bluuebunny/crossref_metadata_2025 huggingface dataset:
Simple and Efficient Multivariate Calibration of Nonlinear Absorption Spectroscopic Data
Authors: Robertsson George
Published: October 2003

This paper presents a simple way to extend the regressor variables in partial least-squares (PLS). The method is particularly suited for nonlinear absorption spectra or any other measurements of the soft saturation type. Absorption below a certain limit is described as linear and above this limit as nonlinear. The extension of the regressor variables consists of the absorbances above the linear range. The proposed method is compared with standard PLS. The proposed method gives more parsimonious models and better predictions than standard PLS for the two data sets used in this study, ultraviolet-visible with absorbances in the region 0–2.9.
New Classical Least-Squares/Partial Least-Squares Hybrid Algorithm for Spectral Analyses
Authors: Haaland David M. , Melgaard David K.
Published: October 2003

A new classical least-squares/partial least-squares (CLS/PLS) hybrid algorithm has been developed that demonstrates the best features of both the CLS and PLS algorithms during the analysis of spectroscopic data. By adding our recently reported prediction-augmented classical least-squares (PACLS) to the hybrid algorithm, we have the additional benefit that known or empirically derived spectral shape information can be incorporated into the hybrid algorithm to correct for the presence of unmodeled sources of spectral variation. A detailed step-by-step description of the new hybrid algorithm in calibration and prediction is presented. The powerful capabilities of the new PACLS/PLS hybrid are demonstrated for near-infrared spectra of dilute aqueous solutions containing the analytes urea, creatinine, and NaCl. The PACLS/PLS method is demonstrated to correct the detrimental effects of unmodeled solution temperature changes and spectrometer drift in the multivariate spectral calibration models. Initially, PLS and PACLS/PLS predictions of analytes from variable-temperature solution spectra were made with models based upon spectra previously taken of the samples at constant temperature. The presence of unmodeled temperature variations and system drift caused the prediction errors from these models to be inflated by more than an order of magnitude relative to the cross-validated errors from the calibrations. PLS achieved improved predictions of the variable-temperature spectra by adding spectra of a few variable-temperature samples into the original calibration data followed by recalibration. PACLS/PLS predictions were corrected for temperature variations and system drift by adding spectral differences of the same subset of samples collected under constant- and variable-temperature conditions to the PACLS prediction portion of the hybrid algorithm during either calibration or prediction. Comparisons of the prediction ability of the hybrid algorithm relative to the PLS method using the same calibration and subset information demonstrated hybrid prediction improvements that were significant at least at the 0.01 level for all three analytes. The new hybrid algorithm has widespread uses, some of which are also discussed in the paper.
Effect of Radical Attack on Bacteria: An Application of FT-IR Spectroscopy
Authors: Melin Anne-Marie , Perromat Annie , Deleris Gérard
Published: October 2003

The radical attack of ascorbic acid was investigated by Fourier transform infrared spectroscopy. This physico-chemical technique was used as a convenient and easy-to-run method to monitor radical-induced damage on three bacterial strains previously included in the Micrococcaceae family. Increasing concentrations of ascorbic acid were added to the culture media during the stationary phase. As soon as the antioxidant defenses of the bacteria were overwhelmed, striking changes occurred in the infrared spectra, especially in the 1700–900 cm−1 region, which is spectroscopically assigned to the amide I and II components of proteins, nucleotide bases, phosphodiester backbone, and sugar rings. These changes were correlated with the oxidant effect of ascorbic acid, but the response to free radicals generated was dependent on the strains. Micrococcus luteus and Kocuria rosea were sensitive to the lowest ascorbic acid concentrations, while a concentration beyond 10 mM was necessary to cause damage to biomolecular components of the radioresistant Deinococcus radiodurans. Thus, Fourier transform infrared analysis allowed a rapid investigation of the metabolic changes caused by radical attack, and the spectral alterations could be correlated with biochemical and phenotypical data.
Comparison of Principal Component Analysis and Generalized Two-Dimensional Correlation Spectroscopy: Spectral Analysis of Synthetic Model System and Near-Infrared Spectra of Milk
Authors: Šašić Slobodan , Ozaki Yukihiro
Published: October 2003

Principal component analysis (PCA) and generalized two-dimensional (2D) correlation spectroscopy have been applied to a two-component spectral model made up of highly overlapped bands and to near-infrared (NIR) spectra of milk. The analyses were made on mean-normalized and mean-centered data of the model. The dynamic loading of PCA is expanded into 2D contour by calculating a variance-covariance matrix. This 2D pattern is compared with a synchronous 2D spectrum calculated by generalized 2D correlation spectroscopy, and a high degree of similarity is discernible between the two kinds of 2D spectra. The one-dimensional (1D) features of the synchronous 2D map, slice spectra, are identical to the dynamic loading as well. We show that, for noncentered data of the model system, only in limited cases can the correlation between the first loadings and synchronous map be established. PCA of the milk spectra yields two factors. The 2D representation of the most important loading is significantly different from the synchronous spectrum calculated by the generalized 2D approach. The slice spectra from which the synchronous spectrum is made are found to be mutually different as one moves along the variable axis. A synchronous 2D map emphasizes only variables with the highest correlation of the spectral intensity changes. On the other hand, PCA is geometrically oriented; thus, as the complexity of the data increases, the differences between PCA and generalized 2D correlation spectroscopy become striking. The selectivity of the asynchronous 2D map is demonstrated for the bands due to milk fat.
Near-Infrared Spectra of Gases: Identification of Mixtures
Authors: Brown Chris W. , Zhou Jing
Published: October 2003

