bluuebunny/crossref_metadata_2025 huggingface dataset:
Raman Microscopy Study of Tyrolite: A Multi-Anion Arsenate Mineral
Authors: Kloprogge J. Theo , Frost Ray L.
Published: October 2003

The Raman spectrum of tyrolite, CaCu5(AsO4)2(CO3)(OH) 4·6H2O, from Brixlegg, Tyrol, Austria, is reported. Comparison with copper hydroxy–arsenate and basic carbonates was used to achieve assignments of the observed bands. The AsO43– group is characterized by two v4 modes around 433 and 480 cm−1 plus a broad band around 840 cm−1 as the v3 overlapping with the v1. The v2 mode is observed as a single band around 355 cm−1. The CO32– v1 mode is observed around 1035 and 1088 cm−1, although this assignment is difficult because of the in-plane OH bending vibrations at similar frequencies. Two v4 modes are assigned to the 717 and 755 cm−1 bands. The v3 mode is present as three bands at 1431, 1463, and 1498 cm−1. A large split caused by bridging carbonates may explain the band at 1370 cm−1. The H2O bending region shows two bands at 1635 and 1667 cm−1 together with stretching modes around 3204 and 3303 cm−1, the first associated with adsorbed H2O, while the second indicates more strongly bonded H2O. Three bands around 3534, 3438, and 3379 cm−1 are assigned to OH stretching modes of the OH groups in the crystal structure. The 202, 262, 301, 524, and 534 cm−1 bands are assigned to Cu–OH bending and stretching modes, whereas the bands around 179, 202, and 217 cm−1 are ascribed to O–(Ca, Cu)–O(H) with the O(H) at much greater distance from the cation. The bands around 503, 570, and 598 cm−1 are ascribed to the Cu–O stretching modes.
On-Line Monitoring of a Latex Emulsion Polymerization by Fiber-Optic FT-Raman Spectroscopy. Part I: Calibration
Authors: Bauer Corinne , Amram Bruno , Agnely Mathias , Charmot Dominique , Sawatzki Jurgen , Dupuy Nathalie , Huvenne Jean-Pierre
Published: October 2003

The on-line monitoring of a styrene/butadiene latex emulsion polymerization was completed. Our aim was to determine in real time the dry extract percentage or the amount of styrene monomer in the reactor. We constructed two partial least-squares (PLS) calibration models with mean-centered spectra over the 3500–2700 U 1800–500 cm−1 spectral range. Four factors were required to model the evolution of the dry extract, and a two-factors model calibrated the amount of free styrene. The results were very satisfactory: the dry extract was predicted with a root mean squared error of prediction (RMSEP) lower than 1% over the 2–50% dry extract range, and for the amount of styrene monomer, the RMSEP was lower than 5000 ppm over the 0–70 000 ppm range. The nonlinear effects of temperature and water reabsorption were considered, and they did not prevent PLS from giving good-quality results.
Fluorescence-Based Method Designed for Quantitative Measurement of Fuel Film Thickness during Cold-Start of Engines
Authors: Yang Jiemin , Melton Lynn A.
Published: October 2003

The liquid fuel that accumulates in the engine manifold and cylinders during cold start conditions is thought to contribute significantly to excess hydrocarbon emissions. Two fluorescent dopants, cyclohexanone and 2-methyl-cyclopentanone, have been tested for use as fluorescent markers for quantitative two-dimensional (2D) imaging of the thickness of automotive fuel films in the range 0–1 mm. These dopants are co-evaporative with synthetic automotive fuel and have fluorescence that is virtually independent of oxygen concentration equivalent to saturation under 5 atm air at temperatures of 20–200 °C. Selection, calibration procedures, and (nonengine) demonstration laser-induced-fluorescence (LIF) imaging experiments are discussed.
Spark-Induced Breakdown Spectroscopy: A New Technique for Monitoring Heavy Metals
Authors: Hunter A. J. R. , Davis S. J. , Piper L. G. , Holtzclaw K. W. , Fraser M. E.
Published: October 2003

This paper presents the development and testing of a new real-time monitoring technique for heavy metal aerosols and particulates in air based on spark-induced breakdown spectroscopy (SIBS). The technique is based on temporally resolved atomic emission resulting from excitation of the aerosol-laden air sample in a high-energy electrically generated spark. A complete prototype monitor comprised of spark power supply, sample chamber, bandpass-filtered radiometric detector, and computer for real-time data acquisition and display has been assembled, calibrated, and tested. The lower limits of detection for lead and chromium are 10 μg/m3. The monitor has been successfully applied as a continuous emissions monitor for lead and chromium in a simulated combustion flue gas at a joint EPA/DOE test, for fugitive chromium emissions above a hard chrome plating tank, and for airborne particulate lead at an indoor firing range. The monitor has also demonstrated the capability to detect cadmium, mercury, selenium, antimony, arsenic, uranium, and thorium.
Characterization of Visible Spectral Intensity Variations of Wholesome and Unwholesome Chicken Meats with Two-Dimensional Correlation Spectroscopy
Authors: Liu Yongliang , Chen Yud-Ren , Ozaki Yukihiro
Published: October 2003

