bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Fluorescent Reporter Group Structure on the Dynamics Surrounding Cysteine-26 in Spinach Calmodulin: A Model Biorecognition Element
Authors: Watkins A. Neal , Bright Frank V.
Published: October 2003

Conformational changes associated with the Ca2+-dependent activation of spinach calmodulin (CaM) have been assessed in aqueous solution by using steady-state and frequency-domain fluorescence spectroscopy of acrylodan-, fluorescein-, and tetramethylrhodamine-labeled CaM. Spinach CaM was site-selectively labeled at cysteine-26 so we could study the dynamics at a well-defined location within the protein. By using multiple fluorophores attached to the same site, we determined the Ca2+-dependent changes in the CaM global rotational dynamics, and also determined how the local fluorophore dynamics were affected by the fluorophore polarity, size, and charge. Upon binding Ca2+ at pH 7.00, spinach CaM changes its conformation by exposing the acrylodan fluorescent reporter group to a more dipolar environment. There is also a concomitant increase in the fluorescein pKa when Ca2+ binds to CaM. The global motions of spinach CaM are described by rotational reorientation times of 8.4 and 10.5 ns for the apo- and Ca2+ -saturated CaM at 23 °C. In light of all the available data in the literature on CaM, these results are consistent with a small expansion of the CaM globular domains, a bending and/or rotation of the central peptide chain that connects the globular domains that host the four Ca2+ binding sites (two per domain) in such a way that residues 27 and 139 are brought closer to one another, and/or a difference in the degree of hydration between the apo- and Ca2+ -saturated CaM.
Electrothermal Atomization Laser-Excited Atomic Fluorescence Spectroscopy for the Determination of Indium
Authors: Aucélio R. Q. , Smith B. W. , Winefordner J. D.
Published: October 2003

A dye laser pumped by a high-repetition-rate copper vapor laser was used as the excitation source to determine indium at parts-pertrillion level by electrothermal atomization laser-excited atomic fluorescence spectrometry (ETA-LEAFS). A comparison was made between wall atomization, in pyrolytic and nonpyrolytic graphite tubes, and platform atomization. The influence of several chemical modifiers either in solution or precoated in the graphite tube was evaluated. The influence of several acids and NaOH in the analyte solution was also studied. Optimization of the analytical conditions was carried out to achieve the best signal-to-background ratio and consequently an absolute limit of detection of 1 fg. Some possible interferents of the method were evaluated. The method was evaluated by determining indium in blood, urine, soil, and urban dust samples. Recoveries between 99.17 and 109.17% are reported. A precision of 4.1% at the 10 ng g−1 level in water standards was achieved.
Pulse Thermal Lens Spectrometry of β-Carotene in Flow Systems at Atmospheric- and High-Pressure Conditions
Authors: Amador-Hernandez J. , Fernandez-Romero J. M. , Ramis-Ramos G. , De Castro M. D. Luque
Published: October 2003

A dual-laser thermal lens spectrometer with a pulse pump-probe coaxial configuration was constructed, optimized, and used to study the influence of flow rate, cell design, nature of the solvent, photostability of the chromophore, and pressure up to 80 atm. β-carotene solutions in 2-propanol, n-hexane, and carbon tetrachloride were pumped through a quartz cell (10 mm pathlength, 30 μL internal volume) and a stainless steel cell (50 mm pathlength, 350 μL internal volume). With β-carotene, flow produces a relative thermal lens spectrometry (TLS) signal magnitude increase owing to replacement of photobleached analyte in the beam region. The effects of pressure in the different solvents are compared and discussed; the relative TLS signal magnitude decreased when pressure increased, but less in carbon tetrachloride than in the other solvents. Limit of detection for β-carotene in carbon tetrachloride at 0.4 mL min-1 and 1 atm were 2 × 10-5 absorbance units.
Initiation Reactions of Lipid Peroxidation: A Raman Spectroscopic and Quantum-Mechanical Study
Authors: Tachikawa Hiroyasu , Polášek Martin , Huang Joan Q. , Leszczynski Jerzy , Salahudeen Abdulla K. , Kwiatkowski Józef S.
Published: October 2003

