bluuebunny/crossref_metadata_2025 huggingface dataset:
Aminopeptidase Profiling Using a Time-Resolved, 96-Well Plate Filter Fluorimeter
Authors: Mossman D. M. , Lytle F. E. , Huber D. M.
Published: October 2003

A novel fluorimeter has been developed that combines the selectivity of time-resolved detection and the sample throughput of a 96-well plate reader. With improved background rejection via temporal resolution, a reduction in the limit of detection by a factor of 600 was attained over that of a commercially available 96-well plate fluorimeter. The excellent limit of detection was utilized to differentiate two closely related species of Pseudomonas, P. fluorescens and P. aureofaciens, at a bacterial concentration of 500,000 cells per well with only 15 min of incubation. High sample throughput was demonstrated by incubation of six bacteria samples and data collection in an amino acid 12-nutrient profile within 30 min.
Potential for an Atmospheric-Pressure Low-Power Microwave-Induced Plasma Ionization Source for Mass Spectrometry
Authors: Vela Nohora P. , Caruso Joseph A. , Satzger R. Duane
Published: October 2003

The potential for using the microwave-induced plasma (MIP) as an ionization source is further explored. This source operates at atmospheric pressure, minimizing pumping problems and, through power and gas-flow adjustment, offers the possibility of selecting from elemental spectra to fragmentation spectra resembling those from electron impact sources. The effect of microwave power, carrier gas-flow rate, and injector-prob e configuration in the production of fragment ions is demonstrated with the use of perfluorotributylamine and tetramethyltin. Initial potential for liquid-sample introduction to the MIP is accomplished by using a direct-injection nebulizer (DIN) at higher reproducibility levels than in earlier studies.
Quantitative Analysis of Peptides with NMR Spectroscopy
Authors: Larive Cynthia K. , Jayawickrama Dimuthu , Orfi Laszlo
Published: October 2003

The determination of peptide concentration with 1H nuclear magnetic resonance (NMR) spectroscopy using an internal standard or an external standard in a sealed glass capillary was investigated for three tyrosine-containing tripeptides. Trimethylsilylpropionic acid (TSP) and maleic acid were tested as external standards for quantitation by proton NMR. Although comparable results were obtained for either standard, the performance of maleic acid was found to be superior because of its better long-term stability in the sealed capillary. Loss of TSP from solution occurred over time due to adsorption onto the walls of the capillary, necessitating frequent recalibration against the primary standard, potassium acid phthalate (KHP). The peptide contents of solid peptides determined with 1H NMR are compared with those obtained from ultraviolet (UV) absorbance measurements of the tyrosine chromophore. The versatility of NMR for the quantitative analysis of peptides that do not contain an appropriate UV chromophore make it well-suited for the determination of peptide concentration in aggregation studies or for the preparation of solutions for high-throughput screening of biological activity.
Waveguide Capillary Cell for Low-Refractive-Index Liquids
Authors: Altkorn Robert , Koev Ilia , Gottlieb Amos
Published: October 2003

We describe a waveguide capillary cell based on a fused-silica tube coated externally with a thin layer of a low-refractive-index ( n = 1.31) fluoropolymer. When filled with a transparent liquid of refractive index greater than that of the fluoropolymer, the cell is capable of transmitting light through total internal reflection. Loss below 1 dB/m is demonstrated throughout much of the visible region for a 530-μm-i.d., 660-μm-o.d. cell filled with water.
Variable Selection in Multivariate Calibration of a Spectroscopic Glucose Sensor
Authors: McShane Michael J. , Coté Gerard L. , Spiegelman Clifford
Published: October 2003

A variable selection method that reduces prediction bias in partial least-squares regression models was developed and applied to near-infrared absorbance spectra of glucose in pH buffer and cell culture medium. Comparisons between calibration and prediction capability for full spectra and reduced sets were completed. Variable selection resulted in statistically equivalent errors while reducing the number of wavelengths needed to fit the calibration data and predict concentrations from new spectra. Fewer than 25 wavelengths were selected to produce errors statistically equivalent to those yielded by the full set containing over 500 wavelengths. The algorithm correctly chose the glucose absorption peak areas as the information-carrying spectral regions.
Studying the Curing Kinetics of a Diacrylate by Using Infrared Spectroscopy
Authors: Wall Bentley G. , Koenig Jack L.
Published: October 2003

Fourier transform infrared (FT-IR) spectroscopy was used to study the photopolymerization of 4,4'-bis(acryloyl)biphenyl (BAB), dispersed in the liquid crystal (E7). The infrared absorbance of the carbon–carbon double bond of the acrylate group was monitored to follow the course of the polymerization and to determine the extent of cure. It was also observed that a major change in the character of the infrared absorbance band shape and position of the acrylate carbonyl group accompanied the reduction of the carbon–carbon double-bond absorbance. Curing was found to be rapid, on the order of minutes. It was found that the reaction did not proceed appreciably after a brief initial exposure to ultraviolet (UV) radiation. This result implies that this type of system may be time-stable with programmable degrees of cure. It was also discovered that single continuous doses of UV exposure produced a higher degree of cure than equivalent UV exposure times administered in multiple shorter doses. This observation indicates the existence of a relatively long induction period in this system. The long induction period may be caused by a UV screening effect due to the other components of this system.
New Technique Allowing FT-Raman Measurements of Rotating Samples
Authors: Salzer R. , Roland U. , Born R. , Sawatzki J.
Published: October 2003

