavelength Selection
Authors: Anderson Kelly J. , Kalivas John H.
Published: October 2003

Recent work has shown that ridge regression (RR) is Pareto to partial least squares (PLS) and principal component regression (PCR) when the variance indicator Euclidian norm of the regression coefficients, ‖p̂‖, is plotted against the bias indicator root mean square error of calibration (RMSEC). Simplex optimization demonstrates that RR is Pareto for several other spectral data sets when ‖p̂‖ is used with RMSEC and the root mean square error of evaluation (RMSEE) as optimization criteria. From this investigation, it was observed that while RR is Pareto optimal, PLS and PCR harmonious models are near equivalent to harmonious RR models. Additionally, it was found that RR is Pareto robust, i.e., models formed at one temperature were then used to predict samples at another temperature. Wavelength selection is commonly performed to improve analysis results such that bias indicators RMSEC, RMSEE, root mean square error of validation, or root mean square error of cross-validation decrease using a subset of wavelengths. Just as critical to an analysis of selected wavelengths is an assessment of variance. Using wavelengths deemed optimal in a previous study, this paper reports on the variance/bias tradeoff. An approach that forms the Pareto model with a Pareto wavelength subset is suggested.
Band Centers and Track Finding for Large Two-Dimensional Infrared Spectroscopic Arrays
Authors: Chen Li , Garland Marc
Published: October 2003

An efficient two-dimensional (2D) peak-finding algorithm is proposed to find peak maps that specify the peak centers of all bands in two-dimensional arrays of time-series infrared spectral data. The algorithm combines the second-derivative method with the intrinsic characteristics of 2D infrared reaction spectral data. Initially, the second-derivative method is used to detect all possible peak center positions, and then three criteria drawn from characteristics of 2D continuous spectral data are employed to filter peak positions. Four 2D peak maps are generated in a sequential order, with better and better approximations to the peak center positions being obtained in each. The 2D peak-finding algorithm has been successfully applied to both simulated spectra (to initially evaluate the algorithm) and then real 2D experimental spectra. The resulting peak maps exhibit very good estimates of the peak center positions. An ordering from the most significant to the least significant bands is obtained. The final peak maps can be used as starting parameters for various applications including the computationally intensive curve-fitting of time-series data.
Computationally Efficient Curve-Fitting Procedure for Large Two-Dimensional Experimental Infrared Spectroscopic Arrays Using the Pearson VII Model
Authors: Chen Li , Garland Marc
Published: October 2003

Extraction of quantitative information from large sets of sequential time-series spectra (two-dimensional, 2D, data) using a curve-fitting procedure is investigated. The difference between any experimental spectrum and any curve-fitted spectrum is constructed in a least-squares manner and the Pearson VII model is selected as the general band-shape function for the infrared absorbance spectra. The starting point for the curve-fitting procedure is a 2D peak map. Next, an interior spectrum from the 2D array is chosen, initial guesses of the band parameters are provided by an initialization scheme, and curve fitting is performed. Once optimal values of the Pearson VII model band parameters are obtained from the starting spectrum in the 2D array, these are then used as reasonable and judicious initial guesses for subsequent curve fitting of the neighboring spectra in the time series. This increases computational efficiency enormously. By adjusting the band center positions for moving bands, and re-optimizing each subsequent curve-fitting calculation to account for changing band shapes, the entire 2D array is rapidly and efficiently modeled. A 2D experimental spectroscopic time-series array from a homogeneous rhodium-catalyzed hydroformylation reaction was successfully curve fitted in this manner. The procedure holds considerable promise for the curve fitting of massive time-series spectroscopic data, such as that arising from on-line process monitoring of expensive value-added specialty chemical and pharmaceutical syntheses.
Determination of Trace Metals in Drinking Water Using Solid-Phase Extraction Disks and X-ray Fluorescence Spectrometry
Authors: Hou Xiandeng , Peters Heather L. , Yang Zheng , Wagner Karl A. , Batchelor James D. , Daniel Meredith M. , Jones Bradley T.
Published: October 2003