Near-infrared (NIR) Raman spectroscopy has been used to observe the spectrum changes of linolenic acid during the iron-dependent lipid peroxidation reactions. The intensity of several bands including those at 726, 977, 1264, 1658, and 3014 cm−1 decreased after lipid peroxidation. Other notable changes after lipid peroxidation include the appearance of a couple of new bands at 1165 and 1638 cm−1. The Raman spectrum change was suppressed by an antioxidant, 21-aminosteroid. Harmonic ab initio vibrational analysis was performed for two model structures: one for the pure linolenic acid and another for a peroxidation product. The calculations by the Hartree–Fock (HF) method and a density functional theory (DFT) indicate that a new band which appeared at 1638 cm−1 after lipid peroxidation is due to the rearrangement of skeletal double bonds.
Sampling Considerations for FT-Raman Spectroscopy of Polymers and Solutions
Authors: Barrera Brian A. , Sommer André J.
Published: October 2003

The apparent absorption coefficient and optimal sample thickness for Fourier transform (FT)-Raman analysis of polyethylene, polyethylene terephthalate, cellulose, and cyclohexane were experimentally determined. With the use of these results, a relationship was developed that permits the optimal sample thickness for FT-Raman measurements to be determined by simply measuring the absorbance spectrum of a sample whose thickness is known. For samples with an apparent absorption coefficient of less than 0.08 cm−1, the sampling depth is limited by the depth of view of the instrument. For samples with an apparent absorption coefficient greater than 0.08 cm−1, the samples' optical and physical properties limit the sampling depth. The results are discussed in the context of scattering theory, sampling considerations, and spectral artifacts. Sampling considerations include the application of FT-Raman spectroscopy to the study of coated materials and layered structures.
Degradation of Urethane-Foam-Backed Poly(Vinyl Chloride) Studied Using Raman and Fluorescence Microscopy
Authors: Remillard J. T. , Jones J. R. , Poindexter B. D. , Helms J. H. , Weber W. H.
Published: October 2003

Urethane-foam-backed poly(vinyl chloride) (PVC) degrades through dehydrochlorination, a process that results in the formation of conjugated polyene sequences within the backbone of the polymer. Raman spectroscopy at 633 nm and a combination of fluorescence spectroscopy and microscopy with blue excitation have been used to quantify the temporal degradation of two commercial foam/ vinyl composites. Since the resonance behavior of polyenes depends on their conjugation lengths, the Raman and fluorescence measurements were most sensitive to polyenes with conjugation lengths of ≥20 and ∼10, respectively. Durability tests were performed by weathering samples in the field for 35 months and in ovens at temperatures of 100 and 120°C for ∼500 h. For the field-weathered samples, the integrated fluorescence intensity correlates well with the polyene concentration as determined by Raman measurements, which suggests that for these aging conditions the kinetics controlling the steady-state populations of short- and long-length polyene sequences are similar. The results from the laboratory-weathered samples are consistent with the conclusion that short-conjugation-length polyenes form first and then propagate to longer conjugation lengths as degradation progresses. Most importantly, this work demonstrates that the relatively simpler fluorescence imaging techniques can be extremely useful in determining the comparative weatherability of different foam/vinyl composites.
Infrared Microspectroscopic Investigation of the Diffusion of E7 into Poly(Butyl Methacrylate)
Authors: Wall Bentley G. , Koenig Jack L.
Published: October 2003

The components of a liquid crystal mixture (E7) have been shown to diffuse at different rates in polymer-dispersed liquid crystals (PDLCs). It was observed in this work that liquid crystals of different molecular weights diffuse into poly(butyl methacrylate) (PBMA) at different rates at a constant temperature. It was also determined that the components in a liquid crystal mixture diffuse into the polymer at different rates. The effect is quite small under normal conditions, so elevated temperatures, simplified diffusion boundaries, and extended time scales were employed to magnify the diffusion separation effects for study. This work demonstrates that the components of E7 diffuse at different rates. Practically, the short phase separation times experienced during the generation of a PDLC may be insufficient to promote this effect to the point where optical properties are adversely affected.
Optimization of Two Fourier Transform Infrared Least-Squares Multivariate Analysis Methods for the Simultaneous Quantitation of Mixtures of Three Metal-Carbonyl Complexes in the Picomole Range
Authors: Salmain Michèle , Varenne Anne , Vessières Anne , Jaouen Gérard
Published: October 2003