Sample rotation combined with Fourier transform (FT)-Raman spectroscopy usually results in spectra severely distorted by a double modulation of the scattered light emitted by the substance under study. In the case of accurately aligned solid samples, the disturbance modulation is mainly due to an optical inhomogeneity of the surface, e.g., a certain surface roughness. The application of the step-scan technique permits the laterally resolved investigation of rotating samples when the movement of the interferometer mirror of the FT-Raman spectrometer is synchronized to the rotation of the sample. Routine FT near-infrared (NIR) Raman spectroscopic measurements of thermally sensitive and inhomogeneous solid samples that require the application of a spinning-sample arrangement become possible. Moreover, information about the angular dependence of the physical and chemical surface composition of the solid samples, i.e., a lateral resolution, can be obtained.
Characterization of Metal Ion Binding Sites on Datura Innoxia by Using Lanthanide Ion Probe Spectroscopy
Authors: Drake Lawrence R. , Hensman Carl E. , Lin Shan , Rayson Gary D. , Jackson Paul J.
Published: October 2003

The excitation spectra associated with the 7F0↦5D0 transition of Eu+3 has been used to examine the binding sites on cell wall fragments of Datura innoxia. Both native and esterified cell wall fragments were each examined at pH 5 and pH 2 to determine the contributions to metal ion sorption from both the carboxylate and sulfonate functional groups. The excitation spectra have been de-convoluted into the individual groups responsible for metal ion uptake. At least four unique binding sites can be described as being responsible for metal ion uptake. The higher affinity sites involve carboxylates in the binding of Eu+3 in a tridentate (3:1 ligand-to-metal ratio) configuration.
New Optical Depth-Profiling Technique by Use of the Multiple-Frequency Approach with Single ATR FT-IR Spectrum: Theoretical Development
Authors: Ekgasit Sanong , Ishida Hatsuo
Published: October 2003

A new depth-profiling technique by attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy by using the multiple-frequency approach has been developed. The technique utilizes spectral intensities at various frequencies of a single spectrum for the depth-profiling calculation. Any spectrum at an incident angle greater than the critical angle with an incident beam of known degree of polarization may be used. A multiple-reflection attachment can be used to obtain a spectrum with a high signal-to-noise (S/N) ratio and to perform real-time depth-profiling analysis. Neither an estimated profile nor any information about the profile is required for the calculation. The new technique consists of three calculation steps, including estimation of the volume-fraction profile by linear equations of absorptance, linear least-squares fitting of absorptance, and nonlinear fitting of reflectance. Simulated spectra with added white noise are used to verify the applicability of the newly developed technique. The accuracy and spatial resolution of the technique have been verified by various types of profiles and degrees of polarization.
FT-Raman Spectroscopy of Wood: Identifying Contributions of Lignin and Carbohydrate Polymers in the Spectrum of Black Spruce (Picea Mariana)
Authors: Agarwal Umesh P. , Ralph Sally A.
Published: October 2003

Good-quality Raman spectra of most wood species can now be obtained by using near-infrared Fourier transform Raman spectroscopy. To make effective use of such spectroscopic information, one needs to interpret the data in terms of contributions from various wood components and, for each component polymer, in terms of vibrational modes of its substructural units/groups. In the present work, Raman spectral features of black spruce (Picea mariana) wood were associated with lignin and/or carbohydrate polymers. Lignin's spectral contributions were recognized in several ways. In addition to spectra of milled-wood and enzyme lignins, a spectrum of native lignin was obtained by subtracting the spectrum of acid chlorite delignified black spruce from the spectrum of an untreated wood sample. A comparison of lignin spectra indicated that the Raman features of the three lignins are very similar. Raman contributions of carbohydrate polymers, namely, those of cellulose and hemicellulose, were identified by using authentic and/or isolated samples and, in the case of cellulose, by using previously published spectra. Such an analysis showed that the hemicellulose present in black spruce did not give rise to any new, unique features that were not already present due to cellulose. Therefore, it was concluded that the hemicellulose contribution is broad and is hidden under the Raman contribution of cellulose. Also, peak positions of lignin contributions did not overlap with those of cellulose, and there were spectral regions where either lignin or cellulose contributed.
Hydrogen Sulfide Detection by UV-Assisted Infrared Spectrometry
Authors: Larsen Elisabeth S. , Hong William W. , Spartz Martin L.
Published: October 2003

