bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic FT-IR Spectroscopic Studies of Silk Fibroin Films
Authors: Sonoyama Masashi , Miyazawa Mitsuhiro , Katagiri Gen , Ishida Hideyuki
Published: October 2003

Dynamic FT-IR spectra in the amide I region were measured for silk fibroin cast films. Phase analyses of the dynamic spectra were carried out in order to separate them into several components which are due to the secondary structures of fibroin. These observations showed that peak positions of the amide I bands were in good agreement with those obtained by Fourier self-deconvolution procedures. In conclusion, phase analysis of dynamic FT-IR spectra is a powerful technique for separation of highly overlapping bands.
Time- and Energy-Resolved Emission Spectroscopy Using a Step-Scan FT Spectrometer Combined with Correlational Analysis Techniques
Authors: Thonke K. , Baier T. , Hamann J. , Scheerer O. , Sauer R.
Published: October 2003

The decay of photoluminescence emission signals on the time scale from microseconds to seconds can be measured with superior dynamics and signal-to-noise ratio by a new method which makes use of correlation analysis with pseudorandom binary sequences. Instead of excitation of the sample by one short laser pulse for each decay cycle (which results in low average emission intensity), the sample is pumped with a continuous-wave laser modulated by a pseudorandom sequence with δ-function-like autocorrelation properties. Therefore, on the time average half of the exciting laser power pumps the sample, and the resulting high emission intensity allows recording of photoluminescence decays over as many as four orders of magnitude within measurement times of 10 min. When this technique is combined with a step-scan Fourier transform spectrometer, both time and energy resolution can be obtained simultaneously. For each interferometer step, the sample response to the excitation sequence is recorded, later autocorrelated digitally, and combined to interferograms for each time step, and finally Fourier transformed. With this technique, time-resolved high-sensitivity spectra can be recorded in the NIR, where only detectors with relatively poor detectivity ( D) are available, and in the visible spectral range. Preliminary results obtained from relatively slow emission processes at defects in semiconductors are presented, which show decay constants on microsecond to millisecond scales.
Step-Scan FT-IR Photoacoustic Spectroscopy: The Signal Phase
Authors: Wahls M. W. C. , Toutenhoofd J. P. , Leyte-Zuiderweg L. H. , de Bleijser J. , Leyte J. C.
Published: October 2003

The model of Rosencwaig and Gersho for the photoacoustic effect is tested. The use of carbon black samples as a phase reference to estimate the apparatus phase φapp from the experimental signal phase φexp turned out to be ambiguous. A new method is presented to correct the experimental signal phases φexp of polymer films for the apparatus phase φapp. The photoacoustic signal phase of some well-defined poly(ethyleneterephthalate) (PET) films is obtained. As a phase reference, transparent thermally thick polymer films were found to be more convenient and dependable than carbon black samples. The resulting phase spectra of thermally thick and thermally thin PET films confirm the Rosencwaig–Gersho theory.
Molecular Reaction Mechanisms of Proteins Monitored by Nanosecond Step-Scan FT-IR Difference Spectroscopy
Authors: Rammelsberg Robin , Heβling Benedikt , Chorongiewski Harald , Gerwert Klaus
Published: October 2003

Step-scan FT-IR difference spectroscopy with 100-ns time resolution is applied to the membrane protein bacteriorhodopsin. The experimetal setup and data acquisition are described in great detail. The IR absorbance changes accompanying bacteriorhodopsin's photocycle are presented in a three-dimensional representation. The data quality allows one, for example, to resolve the biphasic rise of the photocycle-intermediate M. A bacteriorhodopsin's proton pump model based on the FT-IR works is presented.
Application of a New Quantitative Optical Depth Profiling Technique for the Diffusion of Polymers
Authors: Ekgasit Sanong , Ishida Hatsuo
Published: October 2003

The concentration profiles of amorphous polystyrene in a polystyrene/polyvinyl methyl ether laminated film after heat treatments have been investigated by a new depth profiling technique using multiple-angle attenuated total reflection Fourier transform infrared (ATR/FT-IR) spectroscopy. An estimated profile or information about the wave form of the profile is not required in order to perform the depth profiling calculation. All angle-dependent spectra are obtained with a nonpolarized incident beam of known degree of polarization. The accuracy of the calculated profiles has been confirmed by comparisons between spectral intensities from experiment and those from exact optical theory at frequencies other than the profiling frequency. The quantitative nature of this technique has been shown via consistent areas under the volume fraction profiles of polystyrene in the laminated film after consecutive heat treatments.
Infrared Crystallography: Structural Refinement through Spectroscopy
Authors: Sage J. Timothy
Published: October 2003

A method for determining the orientation of individual bonds within complex macromolecules from polarized IR measurements on oriented single crystals is described. At present, X-ray diffraction is the principal technique used to define the global structure and orientation of macromolecules in the crystalline state. However, resolution limitations and conformational disorder limit the accuracy of the resulting structural model. A quantitative understanding of protein function often requires a more precise description of structural features at a localized active site. Polarized IR measurements of internal stretching bands of N−3, CN−, OCN−, and SCN− bound at the ferric heme iron of single crystals of myoglobin are presented. A synthesis of such measurements on different crystal forms leads to an N−3 orientation consistent with IR measurements on both P21 and P212121 crystals, but significantly different from the orientation reported in X-ray crystal structures. Subtle structural changes between these two crystal forms of the CN− complex may account for small differences in the stretching frequency and orientation of the C–N bond.
Mid-Ir Fel User Facility Felix
Authors: van der Meer A. F. G. , van der Wiel M. J.
Published: October 2003