In order to develop a simultaneous multi-carbonyl metallo immuno assay (multi-CMIA) associated with Fourier transform infrared spectroscopy as the detection method, we thoroughly studied two multivariate analysis methods for the quantitation of mixtures of metal-carbonyl complexes from their infrared spectra restricted to the region of the vco vibration modes (1850–2200 cm−1). These two methods were based on classical least-squares (CLS) and partial least-squares (PLS) algorithms. The influence of some of the parameters involved in the calibration stage (spectral intervals, nature and number of calibration spectra) was studied for both multivariate methods. With optimized calibration models, we showed that either artificial or real mixtures of three metal-carbonyl complexes could be simultaneously quantified in the 10–100 pmol range, which is the working area of CMIA experiments, with relative errors around 6%.
Extending the Range of Beer's Law in FT-IR Spectrometry. Part I: Theoretical Study of Norton—Beer Apodization Functions
Authors: Zhu Changjiang , Griffiths Peter R.
Published: October 2003

Beer's law is obeyed when the measured value of absorbance varies linearly with concentration in the absence of chemical effects. The absorbance range over which bands measured on any type of spectrometer obey Beer's law depends on the ratio of the resolution to the full width at half-height of the analytical band, often called the resolution parameter, ρ, and the instrument line shape (ILS) function of the spectrometer. Apodization functions are used widely in Fourier transform infrared (FT-IR) spectrometry to change the instrument line shape function. For Lorentzian bands, it is well known that when ρ is about 1 and the spectrum is computed with a triangular apodization function, there is a negative deviation from Beer's law when the true peak absorbance is high, whereas the use of boxcar truncation results in a positive deviation. In this paper, the possibility of extending the linear range of Beer's law by applying optimized apodization functions of the type proposed by Norton and Beer has been investigated. This theoretical study shows that the linear range of Beer's law plots for spectra measured at moderate resolution can be extended to peak absorbances greater than 2 with the use of any of the Norton Beer apodization functions. Linear plots of the apparent absorbance of a band against analyte concentration can be obtained even for bands of absorbance substantially greater than 3, although a nonzero intercept on the absorbance axis may be observed.
Optical Wedge Effects in Instruments and Standards for Molecular Absorption Spectrophotometry
Authors: Travis John C. , Smith Melody V. , Kramer Gary W.
Published: October 2003

The optical wedge of some older, individual solid NIST absorbance filter standards has been found to cause bias in the indicated absorbance readings of certain instruments. In a collimated-beam spectrophotometer, the sample beam is deflected by about half of the wedge angle in the sample. For inverted geometry designs, small deflections can give rise to large changes in the field of view of the entrance slit of the spectrometer downstream from the sample. Beam deflection is also found to induce small apparent wavelength shifts in data taken through a wedged sample, resulting in spectral artifacts derived from spectral features of the system or of an absorbing sample. These spectral artifacts turn out to be robust, and simple cell-reversal difference spectra can provide useful diagnostic indicators of optical wedge. Solid photometric standards are found to be reliable, if manufactured to wedge angles of less than 0.1 mrad. Despite a wedge tolerance of 0.9 mrad in the sealed cuvettes of a wavelength standard, wavelength shifts are shown to be negligible when compared to the stated uncertainties. For normal use, accuracy may be achieved by utilizing the same cell in the same orientation for both background and sample spectra or by hand selection of cells.
Extremely Large Enhancement Factors in Surface-Enhanced Raman Scattering for Molecules on Colloidal Gold Clusters
Authors: Kneipp Katrin , Kneipp Harald , Manoharan Ramasamy , Hanlon Eugene B. , Itzkan Irving , Dasari Ramachandra R. , Feld Michael S.
Published: October 2003

In agreement with previous results reported for colloidal silver clusters, effective surface-enhanced Raman cross sections of about 10-16 cm2 per molecule, corresponding to enhancement factors on the order of 1014, have also been obtained for molecules attached to colloidal gold clusters. Spatially isolated nearly spherical colloidal gold particles of about 60 nm size show maximum enhancement factors on the order of 103 at 514 nm excitation, close to the single plasmon resonance. The enhancement factor increases by eleven orders of magnitude when colloidal gold clusters are formed by aggregation of the gold colloids and when near-infrared excitation is applied. The large effective surface-enhanced Raman cross section has been estimated by a straightforward method based on steady-state population redistribution due to the pumping of molecules to the first excited vibrational state via the strongly enhanced Raman process. Our experimental finding confirms the important role of colloidal clusters for extremely large surface-enhanced Raman scattering (SERS) enhancement factors. Simultaneously, it suggests colloidal gold clusters as a substrate for high-sensitivity surface-enhanced Raman scattering, which can provide an enhancement level sufficient for Raman single molecule detection. Due to its chemical inactivity, gold might have some advantages compared to silver, particularly in biomedical spectroscopy.
Interference of Linear and Nonlinear Optical Effects in Second-Harmonic Generation from Metal/Liquid Interfaces
Authors: Walters M. J. , Roy D.
Published: October 2003