Ultraviolet (UV)-assisted infrared (IR) spectroscopy has been evaluated for its potential usage and feasibility to indirectly detect hydrogen sulfide gas. Hydrogen sulfide (H2S) is a weakly IR-absorbing compound, and its detection by IR methods is further complicated by severe water interferences. However, H2S can readily be converted to sulfur dioxide (SO2), a strong IR absorber, via ultraviolet irradiation. A multipass IR White cell equipped with an internal mercury germicidal UV lamp has been interfaced to a Bomem MB series Fourier transform infrared (FT-IR) spectrometer. The conversion of hydrogen sulfide to sulfur dioxide (SO2) was tested in five matrices: nitrogen, ambient air, moisturized ambient air, dried ambient air, and zero-grade air. The conversion efficiency of H2S to SO2 in nitrogen, containing a negligible amount of oxygen, was approximately 25% and peaked at approximately 6 min of UV irradiation. In ambient air, the conversion efficiency was calculated to be ∼45% and peaked at 35 s of irradiation, while in the dried ambient air the SO2 concentration peaked in 85 s. In ambient air, the generated SO2 was destroyed during its production and was below detection within 90 s of irradiation. In the dried ambient air, the generated SO2 was still detectable at 120 s of irradiation. Moisturized ambient air was investigated to determine the degree of SO2 loss due to reaction with H2O. From these data, it appears that the water molecule and SO2 photolysis contribute only slightly to the SO2 loss. The greatest loss is apparently caused by reactive radicals such as ·OH generated during UV irradiation. Index Headings: FT-IR; UV photolysis; Vapor phase; H2S; SO2; Environmental analysis.
Low-Frequency Raman Spectra Using Synchronously Scanned Optical Parametric Oscillator CARS
Authors: Chen Peter C. , Pinnix Michon
Published: October 2003

Synchronously scanned optical parametric oscillator (OPO) coherent anti-Stokes Raman spectroscopy (CARS) is a new technique that can be used with single-wavelength detection in order to reject background stray light and eliminate spectral interference. In this paper, results are presented illustrating the use of this method to also reject stray light from Rayleigh scattering without attenuation of the Raman signal, resulting in the ability to probe low-frequency Raman levels.
Highly Sensitive Biochemical Analysis Using Low-Temperature Infrared Spectroscopy Measurements
Authors: Fujii Toshiko , Miyahara Yuji , Watanabe Yoshio
Published: October 2003

A sensitive infrared spectroscopic analysis of biochemical components in an aqueous solution is described. The infrared spectrum of an aqueous solution containing glucose, urea, and creatinine was measured at −4.7 °C by Fourier transform infrared spectroscopy (FT-IR) with an attenuated total reflection (ATR) crystal. The infrared absorption bands of these components increased by about 100 times at −4.7 °C as compared with those measured at 22 °C. This increase in the infrared absorption bands was found to occur because of segregation of the components toward the surface of the ATR crystal caused by solidification of the sample solution. The creatinine concentration in an aqueous solution, prepared in the physiological range of human blood, was also estimated at −4.7 and 22 °C by using the partial least-squares (PLS) method. The correlation coefficient between the predicted concentrations by PLS and the prepared concentrations was 0.95 at −4.7 °C, but was 0.07 at 22 °C. Thus, the precision of the determination of creatinine was remarkably improved by using the low-temperature measurement. Index Headings: Biochemical analysis; Low-temperature infrared spectroscopy; Solidification.
Generalized Two-Dimensional Fourier Transform Infrared Photoacoustic Spectral Depth-Profiling Analysis
Authors: Jiang Eric Y. , McCarthy William J. , Drapcho David L. , Crocombe Richard A.
Published: October 2003

This paper reports the first application of a generalized two-dimensional (G2D) correlation method in photoacoustic spectral depth-profiling analysis of laminate/heterogeneous samples. In this method, photoacoustic magnitude spectra at different modulation frequencies are used to generate two-dimensional (2D) correlation spectra. The relative spatial origins of correlated signals are then determined from the signs of the corresponding contours. The unique features and advantages of this technique over previously reported depth-profiling methods are demonstrated and discussed. These include simplification of step-scan photoacoustic phase-modulation experiments as well as 2D correlation-analysis rules, avoidance of phase-related negative-band ambiguities, and enhancement of both spectral and depth resolutions, etc. The recently developed software-based digital signal-processing (DSP) technique for step-scan photoacoustic measurements offers an efficient means (sampling-depth multiplexing advantage) to collect within a single scan all necessary data for this type of 2D correlation analysis. Index Headings: Photoacoustic; PAS; Two-dimensional; Step-scan; FT-IR; Depth profiling; Polymer films; DSP.
Spectroscopic Sensing with a Highly Transparent, Ion-Exchangeable Polymer Blend
Authors: Gao Letian , Seliskar Carl J. , Milstein Lisa
Published: October 2003

A polymer blend formulation originally patented by the National Aeronaticautical and Space Administration (NASA) has been modified for use in spectroscopic sensing. The cured polymer blend is a mixture of poly(acrylic acid) in glutaraldehyde cross-linked poly(vinyl alcohol). We have optimized the composition and the casting of the blend for optical sensing. The blend has clear ultraviolet (UV) and visible spectral regions for direct spectroscopic sensing, and it is an excellent absorber of many inorganic and organic cations from aqueous solution. The kinetics of the uptake of [Ru(BiPy)3]2+ and rhodamine 620 are presented as examples of complex ion preconcentration by the blend. With only the polymer blend directly applied as a fiber-optic cladding, aqueous Cu2+ ion can be detected as low as 10−6 M by using a light-emitting diode at 810 nm as a light source. A blend-clad fiber-optic sensor can be regenerated at least 25× without significant deterioration. The polymer blend can also trap hydrophobic compleximetric reagents added during the curing of the cross-linked blend. A prototype compleximetric dye-based evanescent-wave fiber-optic sensor using 1-(2'-pyridylazo)-2-naphthol was developed to detect aqueous Co2+ with a red HeNe laser light source. The Co2+ ion could be detected as low as 10−7 M.
FT-Raman Polarization Spectroscopy of Nonmesogenic Guest Molecules Oriented in Nematic Liquid Crystal Solvents
Authors: Andreev G. N. , Jordanov B. , Korte E. H. , Schrader B.
Published: October 2003