The relative merit of the use of the free electron laser for infrared experiments (FELIX) for spectroscopy is discussed and illustrated with some examples.
Absolute Detector Calibration Applied to Nonlinearity Error Correction in FT-IR Measurements
Authors: Zhang Z. M. , Zhu C. J. , Hanssen L. M.
Published: October 2003

A method for correcting the effects of detector nonlinearity in Fourier transform infrared (FT-IR) spectrometers has been developed. The method incorporates directly measured results. No adjustable parameters are used. The absolute responsivity of two HgCdTe (MCT) detector/preamplifier systems as a function of incident photon flux was calibrated against a transfer-standard Ge detector with a diode laser source at 1.32 μm. With the use of the MCT detector, preliminary measurements were made on an FT-IR spectrometer in both the near- and mid-infrared spectral regions. The measured nonlinear interferograms were corrected by using the detector response curve and the measured dc output of the preamplifier. In the resultant spectra, the nonzero values in the spectral region below the detector cutoff frequency were significantly reduced when the corrected interferograms were used. The transmittance spectra of a Si wafer and a neutral-density filter were measured with an MCT detector and a deuterated triglycine sulfate (DTGS) detector. Errors in transmittance caused by detector nonlinearity were greatly reduced with the use of the correction method.
Ten-Nanosecond Step-Scan FT-IR Absorption Difference Time-Resolved Spectroscopy: Applications to Excited States of Transition Metal Complexes
Authors: Chen Pingyun , Palmer Richard A.
Published: October 2003

Ten-nanosecond time resolution has been achieved with step-scan FT-IR absorbance difference spectroscopy (S2FT-IR Δ A TRS) and demonstrated by measuring Δ A spectra of fac-[Re(bpy)(CO)3Cl] and cis-[Os(bpy)2(CO)(4,4′-bpy)]2+ (bpy = 2,2′-bipyridine; 4,4′-bpy=4,4′-bipyridine) in CH3CN solution, following 355-nm laser excitation. In both complexes, the large shifts in (CO) to higher energy are consistent with the assignment that the lowest-energy excited states are metal-to-ligand charge transfer in nature. For [Os(bpy)2(CO)(4,4′-bpy)]2+, it is also possible to measure the excited-state decay kinetics, again with 10-ns resolution. In addition, Δ A bands are observed that are related to excited-state vibrations of the bipyridine ligands. Δ A spectra of good signal-to-noise ratio can be obtained for complexes with lifetimes as short as 10 ns.
Amplitude Spectrum Analysis of Dynamic FT-IR Spectra of Uniaxially Drawn Poly(Ethylene Terephthalate) Film with a Variable-Temperature Polymer Stretcher
Authors: Sonoyama Masashi , Shoda Kunihiro , Katagiri Gen , Ishida Hideyuki , Nakano Tatsuhiko , Shimada Shigeru , Yokoyama Toru , Toriumi Toriumi
Published: October 2003

Dynamic FT-IR spectra of uniaxially 5×-drawn poly(ethylene terephthalate) (PET) film at a temperature of 30 to 150 °C were measured with the use of a variable-temperature polymer stretcher, and amplitude spectrum analyses of the dynamic spectra were carried out. A drastic decrease in dynamic variations of the trans C–O stretching band was observed above the glass-to-rubber transition temperature. This observation suggests that the trans C–O bond in the ethylene glycol unit is closely related to changes in macroscopic mechanical properties of PET film in the glass-to-rubber transition.
Two-Dimensional FT-IR Spectroscopy: A Powerful Method to Study the Secondary Structure of Proteins Using H-D Exchange
Authors: Nabet Anne , Pézolet Michel
Published: October 2003

Two-dimensional infrared spectroscopy has been used for the first time to study the conformation of proteins by hydrogen–deuterium exchange. In order to generate the two-dimensional synchronous and asynchronous maps, hydrogen–deuterium exchange of the amide protons of proteins deposited on attenuated total reflection crystals has been used as an external perturbation. Owing to the fact that the amide protons associated with each conformation are not exchanged at the same rate, the different conformational contributions of the amide bands could be separated. The use of different sampling time domains turned out to be very helpful in order to separate more efficiently the fast kinetics from the slower ones. The results obtained on myoglobin show that this method is particularly useful to unravel the different components under the poorly resolved amide I, II, and II' bands of proteins. The analysis of the synchronous and asynchronous maps of myoglobin demonstrates that the amide I band of this protein is composed of at least four components that could be assigned to α-helical, intermolecular β-sheet, β-turn, and random coil conformations.
Infrared Studies of Novel Optically Responsive Materials: Orientation Characteristics of Sulfonated Polystyrene/Poly(Diallyldimethylammonium Chloride) Ionic Polymer Multilayers on Patterned Self-Assembled Monolayers
Authors: Gregoriou Vasilis G. , Hapanowicz Rick , Clark Sarah L. , Hammond Paula T.
Published: October 2003

Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) is utilized in the characterization of a new class of polymeric materials that exhibit unique optical properties. The differential nature of PM-IRRAS, coupled with the fact that the experiment was performed on a commercially available hardware setup, makes the technique ideal for studying selectively deposited polyion multilayers on metal surfaces. The system under study was a polymeric thin film of alternating bilayers of sulfonated polystyrene/poly(diallyldimethylammonium chloride) (SPS/PDAC) fabricated by ionic multilayer assembly. Specifically, patterned self-assembled monolayers (SAMs) of (Ω-functionalized alkane thiolates were used as the molecular template. Alternating layers of polyanion and polycation were then selectively adsorbed onto specific regions of the surface to form a patterned films of thicknesses from 150 to 400 Å. The total thickness of the film was measured at 150 Å with the use of ellipsometry. Polyion conformation plays a crucial role in the selectivity of the patterned film, film surface characteristics, and ultimately, the ability of these systems to function as optical devices. The infrared spectroscopic data give insight into chemical composition and conformation and show that the molecular orientation of polyions in these polymeric multilayer structures depends on the ionic content of the initial solutions.
Chemical Mapping in the Mid- and Near-IR Spectral Regions by Hadamard Transform/FT-IR Spectrometry
Authors: Bellamy M. K. , Mortensen A. N. , Hammaker R. M. , Fateley W. G.
Published: October 2003

A movable two-dimensional (2D) Hadamard encoding mask is obtained and combined with conventional FT-IR spectrometers for use in both the mid- and near-infrared spectral regions. Chemical maps and spectra of individual pixels of the maps can be obtained from heterogeneous samples by using this combination of a move-able 2D Hadamard encoding mask and an FT-IR spectrometer. We call the procedure Hadamard transform/FT-IR spectrometry. Spectra of usable signal-to-noise ratio and reliable chemical maps are obtained in reasonable data acquisition and processing time.
Asynchronous Time-Resolved FT-IR Study of the Dynamical Behavior of Ferroelectric Liquid Crystal with a Tolane Ring
Authors: Katayama N. , Czarnecki M. A. , Satoh M. , Watanabe T. , Ozaki Y.
Published: October 2003

Transient infrared spectra of a ferroelectric liquid crystal with a tolane ring, ( S)-4-methylhexyl-4-[4-(decyloxy)phenylethynyl]-2-fluorobenzate, in the smectic C phase have been measured under various temperatures and voltages by use of an asynchronous time-resolved FT-IR method. The effects of temperature and voltage on the rate and tilt angle of the electric field-induced reorientation of the molecule have been studied. The absolute values of the observed intensity changes and their sign during the switching can be explained by the static properties of the sample. The spectra obtained under the different experimental conditions suggest that the temperature and applied voltage alter the tilt angle and angular velocity of reorientation of the liquid crystal, respectively. Dominant infrared bands show very similar time-dependent intensity changes under various conditions, indicating that the whole molecule reorients simultaneously irrespective of temperature and the applied field strength as though the molecule were a rigid rod.
In situ Spectroscopy of Polymers Subjected to Supercritical CO2: Plasticization and Dye Impregnation
Authors: Kazarian Sergei G. , Brantley Noel H. , West Barry L. , Vincent Michael F. , Eckert Charles A.
Published: October 2003

In situ FT-IR spectroscopy has been used to study poly(methyl methacrylate) films subjected to high-pressure and supercritical CO2. Spectral changes indicate increased molecular mobility of ester groups due to the plasticization effect of CO2 on PMMA. This increase in PMMA segmental mobility has been used to impregnate Disperse Red 1 dye (DR1) into polymer film from a supercritical fluid solution. The enhanced diffusion process was observed in situ via FT-IR and UV/vis spectroscopy.
Surface-Enhanced Vibrational Spectroscopy: A New Tool in Chemical IR Sensing?
Authors: Kellner R. , Mizaikoff B. , Jakusch M. , Wanzenböck H. D. , Weissenbacher N.
Published: October 2003

In order to further improve the sensitivity of chemical IR sensors, research into a significant change in the signal generation mechanism was carried out. This effort was realized by generating the surface-enhanced IR absorption and Raman-scattering effect at silver- and gold-island-covered Ge- and ZnSe ATR surfaces for surface-enhanced infrared absorption (SEIRA) and Ag-layer-covered brass plates for surface-enhanced Raman scattering (SERS), respectively, and linking the optimized tools to the IR sensor concept. By careful optimization of the generation of silver-island and gold-island films on Ge reflection elements, intensity gains by a factor of 50 were achieved. Chemical interactions between the silver-island layer and the various analytes investigated up to now (p-nitro benzoic acid, as a model compound, and selected aromatic and chlorinated pesticides) are likely, as indicated by significant IR spectral changes; the substances are, however, bound to the surfaces in a reversible manner. This property of the novel SEIRA sensor can be favorably exploited in flow-through systems. In a similar way, by a specially optimized treatment of anodically oxidized brass plates in a silver bath, repeatably usable SERS targets for the trace analysis of pesticide mixtures in aqueous systems could be developed. A signal enhancement factor of 1.4 million was obtained with pyridine as the standard sample. The data shown in this work suggest that both SEIRA and SERS can be coupled to a flow injection system in a reversible way for the molecular-specific trace analysis of organic compounds in aqueous solutions.
Comparison of Step-Scan and Rapid-Scan Approaches to the Measurement of Mid-Infrared Fourier Transform Vibrational Circular Dichroism
Authors: Long Fujin , Freedman Teresa B. , Hapanowicz Rick , Nafie Laurence A.
Published: October 2003