A 100-compound near-infrared (IR) spectral library of environmentally important gases was generated. All the library spectra were measured from 4000 to 9000 cm−1 at a resolution of 2 cm−1. Spectra of 17 test mixtures including 9 two-component mixtures, 5 three-component mixtures, and 3 four-component mixtures were measured. Two of the 9 two-component mixture spectra were measured at a resolution of 8 cm−1 and two at 16 cm−1; all the other mixtures were measured at 2 cm−1 resolution. A mixture search routine was used for identifying the components in the mixtures. In a search using the near-IR region of 4000 to 8000 cm−1, all components in the 9 two-component mixtures, all components in 5 three-component mixtures except for one component ( o-xylene in a mixture of the three xylenes) and all components in the 3 four-component mixtures except for one component (a ketone) were correctly identified. The mixture search was repeated with the 4000 to 6200 cm−1 region and all components in all the 17 mixtures were correctly identified. Thus, by the decision to limit the near-IR fingerprint region of 4000–5000 cm−1 and the overtone region of the C-H stretching vibration at 5600–6200 cm−1, the informational content was optimized. The results suggest that the 4000–6200 cm−1 region could be used for monitoring gas mixtures.
Nonlinearity of Beer's Law in Gas-Phase FT-IR Spectroscopy
Authors: Ahro Mikko , Kauppinen Jyrki
Published: October 2003

The nonlinear deviation from Beer's law due to a finite instrumental resolution has been studied by taking the shape of the spectrum into account. The phenomenon has been studied as a function of resolution theoretically and by simulations. The results show that the nonlinearity is constant in the part of interferogram between the vibrational structure and rotational structure since there is very small signal in that region. The study suggests that the optimal resolution has to be decided by the width of the vibrational bands rather than by the width of the rotational lines.
Selecting Two-Dimensional Cross-Correlation Functions to Enhance Interpretation of Near-Infrared Spectra of Proteins
Authors: Buchet R. , Wu Y. , Lachenal G. , Raimbault C. , Ozaki Y.
Published: October 2003

Two-dimensional infrared (2D-IR) cross-correlation can facilitate the interpretation of infrared spectra. However, the fluctuation of noise and the overlapped component bands often complicate the analysis of 2D-IR spectra. The ratio of asynchronous to synchronous correlation functions ( F) can serve as a control of coherence for the cross peaks in 2D correlation maps. A synchronous cross peak with an F value close to 0 corresponds to the good coherence of cross-correlated pair of signals, more likely reflecting a true synchronous cross peak, while a large F value associated with a synchronous cross peak is more likely a false cross peak. Similarly, the noncoherence of asynchronous cross peaks can be checked by computing their F values. In this case, large F values are associated with true asynchronous correlation peaks, while small F values are more likely false asynchronous cross peaks. This approach has been tested on smoothed and unsmoothed near-infrared (NIR) spectra of human serum albumin (HSA) in aqueous solutions. A set of NIR spectra of HSA with increasing concentration were measured to generate 2D correlation maps. Unsmoothed spectra permitted the acquisition of synchronous and asynchronous 2D correlation maps containing all putative cross peaks in addition to artifacts generating by the fluctuation of noise or band overlapping. The control of coherence of pairs of signals on each cross peak, based on their F values, facilitated the interpretation of 2D-NIR maps, by improving the selection of true cross peaks from false cross peaks. The smoothed NIR spectra provided cross peaks without any artifacts in the synchronous and asynchronous correlation maps. The selection of cross peaks based on their F values confirmed the absence of false cross peaks in the case of smoothed spectra. Despite some limitations as discussed in this report, this procedure is straightforward to implement and will make the analysis of 2D vibrational spectra much easier.
Wavelength—Wavelength and Sample—Sample Two-Dimensional Correlation Analyses of Short-Wave Near-Infrared Spectra of Raw Milk
Authors: Šašić Slobodan , Ozaki Yukihiro
Published: October 2003

Short-wave near-infrared (NIR) spectra of raw milk have been analyzed in the 800–1100 nm region by two-dimensional (2D) correlation spectroscopy. In this study, we have used both the well-known generalized 2D correlation spectroscopy method, which yields correlation coefficients among spectral variances on all the wavelength points (wavelength-wavelength correlation), and a novel sample-sample correlation spectroscopy method, which gives correlation coefficients among the concentration dynamics of the species in the system. The sample-sample correlation spectroscopy develops correlation maps with the samples on the axes. First, a set of 34 spectra was ordered according to increasing fat content, while all other milk components varied freely. Both synchronous and asynchronous wavelength-wavelength correlation maps have shown strong baseline changes despite the use of multiplicative scatter correction as a pretreatment. Bands at 930 and 970 nm due to fat and water, respectively, have been found to be the most significant spectral features. The synchronous sample-sample correlation map was calculated from the original data matrix and was compared with the outer product of the fat concentration vector. The comparison has revealed that the main spectral variances in the raw milk spectra in the short-wave NIR region are due to fat. The same procedure was repeated for a set of 15 samples that contained a constant fat content and were ordered according to increasing protein content. Poor agreement was found between the outer product of the protein concentration vector and the synchronous sample-sample correlation map. This result suggests that the spectral variances in raw milk spectra that have a constant fat content are due not exclusively to proteins but also due to other milk components. Comparisons of partial least-squares (PLS) regression analysis of fat and proteins and both sample-sample and wavelength-wavelength 2D correlation analyses of raw milk spectra have been made.
Application of Near-Infrared Spectroscopy to the Study of Alumina Phases
Authors: Ruan Huada D. , Frost Ray L. , Kloprogge J. Theo
Published: October 2003