The experimental technique for Raman spectroscopic measurements of aligned liquid crystals was adopted for studying the orientation of nonmesogenic guest molecules dissolved in nematic liquid crystal hosts. Polarization FT-Raman spectra of diphenylacetylene (tolane) dissolved in nematic liquid crystals of 4-alkyl-4'-cyanobicyclohexyl type (ZLI-1695) have been recorded. The intensity ratios, R = IYY /IZZ, of the bands polarized perpendicular ( IYY) to the preferred molecular orientation, and parallel ( IZZ) to it, are rediscussed. A clear polarization equivalent to that of the host was found for the guest molecule tolane. The obtained data serve for determining the symmetry properties of the observed vibrations of the dissolved molecule.
Transmission μ-FT-IR Cell for Boundary Layer Studies
Authors: Self Valerie A. , Sermon Paul A.
Published: October 2003

Recently the present authors described a novel reflectance μ-FT-IR cell for the study of catalyst surfaces (and adsorbates thereon) with spatial resolution. Here, details are given of a transmission μ-FT-IR cell for on-line spatially resolved studies of boundary layers (and oscillatory behavior) produced around a Pt wire during its catalysis of CO oxidation. The CO–O2 reaction has been followed in terms of absorption at 2180 cm-1 and energy emission over the IR range and may (1) involve a boundary layer at 1–2 mm out from the Pt wire surface at a Reynolds number of 1064; (2) vary in rate with the microchemistry (or surface temperature) of the Pt wire surface along its length; and (3) show oscillations in rate, which depend upon position in the reactant flow relative to the catalyst surface but which are far more substantial in amplitude than previously suspected, possibly because the wire is not averaging over unsynchronized reaction domains but is partially resolving these spatially. Some restructuring of the Pt wire is seen as a result of the reaction, in line with expectation.
Comparison of Near-IR, Raman, and Mid-IR Spectroscopies for the Determination of BTEX in Petroleum Fuels
Authors: Cooper John B. , Wise Kent L. , Welch William T. , Sumner Michael B. , Wilt Brian K. , Bledsoe Roger R.
Published: October 2003

We report for the first time a direct comparison of the three most common vibrational analysis techniques for the determination of individual BTEX components (benzene, toluene, ethylbenzene, ortho-xylene, meta-xylene, and para-xylene) in blended commercial gasolines. Partial least-squares (PLS) regression models were constructed for each BTEX component by using each of the three spectroscopic techniques. A minimum of 120 types of blended gasolines were used in the training set for each BTEX component. Leave-one-out validation of the training sets yields lower standard errors for Raman and mid-IR spectroscopies when compared to near-IR for all six BTEX components. In general, mid-IR has slightly lower standard errors than Raman. These trends are upheld when the models are tested by using independent test sets with a minimum of 40 types of blended gasolines (all of which differ in composition from the training set).
Thermodynamic Parameters of the Inclusion Complexes of 2-Methylnaphthoate and α- and β-Cyclodextrins
Authors: Madrid Jose Manuel , Mendicuti Francisco
Published: October 2003

Steady-state fluorescence has been used to study the inclusion complexes of 2-methylnaphthoate (MN) with α- and β-cyclodextrins (CDs). Emission spectra of MN show two bands that are very sensitive to the CD concentration and temperature. The stoichiometry and formation constants of these complexes were investigated by obtaining the ratio of the two bands. Results showed identical stoichiometry (1:1) for both MN/α-CD and MN/β-CD complexes. However, the estimated formation constants were quite different. The thermodynamic parameters Δ H and Δ S were obtained from vant'Hoff plots. Results showed that MN/α-CD complexation is accompanied by an high enthalpy change, while MN/β-CD complexation is mainly en tropically favored. Anisotropy measurements were used to interpret the different signs of Δ S upon inclusion for both complexes. In addition, 2-methylnaphthoate seems to be a good probe for estimating microenvironmental polarity. Effective dielectric constants of inner α- and β-CD cavities were evaluated.
Characterization of Tear Gas Residues by Ion Mobility Spectrometry
Authors: Allinson Graeme , McLeod Cameron W.
Published: October 2003

In this study a hand-held ion mobility spectrometer was used to characterize the vapors produced by α-chloroacetophenone (CN) and 2-chlorobenzylidenemalononitrile (CS), their isomers, and then-degradation products at ambient temperature and 50 °C, and in both the positive- and negative-ion acquisition modes. Minimum determinable residues were as follows: in the negative-ion acquisition mode at ambient temperature, CN 0.5 μg, CS 10 mg; at 50 °C, CN 0.5 μg, CS 16 μg; and in the positive-ion acquisition mode at ambient temperature, CN 0.5 μg, CS not detected; at 50 °C, CN 0.1 μg, CS not detected. The steady-state reproducibility was found to be independent of ion acquisition mode but dependent on signal intensity and background noise [relative standard deviation (RSD) 3–17%]—the smaller the signal, the greater the variation. The day-to-day variation in positive- and negative-mode signal intensities showed the same trends (RSD 3–33%). By comparing positive- and negative-ion mode spectra, it was possible to differentiate not only between CN and CS but also between their isomers and breakdown products.
Fluorescence of Limestones and Limestone Components
Authors: Wang Jue , Wu Xu , Mullins Oliver C.
Published: October 2003