We report mid-infrared Fourier transform vibrational circular dichroism (FT-VCD) spectra obtained by using three different measurement schemes: the traditional sequential rapid-scan method, a new simultaneous rapid-scan method, and the step-scan method. We also provide a description of the optical setup used to obtain the VCD spectra. Using this optical layout, we are able to measure FT-VCD spectra for single enantiomers of the chiral sample with low levels of interfering artifacts and for collection times as fast as one minute. For approximately 20 min of spectral collection, the three FT-VCD measurements approaches tested here yield nearly the same signal quality. The approach with the highest quality, by a small margin, was the simultaneous rapid-scan method. Next was the sequential rapid-scan approach, followed closely by the step-scan method. VCD spectra and noise curves obtained with these different measurement techniques are presented and compared, and their relative advantages and disadvantages are discussed.
In situ Anti-Stokes Raman Monitoring of Gel-to-Anatase Phase Transformation of Titania
Authors: Iida Yasuo , Furukawa Masamichi , Kato Kazumi , Morikawa Hisashi
Published: October 2003

The phase transformation from a gel of titanium alkoxide to crystalline anatase was observed in situ by anti-Stokes Raman scattering. Utilization of anti-Stokes scattering eliminates interference from the fluorescence of decomposing organic residuals during the pyrolysis process. The anti-Stokes Raman spectra suggest a highly disordered structure during the pyrolysis process. The structure of the titania gel, which is characterized by broad Raman peaks around 440 and 620 cm−1, was transformed into the amorphous structure by increasing the temperature up to 200–300 °C. This amorphous structure is supported by a flat Raman spectrum lacking specific features in the wavenumber region from 200 to 1000 cm−1. A partially crystallized gel also exhibits the further progress of amorphization during the pyrolysis process, which is explained by the disordering of the local structure of the gel due to the generation of pyrolyzed organic species.
Spectrofluorimetric Study of the Inclusion Complex of 7-Hydroxymethylnalidixic Acid with γ-Cyclodextrin in Aqueous Solution
Authors: Durán-Merás Isabel , De La Peña Arsenio Muñoz , Salinas Francisco , Cáceres Isabel Rodríguez
Published: October 2003

A fluorimetric study on the spectral characteristics and acid-base behavior of 7-hydroxymethylnalidixic acid has been performed. The host–guest complexation process between γ-cyclodextrin and 7-hydroxymethylnalid ixic acid has also been investigated by fluorescence spectroscopy. Scatchard and Benesi-Hildebr and methods have been applied to determine the stoichiometry of the complex, and a 1:1 stoichiometric ratio has been established. A K1 = 118 ± 25 M−1 formation constant has been calculated for the inclusion complex, by using the changes produced on the fluorescence of 7-hydroxymethylnalid ixic acid, when it is included on the hydrophobic cyclodextrin cavity. A fluorimetric method of determination of 7-hydroxymethylnalid ixic acid, in γ-cyclodextrin aqueous solution, has been proposed. The analytical parameters and detection and quantification limits of the method have been determined.
Wavelength Selection Characterization for NIR Spectra
Authors: Brenchley Jason M. , Hörchner Uwe , Kalivas John H.
Published: October 2003

For quantitative analysis of samples based on near-infrared (NIR) spectra, it is common practice to use full spectra in conjunction with partial least-squares (PLS) or principal component regression. Alternatively, least-squares (LS) can be used provided that proper wavelengths have been selected. Recently, optimization algorithms such as simulated annealing and the genetic algorithm have been applied to the selection of individual wavelengths. These algorithms are touted as global optimizers capable of locating the best set of parameters for a given large-scale optimization problem. Optimization methods such as simulated annealing and the genetic algorithm can become time intensive. Excessive computer time may be due not to computations but to the need to determine proper operational parameters to ensure acceptable optimization results. In order to reduce the time to select wavelengths, a different approach consists of selecting wavelengths directly on the basis of spectral criteria. This paper shows that results are not acceptable when one is separately using the criteria of large wavelength correlations to the prediction property, wavelengths associated with large values in loading vectors from PLS or derived from the singular value decomposition (SVD) of the spectra, and wavelengths associated with large PLS regression coefficients. However, it is demonstrated that acceptable results can be produced by using wavelength regions simultaneously associated with large correlations and loading values provided that the level of noise for identified wavelengths is also acceptable. Thus, this paper shows that, rather than using time-consuming optimization algorithms that generally select individual wavelengths, one can achieve improved results based on wavelength windows directly selected. In other words, the described approach is founded on the exclusion of spectral regions rather than the search for distinct wavelengths. As part of the NIR spectral characterization, it is shown that certain loading vectors from the SVD of spectra are equivalent to correlograms for prediction properties. The same is shown to be true for PLS loading vectors. This type of analysis is useful for determining dominant properties of spectra, i.e., primary properties responsible for spectral variations.
Characterization of Particulates Accompanying Laser Ablation of NaNO3
Authors: Webb R. L. , Dickinson J. T. , Exarhos G. J.
Published: October 2003