Near-infrared (IR) spectroscopy has been used to distinguish between alumina oxo and hydroxy phases. Two near-IR spectral regions are identified for this function: (1) the high-frequency region between 6400 and 7400 cm−1, attributed to the first overtone of the hydroxyl stretching mode, and (2) the 4000–4800 cm−1 region attributed to the combination of the stretching and deformation modes of the AlOH units. Near-IR spectroscopy allows the study and differentiation of the hydroxy and oxo(hydroxy) alumina phases, since each phase has its own characteristic spectrum. The spectrum of bayerite resembles that of gibbsite, whereas the spectrum of boehmite is similar to that of diaspore. Bayerite has four characteristic near-IR bands at 7218, 7128, 6996, and 6895 cm−1. Gibbsite shows five major bands at 7151, 7052, 6958, 6898, and 6845 cm−1. Boehmite displays three near-IR bands at 7152, 7065, and 6960 cm−1. Diaspore shows a prominent band at around 7176 cm−1. The use of near-IR reflectance spectroscopy to study alumina surfaces has a wide application, particularly with thin films and surfaces. The technique is rapid and accurate. Near-IR, because of its sensitivity, can be used in reflectance mode for the on-line processing of bauxitic minerals.
New Approach for Spectral Characterization of Crude Oil Using Time-Resolved Fluorescence Spectra
Authors: Hegazi E. , Hamdan A. , Mastromarino J.
Published: October 2003

Spectral characterization of four crude oils was attempted by using a different approach for time-resolved laser-induced fluorescence (TRF) techniques. The TRF spectra were excited by pulsed UV laser radiation at 250 nm and were measured at specific time windows of equal gate widths along the trailing edge of the pulsed laser. Contour diagrams of equal fluorescence intensities were then constructed to serve as unique fingerprints for the crude oils. The method does not require that the laser pulse be deconvoluted from the fluorescence signal, which makes it attractive for remote characterization of crude oil.
Chelation Number of Terbium Dipicolinate: Effects on Photoluminescence Lifetime and Intensity
Authors: Rosen David L. , Niles Stanley
Published: October 2003

Time-resolved photoluminescence was studied as a function of chelation number in terbium dipicolinate. We excited the ligand (dipicolinate) with UV (250 to 330 nm) and collected the emission from the cation (terbium) in the visible region (450 to 700 nm). The luminescence of Tb(dpa) n3–2 n followed a monoexponential decay, with a lifetime (0.66 to 2.0 ms) that decreased continuously as the terbium chloride concentration increased. The luminescence lifetime of Tb(dpa)+ was 0.66 ms. We measured the luminescence decay time, the peak intensity, and the total time-integrated intensity as a function of terbium chloride concentration at two dipicolinic acid concentrations and fitted the results to functions of terbium dipicolinate concentration. We used a model with rapid ligand exchange and rapid back-transfer of energy to fit the data to first order. We also present molar absorptivity spectra of complexes with different chelation numbers.
Use of a 2D to 1D Dimension Reduction Fiber-Optic Array for Multiwavelength Imaging Sensors
Authors: Schiza Maria V. , Nelson Matthew P. , Myrick M. L. , Angel S. Michael
Published: October 2003

A dimension reduction fiber-optic array is used to measure the response of a stacked-layer, image-guide CO2/O2 sensor, simultaneously at several different wavelengths. Two different image-guide CO2/O2 sensor configurations are described: a stacked-layer sensor, where luminescence indicators for CO2 and O2 are uniformly coated on the tip of the sensor; and a side-by-side coated sensor where the two indicators are coated on different halves of the fiber tip. It is shown that a single image-guide measurement, made by using the dimension reduction array, can be used to generate response plots, intensity profiles, and reconstructed images at different luminescence wavelengths. The spatial resolution of an image guide sensor is limited by the number of fibers used to construct the dimension reduction array.
Negligible Sample Heating from Synchrotron Infrared Beam
Authors: Martin Michael C. , Tsvetkova Nelly M. , Crowe John H. , McKinney Wayne R.
Published: October 2003