Generalized two-dimensional (2D) correlation analysis of visible spectra (400–700 nm) was performed to characterize the spectral intensity variations of wholesome and five different classes of unwholesome chicken meats. The meats were obtained from the chicken carcasses that were judged to be wholesome or condemned by a Food Safety and Inspection Service (FSIS) veterinarian at a poultry processing plant. The unwholesome carcasses were condemned either because they were improperly bled (cadaver) or showed a disease symptom such as air-sacculitis, ascites, septicemia, or tumors. The results showed that there are at least three prominent bands around 445, 485, and 560 nm that could be attributed to deoxymyoglobin, metmyoglobin, and oxymyoglobin absorption, respectively. The results also demonstrated that deoxymyoglobin, metmyoglobin, and oxymyoglobin components coexist in all meats. There is, however, a clear indication that there were more variations in oxymyoglobin and deoxymyoglobin and less variations in metmyoglobin in the wholesome and cadaver meats than in the diseased meats. The asynchronous spectral analysis of the wholesome and unwholesome meats revealed that the spectral intensity change at the 485 nm band occurs later than those of the 445 and 560 nm bands. It indicates that metmyoglobin, the degraded species of both the deoxymyoglobin and oxymyoglobin, mainly existed in the diseased meats.
Comparison of Multivariate Calibration Techniques Applied to Experimental NIR Data Sets
Authors: Centner Vítézslav , Verdú-Andrés Jorge , Walczak Beata , Jouan-Rimbaud Delphine , Despagne Frédéric , Pasti Luisa , Poppi Ronei , Massart Désiré-Luc , de Noord Onno E.
Published: October 2003

The present study compares the performance of different multivariate calibration techniques applied to four near-infrared data sets when test samples are well within the calibration domain. Three types of problems are discussed: the nonlinear calibration, the calibration using heterogeneous data sets, and the calibration in the presence of irrelevant information in the set of predictors. Recommendations are derived from the comparison, which should help to guide a nonchemometrician through the selection of an appropriate calibration method for a particular type of calibration data. A flexible methodology is proposed to allow selection of an appropriate calibration technique for a given calibration problem.
Linearity of Near-Infrared Spectra of Alkanes
Authors: Mullins Oliver C. , Joshi Nikhil B. , Groenzin Henning , Daigle Tim , Crowell Chris , Joseph M. T. , Jamaluddin Abul
Published: October 2003

Near-infrared (NIR) spectroscopy is used to monitor a large variety of process flow streams. Hydrocarbons with their strong and resolvable NIR spectral signatures are good candidate analytes. NIR has been exploited to monitor many chemical properties for optimal hydrocarbon utilization particularly for well-characterized flow streams of small variability for end users. The utility of NIR in the context of the production of hydrocarbon resources necessitates application over a much broader range of flow stream conditions. Here we examine the spectral impact of variable temperature, pressure, and composition to determine the robustness of NIR methods in upstream applications.
Advanced Analysis, Processing, and Visualization Algorithms for Multiparameter Spectroscopic Data
Authors: Morháč Miroslav , Kliman Ján , Matoušek Vladislav , Veselský Martin , Turzo Ivan
Published: October 2003

In this paper the efficient algorithms to analyze multiparameter γ-ray spectra are presented. They allow one to search for peaks, to separate peaks from background, and to improve resolution in 1-, 2-, and 3-parameter γ-ray spectra. The algorithms presented are implemented in a package for nuclear data acquisition, processing, and visualization.
s- and p-Polarized Infrared Specular Reflectance of Vitreous Silica at Oblique Incidences: Detection of LO Modes
Authors: Trasferetti B. C. , Davanzo C. U.
Published: October 2003

Infrared (IR) specular reflectance spectra of a semi-infinite sample of vitreous silica (v-SiO2) were obtained with the use of both s- and p-polarized light and oblique incidence angles. The optical constants of the material and hence its longitudinal optic/transverse optic (LO-TO) functions were determined through the Kramers–Krönig analysis (KKA) of its s-polarized 20° off-normal reflectance spectrum. p-Polarized spectra had their reflection maxima blue-shifting as the incidence angle increased, while they remained unchanged for the s-polarized spectra. Since an LO mode generally lies at wavenumbers higher than its respective TO mode, such a blue shift may be due to the detection of the LO mode in addition to the TO mode as incidence angle increased. The only exception to this observation was the high-frequency shoulder, which underwent a sharp intensification as the incidence increased. The present work shows that it is indeed brought about by the weakly IR active asymmetrical mode (AS2) but only because it takes place immediately after the intense AS1 mode, which causes the refraction index spectrum to have a broad dip below unity. Such a dip is proven to be responsible for the sharp increase in the high-frequency shoulder of the reflectance spectra.
Resolution Enhancement of Composite Spectra with Fractal Noise in Derivative Spectrometry
Authors: Kharintsev S. S. , Kamalova D. I. , Salakhov M. Kh.
Published: October 2003

The problem of improving the resolution of composite spectra with statistically self-similar (fractal) noise is considered within the framework of derivative spectrometry. An algorithm of the numerical differentiation of an arbitrary (including fractional) order of spectra is produced by the statistical regularization method taking into account a priori information on statistical properties of the fractal noise. Fractal noise is analyzed in terms of the statistical Hurst method. The efficiency and expedience of this algorithm are exemplified by treating simulated and experimental IR spectra.
Microchip Lasers as a Compact Excitation Source for Raman Spectroscopy
Authors: Schulte Alfons , Fredricksen Chris , Buchter Scott , Mizell Greg
Published: October 2003