The fluorescence of a series of limestones has been investigated; the relative fluorescence intensities of these limestones differ by a factor of 10. With UV excitation, the fluorescence spectra of these limestones exhibit two distinct peaks, one blue and one red; the relative magnitude of the blue peak is larger for more fluorescent limestone. The limestones were digested, allowing for isolation of different limestone components, which are acid-extractable organics, bitumen, and kerogen. With the correlation of fluorescence spectra and intensities, it has been established that the acid extract fraction produces the blue peak in the rocks. Concentrated bitumen produces red fluorescence, contributing to the red peak of the rock. Generally, the limestone kerogens are found to possess very low fluorescence, in contrast to carbonaceous shale kerogens, and probably do not contribute to rock fluorescence.
Scanning Tunneling Microscope Study of Etch Pits on Highly Oriented Pyrolytic Graphite Heated in an Atomic Absorption Electrothermal Analyzer
Authors: Vandervoort Kurt G. , McLain Kristin N. , Butcher David J.
Published: October 2003

Scanning tunneling microscopy (STM) was used to elucidate monolayer etch pits that form on highly oriented pyrolytic graphite (HOPG) heated in an electrothermal analyzer. Pits form at elevated temperatures due to reactions between oxygen and exposed carbon edge atoms (defects) and additionally with intraplanar carbon atoms (through abstraction). Samples of HOPG without analyte or matrix modifier were placed in the depression of a pure pyrolytic graphite platform and heated by using standard analysis furnace programs. Under argon stop-flow conditions, pits form in less than a second at atomization temperatures equal to and above 1200 °C. With low argon flow rates (40 mL/min), pits formed at atomization temperatures equal to and greater than 1750 °C in less than a second. Quantitative pit formation rates were used to indicate oxygen partial pressure, which may be as high as ∼ 10−3 atm at 1200 °C. Reaction rates were used to predict surface degradation due to oxygen attack and determine that 1-μm depth normal to the surface would be removed by 200 successive 5-second-period furnace firings at 1200 °C. Implications for increases in surface reactivity and analyte intercalation are discussed.
Depth Profiling Study of Effect of Annealing Temperature on Polymer/Polymer Interfaces in Laminates Using Confocal Raman Microspectroscopy
Authors: Hajatdoost Sohail , Olsthoorn Maurien , Yarwood Jack
Published: October 2003

The effect of annealing temperature on molecular interactions at the interface of polymer laminates is reported. Depth profiling has been carried out by using confocal Raman microspectroscopy to study poly(acrylonitrile)/poly(vinyl alcohol) (PAN/PVOH) and poly(acrylonitrile)/poly(acrylic acid) (PAN/PAA) laminates. The laminates have been annealed at 65, 75, and 90 °C. It is demonstrated that the degree of hydrogen-bonding interaction between the nitrile and alcohol groups near the interfacial region changes between laminates annealed at different temperatures. Increasing the annealing temperature up to near the glass transition temperature, Tg, of both polymers facilitates hydrogen bonding. However, above Tg, as a result of molecular flexibility, weakening of such interactions begins. Due to the lower molecular weight of PAA, and thus greater mobility in comparison with PVOH, the interfacial region of a PAN/PAA laminate is broader than that of a PAN/PVOH laminate. Hydrogen-bonding interaction between PAN and PAA was not observed. This result is rationalized by the hypothesis that, as a result of intramolecular interaction between the carbonyl and hydroxyl groups of PAA, formation of intermolecular hydrogen bonding has been hindered. In addition, the variations in the full width at half-height (FWHH) of the v(C≡N) band of a PAN–PVOH blend has been mapped by using the same technique.
Examination of Criteria for Local Model Principal Component Regression
Authors: Bakken Gregory A. , Long Dixie R. , Kalivas John H.
Published: October 2003

In analytical chemistry, principal component regression (PCR) is widely used as a method for calibration and prediction. The motivation behind PCR is to select factors associated with predictive information and eliminate those associated with noise. The classical approach, referred to as top-down selection, chooses sequential factors based on singular value magnitudes, and the same factors are used for all future unknown samples; i.e., a global model is formed. The number of factors needed is often determined through cross-validation on the calibration samples or with an external validation set. Alternatively, a model developed specific to an unknown sample, i.e., a local model or sample-dependent model, could offer improved accuracy. The idea behind sample-dependent PCR is that factors associated with small singular values not included in a top-down PCR model can still contain relevant predictive information. This paper shows that local models generated by selecting factors on a sample-by-sample basis often reduce prediction errors compared with those for the global top-down model. However, evidence is also provided that supports the use of global top-down models. Several criteria are proposed and examined for selecting factors on a sample-dependent basis. Observations and conclusions presented are based on two near-infrared data sets.
Comparison of Univariate and Multivariate Strategies for the Determination of Sucrose in Fruit Juices by Automated Flow Injection Analysis with Fourier Transform Infrared Detection
Authors: Kellner R. , Lendl B. , Wells I. , Worsfold P. J.
Published: October 2003