The use of synchrotron sources for infrared (IR) spectromicroscopy provides greatly increased brightness that enables high-quality IR measurements at diffraction-limited spatial resolutions. This capability permits synchrotron-based IR spectromicroscopy to be applied to biological applications at spatial resolutions on the order of the size of a single mammalian cell. The question then arises, “Does the intense synchrotron beam harm biological samples?” Mid-IR photons are too low in energy to break bonds directly; however, they could cause damage to biological molecules due to heating. In this work, we present measurements that show negligible sample heating effects from a diffraction-limited synchrotron IR source. The sample used is fully hydrated lipid bilayers composed of dipalmitoylphosphatidylcholine (DPPC), which undergoes a phase transition from a gel into a liquid-crystalline state at about 315 K during heating. Several IR-active vibrational modes clearly shift in frequency when the sample passes through the phase transition. We calibrate and then use these shifting vibrational modes as an in situ temperature sensor.
Characteristics of a High-Power Microwave-Induced Helium Plasma at Atmospheric Pressure for the Determination of Nonmetals in Aqueous Solution
Authors: Yamada Hirofumi , Okamoto Yukio
Published: October 2003

A high-power [∼ 1000 W continuous wave (CW), 2.45 GHz] annular-shaped microwave-induced helium plasma (He-MIP) was developed for the determination of nonmetals in aqueous solutions, and the characteristics are presented. The plasma was generated at atmospheric pressure by an Okamoto cavity that was modified to focus the energy. No external cooling was used to stabilize the plasma. An aqueous solution was injected into the plasma by an ultrasonic system with desolvation and condensation. The electron density and iron-excitation temperature were on the order of 1014/cm3 and 5000 K, respectively. Introduction of aqueous chloride in the form of NaCl and bromide in the form of KBr produced intense ion emission, and detection limits of 100 ppb for Cl(II) (479.5 nm) and 200 ppb for Br(II) (470.5 nm) were obtained.
Species-Selected Mass-Analyzed Threshold Ionization Spectra of m-Fluoroaniline Cation
Authors: Lin J. L. , Lin K. C. , Tzeng W. B.
Published: October 2003

Two-color resonant, two-photon mass-analyzed threshold ionization (MATI) spectroscopy was used to probe the ionic properties of m-fluoroaniline (MFA). The species selection from a mixture was achieved by tuning the frequency of the excitation laser to a specific intermediate level of MFA for the successive excitation, followed by pulsed field ionization. The MATI spectra were recorded by ionizing via the 00 vibrationless and the 41, 151, and 9b1 vibrational levels in the S1 state. The adiabatic ionization energy of MFA was determined to be 64 159 ± 5 cm−1 (7.9542 ± 0.0006 eV). Analysis of the spectral features shows that the active modes of the ion are closely related to the specified vibrations of the neutral. These findings indicate that the geometry of the ion is quite similar to that of the neutral in the S1 state.
Ultraviolet Absorption Spectra of Carbon Dioxide and Oxygen at Elevated Temperatures
Authors: Joutsenoja T. , D'Anna A. , D'Alessio A. , Nazzaro M. I.
Published: October 2003

Measurements of ultraviolet absorption spectra in lean and stochiometric premixed C2H4/O2 flames have been performed with different flame temperatures (1400–1700 K). The spectra of the light transmitted through the flame were measured in the 200–270 nm range by using as an incoherent broadband light source the plasma kernel of optical breakdown generated by a focused pulsed laser beam. Measurements were performed far downstream of the main flame zone in a region where the concentrations of flame products reach equilibrium values. CO2 and O2 are the major absorbing species, and their absorption cross sections at flame temperature have been evaluated by changing the flame conditions and thus obtaining different concentration of these species at the flame exit. At temperatures above 1500 K there is strong absorption (σa > 10−20 cm2) due to both CO2 and O2 in the 200–230 nm range. A clear increase can be seen in absorption of both CO2 and O2 with increasing temperature. CO2 absorption cross sections also show a different dependence with respect to temperature for the different wavelengths.
Resonance Raman and UV-Visible Spectroscopic Studies of Water-Soluble Sapphyrin Derivative: Drug Localization in Tumor and Normal Mice Tissues
Authors: Synytsya Alla , Král Vladimír , Poučková Pavla , Volka Karel
Published: October 2003

Resonance Raman (RR) and UV-visible (UV-vis) spectroscopy have been applied to the study of sapphyrin localization in tumor human pancreatic adenocarcinoma-bearing mice. The photosensitizer was subcutaneously injected, and the kinetics of drug biodistribution have been followed in a time scale from 1 to 9 days. RR spectra of tumor and tissue samples and UV-vis absorption spectra of tissue extracts in water/methanol (1:4 v/v) mixture were measured. Spectral data were used to identify the presence and to estimate the relative content of sapphyrin in various tissues at various times after the last injection. Results showed a preferential localization of sapphyrin in tumor tissue. Maximal content of drug in tumor tissue was observed at 6 days after the last injection. Results obtained by RR and UV-vis spectroscopy were in good agreement with each other.
Cytochrome Spectroscopy in Scattering Suspensions Containing Mitochondria and Red Blood Cells
Authors: Hull Edward L. , Foster Thomas H.
Published: October 2003

Steady-state spatially resolved diffuse reflectance spectroscopy is used to reconstruct absolute visible absorption spectra (λ 450–610 nm) of tissue-simulating phantoms that contain intact mitochondria and red blood cells in physiologically relevant proportions. The spectra are analyzed to extract independent fitted concentrations of oxy- and deoxyhemoglobin and of oxidized and reduced mitochondria. The resulting hemoglobin oxygen-dissociation and mitochondrial oxidation-reduction curves exhibit p50 parameters of 25 and 2.5 torr, respectively, in agreement with published values. These results demonstrate the potential for absolute quantitative cytochrome spectroscopy of tissue in the presence of hemoglobin in the visible wavelength region. Extension of these measurements to the in vivo case is discussed.
Time-Resolved FT-IR Spectroscopy of Chemical Reactions in Solution by Fast Diffusion-Based Mixing in a Micromachined Flow Cell
Authors: Hinsmann Peter , Haberkorn Michael , Frank Johannes , Svasek Peter , Harasek Michael , Lendl Bernhard
Published: October 2003