The application of a new microchip laser source for Raman spectral measurements is demonstrated. The performance of the device is evaluated and illustrated by Raman spectra of diamond thin films and a solid-state laser host material.
Univariate and Multivariate Calibration for the Quantitative Determination of Methyl-Parathion in Pesticide Formulations by FT-Raman Spectroscopy
Authors: Skoulika Stavroula G. , Georgiou Constantinos A.
Published: October 2003

A Fourier transform (FT)-Raman method for the quantitative determination of methyl-parathion in pesticide formulations is described. The proposed method was applied to the analysis of formulations of methyl-parathion. Univariate and multivariate calibration were used and compared for quantitative analysis. Bands observed at 634, 661, 1113, 1348, and 1527 cm−1 were used for univariate calibration. Calibration curves were linear (correlation coefficients: 0.996–0.998 and 0.994–0.999 for band intensity and band area measurements, respectively) in the concentration range of 0.6–3.75 M for the 634, 661, and 1527 cm−1 bands; 0.05–3.75 M for the 1113 cm−1 band; and 0.1–3.75 M for the 1348 cm−1 band. Precision ranged from 0.5 to 5.2% and 0.1 to 6.8% relative standard deviation (RSD) ( n = 4) for band intensity and band area measurements, respectively. Spectra normalization against the 802 cm−1 cyclohexane band improved the long-term stability of calibration, allowing the use of calibration data acquired 30 days prior to analysis. The application of the method was extended through multivariate calibration by multiple linear regression using the 858 and 2952 cm−1 bands. Results obtained compare well with those obtained by the high-performance liquid chromatography (HPLC) reference method. The FT-Raman method developed is rapid, simple, and safe, as toxic samples are analyzed “as received” without sample pretreatment.
Surface-Enhanced Raman Scattering from Substrates with Conducting or Insulator Overlayers: Electromagnetic Model Predictions and Comparisons with Experiment
Authors: Wasileski Sally A. , Zou Shouzhong , Weaver Michael J.
Published: October 2003

Model electromagnetic (EM) calculations are presented of the surface-enhanced Raman scattering (SERS) intensities expected for gold and silver particles coated with conducting as well as insulating dielectric films, with the objective of assessing their thickness-dependent properties and hence the anticipated scope of such “overlayer SERS” tactics to chemically diverse interfacial materials. Most calculations refer to Raman enhancements at the film outer edge, relevant to species adsorbed on the overlayer. Spheroidal and spherical metal particles are treated by using the electrostatic approximation, with a first-order electrodynamic correction for “radiation damping”, in vacuum and aqueous environments. The presence of simple insulating dielectric (such as organic) overlayers yields progressive decays in the calculated Raman enhancement factor, G, at the film edge with increasing thickness, d, throughout the visible optical region of experimental significance, even though the largest G values are necessarily obtained close to the plasmon resonance energy. These G–d dependencies are markedly milder than predicted for bare metal particles in water or vacuum, suggesting the potential broad-based analytical utility of nanoscale (∼ 1–10 nm thick) molecular dielectric overlayers in SERS. Furthermore, Raman enhancements increasing with film thicknesses are typically obtained at locations close to the inner film edge, relevant to moieties imbedded in dielectric overlayers. Sharper G–d decays are predicted at the film edge of transition-metal overlayers, especially near the plasmon resonance; unlike dielectric insulators, the metal overlayers progressively “quench” the optical frequency-dependent enhancement at the film edge arising from substrate plasmon resonance. Reasonable agreement is obtained in comparison with the Raman intensity-thickness dependence measured for chemisorbed carbon monoxide on rhodium films electrodeposited onto gold. The model calculations can also account qualitatively for the nonmonotonic Raman intensity-thickness dependencies observed for phonon bands from semiconducting (cadmium chalcogenide) overlayers on gold, attributed to film-induced redshifts in the substrate plasmon resonance. More general implications for the analytical utility of “overlayer SERS” tactics are also pointed out.
Mapping Lipid Oxidation in Chicken Meat by Multispectral Imaging of Autofluorescence
Authors: Wold J. P. , Kvaal K.
Published: October 2003

Multispectral imaging of autofluorescence was carried out to investigate the feasibility of mapping the degree of lipid oxidation in ground chicken meat. Meat samples from both breast and thighs were collected from 32 chickens, ground and freeze-stored for different time intervals. Sixteen samples were imaged at the time, making up two sets of multispectral images, A and B. Lipid oxidation was measured by a method using 2-thiobarbituric acid reactive substances (TBARS), and samples were in the range 0.15–3.23. Principal component analysis was performed on image set A, and variation in score images of the two first components corresponded well with lipid oxidation reference values. The multivariate image regression model based on image set A was tested on set B. Pixel-wise prediction gave large individual errors, but averaging predicted values within samples improved accuracy and resulted in a correlation of 0.98. Increasing the amount of spatial variation (number of pixel vectors) in the regression models led to more robust models with lower prediction errors. The technique has potential for nondestructive investigation of distribution and kinetics of lipid oxidation in food.
Time-Resolved Laser-Excited Shpol'skii Spectrometry with a Fiber-Optic Probe and ICCD Camera
Authors: Bystol Adam J. , Campiglia Andres D. , Gillispie Gregory D.
Published: October 2003

