bluuebunny/crossref_metadata_2025 huggingface dataset:
Sizing of Polymer-Coated Spherical Air Bubbles
Authors: Sbanski O. , Kiefer W. , Popp J. , Lankers M. , Räßling G.
Published: October 2003

In this paper we present a fast analytical approach based on Lorenz–Mie theory, which allows us to determine the unknown shell and core radii of two-layered microparticles with refractive indices of 1.0 (air) of the core and 1.5 of the shell, e.g., polymer-coated air bubbles. For this to be achieved, a single particle has to be illuminated (sequentially) both with monochromatic laser light and with a white light source, and the scattered light intensity has to be recorded as a function of the scattering angle in the range from 0° to 170°. Using the autocorrelation and the Fourier transformation of these phase functions, one can deduce the unknown inner and outer radii by comparison with theoretically calculated gauge curves.
Fluorescence Excitation Volume in Two-Photon Microscopy by Autocorrelation Spectroscopy and Photon Counting Histogram
Authors: Chirico Giuseppe , Olivini Francesca , Beretta Sabrina
Published: October 2003

We compare two methods for the measurement of the excitation volume of an optical inverted microscope for two-photon excited fluorescence spectroscopy. The measure of the decay time of the fluorescence autocorrelation function gives the particles' diffusion time in the excitation volume, and from an a priori knowledge of the diffusion coefficient we can estimate the excitation volume. On the other hand, we can count the average number of particles in the excitation volume by analyzing the histogram of the fluorescence photon counting, and from the knowledge of the fluorophores' concentration we obtain the excitation volume. We show that the measurements of the excitation volume based on the analysis of the correlation function are very close, for a wide range of excitation volumes (0.1 fL < VEXC < 6 fL), to those obtained with no a priori assumptions from the analysis of the photon counting histograms. Moreover, we suggest that the study of the relation between the average number of particles in the excitation volume and the nominal concentration can be a valuable tool in verifying the good alignment of the optical setup.
Examination of the Effect of Heating on the Secondary Structure of Avidin and Avidin—Biotin Complex by Resolution-Enhanced Two-Dimensional Infrared Correlation Spectroscopy
Authors: Ismoyo Fenny , Wang Yan , Ismail Ashraf A.
Published: October 2003

The Fourier transform infrared (FT-IR) spectra of avidin dissolved in D2O in the absence and the presence of biotin were recorded as a function of temperature over the range of 25–95 °C. At ambient temperature, the spectra revealed differences in secondary structure between uncomplexed avidin and avidin complexed to biotin. In the presence of biotin, avidin underwent slower H–D exchange, demonstrating that when complexed to biotin, avidin adopts a more compact structure that is less accessible to solvent molecules. In addition, examination of the amide I' band in the spectrum of the avidin–biotin complex revealed the presence of a new intramolecular β-sheet structure that is less exposed to solvent. Upon heating to 85 °C, aggregation of avidin occurred with the formation of extended intermolecular antiparallel β-sheet structures. When avidin was complexed to biotin, significant changes in its secondary structure were observed with increasing temperature, but the majority of these changes were found to be reversible upon decreasing the temperature, and no spectral bands associated with aggregate formation were observed over the temperature range examined. The effect of increasing temperature on the secondary structure of avidin in the presence and absence of biotin was further investigated by two-dimensional infrared (2D-IR) correlation spectroscopy. The 2D analysis of the spectra of the avidin–biotin complex was facilitated by the use of Fourier self-deconvolved spectra to generate the synchronous and asynchronous 2D contour maps, providing very sharp and well-resolved cross peaks. Examination of the synchronous and asynchronous contour maps generated from the IR spectra of avidin recorded as a function of increasing temperature revealed that the unfolding of α-helical structures and the disruption of turns preceded the unfolding of the β-sheet structures within the avidin. Subsequently, the unfolded protein formed intermolecular antiparallel β-sheet structures. The resultant β-sheet structures did not change upon cooling of the solution to ambient temperature. The avidin–biotin complex unfolded via a different pathway, following a sequence of events where the extended β-sheet structure unfolds first, followed by the unfolding of α-helical structures. This behavior in turn is followed by an increase in the antiparallel β-sheet structures. Upon cooling of the solution, the avidin–biotin complex refolded via the same pathway. These studies reveal the potential benefit of employing resolution-enhanced two-dimensional (RE-2D) IR correlation spectroscopy in the study of protein dynamics.
Comparative Two-Dimensional Fourier Transform Infrared Correlation Spectroscopic Study on the Spontaneous, Pressure-, and Temperature-Enhanced H/D Exchange in β-Lactalbumin
Authors: Dzwolak Wojciech , Kato Minoru , Shimizu Akio , Taniguchi Yoshihiro
Published: October 2003

Two-dimensional Fourier transform infrared FT-IR was applied for the examination of the H/D exchange process in D2O solutions of bovine α-lactalbumin. The slow spontaneous H/D exchange at 25 °C was compared with pressure-enhanced and temperature-enhanced H/D exchange. The H/D-exchange process, which takes 48 h at 25 °C and under atmospheric pressure, is completed within 3 h when pressure is gradually elevated up to 180 MPa, or when temperature is increased up to 42.5 °C. Although the slow room-temperature H/D exchange and the fast pressure or temperature-enhanced H/D exchange feature a high degree of similarity between the corresponding second-derivative spectra, the two-dimensional (2D) FT-IR correlation maps revealed that upon the heat treatment the order in which the H/D exchange takes place in the structural domains of α-lactalbumin is altered. It has been observed that these differences can be explained in light of the known properties of α-lactalbumin and the crystallographic data.
Infrared Rheo-Optics of Bombyx Mori Fibroin Film by Dynamic Step-Scan FT-IR Spectroscopy Combined with Digital Signal Processing
Authors: Sonoyama Masashi , Nakano Tatsuhiko
Published: October 2003