We present observations of submicrometer- to micrometer-sized particles generated by high-fluence (≥10 J/cm2) 248-nm laser ablation of single-crystal NaNO3 in vacuum and at atmospheric pressure. Small particles (50–200 nm in diameter) are ejected by hydrodynamic sputtering. Larger particles (1–20 μm in diameter) are produced by cavitation and spallation in the melt. Many particles formed in air carry electric charge, with roughly equal numbers of positively and negatively charged particles. The particle composition is consistent with substantial nitrate decomposition. The implications of these observations with respect to laser-based chemical analysis are discussed.
Estimating Optimum Filter Length in Linear Prediction
Authors: Sievänen O.-P.
Published: October 2003

In this article a new method to estimate optimum filter length in linear prediction is described. Linear prediction was used to enhance resolution of a spectrum. In particular, the dependence of prediction error on filter length has been studied. With calculations of simulated spectra it is shown that the prediction error falls rapidly when the filter length attains its optimum value. This effect is quite pronounced when the spectrum has a good signal-to-noise ratio and the modified covariance method is used to calculate prediction filter coefficients. The method is illustrated with applications to real Raman spectra.
Analytical Method of Estimating Chemometric Prediction Error
Authors: Berger Andrew J. , Feld Michael S.
Published: October 2003

We present an analytical formula that estimates the uncertainty in concentrations predicted by linear multivariate calibration, particularly partial least-squares (PLS). We emphasize the analysis of spectroscopic data. The derivation addresses the important limit in which calibration error is negligible in comparison to noise in the prediction spectra. The formula is expressed in terms of standard PLS calibration parameters and the amplitude of spectral noise; it is therefore straightforward to evaluate. To test the formula, we performed PLS analysis upon simulated spectra and upon experimental Raman spectra of dissolved biological analytes in water. In each instance, the root-mean-squared error of prediction was compared to the estimate from the formula. Accurate uncertainty estimates were obtained in cases where calibration noise was lower than prediction noise, and surprisingly good estimates were obtained even when the noise levels were equal. By comparing measured and estimated uncertainties, we assessed the robustness of each PLS calibration model. The scaling of prediction uncertainty with the spectral signal-to-noise ratio is also discussed.
Analysis of 1H and 13C{1H} NMR Spectral Parameters of Diphenylchloroarsine, Diphenylcyanoarsine, and 10-Chloro- 5,10-Dihydrophenarsazine: Identification of the Compounds through Reference to Simulated Spectra
Authors: Mesilaakso Markku , Tolppa Eeva-Liisa , Nousiainen Paula
Published: October 2003

The 1H and 13C{1H} nuclear magnetic resonance (NMR) spectra of diphenylchloroarsine, diphenylcyanoarsine, and 10-chloro-5,10-dihydrophenarsazine were recorded from samples prepared in CDCl3, CD2Cl2, and (CD3)2CO. Spectra were analyzed, and detailed 1H NMR spectral parameters were determined by iterative analysis. Simulation of spectra and their use as reference spectra for identification of the compounds under different conditions are discussed.
Observation of Atom and Ion Clouds Produced from Single Droplets of Sample in Inductively Coupled Plasmas by Optical Emission and Laser-Induced Fluorescence Imaging
Authors: Olesik John W. , Kinzer Jeffery A. , McGowan Garrett J.
Published: October 2003

An instrument to obtain optical emission and laser-induced fluorescence images of atom or ion clouds, each produced from isolated, monodisperse droplets of sample in an inductively coupled plasma, is described. An excimer laser pumped dye laser is used to produce a large (28-mm × 24-mm) beam for saturated fluorescence from atoms or ions throughout a large portion of the ICP. An intensified charge-coupled device (ICCD) detects optical emission or laser induced fluorescence snapshot images at the focal plane of an aberration-corrected slitless spectrograph. Images produced from a single laser pulse can be detected. Double-exposure emission images with 1-μs gate times can be acquired to monitor the movement of atom or ion clouds produced from a single droplet of sample solution. Variations in the number of atoms or ions produced as a function of time (or height) in the plasma can be monitored. Excitation in the plasma can be assessed from ratios of emission to fluorescence intensities.
Newton Method of Successive Approximations for the Linearization of the Calibration Curves of Chromium, Copper, Lead, Manganese, Silver, and Thallium in Zeeman Graphite Furnace Atomic Absorption Spectrometry
Authors: Yuzefovsky Alexander I. , Lonardo Robert F. , Zhou Jack X. , Michel Robert G.
Published: October 2003

A new approach for the linearization of calibration curves in graphite furnace atomic absorption spectrometry (GFAAS) with Zeeman background correction was tested experimentally in an intermediate concentration region before rollover. The computational procedure employed the Newton method of successive approximations and was based on the theoretical model of L'vov et al. The calculations were based on three measured parameters: the rollover absorbance, Ar; the sensitivity ratio at the rollover point, R′; and the original background-corrected peak absorbances Az. This computational procedure generated corrected normalized integrated absorbance values A0,n with the slope identical to the slope of the original linear part of the calibration curve. The new computational procedure was employed for the linearization of calibration curves of chromium, copper, lead, manganese, silver, and thallium in Zeeman GFAAS under stabilized temperature platform furnace (STPF) conditions. Overall, the new computational procedure was able to extend the linear range of the calibration curves by a factor of 2–3 for the tested elements.
Calibration Transfer from Sample Cell to Fiber-Optic Probe
Authors: Chen Chi-Shi , Brown Chris W. , Lo Su-Chin
Published: October 2003