Improved methodology for chemical analysis via laser-excited Shpol'skii spectrometry is reported. The complications of traditional methodology for measurements at liquid nitrogen temperature are avoided by freezing the distal end of a bifurcated fiber-optic probe directly into the sample matrix. Emission wavelength-time matrices were rapidly collected by automatically incrementing the gate delay of an intensified charge-coupled device (ICCD) camera relative to the laser excitation pulse. The excitation source is a compact frequency-doubled tunable dye laser whose bandwidth (<0.03 nm) is well matched for Shpol'skii spectroscopy. Data reproducibility for quantitative analysis purposes and analytical figures of merit are demonstrated for several polycyclic aromatic hydrocarbons at 77 K. Although not attempted in this study, time-resolved excitation-emission matrices could easily be collected with this instrumental system.
Modeling and Measuring the Effect of Refraction on the Depth Resolution of Confocal Raman Microscopy
Authors: Everall Neil J.
Published: October 2003

A simple ray-tracing analysis has been used to predict the effect of refraction at the sample/air interface, on the depth resolution of confocal Raman microscopy. This analysis applies to the “z-scanning”, or “optical sectioning”, approach to obtaining depth profiles, where the laser beam is incident normal to the sample surface, and spectra are recorded sequentially as the focus is moved deeper into the material. It is shown that when a “dry” metallurgical objective (the most common configuration for commercial Raman microscopes) is used, both the position and the depth of focus increase dramatically as the beam is focused deeper into the sample. It quickly becomes impossible to obtain “pure” spectra of thin layers that are buried more than a few micrometers below the air interface. Equations are presented which model the intensity response expected when focusing through a coating into a substrate. The model requires knowledge of the sample refractive index, the numerical aperture, and the laser beam intensity distribution at the limiting aperture, of the objective. Given these values, one can predict the substrate Raman intensity as a function of the nominal focal point within the sample. For a 36 μm coating on a thick substrate, we predict that even for a perfectly sharp interface (<<1 μm), substrate bands rise slowly (over an apparent distance of 10 μm or more), and are strong when the focus is apparently only ∼ 18 μm below the air/coating interface. This prediction was confirmed through experimental observation. The model was also used to analyze literature data that had been interpreted previously as showing interfacial diffusion in polymer laminates. The model correctly reproduced the main features of the observed data without invoking interfacial penetration—the optical aberrations alone accounted for almost all the observed broadening and the fact that the apparent thickness of the buried layer is also distorted. It was concluded that, with the use of this illumination geometry, it is very difficult to detect or quantify interfacial broadening unless it occurs on a very large scale indeed (tens of micrometers). It is concluded that ‘optical sectioning’ cannot be recommended for quantitative depth profiling at significant depths using metallurgical objectives. The optimum practical solution is to cut a cross section and map laterally across the sample, thereby utilizing and maintaining the excellent (lateral) resolution of the Raman microprobe. An alternative solution is to use an immersion objective to minimize refraction at the sample surface.
Method to Determine Chemical Composition Distribution on Matte Coating Surfaces Using Raman Microscopy
Authors: Han Hank Z. Y. , Lee S. S. , Månson J.-A. E. , Hilborn Jons G.
Published: October 2003

A method to obtain quantitative information about the chemical composition spatial distribution on rough ( Ra between half a micrometer and tens of micrometers) surfaces is developed by using a Raman microscopy technique. It is tested on a wrinkled polyester-urethane-acrylate powder coating surfaces with pronounced star-patterned (mountains and valleys) structures. Raman spectra at different features on the surface are analyzed quantitatively by using a least-squares fitting method based on coating components' spectra, taking into account chemical reactions which occurred during cure. This method is able to extract the same information as qualitative analysis could from component Raman peaks when large composition heterogeneity occurs. In addition, it provides more subtle information when chemical composition distribution is less marked. This feature is particularly useful for establishing the cause of sophisticated surface structures. The origin of the surface structures is attributed to spinodal decomposition frozen by chemical reactions during cure.
Caries Detection by Diode Laser Raman Spectroscopy
Authors: Hill Wieland , Petrou Verena
Published: October 2003

Carious lesions can be distinguished from sound hard tooth tissues because their near-infrared Raman spectra exhibit an increased luminescence. A comparison of the ratio between luminescence and Raman band intensities for diseased and healthy areas of the tooth gives a measure for the stage of the disease. Intraoral analyses can be made in a reasonable time with the use of a diode laser, a fiber-optic Raman probe, and a compact spectrograph without moving optics. An excitation wavelength of 785 nm gives sufficient contrast between sound and carious tissue and allows a sensitive detection of the weak Raman scattering by silicon detectors.
Determination of Two-Dimensional Correlation Spectra Using the Hilbert Transform
Authors: Noda I.
Published: October 2003

A computationally efficient numerical procedure to generate two-dimensional (2D) correlation spectra from a set of spectral data collected at certain discrete intervals of an external physical variable, such as time, temperature, pressure, etc., is proposed. The method is based on the use of a discrete Hilbert transform algorithm which carries out the time-domain orthogonal transformation of dynamic spectra. The direct computation of a discrete Hilbert transform provides a definite computational advantage over the more traditional fast Fourier transform route, as long as the total number of discrete spectral data traces does not significantly exceed 40. Furthermore, the mathematical equivalence between the Hilbert transform approach and the original formal definition based on the Fourier transform offers an additional useful insight into the true nature of the asynchronous 2D spectrum, which may be regarded as a time-domain cross-correlation function between orthogonally transformed dynamic spectral intensity variations.
Mid-Infrared Spectroscopic Determination of Sugar Contents in Plant-Cell Culture Media Using an ATR Method
Authors: Hashimoto Atsushi , Kameoka Takaharu
Published: October 2003