A convenient method is described for monitoring Cd, Ni, Cu, and Pb at trace levels in drinking water samples. These metals are pre-concentrated on a chelating solid-phase extraction disk and then determined by X-ray fluorescence spectrometry. The method tolerates a wide pH range (pH 6–14) and a large amount of alkaline and alkaline earth elements. The preconcentration factor is well over 1600, assuming a 1 L water sample volume. The limits of detection for Cd, Ni, Cu, and Pb are 3.8, 0.6, 0.4, and 0.3 ng/mL, respectively. These are well below the federal maximum contaminant level values, which are 5, 100, 1300, and 15 ng/mL, respectively. The proposed method has many advantages including ease of operation, multielement capability, nondestructiveness, high sensitivity, and relative cost efficiency. The solid-phase extraction step can be conducted in the field and then the disks can be mailed to a laboratory for the analysis, eliminating the cost of transporting large volumes of water samples. Furthermore, the color of the used extraction disk provides an initial estimate of the degree of contamination for some transition metals (for example, Ni and Cu). Thus, the overall cost for analysis of metals in drinking water can be minimized by implementing the method, and small water supply companies with limited budgets will be better able to comply with the Safe Drinking Water Act.
Chemical Imaging Using Microline Laser Ablation: Performance Comparison of Gaussian and Flat Top Lasers
Authors: Mateo M. P. , Cabalín L. M. , Laserna J. J.
Published: October 2003

In previous studies, the potential of a microline imaging arrangement for surface characterization of solid samples in air at atmospheric pressure using laser-induced plasma spectrometry (LIPS) has been demonstrated. An improvement of this approach to obtain a uniform ablation along the microline focus that leads to a representative spatial distribution of elements on the sample surface is presented. For this purpose, the influence of beam energy distribution of two types of Nd: YAG pulsed lasers (a Gaussian laser and a flat top laser) on lateral resolution, intensity profiles of elements, chemical distribution maps, and plasma electron temperature has been investigated. As models of homogeneous and compositionally patterned samples, a stainless steel sample and a photovoltaic cell were chosen for this study. The results demonstrated that the Gaussian laser provides the best lateral resolution, but more redeposition at both sides of the microline crater, while the chemical maps obtained with the flat top laser matched with the distribution of the constituents of the sample surface.
Spectral Pattern Recognition of in Situ FT-IR Spectroscopic Reaction Data Using Minimization of Entropy and Spectral Similarity (MESS): Application to the Homogeneous Rhodium Catalyzed Hydroformylation of Isoprene
Authors: Chen Li , Chew Wee , Garland Marc
Published: October 2003

An improved algorithm using minimization of entropy and spectral similarity (MESS) was tested to recover pure component spectra from in situ experimental Fourier transform infrared (FT-IR) reaction spectral data, which were collected from a homogeneous rhodium catalyzed hydroformylation of isoprene. The experimental spectra are complicated and highly overlapping because of the presence of multiple intermediate products in this reaction system. The traditional entropy minimization method fails to resolve real reaction mixture spectra, but MESS can successfully reconstruct pure component spectra of unknown intermediate products for real reaction systems by the addition of minimization of spectral similarity. The quantitative measure of spectral similarity between two spectra was given by their inner products. The results indicate that MESS is a stable and useful algorithm for spectral pattern recognition of highly overlapped experimental reaction spectra. Comparison is also made between MESS, entropy minimization, simple-to-use interactive self-modeling mixture analysis (SIMPLISMA), interactive principle component analysis (IPCA), and orthogonal projection approach–alternating least squares (OPA-ALS).
Electric-Field-Induced Reorientation of Liquid Crystalline p-Cyanophenyl-p-n-Alkylbenzoates: A Time-Resolved Study by Fourier Transform Infrared Transmission and Attenuated Total Reflection Spectroscopy
Authors: Klimov E. , Fuelleborn M. , Siesler H. W.
Published: October 2003

Time-resolved polarization Fourier transform infrared (FT-IR) transmission and attenuated total reflection (ATR) spectroscopy were applied to investigate the reorientation phenomena of the three members of the homologous series of nematic liquid crystalline p-cyanophenyl-p-n-alkylbenzoates 6CPB, 7CPB, and 10CPB under the external perturbation of an electric field. In conjunction with a newly constructed measurement cell, this method allowed us to differentiate the response of the LC system in the surface layer and in the bulk of the cell at different temperatures and voltages. The relaxation time of the LC molecules close to the wall of the cell was found to be shorter than in the bulk. However, at a field strength of 7 V, the initial orientation in the bulk preceeds the analogous process in the surface region.
Attenuated Total Reflection Surface-Enhanced Infrared Absorption Spectroscopy of Carboxyl Terminated Self-Assembled Monolayers on Gold
Authors: Goutev Nikolay , Futamata Masayuki
Published: October 2003