A new concept for the study of chemical reactions in solution by time-resolved Fourier transform infrared spectroscopy (TR/FT-IR) is presented. The key element of this concept is a micromachined mixing unit for fast and highly reproducible diffusion-based mixing that is incorporated in a flow cell for transmission measurements and operated in the stopped-flow mode. The mixing unit achieves multilamination of two liquid streamlines inside the flow cell. When the flow in both feeding channels is maintained, there is almost no mixing of the liquids, because of the short residence time inside the mixer, hence allowing for the recording of a reference spectrum of the reactants prior to reaction. When the flow is stopped by rapid switching of a dedicated injection valve, highly reproducible diffusion-controlled mixing takes place inside the flow cell so that spectral changes induced by the reaction under investigation can be directly followed. The total volume required for one experiment is ∼ 5 μL, and mixing times achieved so far are in the millisecond range. Factors governing time resolution in this new concept are the time required to stop the flow, the spacing of the individual streamlines, the diffusion coefficients of the reactants involved, and the signal strength of the spectral changes induced by the reaction under study. In this paper, the possibilities and limitations of the new concept are studied with the use of three model reactions, which are an acid-base neutralization reaction, the addition of sulfite to formaldehyde, and the basic hydrolysis of methyl monochloroacetate. In addition, the complete mixing process in the system was studied by computational fluid dynamics (CFD) simulations, which provided valuable insights into details of the mixing process itself as well as confirming the experimental results obtained.
Oxygen Quenching Measurements for the S1 and S2 Fluorescence of Gas-Phase Fluoranthene
Authors: Sassu Lorenzo , Perezzani Laura , Ivancic William A. , Barnes Russell H. , Wabuyele Busolo Wa
Published: October 2003

The fluorescence emission of the fluoranthene molecule has been investigated at excitation wavelengths varying from 240 to 360 nm, and conducted from near collision-free conditions to atmosphericpressure conditions. The oxygen quenching rate for the fluorescence of the F1 band (S1 → S0 transition) of fluoranthene at 340 nm excitation wavelength was found to be 1 × 109 L mol−1 s−1. The quenching rate for the F2 band (S2 → S0 transition) was found to be 100-fold greater for the wavelength region investigated. The wavelength dependency of the oxygen-quenching constants of the two transitions was also established in the excitation range from 240 to 332 nm. The influence of oxygen and nitrogen pressure on the spectral fluorescence bandwidth of fluoranthene and the oxygen-quenching constants for the S1 and S2 bands are reported. The results shed some light on fluoranthene's unusual inertness to oxygen quenching.
Two-Photon Fluorescence Polarization Anisotropy Decay on Highly Diluted Solutions by Phase Fluorometry
Authors: Olivini Francesca , Beretta Sabrina , Chirico Giuseppe
Published: October 2003

We report here the phase-sensitive measurements of two-photon fluorescence polarization anisotropy (FPA) on highly diluted solutions. We first describe the characterization of the response of the two-photon microscope to the light polarization and its test by means of measurements of the FPA on rhodamine 6G as a function of the viscosity. Further, we report the study of the FPA at high dilutions on a globular protein, the beta-lactoglobulin B (BLG) labeled with Alexa 532. The number of molecules (from 0.4 to 17 molecules per excitation volume) is measured by means of fluorescence correlation spectroscopy (FCS). The average rotational and translational diffusion coefficients measured with the FPA and FCS methods are in good agreement with the protein size and do not show a substantial dependence on the protein concentration, despite the very low signal (≌3 times the background) observed for highly diluted solutions.
Masking, Photobleaching, and Spreading Effects in Hadamard Transform Imaging and Spectroscopy Systems
Authors: Hanley Quentin S.
Published: October 2003