An automated technique for the determination of sucrose by flow injection analysis with Fourier transform infrared detection is presented. Two approaches to the quantitation of sucrose in synthetic and real sample matrices have been explored. The first was based on the on-line enzymatic hydrolysis of sucrose to α-d-glucose and β-D-fructose by β-fructosidase, with difference measurements being performed by using a flow injection manifold with two internally coupled injection valves. The manifold was optimized with time-resolved software and then automated with a custom-built TTL interface to transfer signals from the controlling program to the external apparatus. Univariate calibration was performed on the difference signals between the sucrose samples with and without enzyme hydrolysis. The second approach, using multivariate data analysis, negated the need for sample treatment and produced similar errors for the prediction of sucrose in different matrices within the established linear range of 0 to 100 mM. Both approaches have been successfully applied to the determination of sucrose in fruit juices.
Rutherford Backscattering Spectrometry Investigation of the Permeability of Pyrolytically Coated Graphite Substrates
Authors: Eloi Corinne C. , Robertson J. David , Majidi Vahid
Published: October 2003

Rutherford backscattering spectrometry (RBS) and scanning electron microscopy (SEM) were used to investigate the interactions of analytes with pyrolytically coated graphite, which is typically used in graphite furnace atomic absorption spectrometry (GFAAS). Chemical species were found to migrate into the bulk of the graphite, up to depths of at least 3 μm, when deposited in a solution form on a nontreated or an oxygen-pretreated graphite flat. Because this migration was not observed when the analyte was deposited by vapor deposition or laser ablation, we conclude that the analyte migration proceeds via capillary action, as in the case of polycrystalline graphite. Pretreatment of the graphite flat with hydrogen prevented migration of the analytes into the bulk of the graphite when they were deposited in solution form.
Effect of Data Preprocessing Methods in Near-Infrared Diffuse Reflectance Spectroscopy for the Determination of the Active Compound in a Pharmaceutical Preparation
Authors: Blanco M. , Coello J. , Iturriaga H. , Maspoch S. , de la Pezuela C.
Published: October 2003

Near-infrared diffuse reflectance spectroscopy (NIRS) with a fiber-optic probe was used for the determination of the active compound in a commercial pharmaceutical preparation. In order to reduce the strong scatter in the spectra and prevent scatter-induced changes in measurements from prevailing over concentration-induced changes, several data preprocessing methods were tested: normalization, derivatives, multiplicative scatter correction, standard normal variate, and detrending. The effectiveness for reducing the scattering of each data preprocessing was assessed, and the best results were obtained with the use of the second derivative. The effect of the treatments on the quantitation of the active compound by partial least-squares regression (PLSR) was studied, similar results being obtained in all cases, with a relative standard error of prediction lower than 1.55%.
Diffusion Kinetics of TNT in Acrylonitrile—Butadiene Rubber via FT-IR/ATR Spectroscopy
Authors: Tung Y. S. , Mu R. , Henderson D. O. , Curby W. A.
Published: October 2003

We have used the FT-IR/ATR technique to investigate TNT diffusion in acrylonitrile–butadiene rubber (NBR) at 93, 103, and 113 °C. An analysis of the frequency and intensity of the NO2 symmetric and asymmetric stretch vibrations suggests that TNT diffused in NBR is in an isolated molecular state and/or cluster form. The diffusion process can be well-described by Fickian kinetics. The kinetic model fitting shows that the diffusion coefficient of TNT in NBR is on the order of 10−7 cm2/s and the activation energy is in the range of 30–35 kJ/mol.
MPSS: A New Scattering Technique for Sensitive Measuring of the Total Absorption of Fluids
Authors: Mittenzwey K.-H. , Sinn G.
Published: October 2003

Optical methods are appropriate tools to detect organic micro-pollutants in fluids. A simple technique is introduced which uses radiation scattered elastically by the fluid. Two different signals are measured: (1) the linear or conventional scattering (CS), which occurs at short pathlengths of the incidence radiation in the fluid, and (2) the multipath-saturation scattering (MPSS) originating at long pathlengths, e.g., in multipath-reflection cuvettes, where the radiation is fully absorbed by the fluid. A relation between the scattering signals and the total absorption coefficient of the fluid is theoretically derived. A simple experiment is performed that takes into consideration the scattering of distilled water polluted with azobenzene and quinine-sulfate. A xenon lamp and a nitrogen laser are used to generate CS and MPSS. The scattering ratio CS/MPSS yields the total absorption directly. In comparison to the conventional absorption technique, CS/MPSS is characterized by a higher sensitivity.
High-Resolution Inductively Coupled Plasma Atomic Emission Spectrometry for the Determination of Burnup in Spent Nuclear Fuel
Authors: Goodall Phillip , Johnson Stephen G.
Published: October 2003

The development of a method for the estimation of burnup of nuclear fuels by the determination of 236U by high-resolution inductively coupled plasma spectrometry has been demonstrated. Linear calibration curves are obtained and a limit of quantification of ∼ 3 atom % burnup established. The precision, in terms of the relative standard deviation (RSD) of the determination, was 3.7% RSD for 1.58 atom % of 236U. These results were obtained by using a spectrometer with a resolving power of 2.3 × 105 and with the application of a spectral deconvolution using a nonlinear curve-fitting algorithm. A complementary method, the determination of 139La, was also investigated and proved to be accurate (recovery = 101.5%) and precise (RSD = 2.2%) with a limit of quantification of ∼ 0.5 atom % burnup. These methods were developed with the use of model solutions which approximate digests of irradiated fuels but which contained no active fission product species.
Near-Infrared Raman Spectrometer Systems for Human Tissue Studies
Authors: Brennan James F. , Wang Yang , Dasari Ramachandra R. , Feld Michael S.
Published: October 2003