A calibration transfer method, piecewise direct standardization (PDS), was applied to a set of two-component samples measured on the same UV-visible spectrometer with the use of a cuvette cell with a 10-mm pathlength and a fiber-optic probe with a 2-mm pathlength. Piecewise direct standardization proceeds by determining a structured transformation matrix using the spectra of a few samples measured with both devices. This transformation matrix can then be used to transform any spectrum measured on one device to that obtained on another device, thereby making the calibration model transferable between devices. We used the spectra measured in a cuvette as the standard set and transferred the calibration model obtained for these spectra to spectra measured with a 2-mm fiber-optic probe on the same instrument. The total standard error of prediction (SEP) for the fiber-optic probe was 5.84 before the calibration transfer and 1.87 afterwards. Spectra were also processed by taking the Fourier transform prior to the calibration transfer. The 512 data points in each spectrum were compressed to 32 terms, starting with the first term after the dc offset. This processing reduced the background and the noise. As a consequence, in the Fourier domain, the total SEP was 5.69 before the calibration standardization and 0.79 after the calibration standardization. A calibration transfer was also performed between two fiber-optic probes; the total SEP in the spectral domain was 2.16 prior to the transfer and 1.04 after the transfer, whereas in the Fourier domain the SEP was 1.50 prior to the transfer and 0.77 after the transfer.
Application of Molecular Spectroscopy in the Mid-Infrared Region to the Determination of Glucose and Cholesterol in Whole Blood and in Blood Serum
Authors: Budínová G. , Salva J. , Volka K.
Published: October 2003

The feasibility of applying molecular spectroscopy in the mid-infrared region to the quantitation of glucose and cholesterol in whole blood and in blood serum was examined by measuring the samples in the dry state on a polyethylene carrier. The partial least-squares (PLS) algorithm was employed to set up the calibration models. Analysis was performed by normalizing the spectra to a standard area. Evidence that this approach is warranted was obtained through experiments where potassium thiocyanate served as the internal standard. The following average PRESS1/2 values (PRESS stands for prediction residual error sum of squares) emerged from the calibration: glucose, 22.3 mg/dL; cholesterol, 31.3 mg/dL. Such errors are comparable with those achieved in attenuated total reflectance (ATR) measurements. The calibration models set up for blood serum samples fit better than those for whole blood samples. If the procedure of sample application onto the carrier is improved, the method may work well for the determination of glucose and cholesterol in whole blood and in blood serum.
Improved Prediction Error Estimates for Multivariate Calibration by Correcting for the Measurement Error in the Reference Values
Authors: Faber Klaas , Kowalski Bruce R.
Published: October 2003

The validation of multivariate calibration models using measured reference values leads to a so-called apparent prediction error estimate, which is systematically larger than the true prediction error. The reason for this difference is clear: the measured reference values contain an irrelevant random component, the measurement error, which cannot be predicted by any model, not even the “true” one. However, the contribution of the measurement error in the reference values to the apparent prediction error estimate is interpreted as an inadequacy of the calibration model rather than an inadequacy of the reference values themselves. This phenomenon of confounding has been pointed out recently by several researchers, but no generally applicable solution was given. In this paper we propose a simple correction procedure that yields a more realistic estimate of the true prediction error. A large potential improvement over the conventional estimate is demonstrated for a variety of applications taken from the literature.
Regularized Method of Spectral Curve Deconvolution
Authors: Buslov Dmitrii K. , Nikonenko Nataliya A.
Published: October 2003

A regularized method of spectral curve deconvolution is proposed. This method is based on three fundamental principles: the regularized method of solving the convolution equation; the use, instead of the apodization function, of the digital low-pass filter, which permits exact knowledge of its characteristics; and the use of the Fourier transform modulus of the spectrum being treated for obtaining a priori information about the frequency characteristics of the solution and noise, required for determination of the optimum parameters of the regularizing operator. The regularized method of de-convolution permits the acquisition of an approximately stable solution for the deconvolution problem of spectral curves, which moves toward an exact solution with the decrease of the experimental spectrum error. Examples are given of the application of the regularized method of deconvolution to simulated and experimental IR spectra. A conclusion about the expediency of using the given method for resolution enhancement in complex spectra is made.
Acousto-Optic Signal Modulation for Atomic Emission Spectrometry Background Correction
Authors: Spudich Thomas M. , Pelz Brian A. , Carnahan Jon W.
Published: October 2003

An acousto-optic diffraction device is mounted within a polychromator to perform spectral shifting for the purpose of background correction for atomic spectrometry. Controlling the applied frequency to the acousto-optic allows “on-line” and “off-line” spectral observations. Preliminary investigations included characterization of the behavior of the photomultiplier tube (PMT) signal output at various acoustic frequencies and applied powers to verify the applicability of the system. Low-rate (0.1 Hz) frequency modulation was performed to successfully test the applicability of the background-correction system.
Method for the Determination of the Composition of Diesel Engine Piston Deposits by Infrared Spectroscopy
Authors: Shurvell H. F. , Clague A. D. H. , Southby M. C.
Published: October 2003