In analyzing the behavior of a Hadamard transform imaging spectroscopic system in an optical sectioning microscope, a previously undescribed masking effect was observed. During the process of characterizing this artifact, it was noted that while many masking errors have been reported previously in the literature, no attempt has been made to classify them or to systematically treat their effects in a variety of imaging and spectroscopy arrangements. Previous reports have documented echo artifacts in one-dimensional Hadamard mask systems based on sequences of length 2 n – 1, for which the echoes are well defined. Other valid cyclic S-sequences, such as those of prime length 4 m + 3 ≠ 2 n – 1, do not exhibit such behavior. Masking errors may be present with these sequences, but they do not appear as echoes. Recovered intensities are observed having both positive and negative magnitude distributed throughout the transform axis. These masking defects appear superficially to be “noise”, making associated errors more difficult to diagnose. Masking effects in two-dimensional systems have not been previously reported. In these, the relationship between the original image and resulting “echoes” can be quite complicated. This paper treats a variety of masking effects theoretically and presents simulations based on that treatment. Mask errors are divided into first- and second-order effects depending on whether the encoding passes through a mask once or twice. Symmetric, asymmetric, and static masking errors in one-dimensional Hadamard transform systems are treated in both first- and second-order arrangements. Where prior data exist, an attempt has been made to collect and categorize known mask-related artifacts and where appropriate provide additional documentation. Mask errors may be spatially varying or spatially invariant over the mask or within a given pixel. In systems which are spatially variant, proper sampling of the image or spectrum by the elements composing the mask is a prerequisite for successful correction of the data. Corrections applied to data from masks with spatially variant errors may cause artifacts to appear and, in some instances, complete correction may be impossible. The effects of photobleaching and mask spreading due to processes such as diffraction or aberrations in both one- and two-dimensional mask systems are investigated. Photobleaching is relatively easy to correct when an exponential decay model is applicable. In second-order systems, mask spreading gives rise to echoes or distortion even in perfectly implemented masks. Mask spreading can, in many cases, be corrected by analyzing the observed “echoes” and building a correction matrix or by using knowledge of the point, line, or other spreading function of the system. Finally, in masks of length 2 n – 1, a few simple rules greatly assist in diagnosing masking effects.
Model of a Fiber-Optic Evanescent-Wave Fluorescence Sensor
Authors: Woerdeman Dara L. , Parnas Richard S.
Published: October 2003

A fiber-optic cure sensor based on evanescent-wave fluorescence spectroscopy has been designed to probe the interphase region of glass-reinforced composites. The size of the interphase can vary significantly, depending on the exact nature of the fiber surface treatment and its interaction with the surrounding resin matrix. In this study, a model based on mode coupling theory is developed to determine whether the fiber provides information about the bulk resin or the interphase between the fiber and the matrix. Model predictions include the fraction of fluorescence signal collected as a function of radial distance from the optical fiber surface. In all cases the refractive index of the fiber is 1.617, the value measured for the fiber used in experiments, while the refractive index of the resin varies from 1.56 to 1.615, values representative of curing epoxy resin. In addition, the penetration depths of the excitation modes are analyzed as a function of the mode group number, as well as the root number, for two resin refractive indices. The dependence of the fluorescence signal on selected excitation and fluorescence modes is also investigated. Finally, we examine the role of coupling optics by analyzing the relationship between penetration depth and the angle between the excitation beam and fiber axis.
Excitation Emission Matrix Spectral Subtraction Fluorescence to Check Adulteration of Petrol by Kerosene
Authors: Patra Digambara , Mishra A. K.
Published: October 2003

The excitation emission matrix spectral subtraction (EEMSS) fluorescence technique was used to estimate adulteration of petrol by kerosene. A calibration graph obtained from the spectral volume with the use of EEMSS fluorescence is found to be efficacious in the whole range 0 to 90% v/v of kerosene. The method is simple, reliable, and superior in terms of both sensitivity (1% v/v) and accuracy compared to any other method. The method gives a good recovery for synthesized adulterated sample.
New Insight into the Mathematical Background of Generalized Two-Dimensional Correlation Spectroscopy and the Influence of Mean Normalization Pretreatment on Two-Dimensional Correlation Spectra
Authors: Šašić Slobodan , Muszynski Andrzej , Ozaki Yukihiro
Published: October 2003

Generalized two-dimensional (2D) correlation spectroscopy is considered from the point of view of linear algebra. It is shown that a synchronous spectrum is the same as the cross-product matrix of the experimental data. An asynchronous spectrum is also treated as the ordered scalar products of the dynamic vectors of the experimental matrix and its Hilbert transformation. This approach connects the theory of generalized 2D correlation spectroscopy with the well-known conceptions of classic correlation analysis. The importance of spectral normalization in the 2D correlation analysis and its influence on the 2D correlation spectra is also investigated. All calculations were done on a synthetic spectral model consisting of two components. The synchronous spectra obtained from the model matrix were compared with those obtained after spectral mean normalization. It was found that the results strongly depend on the pretreatment. We plotted the Hilbert transformation of the meancentered model and found that the normalization leads to the disappearance of the asynchronous spectra in the two-component system. Also, it has been concluded that the influence of normalization is important just for the systems with large intensity variations. All the results presented here are quite general and can be applied irrespective of the nature of the perturbation.
Determination of Free Fatty Acids in Edible Oils by Continuous-Flow Analysis with FT-IR Spectroscopic Detection
Authors: Cañada María Jose Ayora , Medina Antonio Ruiz , Lendl Bernhard
Published: October 2003

A flow injection system with Fourier transform infrared spectroscopic detection was developed for the rapid determination of the free fatty acid content in edible oils. The method is based on complete deprotonation of the free fatty acids and evaluation of the intensity of the vas-(COO−) band formed at 1570 cm−1 with respect to a baseline point at 1534 cm−1. Upon deprotonation the absorption of the carboxylic acid moieties is shifted toward lower frequency, thus avoiding spectral interferences of the v-C=O from esters, ketones, or aldehydes also present in the sample. Optimum operational conditions were obtained by merging the sample stream first with a carrier stream of 25% (v/v) toluene in 2-propanol followed by merging with a 0.3 M solution of KOH in the same solvent mixture and measurement of the obtained solution after a short (2 s) reaction time. In this way saponification of the oil could be reduced to a minimum, whereas deprotonation was already completed. The obtained calibration curve was linear from 0 to 2.5% oleic acid, and the coefficient of variation of the method was 3.3%. The developed method was applied to the determination of the total amount of free fatty acids in olive, sunflower, and corn oils, delivering results that were in good agreement with those obtained by the official reference method proposed by the European Community. Furthermore, due to its high degree of automation and throughput (40 samples h−1), the developed method is suitable for quality control in routine applications.
Attenuated Total Internal Reflection Infrared Mapping Microspectroscopy Using an Imaging Microscope
Authors: Sommer André J. , Tisinger Louis G. , Marcott Curtis , Story Gloria M.
Published: October 2003