Recently developed dynamic step-scan FT-IR spectroscopy combined with software-based digital signal processing (DSP) was applied for infrared rheo-optical measurements of isotactic polypropylene and regenerated Bombyx mori silk fibroin film undergoing sinusoidal mechanical strain. Comparative measurements of dynamic infrared spectra of polypropylene film using the DSP-based method and two lock-in amplifiers (LIAs) indicated that a high signal-to-noise ratio (SNR) advantage is attained by the DSP method compared with the LIA method. With the DSP technique, dynamic spectra of Bombyx mori silk fibroin film with high SNR were successfully recorded in the whole mid-infrared region in only 30 min. The dynamic spectra revealed that stress-induced dynamic reorientation in fibroin film is mainly localized in the segment with β-sheet conformation and is almost synchronous with the applied mechanical strain. Two-dimensional (2D) correlation analyses of the dynamic spectra showed that (1) the broad amide I band is resolved into three components whose positions are dependent on secondary structures, (2) the dynamic behavior of tyrosine residues was extracted by separation of the feature due to its aromatic side chains from the broad envelope of the amide I band in the 2D asynchronous map, and (3) the dynamic behavior of the amide A and B modes is the same as that of the amide II mode, when the mechanical strain is applied to fibroin film.
Two-Dimensional Vibrational Correlation Spectroscopic Study on the Crystallization Process of Poly(Ethylene-2,6-Naphthalate)
Authors: Kimura Fumiko , Komatsu Mamoru , Kimura Tsunehisa
Published: October 2003

Conformation changes during the crystallization process of poly(ethylene-2,6-naphthalate), including the induction period, were investigated by means of generalized two-dimensional correlation spectroscopy. A broad carbonyl stretching vibration band, as well as a broad band for a naphthalene ring vibration, was resolved in terms of the coplanarity of the carbonyl and the naphthalene ring. A difference in conformation change was found between cold crystallization and melt crystallization.
Comparison between Conventional Spectral Analysis Methods, Chemometrics, and Two-Dimensional Correlation Spectroscopy in the Analysis of Near-Infrared Spectra of Protein
Authors: Murayama Koichi , Czarnik-Matusewicz Bogsława , Wu Yuqing , Tsenkova Roumiana , Ozaki Yukihiro
Published: October 2003

The present study has aimed at comparing three methods for analyzing near-infrared (NIR) spectra: conventional spectral analysis methods, chemometrics, and generalized two-dimensional (2D) correlation spectroscopy. In a comparison of these approaches, NIR spectra were measured for aqueous solutions of human serum albumin (HSA) with the concentration range of 0.5–5.0 wt %. Synchronous and asynchronous 2D correlation spectra were generated from the concentration-dependent NIR spectral variations of HSA in distilled water. The first and second loadings plots were calculated for principal component analysis (PCA) models based upon the above NIR spectral data. It was found that slice spectra calculated from the synchronous spectra are very close to the first loadings plots and that slice spectra from the asynchronous spectra have a close resemblance to the second loadings plots. The reasons why the synchronous and asynchronous spectra bear close resemblance to the first and second loadings plots for the PCA model, respectively, are discussed in the paper.
Molecular and Lamellar Orientation of α- and β-Transcrystalline Layers in Polypropylene Composites by Polarized Confocal Micro-Raman Spectroscopy: Raman Imaging by Static Point Illumination
Authors: Fernández M. R. , Merino J. C. , Gobernado-Mitre M. I. , Pastor J. M.
Published: October 2003

Crystallization of isotactic polypropylene (iPP) from the melt in the presence of poly(ethyleneterephthalate) (PET) fibers has been shown to produce preferential nucleation at the fiber surfaces leading to formation of columnar or transcrystalline growth. The crystalline development of PP has been examined by using optical microscopy. Polarized confocal micro-Raman spectroscopy was carried out to investigate the qualitative molecular orientation of alpha and beta transcrystalline regions around PET fibers embedded in a PP matrix. Uncoated PET fibers generate alpha transcrystallinity (α-TC) due to its strong α-nucleation ability. By coating the reinforcing PET fibers with the appropriate nucleating agent, one induces beta transcrystallinity (β-TC) in the PET fiber-reinforced iPP composites. α-TC layers have been also observed with the use of PET sheets as nucleating substrates. The spectroscopic results reveal that lamellar orientation in alpha transcrystalline structures differs significantly from the beta form. Furthermore, two different molecular orientations in the α-TC have been detected.
IR Microscopic Imaging of Pathological States and Fracture Healing of Bone
Authors: Mendelsohn Richard , Paschalis Eleftherios P. , Sherman Pamela J. , Boskey Adele L.
Published: October 2003