We have built two types of instruments for near-infrared Raman spectroscopy studies of human tissues, one for laboratory measurements and one for clinical use. The laboratory systems are designed to collect the highest quality spectra possible and allow different excitation/collection wavelengths to be studied. The clinical systems are designed to collect spectra via optical fibers within a few seconds and to be mobile and hospital-compatible. These systems are capable of detecting weak near-infrared Raman bands hidden in large background signals. Calibration and background subtraction procedures are described, and system performance is evaluated.
High-Performance Dual Raman Spectrometer
Authors: Tejeda G. , Fernández-Sánchez J. M. , Montero S.
Published: October 2003

The transformation of an old Raman double monochromator into a dual spectrometer capable of working either as the original instrument or as a very high sensitivity scanning single monochromator with multichannel charge-coupled device (CCD) array detection is described. The merits and limitations of this instrument, particularly suited for medium/low resolution (0.3 to 2 cm−1) Raman spectroscopy in the gas phase, are discussed. Example spectra of O2, N2, CO2, H2O, and CCl4 are shown.
Fluorescein-Labeled DNA Probes for Homogeneous Hybridization Assays: Application to DNA E. Coli Renaturation
Authors: Talavera Eva M. , Alvarez-Pez José M. , Ballesteros Luis , Bermejo Ruperto
Published: October 2003

The sensitivity of the emission intensity of fluorescein to environmental changes opens the possibility for developing homogeneous DNA assays. In this research, we were able to quickly and easily detect nucleic acid renaturation by using an E. coli DNA with approximately 4% conjugation of fluorescein to the N4-aminoethylmodifled cytosine residues. We determined how the emission intensity of fluorescein attached to single-stranded DNA decreases when renatured to double-stranded DNA. The decrease in fluorescence efficiency is due to changes in the fluorescein monoanion–dianion ratio because of pH modifications in the surrounding of the fluorescein label. The decrease in fluorescence intensity was used for analysis of DNA E. coli renaturation kinetics.
Thermal Decomposition of Energetic Materials 70: Kinetics of Organic Peroxide Decomposition Derived from the Filament Control Voltage of T-Jump/FT-IR Spectroscopy
Authors: Williams G. K. , Brill T. B.
Published: October 2003

An evaluation is made about whether T-jump/FT-IR spectroscopy can be used to determine the decomposition kinetics (Arrhenius Ea and ln A parameters) of energetic organic peroxides at high temperature following very rapid heating. Polystyrene peroxide (PSP) and benzoyl peroxide were investigated, but PSP was chosen for detailed study because of its known, simple, decomposition process. The shape of the control voltage trace of the Pt filament yields kinetic constants which are reasonable for O–O bond homolysis as the rate-determining step: Ea = 39 kcal/mol, ln ( A, s−1) = 45.9. These Arrhenius parameters differ from values measured by other methods, but it is found that an isokinetic temperature of 400 ± 20 K exists for all measurements. Thus, all the kinetic measurements appear to reflect the same dominant process (O–O homolysis), but their differences make extrapolation of the rates from the temperature range of measurement to another range inaccurate.
Effect of Temperature on the Stability of Association of Pyrimidine Bases with Serum Albumin: Proton NMR Study
Authors: Sułkowska Anna
Published: October 2003

In a study of the effect of temperature on the interaction of 5-methylcytosine, 1,3-dimethyluracil, thymine, and 2′-deoxythymidine with bovine serum albumin (BSA) in aqueous solution, the proton magnetic resonance technique has been applied. An important broadening of proton resonances is observed in complexes that is due to a restricted mobility of the bonded molecule. A particular effect of BSA concentration on the pyrimidine ring signals or on the C-5 methyl protons of ligands shows the pyrimidine ring of 1,3-dimethyluracil and the methyl groups of 5-methylcytosine, thymine, and 2′-deoxythymidine as primary binding sites in the complex with albumin. The results reflect the existence of hydrophobic interactions between C-5 methyl groups of the ligand and hydrophobic domains of the serum albumin. It seems that in the complex of 1,3-dimethyluracil with BSA the pyrimidine ring plays a primary role in the binding. No strong chemical bonds are present. The temperature effect is characterized by a decrease of interaction at temperatures higher than 300 K and by the release of ligands from their binding sites on the unfolding albumin. The possible importance of direct interactions between pyrimidine bases and albumin has been discussed with respect to the problem of specific interactions between proteins and nucleic acids.
Ultraviolet Spectroscopy for the Analysis of Oil-In-Water Effluent Using Isopropanol as Co-Solvent
Authors: Bastow Trevor , Durnie William H. , Jefferson Alan , Pang James
Published: October 2003

Direct analysis of oily water effluents was investigated as a method for the determination of petroleum hydrocarbons in the discharge from primary oil production facilities. A co-solvent, isopropanol (2-propanol), was chosen that produced a clear, homogeneous solution when added to oil-in-water effluent. The clear solution was then analyzed directly for aromatic hydrocarbon content by using ultraviolet spectroscopy. The concentration of oil in the sample was calculated from a Lambert–Beer plot at 226 nm. The standard used was a sample of oil that best represented the oil that had contacted the water, i.e., current production crude oil.
Structural Characterization of β-Lactoglobulin in Solution Using Two-Dimensional FT Mid-Infrared and FT Near-Infrared Correlation Spectroscopy
Authors: Sefara Nelson L. , Magtoto Noel P. , Richardson Hugh H.
Published: October 2003