Attenuated total internal reflection (ATR) infrared mapping microspectroscopy using an infrared microscope and a focal plane array is investigated and reported. The study demonstrates the advantages of conducting ATR microspectroscopy using a focal plane array detector. These benefits include the rapid acquisition of molecular specific images, ease of sample preparation, and increased spatial resolution. An experimental determination of the spatial resolution found that the combined system operates very close to the diffraction limit, and a 4 magnification factor associated with the germanium internal reflection element was realized. Experiments conducted on several polymer samples and a biological sample demonstrate the future viability of the method.
Compositional Mapping of Poisoning Elements in Automobile Three-Way Catalytic Converters by Using Laser-Induced Breakdown Spectrometry
Authors: Lucena P. , Vadillo J. M. , Laserna J. J.
Published: October 2003

The use of laser-induced breakdown spectrometry (LIBS) for generating two-dimensional (2D) multielemental distribution maps of poisoning agents in automobile three-way catalysts (TWCs) is discussed. A complete in-depth analysis of P, Zn, and Pb at different locations along the central channel of a used TWC in the gas flow direction was performed. The distribution maps for the metals in charge of the catalytic action and for the stabilizer of these metals—i.e., Pt, Pd, and Ce—are also presented. The 2D maps provide a fast, useful, and intuitive tool to visualize the selective distribution of poisoning elements in a used TWC. This study may help explain the deterioration processes of a catalyst with a lifetime of about 30 000 km.
Energy Dependence of Emission Intensity and Temperature in a LIBS Plasma Using Femtosecond Excitation
Authors: Eland Kristine L. , Stratis Dimitra N. , Gold David M. , Goode Scott R. , Angel S. Michael
Published: October 2003

In this paper, we investigate the effect of laser energy on laser-induced breakdown emission intensity and average temperature in a short-pulse plasma generated by using 140 fs laser excitation. Both line emission and continuum background intensity and plasma temperature decrease very rapidly after excitation compared to the more conventional nanosecond pulse excitation. Both emission intensity and plasma temperature increase with increasing laser energy. However, the intensity increase appears to be mostly related to the amount of material ablated. Also, nongated laser-induced breakdown spectroscopy (LIBS) is demonstrated using a high-pulse (1 kHz) pulse repetition rate.
Effect of Optical Interference on Borophosphosilicate Glass Profiles Obtained with a Glow Discharge Optical Emission Spectrometer
Authors: Kimura Shigeharu , Mitsui Yasuhiro
Published: October 2003

We have studied the effect of optical interference on element profiles obtained with a glow discharge optical emission spectrometer (GDS). The specimens were borophosphosilicate glass films deposited on polished silicon wafers. We found that in some cases the interference is accompanied with a beat in the profile: a damping of the sinusoidal wave followed by a recovery. Profilometry showed that the depth resolution is better when the interference continues continuously without a beat. We showed by simulation that the cause of the beat came from variation of the penetration rate throughout the sputtered area.
Simultaneous Determination of Low Parts-per-Billion Level Pb and as in Waters Using Energy-Dispersive X-Ray Fluorescence Spectrometry
Authors: Hettipathirana Terrance D. , Smith Lester H. , Norrish Keith
Published: October 2003

A simple method is described for the simultaneous determination of low parts-per-billion levels of As and Pb in waters. The method is based on the preconcentration of analytes by adsorbing them onto hydrous ferric hydroxide (HFO) impregnated into the 13 mm diameter area at the center of 32 mm diameter circular disks cut from Whatman filter papers. The adsorbed analytes are determined by using thin-layer energy-dispersive X-ray fluorescence spectrometry. The X-ray intensity of As and Pb adsorbed onto HFO is linearly proportional to the concentration up to 80 μg/L. The precision of the method is ∼ 0.5–5%, and the method detection limit for Pb and As in seawater is 0.63 and 0.21 μg/L, respectively. The method was validated by analyzing the certified reference materials SLRS-3 (riverine water), CASS-4 (nearshore seawater), and NASS-5 (offshore seawater) for As. The adsorption characteristics of Pb, As(III), As(V), Se(IV), Se(VI), and Hg onto the HFO impregnated disks, the interspecies adsorption effects, and the use of the standard addition method to compensate for matrix effects are also presented.
Multivariate Calibration for the Determination of Analytes in Urine Using Mid-Infrared Attenuated Total Reflection Spectroscopy
Authors: Heise H. M. , Voigt G. , Lampen P. , Kupper L. , Rudloff S. , Werner G.
Published: October 2003