A simple, rapid, and accurate method for determining sugar contents in plant-cell culture media by mid-infrared (MIR) spectroscopy was developed by using a Fourier transform infrared (FT-IR) spectrometer equipped with an attenuated total reflectance (ATR) accessory. We examined the potential of this method by comparison with a high-performance liquid chromatography (HPLC) method and applied it to the determination of sugar consumption by plant cells. The cultivation was carried out with Nicotiana tabacum cv. Bright Yellow No. 2 cells. We determined that MIR spectroscopy is at least as useful as the HPLC method for the sugar content determination in the culture medium and may be available to monitor the overall cell metabolisms. This study represents an important step in the development of nonintensive on-line monitoring devices for bioreactors and of simple, rapid, and accurate analysis of the cellular metabolism through the composition changes in media.
Thermal Decomposition of Energetic Materials 75. T-Jump/Raman Spectroscopy and its Application to High-Nitrogen Compounds
Authors: Roos B. D. , Brill T. B.
Published: October 2003

Flash pyrolysis of energetic compounds that are unusually rich in nitrogen can be expected to liberate a large amount of N2 among other products. In addition H2 and O2 can be pyrolysis products from other types of energetic compounds. While many kinetics and mechanistic details have been learned from T-jump/FT-IR (Fourier transform infrared) spectroscopy, the development of the complementary method of T-jump/Raman spectroscopy described herein helps to complete the elemental atom balance of the gaseous products. Differential Raman scattering cross sections were determined for many of the common gases resulting from pyrolysis of energetic compounds. The spontaneous Raman scattering by the products of hydrazinium [3-nitro-4-nitraminofurazan], poly(bis(3,3′-azidomethyl)-oxetane), poly(glycidyl azide) as the mono-ol derivative, and 5-nitriminotetrazole were determined. Provided that at least one of the quantified species is common to both the IR and Raman spectra, the Raman-based data can be combined with the IR data to give a properly balanced gasification reaction.
Determination of Organic Contaminants in Aqueous Samples by Near-Infrared Spectroscopy
Authors: Ding Qing , Boyd Brian L. , Small Gary W.
Published: October 2003

The feasibility of determining low levels of organic solvents in water by near-infrared (near-IR) spectroscopy is investigated. Mixture samples of tributyl phosphate (TBP) and methyl iso-butyl ketone (MIBK) are determined in aqueous solutions over the concentration range of 1–160 ppm. Through the use of C–H combination bands in the region of 5000–4000 cm−1, sufficient selectivity is obtained to determine each compound in the presence of the other. Separate multivariate calibration models are computed for each compound by use of a combination of bandpass Fourier digital filtering and partial least-squares (PLS) regression with both analysis of absorbance and single-beam spectra. A genetic algorithm is used to implement a joint optimization of the parameters governing the filtering and PLS calculations. Through the use of this procedure, a calibration model based on absorbance spectra is computed for MIBK with a standard error of prediction (SEP) of 3.82 ppm over the 1–160 ppm range. This five-term model utilizes the spectral range of 4495–4335 cm−1. A similar nine-term model based on absorbance spectra is computed for TBP over the 4620–4320 cm−1 range. For the range of 1–100 ppm, an SEP of 4.84 ppm is achieved. The results obtained from the analysis of single-beam spectra are comparable with those obtained in the analysis of absorbance data. Calibration models computed with samples prepared in natural water are also found to have a similar level of performance. These results establish the feasibility of using near-IR spectroscopy to screen water samples for solvent contamination.
Derivative Preprocessing and Optimal Corrections for Baseline Drift in Multivariate Calibration
Authors: Brown Christopher D. , Vega-Montoto Lorenzo , Wentzell Peter D.
Published: October 2003

The characteristics of baseline drift are discussed from the perspective of error covariance. From this standpoint, the operation of derivative filters as preprocessing tools for multivariate calibration is explored. It is shown that convolution of derivative filter coefficients with the error covariance matrices for the data tend to reduce the contributions of correlated error, thereby reducing the presence of drift noise. This theory is corroborated by examination of experimental error covariance matrices before and after derivative preprocessing. It is proposed that maximum likelihood principal components analysis (MLPCA) is an optimal method for countering the deleterious effects of drift noise when the characteristics of that noise are known, since MLPCA uses error covariance information to perform a maximum likelihood projection of the data. In simulation and experimental studies, the performance of MLPCR and derivative-preprocessed PCR are compared to that of PCR with multivariate calibration data showing significant levels of drift. MLPCR is found to perform as well as or better than derivative PCR (with the best-suited derivative filter characteristics), provided that reasonable estimates of the drift noise characteristics are available. Recommendations are given for the use of MLPCR with poor estimates of the error covariance information.
Investigation of the Temperature Behavior of the Bands Due to the Methylene Stretching Vibrations of Phospholipid Acyl Chains by Two-Dimensional Infrared Correlation Spectroscopy
Authors: Nabet Anne , Auger Michèle , Pézolet Michel
Published: October 2003