The application of IR microscopic imaging to the study of bone disease and fracture healing is demonstrated. Samples of normal and osteoporotic human iliac crest biopsies were prepared and examined at ∼6–10 μm spatial resolution and 8 cm−1 spectral resolution with a 64 × 64 MCT focal plane array detector coupled to a Fourier transform infrared (FT-IR) microscope and a step-scanning interferometer. Two spectral parameters, one that monitors the extent of mineral (hydroxyapatite) formation in the tissue and another that monitors the size/perfection of the crystals, were compared in the samples generated from normal and pathological tissues. The average mineral levels in the osteoporotic sample were reduced by ∼ 40% from the normal. In addition, the crystal size/perfection was substantially enhanced in the disease state. The applicability of IR imaging techniques to the study of therapeutic intervention was also investigated in a study of the effects of estrogen therapy on fracture healing in rat femurs. Femurs were examined by IR microscopic imaging 4 weeks after fracture. IR imaging showed that the mineral level was enhanced in estrogen-treated samples. In addition, the crystals were larger/more perfect in the treated specimens. These data demonstrate the utility of IR spectroscopic imaging for the study of pathological states of hard tissue.
Measurement of the Sensitivity and Photometric Accuracy of FT-IR Spectrometers
Authors: Bowie Bryan T. , Griffiths Peter R.
Published: October 2003

A method has been developed to investigate the sensitivity and photometric accuracy of a Fourier transform infrared (FT-IR) spectrometer by statistically analyzing a set of spectra of a 75 μm thick film of polyethylene terephthalate (PET). These tests were applied to three commercial FT-IR spectrometers. Although the photometric accuracy of all three instruments was generally better than 0.1%, small artifacts that could not be removed by signal averaging were often observed where strong bands should have a transmittance of less than 0.01%. Binding of the moving mirror of one of the spectrometers appeared to degrade its performance. When the standard deviation of the noise on 100% lines was calculated in the conventional way, none of the instruments gave efficient signal averaging after 25 scans had been coadded, because of small slopes in the baseline. By calculation of the noise level by successive difference, signal averaging was improved, but even with this approach the noise level on one of the instruments did not decrease after 100 scans had been averaged.
Two-Photon Excitation in Square and Cylindrical Capillaries
Authors: Zugel S. A. , Lytle F. E.
Published: October 2003

The loss in sensitivity of two-photon excited fluorescence, when switching from a 1 cm cell format to square and cylindrical capillaries, is described quantitatively. Sensitivities are determined with calibration curves, and beam shapes are computed with optical design software. The decreased sensitivity with square capillary (75 μm i.d.) is shown to be the simple result of a truncated pathlength resulting in a factor of ∼ 2 reduction in sensitivity from a 1 cm cell. Cylindrical capillary of the same i.d. is characterized by astigmatism caused by the curved refractive index boundary in addition to the truncation. The astigmatism is determined to be smaller in the thin-walled capillary, allowing for better performance than the thick-walled capillary. In fact, the thin-walled capillary is found to have similar performance to the square capillary.
On the Role of Statistical Weighting in the Least-Squares Analysis of UV-Visible Spectrophotometric Data
Authors: Tellinghuisen Joel
Published: October 2003

Spectrophotometric data are inherently heteroscedastic, which means that least-squares component analyses of absorbance spectra should properly employ weighted fits. The effects of neglecting weights (the common practice) is examined through Monte Carlo calculations on a three-peak model having two closely overlapping components of comparable strength and a third component that appears as a weak shoulder. The results show statistically significant loss of precision in all parameters; however the magnitude of this loss is ≤30% for realistic conditions. For comparison, experimental spectra of I2 in CCl4 (which was the basis for the Monte Carlo test model) are similarly analyzed. These results suggest that model inadequacy is likely to be a greater practical problem than neglect of weights, because the great precision of spectrophotometric data places extreme demands on the fit model. In the present instance, for example, incorporation of a correction term for the sinusoidal error in the spectrometer wavelength significantly reduces the fit chi-square.
Self-Modeling Mixture Analysis by Interactive Principal Component Analysis
Authors: Bu Dongsheng , Brown Chris W.
Published: October 2003

A key procedure for mixture analysis in self-modeling methods is to identify a pure wavelength (or pure variable) for each component in the mixture. A pure wavelength has intensity contributions from only one of the components in a mixture. In this paper, an interactive approach based on principal component analysis (IPCA) is presented for the pure wavelength selection. The approach is developed from a combination of key set factor analysis (KSFA) and SIMPLISMA (simple-to-use interactive self-modeling mixture analysis). Since all significant principal components are included and user interaction is available during the procedure of selecting pure wavelengths, this new approach effectively resolves complicated mixture data containing highly overlapping and nonlinear absorptivities. Moreover, the noise level of the original spectra is determined from secondary principal components and used in the scaling so that pure wavelength selection reflects the signal-to-noise ratio in the data. Simulated three-component mixture spectra are used to demonstrate the IPCA method; this is followed by a general approach for analyzing an esterification reaction using mid-infrared data. The KSFA, SIMPLISMA and IPCA methods are compared by analyzing a set of near-infrared spectra of methane, ethane, and propane mixtures. Results from the three pure wavelength methods are used as inputs to the method of alternating least-squares to produce predicted spectra very similar to the spectra of the pure components.
Formation of a Cesium Plasma by Continuous-Wave Resonance Excitation
Authors: Pappas Dimitri , Smith Benjamin W. , Omenettó Nicolo , Winefordner James D.
Published: October 2003