When a metal/liquid interface is probed with second-harmonic generation, the experimental data can be severely complicated by mixed signatures of linear and nonlinear optical properties of the interface. This problem is demonstrated and clarified in this report with computer simulations for selected electrochemical systems. A phenomenological framework for these simulations is developed. The first- and second-order surface susceptibilities of the metal are treated on equal footing, and their variations due to adsorbate effects are analyzed. Analytical and simulated results are presented for two specific groups of adsorbates. Representative experimental systems of these two groups (electrodeposited Cu and Te on polycrystalline Au) are analyzed in further detail. The calculations are in full agreement with the previously published experimental data for these systems. The present formalism can be extended to other systems and, in a systematic manner, can facilitate the analysis of second-harmonic data for electrochemical systems.
The Spectral Line Narrowing Problem and a Computer Program Based on the Gulf Tuning Method
Authors: Saarinen Pekka E.
Published: October 2003

Discovering the exact positions and heights of spectral lines is a familiar problem to those dealing with line spectra. This information is often obscured by overlap of the individual lines, since spectral lines are always broadened due to, for example, random interactions of radiating particles or the imperfections of the measuring device. Unravelling overlapping lines is, however, a very ill-behaved problem, extremely sensitive to noise. Owing to the very high signal-to-noise ratios attainable by modern spectrometers, this kind of resolution enhancement has now become possible in principle. There nevertheless seems to be a lack of suitable line narrowing algorithms and programs for accomplishing this procedure. In this paper the problem of spectral line narrowing is approached first from a purely theoretical viewpoint. The factors distorting the output of a line narrowing procedure are considered one at a time. After that, a novel line narrowing algorithm, the gulf tuning method, which has been programmed and tested with simulated spectra and real FT-IR spectra, is described.
Interpretation of Two-Dimensional Correlation Spectra: Science or Art?
Authors: Czarnecki Mirosław A.
Published: October 2003

It has been shown that the most common perturbations of conventional (one-dimensional) spectra such as random noise, baseline fluctuations, band position, and width changes may complicate two-dimensional (2D) correlation spectra, sometimes making them completely useless. In addition, two different physical causes may generate similar patterns for the synchronous and asynchronous spectra. Some of these effects, such as random noise and baseline fluctuations, can be eliminated from the input data, and one can recover the original appearance of 2D correlation spectra. The other effects, such as the frequency shift and bandwidth variation, cannot be removed from the experimental spectra. In this instance, the number and position of the correlation peaks can be elucidated by simulation studies. This report presents a few examples of typical patterns found in the synchronous and asynchronous spectra affected by those perturbations. Long streaks in 2D correlation spectra reveal extensive baseline fluctuations in the original data set. A simple offset often significantly reduces the extent of this effect. When no reasonable baseline correlations can be performed, the second derivative may solve this problem. In most cases, the perturbation-averaged spectrum is recommended as a reference. However, it has been proved that the calculation of 2D correlation spectra without any reference spectrum may also provide useful information, especially for data heavily influenced by noise or baseline fluctuations. In the majority of real-world systems, the spectral changes are a continuous function of applied perturbation. Thus, 2D correlation spectra yield information about the relative rate of intensity variations rather than the sequence of spectral events.
Near-IR Calibration Transfer between Different Temperatures
Authors: Lin Jie
Published: October 2003

Calibration transfer between spectra measured at different temperatures was investigated for near-IR spectroscopic determination of NaCl in aqueous solutions. A principal component regression (PCR) calibration model developed at 23.0 °C was transferred to 28.5 °C by using a piecewise direct standardization (PDS) method. The effect of window symmetry on calibration transfer was investigated. Only two transfer samples were needed in obtaining a good calibration transfer. The standard error of prediction (SEP) was 0.048 M NaCl when the calibration model developed at 23.0 °C was used for predictions at 28.5 °C without the standardization. The SEP was reduced to 0.008 M through the standardization, which was very close to 0.006 M obtained from a full set recalibration at 28.5 °C and 0.007 M obtained from a general calibration model based on the spectra measured at different temperatures between 23.0 and 28.5 °C. The calibration transfer from one temperature to another can save a lot of time in remeasuring the calibration samples and redeveloping a new calibration model at a new temperature.
Measurement of Glucose in Water with First-Overtone Near-Infrared Spectra
Authors: Hazen Kevin H. , Arnold Mark A. , Small Gary W.
Published: October 2003