A new recipe for surface-enhanced infrared absorption (SEIRA) active island Au films with improved adhesion in aqueous solution, low resistivity, and enhancement of the infrared (IR) absorption of about 300 was developed. The Au films prepared were utilized in studies of the ionization of self-assembled monolayers of 11-mercaptoundecanoic acid in Na2SO4 aqueous solutions by attenuated total reflection surface-enhanced infrared absorption (ATR-SEIRA) spectroscopy. It was found that the carboxyl end groups of the self-assembled monolayer turn into carboxylate anions on going from anodic to cathodic potentials or from acidic to alkaline pH. The water molecules close to the self-assembled monolayer in acidic solutions or at anodic potentials are preferentially aligned with their dipole moments parallel to the interface. This type of alignment can be ascribed to the dipole–dipole interaction between the carboxyl groups and the water molecules. On the other hand, in alkaline solutions or at cathodic potentials the structure of water close to the self-assembled monolayer is essentially bulk-like, with randomly oriented water molecules. This observation suggests that in alkaline solutions or at cathodic potentials the charge of the carboxylate anions is almost completely compensated for by strongly adsorbed counter cations. As a result, the electric field close to the surface of the ionized self-assembled monolayer is weak and has little influence on the orientation and hydrogen bonding of the water molecules.
Diffusional Fluorescence Quenching of Aromatic Hydrocarbons
Authors: Canuel Clelia , Badre Sophie , Groenzin Henning , Berheide Markus , Mullins Oliver C.
Published: October 2003

The quenching of the fluorescence of five aromatic hydrocarbons by three halogenated organics and by molecular oxygen has been measured. Both fluorescence intensity and fluorescence lifetime measurements have been employed to validate results and interpretation; linear Stern–Volmer analyses are shown to apply throughout. The fluorescence quenching rate constant of molecular oxygen for the five aromatic hydrocarbons is essentially equivalent to the diffusion rate constant independent of the fluorophore excitation energy. The halogenated organic–fluorophore rate constants vary by a factor of 965 and are shown to correlate roughly with the energy difference between the quencher and fluorophore excited electronic states in accord with a standard model of quantum two-level mixing. The value of the coupling interaction energy is ∼2500 cm−1.
Near-Infrared Spectroscopy for On-Line Monitoring of Lube Base Oil Processes
Authors: Chung Hoeil , Ku Min-Sik
Published: October 2003

Near-infrared (NIR) spectroscopy has been utilized for monitoring the pour point of the lube base oil (LBO) process. Using partial least-squares (PLS) regression, necessary spectral features were successfully extracted and correlated to the reference pour-point data. In a preliminary laboratory feasibility study, it was found that PLS calibration performance was largely governed by the accuracy of the reference pour-point analysis. The same NIR spectroscopic methodology was moved to monitor the pour point continuously in an on-line manner. At this time, the NIR spectrometer was calibrated with the existing on-line pour-point analyzer, which was more accurate. In comparison with the on-line pour-point analyzer, NIR spectroscopy provided faster and more repeatable analytical data. With the help of NIR analysis, LBO process variations during product switch can be detected earlier, and necessary process-control strategy can be applied to improve the process efficiency.
Application of Partial Least-Squares Regression to Near-Infrared Reflectance Spectroscopic Determination of Shive Content in Flax
Authors: Sohn Miryeong , Barton Franklin E. , Morrison Wiley H. , Archibald Douglas D.
Published: October 2003

Shive, the nonfiberous core portion of the stem, in flax fiber after retting is related to fiber quality. The objective of this study is to develop a standard calibration model for determining shive content in retted flax by using near-infrared reflectance spectroscopy. Calibration samples were prepared by manually mixing pure, ground shive and pure, ground fiber from flax retted by three different methods (water, dew, and enzyme retting) to provide a wide range of shive content from 0 to 100%. Partial least-squares (PLS) regression was used to generate a calibration model, and spectral data were processed using various pretreatments such as a multiplicative scatter correction (MSC), normalization, derivatives, and Martens' Uncertainty option to improve the calibration model. The calibration model developed with a single sample set resulted in a standard error of 1.8% with one factor. The best algorithm was produced from first-derivative processing of the spectral data. MSC was not effective processing for this model. However, a big bias was observed when independent sample sets were applied to this calibration model to predict shive content in flax fiber. The calibration model developed using a combination sample set showed a slightly higher standard error and number of factors compared to the model for a single sample set, but this model was sufficiently accurate to apply to each sample set. The best algorithm for the combination sample set was generated from second derivatives followed by MSC processing of spectral data and from Martens' Uncertainty option; it resulted in a standard error of 2.3% with 2 factors. The value of the digital second derivative centered at 1674 nm for these spectral data was highly correlated to shive content of flax and could form the basis for a simple, low-cost sensor for the shive or fiber content in retted flax.
New Approach to Generalized Two-Dimensional Correlation Spectroscopy. II: Eigenvalue Manipulation Transformation (EMT) for Noise Suppression
Authors: Jung Young Mee , Kim Seung Bin , Noda Isao
Published: October 2003