The temperature-induced gel-to-liquid crystalline phase transition of dipalmitoylphosphatidylcholine (DPPC) is characterized by a shift towards high frequencies and an increase of the width of the bands due to the methylene stretching vibrations. These spectral modifications are frequently used to measure the conformational order of lipid acyl chains. However, it is not clear whether these bands contain two spectral components due to trans and gauche conformers or whether they gradually shift with temperature. The temperature-induced gel-to-liquid crystalline phase transition of DPPC has been investigated in the present study by two-dimensional infrared (2D-IR) correlation spectroscopy. Our results show that each methylene stretching band in both the synchronous and the asynchronous maps is characterized by two peaks. The same pattern is also observed when the temperature range is restricted to the gel phase. These results were compared to those obtained by spectral simulations using either a single band that shifts in frequency and gets broader with the increase of temperature (shifting-band model), simulating a continuously evolving one-phase system, or a band made of two components (two-band model), simulating the trans and gauche spectral contributions of a two-phase system. The results obtained for the asynchronous maps of the simulated spectra indicate clearly that the experimental results cannot be modeled by a pure two-phase system and are best simulated by the shifting-band model.
Pressure-Dependent Changes in the Infrared C—H Vibrations of Monolayer Films at the Air/Water Interface Revealed by Two-Dimensional Infrared Correlation Spectroscopy
Authors: Elmore Douglas L. , Dluhy Richard A.
Published: October 2003

Two-dimensional infrared correlation analysis (2D-IR) was applied to a set of surface pressure-dependent unpolarized IR spectra of a monolayer film of 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) at the air/water (A/W) interface. The experimentally measured asynchronous 2D-IR spectra were compared with synthetic spectra calculated by using an “overlapped peaks” model vs. a “frequency shifting” model. The results presented here show that when the experimentally observed monolayer IR spectra are acquired as a function of surface pressure, one model cannot be used exclusively for spectral interpretation. In this study, the monolayer IR spectra were divided into a low-pressure region subset (<11 mN/m) and a high-pressure region subset (>11 mN/m). When the monolayer IR spectra acquired as a function of surface pressure are analyzed by 2D correlation methods, the results strongly support the following conclusions: (1) the low-pressure subset, which encompasses both the liquid expanded (LE) and the liquid expanded/liquid condensed (LE/LC) regions of the DPPC monolayer isotherm, is best modeled by two overlapped peaks correlated with ordered and disordered conformational states of the monolayer film; and (2) the high-pressure subset, which reflects solely the liquid condensed (LC) phase of the monolayer isotherm, is best modeled by a single peak, which undergoes a minor frequency shift, and which may be primarily correlated with gradual packing of the liquid condensed structure. This interpretation of the 2D-IR correlation spectra is in agreement with the interpretation of sub-bands seen in polarized monolayer IR spectra previously reported by our laboratory.
Oil and Fat Classification by Selected Bands of Near-Infrared Spectroscopy
Authors: Hourant Pierre , Baeten Vincent , Morales Maria T. , Meurens Marc , Aparicio Ramon
Published: October 2003

One hundred and four edible oil and fat samples from 18 different sources, either vegetable (Brazil nut, coconut, corn, sunflower, walnut, virgin olive, peanut, palm, canola, soybean, sunflower) or animal (tallow and hydrogenated fish), have been analyzed by high-performance gas chromatography (HPGC) and near-infrared spectroscopy (NIRS). Fatty acids were quantified by HPGC. The near-infrared spectral features of the most noteworthy bands were studied and discussed to design a filter-type NIR instrument. An arborescent structure, based on stepwise linear discriminant analysis (SLDA), was built to classify the samples according to their sources. Seven discriminant functions permitted a successive discrimination of saturated fats, corn, soybean, sunflower, canola, peanut, high oleic sunflower, and virgin olive oils. The discriminant functions were based on the absorbance values, between three and five, from the 1700–1800 and 2100–2400 nm regions. Chemical explanations are given in support of the selected wavelengths. The arborescent structure was then checked with a test set, and 90% of the samples were correctly classified.
Spectral Differences between Stratum Corneum and Sebaceous Molecular Components in the Mid-IR
Authors: Brancaleon Lorenzo , Bamberg Michael Paul , Kollias Nikiforos
Published: October 2003

Despite a number of studies on the composition of the lipids of stratum corneum (SC) and sebum, questions remain about the detailed molecular arrangement of the two superficial components of human skin. The investigation of the molecular components of SC in vivo is important to understand the function of what was once thought to be a “dead” epithelium. We have investigated the molecular composition of SC and sebum in vivo, in the mid-infrared, with fiber-based attenuated total reflection Fourier transform infrared spectroscopy (ATR/FT-IR). This technique combines the sensitivity of infrared spectroscopy in detecting molecular composition and conformational order with the capability of probing surfaces to a depth of less than 1 μm. ATR/FT-IR is therefore particularly useful for the investigation of interfaces such as SC and the sebaceous layers. We found that with the use of ATR/FT-IR one can distinguish between the contribution of the molecular components of sebum and SC. The presence of spectral “signatures” of the lipids of sebum allowed us to improve the interpretation of some infrared bands of sebaceous origin as well as of SC in vivo. We also found that ATR/FT-IR can be used to separate the spectral contributions of sebum and SC, and as a method to study the early recovery of superficial lipids after the removal of sebum. Following calibration, a method can be developed to quantify the relative amount of fatty acid in sebum with the use of ATR/FT-IR. We observed that the sebaceous fatty acids that reach the surface of the skin recover at a slower rate than other sebaceous lipids. Our investigation shows that fiber-based ATR/FT-IR is a promising spectroscopic approach to the study of epithelial surfaces and surface contaminants in vivo.
Study of Preprocessing Methods for the Determination of Crystalline Phases in Binary Mixtures of Drug Substances by X-ray Powder Diffraction and Multivariate Calibration
Authors: Artursson Tom , Hagman Anders , Björk Seth , Trygg Johan , Wold Svante , Jacobsson Sven P.
Published: October 2003