A chemical method for separating diesel engine piston deposits into various organic and inorganic components is described. The components are subsequently analyzed by infrared spectroscopy. The method is illustrated with examples of deposits removed from the upper lands and upper ring grooves of pistons taken from heavy-duty diesel engine tests. Subtle chemical differences were observed between two deposits removed from upper lands of pistons taken from diesel engine tests which had been carried out with the use of lubricating oils with different formulations. More obvious differences were found between the deposits taken from the upper land areas and the upper ring grooves. These results indicate that a combined chemical and spectroscopic approach has the potential to provide detailed chemical information about engine deposits.
Near-Infrared Heptamethine Cyanine Dyes: A New Tracer for Solid-Phase Immunoassays
Authors: Williams Richard J. , Peralta Jose Mauro , Tsang Victor C. W. , Narayanan Narasimhachari , Casay Guillermo A. , Lipowska Malgorzata , Strekowski Lucjan , Patonay Gabor
Published: October 2003

Near-infrared (near-IR) fluorescence has been used to develop a solid-phase immunoassay that detects trace amounts of human immunoglobulin (HuIgG). Various concentrations of HuIgG bound to a nitrocellulose surface were determined from the fluorescence generated by near-IR labeled goat anti-human antibody (GAHG) bound to the HuIgG. The GAHG was labeled with a heptamethine cyanine fluorophore that has spectral properties in the near-IR region (above 780 nm). These fluorophores are versatile because they can be modified for several bioanalytical applications. Fluorescence was detected with a near-IR fluorescence instrument previously developed in the laboratory. Two cyanine fluorophore labels were evaluated for the ability to selectively bind to GAHG on a nitrocellulose matrix with a minimal amount of background interference. After the most appropriate near-IR fluorophore was selected, the labeling of GAHG was optimized under aqueous conditions. The most effective GAHG–dye conjugates were used to develop an immunoassay to detect various concentrations of HuIgG. The results are presented, here. Solutions of HuIgG with concentrations as low as 10−10 molar have been detected with a minimum of interference.
Stack Gas Pollutant Detection Using Laser Raman Spectroscopy
Authors: Kumar Praveen C. , Wehrmeyer Joseph A.
Published: October 2003

An experimental system to investigate the feasibility of using laser Raman spectroscopy to detect stack gas pollutants is described. With spontaneous Raman spectroscopy, one unit is capable of measuring all gas species simultaneously and, when applied to a continuous emissions monitoring (CEM) system, could both simplify it and improve reliability. Minimum detectabilities with the use of this weak light scattering process were determined for the three primary pollutants from coal-based power plants: carbon monoxide (CO), sulfur dioxide (SO2), and nitric oxide (NO). A frequency-doubled, pulsed Nd:YAG laser was used to excite the test gas held in a sample cell. A charge-coupled device connected to a spectrometer was used as the detection system, providing complete spectral information. A set of experiments was carried out for different concentrations of the three test gas species. With a 200-s integration time, the following minimum detectability limits were obtained: 100 ppm for SO2, 250 ppm for CO, and 250 ppm for NO. A mixture of all three pollutants in a base of N2 was made to simulate typical stack gas mixtures. Baseline strength and associated shot noise are more severe when gas mixtures are being analyzed. One possible explanation is the broad-band fluorescence of NO2, perhaps produced photolytically. System modifications to improve minimum detectabilities are discussed.
Application of a Spectroscopic Infrared Focal Plane Array Sensor for On-Line Identification of Plastic Waste
Authors: Van Den Broek W. H. A. M. , Wienke D. , Melssen W. J. , Feldhoff R. , Huth-Fehre T. , Kantimm T. , Buydens L. M. C.
Published: October 2003

A spectroscopic near-infrared imaging system, using a focal plane array (FPA) detector, is presented for remote and on-line measurements on a macroscopic scale. On-line spectroscopic imaging requires high-speed sensors and short image processing steps. Therefore, the use of a focal plane array detector in combination with fast chemometric software is investigated. As these new spectroscopic imaging systems generate so much data, multivariate statistical techniques are needed to extract the important information from the multidimensional spectroscopic images. These techniques include principal component analysis (PCA) and linear discriminant analysis (LDA) for supervised classification of spectroscopic image data. Supervised classification is a tedious task in spectroscopic imaging, but a procedure is presented to facilitate this task and to provide more insight into and control over the composition of the datasets. The identification system is constructed, implemented, and tested for a real-world application of plastic identification in municipal solid waste.
Near-Infrared Spectroscopy with a Dispersive Waveguide Device
Authors: Stallard Brian R. , Rowe Robert K. , Howard Arnold J. , Hadley G. Ronald , Vawter Gregory A. , Wendt Joel R. , Fritz Ian J.
Published: October 2003