This paper introduces the concept of eigenvalue manipulating transformation (EMT) of a data matrix for noise suppression in two-dimensional (2D) correlation spectroscopy. The FT-IR spectra of a polystyrene/methyl ethyl ketone/toluene solution mixture during the solvent evaporation process, to which were added a substantial amount of artificial noise, have been analyzed. By uniformly raising the power of a set of eigenvalues, the major eigenvalues become more prominent. As a consequence, minor eigenvectors representing the noise component are no longer strongly represented in the reconstructed data. This EMT operation is similar to the simple truncation of noise-dominated minor factors practiced in standard principal component analysis (PCA), as demonstrated in our preceding paper on PCA-2D correlation spectroscopy. The effect of this new EMT scheme is more gradual, with attractive flexibility to continuously fine-tune the balance between the desired noise reduction effect and the retention of pertinent spectral information.
Use of Broadband, Continuous-Wave Diode Lasers in Cavity Ring-Down Spectroscopy for Liquid Samples
Authors: Hallock A. J. , Berman E. S. F. , Zare R. N.
Published: October 2003

Cavity ring-down spectroscopy (CRDS) is an extremely sensitive absorption technique that has been applied primarily to gas samples, which are characterized by having narrow absorption features. Recently, CRDS has also been applied to liquid samples, which have broad absorption features. The use of small inexpensive diode lasers as light sources for liquid samples is demonstrated. The low cost coupled with the ease and technical straightforwardness of application gives this technique wide appeal.
Safety Considerations for Sample Analysis Using a Near-Infrared (785 nm) Raman Laser Source
Authors: Harvey S. D. , Peters T. J. , Wright B. W.
Published: October 2003

Raman spectroscopy is often considered a nondestructive analytical technique; however, this is not always the case. The 300-mW 785-nm near-infrared (NIR) laser source used with many commercially available instruments has sufficient power to burn samples. This destructive potential is of special concern if the sample is irreplaceable (e.g., fine art, forensic evidence, or for in vivo medical diagnostics) or a hazardous energetic material (explosive or pyrophoric samples). This study quantifies the heat resulting from illuminating an extensive color array with a 785-nm NIR laser and relates these values to the hazards associated with Raman analysis. In general, darker colors were found to be more problematic. Since visible colors are not ideally correlated with absorptive characteristics at 785 nm, predictions based on thermography are not perfect; however, this approximation gives a useful method for predicting the thermal response of unknown samples to NIR exposure. Additionally, experimental studies evaluated the analysis of flammable organic solvents, propellants, military explosives, mixtures containing military explosives, shock-sensitive explosives, and gunpowders (i.e., smokeless, black, and Pyrodex powders). Safety guidelines for analysis are presented.
New Frontiers for Mid-Infrared Sensors: Towards Deep Sea Monitoring with a Submarine FT-IR Sensor System
Authors: Kraft Martin , Jakusch Michael , Karlowatz Manfred , Katzir Abraham , Mizaikoff Boris
Published: October 2003

A sub-sea deployable fiber-optic sensor system for the continuous determination of a range of environmentally relevant volatile organic compounds in seawater has been developed. The prototype of a robust, miniaturized Fourier transform infrared (FT-IR) spectrometer for in situ underwater pollution monitoring was designed, developed, and built in our research group. The assembled instrument is enclosed in a sealed aluminium pressure vessel and is capable of maintenance-free operation in an oceanic environment down to depths of at least 300 m. The whole system can be incorporated either in a tow frame or a remotely operated vehicle (ROV). A suitable fiber-optic sensor head was developed, optimized in terms of sensitivity and hydrodynamics, and connected to the underwater FT-IR spectrometer. Due to a modular system design, various other sensor head configurations could be realized and tested, ensuring facile adaptation of the instrument to future tasks. The sensor system was characterized in a series of laboratory and simulated field tests. The sensor proved to be capable of quantitatively detecting a range of chlorinated hydrocarbons and monocyclic aromatic hydrocarbons in seawater down to the low ppb (μg/L) concentration range, including mixtures of up to 6 components. It has been demonstrated that varying amounts of salinity, turbidity, or humic acids, as well as interfering seawater pollutants, such as aliphatic hydrocarbons or phenols, do not significantly influence the sensor characteristics. In addition, the sensor exhibits sufficient long-time stability and a low susceptibility to sensor fouling.
Development and Optimization of a Mid-Infrared Hollow Waveguide Gas Sensor Combined with a Supported Capillary Membrane Sampler
Authors: De Melas Fabiano , Pustogov Viktor V. , Croitoru Nathan , Mizaikoff Boris
Published: October 2003