The generation of a plasma in cesium vapor via a resonance process is described. The maximum irradiance used was 1.5 W/cm2, which is several orders of magnitude lower than the irradiances conventionally used to form plasmas. Plasma emission consisted of radiative decay from excited-state Cs atoms. Optical emission from the plasma was observed from laser powers of 200 μW with a nonintensified charge-coupled device (CCD). The ionization efficiency of the plasma was approximately 0.001, with the majority of the atoms in the plasma ionized. The plasma was found to behave linearly with respect to laser power; however nonlinear behavior was observed as the number density was altered. A collisional mechanism is proposed for the formation of the plasma.
Surface-Enhanced Raman Scattering and Imaging of Langmuir—Blodgett Monolayers of Bis(Phenethylimido)perylene on Silver Island Films
Authors: Aroca R. F. , Constantino C. J. L. , Duff James
Published: October 2003

The optical spectra of bis(phenethylimido)perylene (PhPTCD) are discussed. Surface-pressure area isotherms of floating Langmuir monomolecular layers have been obtained, and Langmuir-Blodgett (LB) molecular monolayers of the material have been fabricated on silver island substrates for surface-enhanced vibrational studies. The electronic absorption and emission spectra of solutions and thin solid films are described. The vibrational spectra, infrared and Raman for the bulk, and the surface-enhanced Raman (SERS) and resonance Raman scattering (SERRS) spectra of LB monolayers have been obtained. Surface-enhanced fluorescence (SEF) for LB films is also demonstrated. Given the unique properties of the LB coated silver surfaces, the mapping of the SERS/SERRS signal and global Raman images, at a particular vibrational wavenumber, were obtained by using the 780 and 514.5 nm laser lines. The images give a visual picture of the variation of the SERRS and SERS signal intensity on the rough metal surface.
Detection of Nitrate and Sulfate Anions by Normal Raman Spectroscopy and SERS of Cationic-Coated, Silver Substrates
Authors: Mosier-Boss P. A. , Lieberman S. H.
Published: October 2003

The use of normal Raman spectroscopy and surface-enhanced Raman spectroscopy (SERS) of cationic-coated, silver substrates to detect nitrate and sulfate ions in aqueous environments is examined. For normal Raman spectroscopy using near-infrared excitation, a linear concentration response was observed with detection limits of 260 and 440 ppm for nitrate and sulfate, respectively. Detection limits in the low parts-per-million concentration range for these anions are achieved by using cationic-coated, silver SERS substrates. Adsorption of the anions on the cationic-coated SERS substrates is described by a Frumkin isotherm.
Listening to Colloidal Silica Samples: Simultaneous Measurement of Absorbed and Scattered Light Using Pulsed-Laser Photoacoustics
Authors: Small Jeanne Rudzki , Foster Nancy S. , Amonette James E. , Autrey Tom
Published: October 2003

Laser photoacoustic spectroscopy (LPAS) has been used to simultaneously measure scattered light and absorbed light with the use of a single piezoelectric transducer detector. Samples of Ludox™ colloidal silica, with and without added potassium chromate, were illuminated with pulses of 308 or 355 nm light. Signals were measured with a 1 MHz ultrasonic transducer clamped to the side of the cuvette. The resulting oscilloscope tracing shows a pattern of signals originating from light scatter and light absorption that is consistent with experimental geometry and the speeds of light and sound, and linear with incident laser pulse energy. The absorbed light signals are independent of the distance of the laser beam from the transducer, while the scattered light signals are strongly distance-dependent. The absorbed light signals are more indicative of true sample absorbance than are readings from a standard spectrophotometer. A spectrophotometer sums contributions from scattering and absorbance to give an optical density reading, while LPAS separates scattering from absorbance to give quantitative information on each function. Scattered light and fluorescent light behave very similarly in the LPAS technique. Our experiments were done with well-characterized colloidal silica samples, but the technique is readily extended to larger, more heterogeneous, and photochemically complex biological and environmental samples.
Direct Fluorometric Determination of Total Cholesterol in Serum Using Derivatized Cholesterol Oxidase
Authors: Galbán Javier , Sierra José F. , Sebastian José M. López , de Marcos Susana , Castillo Juan R.
Published: October 2003

In this paper the use of cholesterol oxidase derivatized with a fluorescein derivative is proposed for the direct determination of total cholesterol in blood serum. The method is based on the changes in the fluorescence of the solution during the enzymatic reaction (λexe = 498 nm and λem 519 nm). A mathematical model which relates the analytical signal to the total cholesterol concentration was developed, and the model can also be used to obtain some of the thermodynamic constants of the process. The method has a linear response range up to 70 mg/L of cholesterol, a detection limit of 2.5 mg/L, and the precision was 1.0% (40 mg/L cholesterol, n = 10). The method was applied to total cholesterol determination in blood serum samples. The results were compared to those obtained by a commercial analyzer, and statistically similar results were obtained. The use of derivatized cholesterol oxidase makes it possible to simplify the methodology normally used in this type of determination (the indicator reaction is avoided and the number of reagents reduced), with the added advantage that the analytical signal is independent of the concentrations of O2 and cholesterol oxidase.
Noninvasive Measurement of Oxygenation of Hemoglobin by Direct Transmission of Near-Infrared Energy (700–1000 nm) from an Electronically Tuned Ti: Sapphire Laser Driven by a Dual Radio-Frequency Driving Method
Authors: Sato Hidetoshi , Wada Satoshi , Ling Mingyi , Tashiro Hideo
Published: October 2003