In this paper, various preprocessing methods were tested on data generated by X-ray powder diffraction (XRPD) in order to enhance the partial least-squares (PLS) regression modeling performance. The preprocessing methods examined were 22 different discrete wavelet transforms, Fourier transform, Savitzky–Golay, orthogonal signal correction (OSC), and combinations of wavelet transform and OSC, and Fourier transform and OSC. Root mean square error of prediction (RMSEP) of an independent test set was used to measure the performance of the various preprocessing methods. The best PLS model was obtained with a wavelet transform (Symmlet 8), which at the same time compressed the data set by a factor of 9.5. With the use of wavelet and X-ray powder diffraction, concentrations of less than 10% of one crystal from could be detected in a binary mixture. The linear range was found to be in the range 10–70% of the crystalline form of phenacetin, although semiquantitative work could be carried out down to a level of approximately 2%. Furthermore, the wavelet-pretreated models were able to handle admixtures and deliberately added noise.
Analysis of Lignite Using Laser-Induced Breakdown Spectroscopy
Authors: Wallis Fiona J. , Chadwick Bruce L. , Morrison Richard J. S.
Published: October 2003

The application of laser-induced breakdown spectroscopy (LIBS) to the chemical analysis of low-ash lignite has been investigated. A Nd: YAG laser (λ = 1064 nm) is used to induce emission from the ash-forming components, which is then spectrally resolved and analyzed. LIBS analyses of five inorganic components of lignite were shown to be reproducible between sample pellets at a 95% confidence level. Detection limits (in ppm) on an as-received basis of 60 (Ca and Al), 70 (Na), 90 (Fe), and 200 (Mg and Si) were obtained from a study of 30 lignite samples, each of which was interrogated by 300 laser pulses.
Characterization of a Pulsed Glow Discharge Laser Ablation System Using Optical Emission
Authors: Lewis Cris , Doorn Stephen K. , Wayne David M. , King Fred L. , Majidi Vahid
Published: October 2003

Investigations involving laser-based sampling of copper into an auxiliary pulsed glow discharge for ionization and excitation are presented. The interaction of the ablated copper with the auxiliary glow discharge was studied by monitoring the copper atom emission signal at 368.744 nm. Results demonstrate the ability to time ablation appropriately to access specific temporal regions of the pulsed plasma. More specifically, laser-ablated material was introduced into the glow discharge negative glow during the afterpeak. Ionization and excitation was accomplished by collisions with a metastable argon population produced by the glow discharge (Penning ionization) followed by recombination to yield excited-state Cu atoms. The work presented investigates parameters that affect the atomic emission signal intensity of the ablated material, including cathode-to-target distance, discharge gas pressure, and relative timing of discharge and ablation. Results demonstrate that decreasing the glow discharge working gas pressure increases the transport efficiency of laser-ablated material into the negative glow. These investigations are part of an ongoing series of studies on sample introduction schemes that utilize different ionization and excitation mechanisms found in pulsed glow discharge plasmas.
Orientation of Carotenoid Molecules in the Eyespot of Alga: In Situ Polarized Resonance Raman Spectroscopy
Authors: Kubo Yoshiko , Ikeda Teruki , Yang Shi-Yuan , Tsuboi Masamichi
Published: October 2003

Raman spectra of single cells of Euglena and Chlamydomonas have been examined with 514.5 nm excitation at various points within the cells. At every point, two strong bands, which are assignable to carotenoid, appeared at 1530 and 1159 cm−1. By the use of a Raman mapping system, the Raman intensity at 1530 cm−1 has been plotted against the (x,y) coordinate representing a location within the cell. It has been shown that, for both algae examined, the eyespot has a prominently high carotenoid content, and a small amount of carotenoid is uniformly distributed among the chloroplast. The spatial resolution of the mapping system has been shown to be higher than 1 μm, and the Chlamydomonas eyespot has an elongated shape of 1 μm × 2 μm. By use of a polarizer, the carotenoid chains in the Chlamydomonas eyespot have been found to be aligned along its long axis, which is parallel to the body axis.
Chemical Reactions of Single Levitated Inorganic Salt Particles with Ammonia Gas
Authors: Musick J. , Kiefer W. , Popp J.
Published: October 2003