Partial least-squares (PLS) regression analysis was used to build calibration models for three unique spectral data sets of glucose in water. Spectra in the first data set were collected with a 2.0 mm optical pathlength. For these data, the measured root-mean-square (rms) noise of 100% lines over the 5975-5850 cm−1 spectral range was 4.5 micro-absorbance units (μAU). Spectrometer upgrades permitted a 5.2 mm optical pathlength for the second data set, and the resulting spectra had an rms noise of 5.9 μAU. Further spectrometer adjustments allowed the use of a 10.0 mm optical pathlength for the third data set, and the resulting spectral rms noise was 8.4 μAU. In each case, the instrumentation was modified individually in order to provide high radiant powers at the detector while avoiding detector saturation. Poor calibration models for the first data set indicate that a 2.0 mm optical pathlength is insufficient for adequate glucose measurements at clinically relevant concentrations. Calibration and prediction errors for the data collected at 5.2 and 10.0 mm pathlengths ranged from 0.40–0.50 and 0.35–0.40 mM, respectively. Digital Fourier filtering significantly improved model performance by reducing the required number of latent variables (factors) in the PLS models and by reducing the wavelength dependency of these models. For the best calibration model, spectra in the data set corresponding to a 10.0 mm pathlength were Fourier filtered with a Gaussian-shaped filter defined in digital frequency units ( f) by a mean position of 0.0206 f and a standard deviation width of 0.0031 f. These filtered spectra were then submitted to a one-factor PLS model that is limited to the 5975-5850 cm−1 spectral range. Consideration of different spectral ranges and an analysis of spectral loading vectors indicate that the 5920 cm−1 absorption band for glucose is critical for useful analytical measurements.
Origin of Limestone Fluorescence
Authors: Bezouska Joseph R. , Wang Jian , Mullins Oliver C.
Published: October 2003

Fluorescence is commonly used in the oil field for the detection of crude oil and in environmental applications for the detection of refined oils. Spurious fluorescence from minerals can interfere with desired detection. Here, we characterize the fluorescence from limestones in order to understand the origin of limestone fluorescence, in particular to compare and contrast it with other naturally occurring fluorescence. The fluorescence spectra, intensities, and lifetimes of six limestones, ranging in origin and thermal maturity, have been investigated with excitation wavelengths ranging from the ultraviolet through the visible and into the near-infrared. These limestones exhibit fluorescence spectra that are shown to be quite similar to those of crude oils, bitumens, and kerogens. This work strongly supports the conclusion that the fluorescence of limestones is organic in origin. Therefore, differentiation of limestone fluorescence from fluorescence of other organics must be accomplished by using known systematic trends of the fluorescence of naturally occurring organics.
Calibration of Raman Spectrometer Instrument Response Function with Luminescence Standards: An Update
Authors: Frost Kristin J. , McCreery Richard L.
Published: October 2003

An error in a previously reported procedure for correcting Raman spectra for instrument response was corrected, and then the approach was tested against reported values of Raman cross sections. The method uses luminescent standards with known emission curves of intensity vs. Raman shift, expressed in polynomial form. After acquisition of an observed emission curve from the luminescent standard, the correction of observed Raman spectra is automatic. Agreement of corrected peak areas with those calculated from literature cross sections is 5–20%. This correspondence is approximately as good as the agreement between different reported values, and much better than that observed for uncorrected spectra. Due to variations in the luminescence of the materials, it is likely that these or similar Raman intensity standards will be calibrated by the manufacturer or an independent agency.
Measurement of Orientation and Crystallinity in Uniaxially Drawn Poly(Ethylene Terephthalate) Using Polarized Confocal Raman Microscopy
Authors: Everall Neil J.
Published: October 2003