A gas sensor for application in water analysis was developed by combination of a mid-infrared (MIR) hollow waveguide with a Fourier transform infrared (FT-IR) spectrometer and coupling of the hollow waveguide gas sensor module to a supported capillary membrane sampler (SCMS) for continuous liquid-gas extraction. Different hollow waveguides have been characterized in this study for developing an optimized optical configuration. Analysis of industrially relevant compounds has been performed, investigating chlorinated hydrocarbons (CHCs), such as dichloromethane and chloroform, representing highly volatile analytes, and 1,4-dioxane as an example of target compounds with low volatility. The suitability of this spectroscopic IR sensing system for industrial applications is demonstrated under simulated real-world conditions with limits of detection in the ppb (v/v) and ppm (v/v) concentration range for CHCs and 1,4-dioxane, respectively.
In Situ Sensing of Volatile Organic Compounds in Groundwater: First Field Tests of a Mid-Infrared Fiber-Optic Sensing System
Authors: Steiner H. , Jakusch M. , Kraft M. , Karlowatz M. , Baumann T. , Niessner R. , Konz W. , Brandenburg A. , Michel K. , Boussard-Plédel C. , Bureau B. , Lucas J. , Reichlin Y. , Katzir A. , Fleischmann N. , Staubmann K. , Allabashi R. , Bayona J. M. , Mizaikoff B.
Published: October 2003

A prototype mid-infrared sensor system for the determination of volatile organic pollutants in groundwater was developed and tested under real-world conditions. The sensor comprises a portable Fourier transform infrared spectrometer, coupled to the sensor head via mid-infrared transparent silver halide fiber-optic cables. A 10 cm unclad middle section of the 6-m-long fiber is coated with ethylene propylene copolymer in order to enrich the analytes within the penetration depth of the evanescent field protruding from the fiber sensor head. A mixture of tetrachloroethylene, dichlorobenzene, diethyl phthalate, and xylene isomers at concentrations in the low ppm region was investigated qualitatively and quantitatively in an artificial aquifer system filled with Munich gravel. This simulated real-world site at a pilot scale enables in situ studies of the sensor response and spreading of the pollutants injected into the system with controlled groundwater flow. The sensor head was immersed into a monitoring well of the aquifer system at a distance of 1 m downstream of the sample inlet and at a depth of 30 cm. Within one hour, the analytes were clearly identified in the fingerprint region of the IR spectrum (1300 to 700 cm−1). The results have been validated by head-space gas chromatography, using samples collected during the field measurement. Five out of six analytes could be discriminated simultaneously; for two of the analytes the quantitative results are in agreement with the reference analysis.
Error Analysis for Estimation of Trace Vapor Concentration Pathlength in Stack Plumes
Authors: Gallagher Neal B. , Wise Barry M. , Sheen David M.
Published: October 2003

Near-infrared hyperspectral imaging is finding utility in remote sensing applications such as detection and quantification of chemical vapor effluents in stack plumes. Optimizing the sensing system or quantification algorithms is difficult because reference images are rarely well characterized. The present work uses a radiance model for a down-looking scene and a detailed noise model for dispersive and Fourier transform spectrometers to generate well-characterized synthetic data. These data were used with a classical least-squares-based estimator in an error analysis to obtain estimates of different sources of concentration-pathlength quantification error in the remote sensing problem. Contributions to the overall quantification error were the sum of individual error terms related to estimating the background, atmospheric corrections, plume temperature, and instrument signal-to-noise ratio. It was found that the quantification error depended strongly on errors in the background estimate and second-most on instrument signal-to-noise ratio. Decreases in net analyte signal (e.g., due to low analyte absorbance or increasing the number of analytes in the plume) led to increases in the quantification error as expected. These observations have implications on instrument design and strategies for quantification. The outlined approach could be used to estimate detection limits or perform variable selection for given sensing problems.