We have applied an electronically tuned Ti: sapphire (ETT) laser controlled with a dual radio-frequency driving (DRD) method to noninvasive measurements of the transmission spectra of a whole human hand in which the bands due to hemoglobin and lipid were identified. Spectra of a human hand that is more than 3 cm thick were obtained in the spectral range from 700 to 1000 nm, allowing one to probe the oxygenation of hemoglobin (Hb). Our study demonstrates that an ETT laser may be used as a potential light source for near-infrared (NIR) spectroscopy in biomedical applications. For the acquisition of NIR transmission spectra of Hb with a good signal-to-noise ratio, the laser emission was programmed electronically to fill up strong absorption bands due to water, and baseline undulation due to detection sensitivity and light scattering. The present study required more stable control of the ETT laser, so we developed the DRD method, achieving high reliability in wavelength (< 0.1 nm) and in intensity (< ± 2% per average in 10 pulses).
Development and Characterization of Directly Connected Laser Ablation/Low-Pressure Inductively Coupled Plasma Atomic Emission Spectrometry for Solid Sample Analysis
Authors: Lim Jae-Min , Kim Jae-Kuk , Lee Chang-Soon , Back Gern-Ho , Lee Yong-Ill
Published: October 2003

Laser-ablation/low-pressure inductively coupled plasma spectrometry (LA/LP-ICP) has been developed and used for quantitative elemental analysis of National Institute of Standards and Technology (NIST) alloy samples. Laser ablation was performed with a Nd:YAG laser operated in a Q-switched mode at 1064 nm (100 mJ/pulse, 10 Hz). The ablation chamber and ICP torch were directly connected by the use of a step nozzle to improve the precision in measurements and to focus the sample stream into the center of the torch. The plasma in low-pressure argon atmosphere can be easily generated within a wide range of pressure (0.2–5.0 torr) and provides a very stable and clean spectrum at most wavelength regions. The generation of a plasma “core zone”, which gives a concentrated brilliant emission, is essential for the production of efficient plasma emission. The emission of the plasma was monitored with the use of an ultraviolet-visible fiber-optic bundle and an optical multichannel analyzer (OMA). The relative standard deviation (RSD) (%) value of the copper emission intensity without a step nozzle was 11.7%, while that with a three-step nozzle was reduced to about 3.0%. Linear calibration curves were developed for the elements Cu (0.034–1.500%), Cd (0.0007–0.0155%), and Mn (0.0017–0.0480%). Detection limits [signal-to-noise (S/N) = 3] vary with the elements from 1.8 μg/g for Mn to 70.7 μg/g for Cu. Comprehensive details of our experimental apparatus and several discussions of the process studies with the use of this LA/LP-ICP are reported in this work.
Wavelength Calibration of a Dispersive Near-Infrared Spectrometer Using Trichloromethane as a Calibration Standard
Authors: Busch Kenneth W. , Soyemi Olusola , Rabbe Dennis , Humphrey Karalyn , Dundee Ben , Busch Marianna A.
Published: October 2003

Since differences in wavelength calibration between instruments are arguably a primary source of error encountered in the transfer of calibration models from one instrument to another in near-infrared (NIR) spectroscopy, a readily available, convenient, inexpensive secondary wavelength calibration standard for the NIR spectral region is needed. This paper describes the advantages of trichloromethane as a wavelength standard for the calibration of dispersive NIR spectrometers used in the transmission mode. The spectrum of trichloromethane, taken with a Fourier transform NIR spectrometer whose wavenumber scale was calibrated with the ro-vibrational lines of ethyne as determined by the National Institute of Standards and Technology (NIST), is presented. The wavelengths of four strong, sharp, well-resolved bands of trichloromethane were determined with the calibrated Fourier transform NIR spectrometer and were found to be 1152.13 ± 0.01 nm (3 v1), 1410.21 ± 0.01 nm (2 v1 + v4), 1691.9 ± 0.7 nm (2 v1), and 1861.22 ± 0.01 nm ( v1 + 2 v4). These bands were then used to calibrate the wavelength scale of a commercial 0.25 m monochromator equipped with a 300 line mm−1 grating. The calibration revealed that, while the wavelength scale of the monochromator was linear, there was a systematic error of about + 12 nm in the NIR region.
Band Assignment of Near-Infrared Spectra of Milk by Use of Partial Least-Squares Regression
Authors: Šašić Slobodan , Ozaki Yukihiro
Published: October 2003

Band assignment of near-infrared (NIR) spectra of milk has been investigated by the partial least-squares (PLS) regression method in the spectral regions of 1150–1850 and 2030–2380 nm. The shorter wavelength region (1150–1850 nm) was divided into three parts (1150–1350, 1350–1650, and 1650–1850 nm), and each part was analyzed separately. The band assignment was made through the analysis of the shapes of loadings and spectral and concentration variances explained by them. Bands at 1722 and 1754 nm and that at 1208 nm are assigned to first and second overtones of CH2 stretching vibrations of milk fats, respectively. It is revealed from the PLS regression of milk samples with constant protein content and varying fat content that two kinds of water bands exist in the 1350–1650 nm region; the first group of water bands at 1400, 1440, and 1520 nm is dependent upon the fat content, while the second group of bands at 1406 and 1486 nm seems to depend on the protein content. For all three parts in the 1150–1850 nm region it is found that other milk components such as proteins and lactose do not interfere significantly with the fat bands. For the longer wavelength region (2030–2380 nm), bands at 2302 and 2340 nm are assigned to a combination of CH2 symmetric stretching and symmetric bending vibrations of fats. No interference from other bands with the fat bands appears, although this region is rather rich in protein bands. For the proteins, only weak bands are identified at 2056, 2160, 2316, 2340, and 2368 nm. The band at 2056 nm is assigned to a combination of amide A and amide I modes, while the band at 2160 nm is due to that of amide B and amide II modes. The bands at 2316, 2340, and 2368 nm arise from combinations of CH2 stretching and bending modes of protein side chain groups. Other protein bands are strongly masked by baseline slope.
Studies of Self-Association in Alcohols (ROH) as Functions of Concentrations and Temperature. Part II: Curve Resolution of Concentration Series
Authors: Nodland Egil
Published: October 2003