Miniature, low-cost sensors are in demand for a variety of applications in industry, medicine, and environmental sciences. As a first step in developing such a sensor, we have etched a grating into a GaAs rib waveguide to serve as a wavelength-dispersive element. The device was fabricated with the techniques of metal-organic chemical vapor deposition, electron-beam lithography, optical lithography, and reactive ion-beam etching. While full integration is the eventual goal of this work, for the present, a functional spectrometer was constructed with the addition of a discrete source, sample cell, lenses, and detector. The waveguide spectrometer has a spectral resolution of 7.5 nm and a spectral dispersion of 0.11°/ nm. As presently configured, it functions in the spectral range of 1500 to 1600 nm. A demonstration of the analytical capability of the waveguide spectrometer is presented. The problem posed is the determination of diethanol amine in an ethanol solution (about 10 to 100 g/L). This procedure involves the detection of the first overtone of the NH stretch at 1545 nm in a moderately absorbing solvent background. The standard error of prediction for the determination was 5.4 g/L.
Investigation of the Dynamics of Copper Plasma Generated from a Laser-Ablated Target Using Optical Emission Analysis
Authors: Wu J. D. , Pan Q. , Chen S. C.
Published: October 2003

Spatially resolved and integrated spectroscopies, especially temporal emission profile measurements, were used to examine the plume emissions associated with copper plasma generated by 308-nm excimer laser ablation at reduced pressures (< 1.0 × 10−1 Pa), by which the composition and dynamics of the plasma were investigated. It is found that, even for the same emitting species, the temporal and spatial behaviors of the emissions originating from different transitions can be very different. Three types of emission lines are clearly evident, which reveal the characteristics of the plasma. The plasma forms as a result of laser ablation and evolves from breakdown of the ablation-created copper vapor to electron-collisional expansion dynamics. At the initial stage, the plasma involves a large amount of Cu(II) and high energy-excited Cu(I) species, and then evolves to consist mainly of low energy-excited Cu(I) species. The results also show that the plasma maintains higher temperature for a quite a long time, and cool electron-impacting excitations determine the plasma behavior while it expands far away from the target.
Double Polarization Modulation Interferometry
Authors: Polavarapu Prasad L.
Published: October 2003

The concepts of a double polarization modulation interferometer and the experimental measurements verifying these concepts are presented. This interferometer serves as an analytical tool for the characterization of polarization modulation devices. In addition, for polarization difference measurements this interferometer offers four times better efficiency over widely used amplitude-division interferometers.
Use of 13C Nuclear Magnetic Resonance Spectroscopy and Principal Component Analysis for Automated Analysis of Styrene/Butadiene Copolymers
Authors: Walsh Neil G. , Hardy James K. , Rinaldi Peter L.
Published: October 2003

Principal component analysis (PCA) is used here to determine percent composition of the four monomer units styrene, 1,2-butadiene (vinyl), trans-1,4-butadiene ( trans), and cis-1,4-butadiene ( cis) in styrene/butadiene rubber (SBR) copolymers and the three monomer units (vinyl, trans, and cis) in butadiene rubber (BR) polymers. Comparison of PCA with current methods is described. Cluster analysis is used to classify the SBR and BR into groups.
Use of Normalized Relative Line Intensities for Qualitative and Semiquantitative Analysis in Inductively Coupled Plasma Atomic Emission Spectrometry Using a Custom Segmented-Array Charge-Coupled Device Detector. Part III: Application to Laser Ablation
Authors: Cabalin Luisa Maria , Mermet Jean-Michel
Published: October 2003

In a previously published work, a procedure based on both line correlation and normalized line intensity ratios was described to perform qualitative analysis in inductively coupled plasma atomic emission spectrometry based on the use of solutions. In this work, this procedure was applied to dry aerosols obtained by UV laser ablation. Since the procedure relies on the comparison of experimental normalized intensity ratios with stored normalized intensity ratios usually obtained by using synthetic solutions, a limitation was observed because it was found that wet and dry aerosols resulted in different plasma conditions and, therefore, different normalized intensity ratios. This limitation was overcome in the present work by adding a small amount of hydrogen (40 mL min−1) to the gas which carried the ablated material. Plasma conditions were then similar to those observed with aqueous solutions. Good agreement in terms of the normalized intensity ratios was obtained for different types of ablated materials such as steel, glass, and polymers.
Infrared-Optical Characterization of Metallic Island Films
Authors: Röseler Arnulf , Korte Ernst-Heiner
Published: October 2003

The ellipsometric infrared spectra of a metallic island film indicate its potential for surface-enhanced infrared absorption (SEIRA). Such a film is characterized by unique optical constants, and these can be simulated by using an effective-medium approach.
Determination of the Excitation Temperature in a Nonthermodynamic-Equilibrium High-Pressure Helium Microwave Plasma Torch
Authors: Quintero M. C. , Rodero A. , García M. C. , Sola A.
Published: October 2003

This paper analyzes the influence of the departure from thermodynamic equilibrium on three spectroscopic methods for determining the excitation temperature: the classical Boltzmann plot method, the method of absolute intensity measurements, and the method of the ratio of atomic to ionic lines for one element. Use of these methods is illustrated with experiments conducted in a helium microwave plasma in nonthermodynamic equilibrium produced by an axial injection torch at atmospheric pressure. The excitation temperature was determined at a variable microwave power and different positions along the flame. The results are discussed in terms of the atomic-state distribution function (ASDF) calculated for the plasma.