The reagent-free multicomponent analysis of components in urine using mid-infrared spectroscopy possesses many attractions. A population of 67 individual urine samples from children and adults, collected over 24 h, was analyzed for urea, creatinine, uric acid, glucose, total protein, phosphate, and sulfate by using clinical reference methodology. The urine pH value was potentiometrically measured by a glass electrode. Partial least-squares (PLS) calibration models were calculated over optimized, component-specific ranges from attenuated total reflection spectra of the urine samples measured by a micro-Circle cell. Apart from glucose and total protein, for which the spread in urine sample concentrations was too small, calibrations were successful for metabolites such as urea, creatinine, and uric acid. Additionally, concentrations of sulfate and phosphate anions, which show significant mid-infrared absorption bands, could also be quantified. The acid secreted with the urine influences the equilibrium between di- and monobasic phosphate in this biofluid, which is used as the spectroscopic basis for the pH assay presented here. The analytical performance of the reference methods is discussed with regard to evaluating the limitations of the spectroscopic assay. Additionally, aqueous solutions of individual urine components with a spread of concentrations similar to those found in native urine samples were analyzed by using PLS calibrations.
Assessment of the Structure and Predictive Ability of Models Developed for Monitoring Key Analytes in a Submerged Fungal Bioprocess Using Near-Infrared Spectroscopy
Authors: Vaidyanathan Seetharaman , Macaloney Graeme , Harvey Linda M. , McNeil Brian
Published: October 2003

The robustness of models developed for the near-infrared spectroscopic prediction of mycelial biomass, total sugars, and ammonium in a submerged Penicillium chrysogenum bioprocess was assessed by rigorously challenging them with artificially introduced analyte and background matrix variations, so that analyte concentrations were varied in an invariant matrix and vice versa. The models were also challenged by using a data set from a process operated at a different scale from that used in the original model formulation. Simple univariate and bivariate linear regression models, and partial least-squares (PLS) models with as few factors as three and four, performed sufficiently well for predicting analyte concentrations and were robust with respect to the matrix variations tested. However, models based on relatively weaker absorptions, or those that were likely to be influenced by stronger absorbers present in the same matrix, were vulnerable to changes in the matrix. A change in the scale of operation affected models that would be influenced by biomass, possibly due to an influence of the morphology of the mycelial biomass. An analysis of the loading vectors of some PLS models revealed details that were useful in understanding the type of information modeled and the behavior of these models to the variations tested.
Evaluation of a Dual-Beam Near-Infrared Spectrometer Based on Acousto-Optic Tunable Filters
Authors: Guchardi Renato , Pasquini Celio
Published: October 2003

A dual-beam near-infrared (NIR) spectrometer was constructed and evaluated. The instrument was designed to work with the two monochromatic beams produced by each one of the two acousto-optic tunable filters (AOTFs) evaluated, capable of scanning the wavelength range 800–1600 or 1500–2400 nm. Two temperature-controlled, cooled InAs detectors were employed for comparison of the two monochromatic beams produced by the AOTF. Data were obtained in a controlled ambient temperature, (25 ± 1) °C, and were compared for their intensity and wavelength coincidence for each of the 300 values of radio frequency (85–160 and 56–92 MHz) applied to the AOTF. The results show that the two beams present good concordance as a function of the wavelength (mean Δλ <0.30 nm) for both AOTFs investigated. The normalized intensities of the two beams were quite different, and their ratio values (0.9 to 1.2) depend on the wavelength. Inversion of intensities was observed in the present case and can be attributed to the unmatched position of the two detectors and to the difference in responsivity. On the other hand, the use of the two beams revealed that it can provide a robust way to correct for light-source intensity fluctuation as high as 10%. The mean standard deviation for long-term operation and for a zero absorbance baseline was reduced three times when the dual-beam instrument was employed. The instrument has also been evaluated for determination of water in fuel ethanol. The results for water content demonstrate the good analytical performance of the spectrometer with a relative error of 0.07 and 0.03% (w/w) for water determination in the ranges 0.20–10.0 and 0.20–3.00%, respectively.
Optimizing Meta-Parameters in Continuous Piecewise Direct Standardization
Authors: Bärring Hans K. , Boelens Hans F. M. , De Noord Onno E. , Smilde Age K.
Published: October 2003

When in-line or on-line spectroscopy is performed on a process, different types of variations are present in the measured spectrum. The variation due to the chemistry of the process is the wanted variation, which should be used for monitoring the process. Also unwanted variation is present in the measured spectrum. One example is variation due to changes in the temperature of the sample. This unwanted variation will cause deterioration of the performance of the spectroscopic analyzer. In this paper the properties of continuous piecewise direct standardization (CPDS) for temperature corrections in near-infrared (NIR) spectra are discussed. A procedure to obtain sensible settings of the meta-parameters in the CPDS algorithm has been developed. Initial values of the meta-parameters can be found for each data set by looking at spectra as a function of temperature. Particularly, difference spectra are shown to be useful in order to determine the degree of linearity of the spectral disturbances caused by the temperature changes. A cross-validation procedure around these initial settings is proposed to establish the optimum meta-parameters. This procedure was successfully applied to two NIR data sets. For each data set, it was found that CPDS corrected for temperature disturbances in an independent test data set and maintained the prediction errors on the same low level as for a calibration model built at the calibration temperature.