Polarized confocal Raman microscopy has been used to measure molecular orientation in uniaxially drawn poly(ethylene terephthalate) (PET) films, prepared with draw ratios from 1 to 3.5. The P200 values obtained agreed well with those measured with the use of refractive index and infrared dichroism, provided that the numerical aperture (NA) of the microscope objective was not too high. For example, a 0.75 NA objective gave good agreement with IR and refractive index results, but a 0.95 NA objective significantly reduced the measured P200. Corrections for the influence of sample birefringence on the measured Raman intensities were made and found to have a small (∼5%) effect on P200. This result is fortunate, because such corrections demand knowledge of the principal refractive indices of the sample, which may be unavailable. It was also shown that the presence of significant biaxial orientation in these samples did not significantly affect the P200 values computed under the assumption of uniaxial orientation. Orientation measurements were also compared with crystallinity data obtained by confocal Raman mapping through the thickness of a PET film. Significant gradients in both crystallinity and orientation were found through the thickness of the film. Surprisingly, these gradients were in the opposite sense, so regions of high crystallinity correlated with low orientation and vice versa. These results illustrate the extra insight obtained by combining multiple morphological measurements on the same sample.
Integration of Elemental and Molecular Imaging to Characterize Heterogeneous Inorganic Materials
Authors: Schoonover Jon R. , Weesner Forrest , Havrilla George J. , Sparrow Mark , Treado Patrick
Published: October 2003

Spatially resolved elemental and molecular information has been obtained for complex inorganic mixed-phase systems, including plutonium-contaminated ash samples, with the use of micro-X-ray fluorescence (MXRF), micro-Raman, and micro-infrared imaging spectroscopies. Approaches for spatially guided analysis and the combination of multispectral data sets to improve assignment of chemical composition are discussed for two heterogeneous materials. This novel integrated experimental approach provides the advantages of a very small sample size and the ability to correlate elemental analysis with molecular functional group analysis for species identification, as well as insight into chemical interactions in complex matrices.
Determination of Sulfur Species in Asphaltene, Resin, and Oil Fractions of Crude Oils
Authors: Mitra-Kirtley Sudipa , Mullins Oliver C. , Ralston Corie Y. , Sellis Dean , Pareis Courtney
Published: October 2003

Sulfur chemical species have been determined for asphaltenes, resins, and oil fractions of crude oils by using X-ray absorption near-edge structure (XANES) spectroscopy. The prevalent sulfur species are thiophene, sulfide, and sulfoxide. The asphaltene of one crude oil was known to have a very high sulfoxide content; the issue addressed here is whether the sulfoxide polar group is also dominant for sulfur in the resin and the (typically nonpolar) oil fractions of the same crude oil. Results from this study show that large sulfoxide fractions are obtained for all components of this oil. Another crude oil, lower in oxygen, also shows similar sulfur composition in all three fractions; nevertheless, the oil fractions of both crudes tend to have somewhat larger sulfide fractions.
Single-Molecule Detection of a Cyanine Dye in Silver Colloidal Solution Using Near-Infrared Surface-Enhanced Raman Scattering
Authors: Kneipp Katrin , Kneipp Harald , Deinum Geurt , Itzkan Irving , Dasari Ramachandra R. , Feld Michael S.
Published: October 2003

Single-molecule Raman spectroscopy of a cyanine dye in aqueous silver colloidal solution with the use of surface-enhanced Raman scattering at near-infrared excitation (NIR-SERS) is reported. A characteristic Poisson distribution of SERS signals due to the Brownian motion of single dye molecule-loaded silver particles reflects the probability of finding 0, 1, or 2 1,1'-diethyl-2,2'cyanine (PIC) molecules in the probed volume during an actual measurement and is evidence that single-molecule detection by SERS has been achieved. Spectra measured in 1 s collection time with 100 mW nonresonant 830 nm excitation provide a clear “fingerprint” of a single PIC molecule by showing its typical Raman lines between 700 and 1700 cm−1. Single-molecule Raman signals are also detected for the first time at the anti-Stokes side of the excitation laser. Effective Raman cross sections for PIC of ∼10−16 cm2 per molecule can be inferred from the ratio between “pumped” anti-Stokes and Stokes signals.
Effect of the Water Spectrum on the Determination of Dissolved Ammonia, Urea, and Chloride Concentrations by Raman Spectroscopy
Authors: Wang Hsiaoling , Wang Chao , Mann Charles K. , Vickers Thomas J.
Published: October 2003