Self-association of six mono-hydroxyl aliphatic alcohols in CCl4 has been investigated with the use of infrared (IR) spectroscopy and methods for curve resolution. The alcohols were 1-octanol, 1-propanol, 2,4-dimethyl-3-pentanol, 2-methyl-2-propanol, 3-ethyl-3-pentanol, and 3-methyl-2-pentanol. Curve resolution of the OH stretching region assumes that distinct associates due to hydrogen bonding can be regarded as chemical species. The resolution aimed at determining the number, the structure, and the sizes of the associates in different concentration ranges. Analyses of the spectra, in limited concentration ranges, resulted in models containing up to three different species: monomers, open-chain multimers, and cyclic multimers. The size of the multimers was found to increase with increasing alcohol concentration. The resolved concentration profiles enable prediction of molar concentrations of the different alcohol species at all solute concentrations and estimation of the equilibrium constants involved. The molar extinction coefficients for all species at all wavenumbers can also be estimated.
Raman/SEM Chemical Imaging of a Residual Gallium Phase in a Mixed Oxide Feed Surrogate
Authors: Schoonover Jon R. , Saab Andrew , Bridgewater Jon S. , Havrilla George J. , Zugates Christopher T. , Treado Patrick J.
Published: October 2003

An integrated analytical approach, which combines elemental [scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS)] and molecular (Raman) chemical imaging techniques, has been utilized for the characterization of a residual phase of gallium in mixed oxide (MOX) surrogate material. Surrogate MOX materials are comprised of CeO2 in place of PuO2. In real MOX materials, PuO2 is mixed with UO2 as a commercial fuel source. A Ga phase remains in the surrogate sample following reductive heating experiments designed to explore the removal of gallium from weapons-grade plutonium. The SEM/EDS data reveal the concentration of Ga within the grain boundaries of the sample and a distribution of Ce and O throughout the sample matrix. Molecular analysis provided by Raman chemical matrix imaging correlates with the SEM/EDS elemental imaging results. Specifically, the Raman data suggest that the matrix is comprised of CeO2 and grain boundaries are a mixed phase comprised of CeO2 with a form of Ga, most likely a CeGaO3 perovskite phase having a cubic structure.
Characterization of Uranium Oxides Using in Situ Micro-Raman Spectroscopy
Authors: Palacios M. Luisa , Taylor Stuart H.
Published: October 2003

A range of uranium compounds have been characterized using micro-Raman spectroscopy. It is possible to easily distinguish the oxides UO2, α-U3O8, and γ-UO3. Studies have also investigated the Raman spectra of uranium precursors used for the preparation of these oxides. In situ studies to probe the transformation of uranyl nitrate to uranium oxide show that the nitrate is decomposed below 300 °C. Initially an oxide similar to UO3 is produced, and this oxide gradually transforms to U3O8 as the temperature is increased to 550 °C. The use of in situ Raman studies provides a powerful technique to study the mechanism of transformation and the stability of uranium oxides under oxidizing conditions.
Thermodynamic Studies in Subsonic Gas Flows Using a Laser Diode Raman Spectrometer
Authors: Claps R. , Fink M. , Varghese P. , Young D.
Published: October 2003

We present noninvasive, spatially resolved measurements on low-pressure, subsonic, laminar gas flows using Raman spectroscopy. From the Raman signal, the density and temperature of the flow can be extracted directly, with reasonable integration times (∼10 min-1 h). The use of a high-power laser diode makes it a very attractive low-cost, efficient technique. Temperatures studied range from 290 to 790 K; the spatial resolution was 2.5 × 1 mm2 in the flow cross section, and 10–20 μm in the flow direction, within a flow profile of diam. ∼ 15 mm. The flow was generated by a conical double-nozzle system with CO2 as the sample and Ar as the sheath gas. Vibrational and rotational state population and relaxation properties in the gas flow have been studied, and nonequilibrium conditions were found. A computational fluid dynamics (CFD) calculation is compared with the data; it supports the physical model suggested within the experimental errors.
Direct Injection High Efficiency Nebulization in Inductively Coupled Plasma Mass Spectrometry under Cool and Normal Plasma Conditions
Authors: Minnich Michael G. , Montaser Akbar
Published: October 2003