Two-dimensional (2D) FT-IR correlation analysis was applied to both the mid-IR (MIR) and near-IR (NIR) regions to investigate changes in the secondary structures of β-lactoglobulin in D2O (or H2O) solvent systems consisting of varying concentrations of bromoethanol. Mid-IR correlation spectra indicate that the amide I bands corresponding to different structures (i.e., α-helical structures at 1650 cm−1, aggregated β-strands at 1620 cm−1, and β-sheet at 1636 cm−1) exhibit apparently different spectral response towards varying concentrations of bromoethanol. We propose that the mechanism for the conversion of the β-sheet into α-helix occurs in terms of two parallel pathways, i.e., (1) β-sheets → aggregated β-strands →α-helix, and (2) β-sheets →α-helix. Although the amide B/amide II combination bands give no spectral features relating to the secondary structure, changes were found in the C–H combination bands that suggest an interaction between the solvent and the protein.
Si: As Focal-Plane Array Detection for Fourier Transform Spectroscopic Imaging in the Infrared Fingerprint Region
Authors: Lewis E. Neil , Kidder Linda H. , Arens John F. , Peck Michael C. , Levin Ira W.
Published: October 2003

An instrument is described that simultaneously records images and spectra of materials in the infrared fingerprint region using a long-wavelength infrared focal-plane array detector, a step-scan Michelson interferometer, and an infrared microscope. With the combination of step-scan Fourier transform (FT) Michelson interferometry and arsenic-doped silicon (Si: As) focal-plane array image detection, an infrared spectroscopic imaging system has been constructed that maintains both an instrumental multiplex and multichannel advantage and operates from approximately 4000 to 400 cm−1. With this method of mid-infrared spectroscopic imaging, the fidelity of the generated spectral images recorded through the microscope is solely determined by the number of pixels on the focal-plane array detector, and only a few seconds of data acquisition time are required for spectral image acquisition. This seamless combination of spectroscopy for molecular analysis and the power of visualization represents the future of infrared microscopy. Step-scan imaging principles, the operation and characteristics of long-wavelength array detectors, and instrument design details are outlined, and infrared chemical imaging results are presented. The results are discussed with respect to their implications for the chemical analysis of a variety of solid-state materials.
Linear and Nonlinear FEL-SEW Spectroscopic Characterization of Nanometer-Thick Films
Authors: Alieva E. V. , Beitel G. , Kuzik L. A. , Sigarev A. A. , Yakovlev V. A. , Zhizhin G. N. , van der Meer A. F. G. , van der Wiel M. J.
Published: October 2003

The conditions of the existence and transformations of surface electromagnetic waves (SEWs) on metals (surface plasmons) and dielectrics (phonon-polaritons) are discussed. Interferometric SEW experiments provide the possibility for the direct determination of the real and imaginary parts of the dielectric constants at the frequencies in the tuning range of a free electron laser (FEL) without any preliminary models. The important role of the outstanding facilities of FEL—namely, the broad tuning range, high power, narrow bandwidth of emission, and well-collimated beam—in SEW experiments is outlined. It is demonstrated by the examples of the infrared absorption spectra of a Langmuir-Blodgett film on metal, of a metal oxide film, and of polymeric films of nanometer thicknesses on metals. Free surfaces of single-crystal CaF2 and the thin polymeric film were studied by an interferometric experiment for the optical constant determination. Nonlinear spectroscopic applications of the SEW-FEL technique to studies of a second harmonic generation (SHG)—the frequency dependence of efficiency, the angle dependence of SHG, and the influence of a thin-film deposition on a quartz surface—are described.
Design for Supported Planar Waveguides for Obtaining Mid-IR Evanescent-Wave Absorption Spectra from Biomembranes of Individual Cells
Authors: Braiman Mark S. , Plunkett Susan E.
Published: October 2003

We have been developing miniature planar Ge waveguides to detect mid-IR evanescent-wave absorption spectra from the cell membranes of individual intact frog eggs, 1.5-mm in diameter, from Xenopus laevis, with the aim of detecting and analyzing transient conformational changes of voltage-gated ion channel proteins in the membrane. Here we use waveguide optical theory to calculate optimal dimensions for a germanium waveguide to be used as a multiple-internal-reflection ATR element for this purpose. We assume that light from a standard broad-band IR source is coupled efficiently into and out of a planar Ge waveguide, and then onto a small-area MCT detector, by using an IR microscope with a high-numerical-aperture objective. To increase the coupling efficiency even further, we assume that we can fabricate the waveguide with a gradual 7-fold-tapering to the tiny dimensions needed in the sensing region. Then, assuming that ∼ 107 ion channel proteins in an occyte can be made to contact an area of a planar Ge waveguide up to ∼ 200 μm in diameter, we calculate that voltage-gated structural changes in these channel proteins should produce absorbance change signals of ∼ 10−6 if the waveguide sensor thickness is set near the optimal thickness of ∼ 1 μm and the sensor region length is limited to 100 μm. If such a sensor can be fabricated, we calculate that detection of the predicted voltage-gated absorbance changes with a commercial FT-IR microscope should be possible after ∼ 20 min of signal averaging.