The chemical reactions of water droplets containing dissolved salts and of solid salt particles with ammonia gas have been studied. The salts used were MgCl2*6H2O, KNO3, and MgSO4. In contrast to the irreversible formation of a solid ammonium chloride shell when MgCl2*6H2O dissolved in water droplets is used, we observed formation of solid microcrystals when using KNO3 together with ammonia, whereas no reaction was observed in the case of MgSO4. All three inorganic salts act similarly as a sink for ammonia gas, resulting in solid or dissolved NH4 components. Only the system KNO3/NH4NO3 can act as source dependent on the concentration of ammonia gas.
Spectroscopic Investigations of Polyamido Amine Starburst Dendrimers with Reichardt's ET-30 Dye
Authors: Richter-Egger Dana L. , Li Hong , Tucker Sheryl A.
Published: October 2003

The association between Reichardt's ET-30 dye and amine- and carboxylate-terminated polyamido amine (PAMAM) dendrimers was investigated and shown to be different from results reported for micelles and traditional polymers. The absorption spectra illustrated that the solvatochromic, microenvironmental polarity probe associated with PAMAM dendrimers in less polar regions with a polarity comparable to 1-decanol. Model compounds that mimic PAMAMs' surface groups and branching moieties were used to better define the associated dye's location and demonstrated that ET-30 penetrated beyond the dendrimer's surface groups, into the interfacial region. Additionally, changing sample preparation methods controlled the nature and extent of the dye/dendrimer association. Under certain experimental conditions, the dye/dendrimer complexes formed large aggregates.
Protein on Cloths: Evaluation of Analytical Techniques
Authors: Van Dalen Gerard
Published: October 2003

Textile detergency studies require methods which can follow the removal and build-up of proteins on cloths. The suitability of X-ray fluorescence spectrometry (XRF), Fourier transform infrared spectrometry (FT-IR), X-ray photoelectron spectrometry (XPS), and nitrogen analysis for these studies was investigated by analyzing blood- and hemoglobin-stained cloths. Protein was measured via nitrogen by XRF, XPS, and the nitrogen analyzer and via an amide band by FT-IR. FT-IR was used with attenuated total reflection (ATR) and with photoacoustic spectrometry (PAS) as sampling techniques. A logarithmic relationship was found between the nitrogen content analyzed on the surface (XPS, XRF, and FT-IR) and in the bulk (N-analyzer). This result can be caused by the fact that the proteins in the cloths with a low quantity of blood or hemoglobin are located more on the outer layer of the cloth. With XRF, FT-IR/PAS, and XPS a significant difference could be detected between the 1% blood- and hemoglobin-stained cloths and a blank cloth, because protein is concentrated on the outer surface of the cloth. With FT-IR/ATR the 1% level can be detected when one is measuring at three different places. The measured surface areas of XRF, FT-IR/PAS, XPS, and FT-IR/ATR are about 37, 10, 5, and 0.2 mm in diameter, respectively. XRF proved to be the most suitable technique, giving a very fast indication of the amount of nitrogen on the outer micrometer layer of the cloths with an acceptable precision [relative standard deviation (RSD) 6%]. However quantitation is difficult due to the logarithmic relationship. XPS is also a valuable technique because protein on washed cloths is located mainly on the outer nanometer layer. The nitrogen analyzer is suitable for quantitative analysis of protein in the bulk sample. However more than 1% of the original blood stain (= 0.018% N) has to be present on the washed cloths.
Solid-Matrix Luminescence of Hydroxyl Aromatic Metabolites in Urine Fractions with Whatman 1PS Paper
Authors: Smith Barry W. , Hurtubise Robert J.
Published: October 2003

Solid-matrix luminescence was investigated for human biomonitoring that employed room-temperature solid-matrix fluorescence (SMF) and phosphorescence (SMP) for the detection and identification of 1-hydroxypyrene (1-OH-PY), tetrol (I-1), and 9-hydroxy-phenanthrene (9-OH-Phen) in human urine fractions. However, SMF proved to be less sensitive than SMP. For SMP, the compounds were adsorbed on Whatman 1PS paper with thallium nitrate as a heavy-atom salt under neutral or basic conditions. The SMP limits of detection of 16 fmole for I-1 and 39 fmole for 1-OH-PY were acquired. Because 9-OH-Phen appeared to undergo some photobleaching, only estimated limits of detection could be obtained. With the spectral characteristics of the SMP excitation and emission spectra, it was possible to identify all three compounds in spiked urine fractions. For unspiked urine fractions, I-1 and 9-OH-Phen were identified, but 1-OH-PY was not identified because of interference from the SMP of other components.
Enhanced Chemical Classification of Raman Images in the Presence of Strong Fluorescence Interference
Authors: Zhang Dongmao , Ben-Amotz Dor
Published: October 2003

Raman spectra and spectral images containing severe fluorescence interference are analyzed by using a variety of correlation and classification algorithms, both before and after preprocessing with the use of the Savitzky-Golay second-derivative (SGSD) method (and other related methods). Spectral correlation coefficient, principal component, and minimum Euclidean distance analyses demonstrate superior suppression of background and noise interference in Raman spectra when using SGSD preprocessing. The tested spectra include fluorescence interference that is more intense than the Raman features of interest and also contains broad background peaks that vary in shape and intensity from sample to sample. The high chemical information content of the SGSD-processed Raman spectra is demonstrated by using quantitative comparisons of correlation coefficients in a series of synthetic Raman spectra with either different or identical large backgrounds. The practical utility of SGSD in chemical image classification is illustrated by using an experimental Raman image of sugar microcrystals on substrates with large interfering background signals. The functional equivalence of SGSD and other windowed preprocessing algorithms is discussed.