The direct injection high efficiency nebulizer (DIHEN) was investigated for application to inductively coupled plasma mass spectrometry (ICPMS) with a cool plasma. Elements are organized into three categories based on their performance in the cool and normal plasma. Sensitivity, precision, and detection limits are presented for elements (39K, 40Ca, and 56Fe) that suffer from mass spectral interferences (38ArH+, 40Ar+, and 40Ar16O+) derived from the plasma gas. Figures of merit are also reported for a group of elements that are suitable for analysis using either the cool or normal plasma condition. In a departure from previous published accounts, however, a group of elements is investigated that is suitable for analysis in the cool plasma only by measurement of the metal oxide ion because the sensitivity and precision of the atomic ion are inferior to those obtained for the metal oxide ion. The sensitivity and precision obtained for these molecular species are comparable to those obtained for the atomic ions of elements that are suitable for analysis using the cool plasma. Calibration curves for the metal oxide signal as a function of the metal concentration in the cool plasma are linear over six orders of magnitude, covering the concentration range from 1 ppt to 1 ppm. Nerve tonic tablets that contain Na, Mg, K, Ca, and Fe in unspecified amounts were analyzed under cool plasma conditions.
Degenerate Four-Wave Mixing Measurements on Thin Polymer Films
Authors: Rozouvan S. , Schrepp W.
Published: October 2003

We present a model for the description of a thin polymer layer as a set of noninteracting randomly oriented molecules in order to determine dependencies between third-order nonlinear tensor components. The model results in different numbers of independent tensor components for the three-dimensional and two-dimensional cases. Degenerate four-wave mixing measurements with different angles of incidence were experimentally performed to check relations between different tensor components in accordance with the sample thickness. Numerical calculations for diffraction in the Fraunhofer approximation were applied for degenerate four-wave mixing experiments on thin films in order to study the angle dependence of the signal beam. It was shown that the distribution has vividly unsymmetrical character. The difference in the nonlinear tensor values between the traditional and the proposed procedure is almost an order of magnitude.
Time-Resolved Single Photon Counting Study of the Quenching of Fluorescent Probes by Petroleum: Probing the Energy Distribution of the Nonaliphatic Components
Authors: Nicodem David E. , Cunha M. Fernanda V. Da , Guedes Carmen L. B.
Published: October 2003

Index Headings: Petroleum; Fluorescence; Time-resolved single photon counting; TRSPC; Quenching.
Dual-Pulse LIBS Using a Pre-Ablation Spark for Enhanced Ablation and Emission
Authors: Stratis Dimitra N. , Eland Kristine L. , Angel S. Michael
Published: October 2003

In this paper we report the first observations of dual-pulse laser-induced breakdown spectroscopy (LIBS) signal enhancements by using a pre-ablation spark. In this technique a laser pulse is brought in parallel to the sample surface and focused a few millimeters above it to form an air plasma or air spark. A few microseconds later a second laser pulse, which is focused on the sample, ablates sample material and forms the LIBS plasma from which analyte emission occurs. In this way, large LIBS signal enhancements, 11-to 33-fold, are observed for copper and lead, respectively, relative to the signal in the absence of the air spark. In all cases where enhanced LIBS signals are seen, greatly enhanced sample ablation also occurs.
Detection of Chromium Aerosol Using Time-Resolved Laser-Induced Plasma Spectroscopy
Authors: Martin Madhavi , Cheng Meng-Dawn
Published: October 2003

Time-resolved laser-induced plasma spectroscopy (LIPS) has been used as a tool for the detection of chromium in aerosol. In this article, LIPS has been used to achieve the lowest limits of detection for chromium (400 ng/dscm) in droplets. A comparison with other LIPS instruments and inductively coupled plasma atomic emission spectroscopy (ICP-AES) shows that the limits of detection for chromium metal in aerosol range from 12 to 60 μg/dscm and 200 ng/dscm for LIPS and ICP-AES, respectively. We have studied the effects of laser wavelength, excitation energy, and optimum spectrometer delay time to optimize these low limits of detection. A Nd:YAG laser with output wavelengths of 1064, 532, and 266 nm has been used to study the effects of wavelength on laser energy and aerosol interactions—specifically, plasma initiation and efficiency of ionization in the detection of elemental species. Measured time-resolved spectra are used to establish the most appropriate time delay producing an optimum signal-to-background ratio.
Multi-Window Classical Least-Squares Multivariate Calibration Methods for Quantitative ICP-AES Analyses
Authors: Haaland David M. , Chambers William B. , Keenan Michael R. , Melgaard David K.
Published: October 2003

The advent of inductively coupled plasma atomic emission spectrometers (ICP-AES) equipped with charge-coupled device (CCD) detector arrays allows the application of multivariate calibration methods to the quantitative analysis of spectral data. We have applied classical least-squares (CLS) methods to the analysis of a variety of samples containing up to 12 elements plus an internal standard. The elements included in the calibration models were Ag, Al, As, Au, Cd, Cr, Cu, Fe, Ni, Pb, Pd, and Se. By performing the CLS analysis separately in each of 46 spectral windows and by pooling the CLS concentration results for each element in all windows in a statistically efficient manner, we have been able to significantly improve the accuracy and precision of the ICP-AES analyses relative to the univariate and single-window multivariate methods supplied with the spectrometer. This new multi-window CLS (MWCLS) approach simplifies the analyses by providing a single concentration determination for each element from all spectral windows. Thus, the analyst does not have to perform the tedious task of reviewing the results from each window in an attempt to decide the correct value among discrepant analyses in one or more windows for each element. Furthermore, it is not necessary to construct a spectral correction model for each window prior to calibration and analysis. When one or more interfering elements were present, the new MWCLS method was able to reduce prediction errors compared to the single-window multivariate and univariate predictions. The MWCLS detection limits in the presence of multiple interferences are 15 ng/g (i.e., 15 ppb) or better for each element. In addition, errors with the new method are only slightly inflated when only a single target element is included in the calibration (i.e., knowledge of all other elements is excluded during calibration). The MWCLS method is found to be vastly superior to partial least-squares (PLS) in this case of limited numbers of calibration samples.
New Prediction-Augmented Classical Least-Squares (PACLS) Methods: Application to Unmodeled Interferents
Authors: Haaland David M. , Melgaard David K.
Published: October 2003

A significant improvement to the classical least-squares (CLS) multivariate analysis method has been developed. The new method, called prediction-augmented classical least-squares (PACLS), removes the restriction for CLS that all interfering spectral species must be known and their concentrations included during the calibration. We demonstrate that PACLS can correct inadequate CLS models if spectral components left out of the calibration can be identified and if their “spectral shapes” can be derived and added during a PACLS prediction step. The new PACLS method is demonstrated for a system of dilute aqueous solutions containing urea, creatinine, and NaCl analytes with and without temperature variations. We demonstrate that if CLS calibrations are performed with only a single analyte's concentrations, then there is little, if any, prediction ability. However, if pure-component spectra of analytes left out of the calibration are independently obtained and added during PACLS prediction, then the CLS prediction ability is corrected and predictions become comparable to that of a CLS calibration that contains all analyte concentrations. It is also demonstrated that constant-temperature CLS models can be used to predict variable-temperature data by employing the PACLS method augmented by the spectral shape of a temperature change of the water solvent. In this case, PACLS can also be used to predict sample temperature with a standard error of prediction of 0.07 °C even though the calibration data did not contain temperature variations. The PACLS method is also shown to be capable of modeling system drift to maintain a calibration in the presence of spectrometer drift.
Using Genetic Algorithms to Select Wavelengths in Near-Infrared Spectra: Application to Sugar Content Prediction in Cherries
Authors: Roger J. M. , Bellon-Maurel V.
Published: October 2003

The best parameter for evaluating fruit taste quality is sugar content. This parameter can be nondestructively measured by nearinfrared spectrometry. Models that give the best performances are based on classical partial least-squares regression (PLSR) applied over the whole spectrum. Selecting the best wavelengths improves the precision and the robustness of these models. Genetic algorithms (GAs) applied to the results of a cross-validation make this selection in a stochastic way. The influence of GA tuning and of the cross-validation parameters is discussed. An application of this technique on cherry samples decreases the cross-validation error by 20% and divides the prediction error by more than 3.
Influence of Laser Illumination Geometry on the Power Distribution Advantage
Authors: Zhang Dongmao , Hanna Jeanette D. , Jiang Yanan , Ben-Amotz Dor
Published: October 2003

The power distribution advantage, used to limit surface optical damage by distributing laser power over a wide area, is found to depend not only on the area but also on the geometry of the illuminated region. This is demonstrated by using both theoretical heat transport calculations and experimental laser optical damage measurements. For a circular or rectangular illumination region, the power distribution advantage is a strongly nonlinear function of illumination area. For long irradiation times typical of those used in Raman imaging applications, the power required to reach a specified damage threshold temperature scales as the square root of the illumination area. However, for illumination times that are short in comparison with the ratio of the illumination area to the thermal diffusivity of the sample, the power distribution advantage is a more linear function of illumination area. Experimental measurements of the melting threshold of black plastic as a function of laser spot size confirm the theoretical predictions in both the long and short irradiation time limits.
New 224 nm Hollow Cathode Laser-UV Raman Spectrometer
Authors: Sparrow Mark C. , Jackovitz John F. , Munro Calum H. , Hug William F. , Asher Sanford A.
Published: October 2003

We have developed an optimized high-throughput UV Raman spectrometer that utilizes a simple, inexpensive new 224.3 nm hollow cathode laser. This quasi-continuous wave (CW) 224.3 nm laser can be used to detect sub-ppm concentrations of aromatic and polycyclic aromatic hydrocarbons in aqueous solutions. This excitation is also useful for studying aromatic amino acids in proteins. We demonstrate the utility of this spectrometer to study the environments of tyr and trp in horse heart myoglobin.
Mediaeval Pigments in the Monastery of San Baudelio, Spain: A Raman Spectroscopic Analysis
Authors: Edwards H. G. M. , Rull F. , Vandenabeele P. , Newton E. M. , Moens L. , Medina J. , Garcia C.
Published: October 2003

The Raman spectra of specimens of the 11th century mediaeval wall paintings from the small, isolated monastery of San Baudelio de Casillas, Soria, Spain, have revealed a color palette based on haematite, charcoal/soot, litharge, goethite, minium, and a copper salt (probably malachite or verdigris). Unlike other mediaeval artworks of the same period found in Castille y Leon in the northern part of the Duero River (Burgos and Leon), which contain a rich blend of pure and mixed pigments such as cinnabar, realgar, orpiment, barytes, and lapis lazuli, none of these are found to occur at this site. Similarly, litharge has not been identified previously at these other sites north of the Duero River. The materials found in the present study were probably all available in the immediate vicinity of the monastery and confirm the recorded history that the inhabitants were of a closed order from the Arabic kingdom of Cordoba, with little outside contact.