The effect of large, changing concentrations of electrolytes on the behavior of the OH stretching band of water have been investigated with the aim of developing methods for compensating for spectral interferences when solute NH bands are made the basis for mixture analyses. With the use of urea and ammonium salts as analytes, it was found that changing electrolyte concentrations affect the shape of the water band but do not appreciably affect the shapes of either the ammonium ion or urea Raman lines. Chlorides, nitrates, and mixtures of these were used as electrolytes. The identity of the anion had a significant effect on the shape of the OH band. Two methods of compensation were used. One involved factor analyzing the spectra of a set of solutions that contained chlorides and nitrates that are Raman inactive in the vicinity of the OH stretching band. The principal abstract factors were used in place of a water reference for a least-squares mixture analysis. The other method was application of partial least-squares. In addition to urea and ammonium ion, the concentration of KCl and the ionic strength of the system can be determined in the partial least-squares approach with limits of detection better than 0.1 M.
Spectroscopy of Concentrated Sodium Aluminate Solutions
Authors: Watling Helen
Published: October 2003

Sodium aluminate solutions have been investigated by infrared absorption and Raman scattering in a broad concentration range in order to detect possible changes in aluminate ion species and distribution. Concentration-dependent changes in spectra include shifts in frequency at maximum band intensity, a loss of proportionality in band intensities, and the appearance of new vibrational bands or the increased asymmetry of existing ones. Changes in infrared spectra correlate well with those observed for Raman spectra and are consistent with the presence of more than one aluminate ion species in equilibrium in concentrated aluminate solutions. Assuming that the observed effects are due to changed solution speciation, it is found that the maximum concentration of Al(OH)4 occurs in solutions of 4–5 M aluminum, and that other species become relatively more abundant as the aluminum concentration is increased. Comparison of solution spectra with spectra of crystalline aluminates indicates that new species are likely to be oligomeric and polymeric anions in which aluminum is mainly 4-coordinate, but the possibility of low concentrations of aluminate species containing 6-coordinate aluminum cannot be excluded.
Characterization of Peat Fulvic Acid Fractions by Means of FT-IR, SERS, and 1H, 13C NMR Spectroscopy
Authors: Francioso O. , Sánchez-Cortés S. , Tugnoli V. , Ciavatta C. , Gessa C.
Published: October 2003

Fourier transform infrared (FT-IR), surface-enhanced Raman spectroscopy (SERS), and nuclear magnetic resonance (NMR) (1H and 13C) have been applied to the characterization of un fractionated and fractionated fulvic acids extracted from an Irish peat. Raman study of these compounds is possible on rough metallic surfaces, which enhance the Raman signal and quench the high fluorescence. The application of these spectroscopic techniques has provided important structural information concerning the aromaticity and the carboxylate and carbohydrate group contents in each fraction. In addition, a SERS study at different pH levels has revealed interesting interfacial behavior of these components based on electric charge and conformational changes.
Characterization of a Rugged, Open-Gap Flow Cell for Confocal Laser-Induced Fluorescence Detection in Capillary Electrophoresis
Authors: Gallaher David L. , Johnson Mitchell E.
Published: October 2003

Construction details and performance characteristics of an open-gap flow cell for fluorescence detection in capillary electrophoresis are described. The flow cell is created by separating two pieces of capillary by a small (90 μm) gap. The gap is surrounded with buffer and grounded, and the application of electric fields to both inlet and outlet capillaries causes the material in the inlet capillary to flow across the gap. The use of a simple confocal optical arrangement for laser-induced fluorescence detection allows straightforward application of the gap flow cell to detection in capillary electrophoresis. The signal-to-noise ratio is measured to be about a factor of 2 better than that for on-column confocal detection at nanomolar concentrations over a wide range of pinhole diameters. The detection limit for fluorescein isothiocyanate is in the low picomolar range. Detection of a simple mixture of amino acids that have been derivatized with fluorescein isothiocyan ate demonstrates the stability and utility of the gap. Increased tailing is observed with the gap cell, with average asymmetry of about 1.4 near the center of the gap. Dispersion characteristics as a function of position in the gap are interpreted as dilution of the analyte as it flows across the gap. Fortunately, resolution and theoretical plates, measured by using least-squares fitting, are not significantly different from on-column separations, in spite of the tailing.
Continuous Air Monitoring Using Inductively Coupled Plasma Atomic Emission Spectrometry: Correction of Spectral Interferences Arising from CN Emission
Authors: Seltzer Michael D.
Published: October 2003

Introduction of sample stream air into an argon inductively coupled plasma permits continuous monitoring of hazardous air pollutant metals in combustion flue gases. Along with entrained particulates and metal vapors, various molecular components of the flue gas are introduced into the plasma. These species, and reaction products thereof, also undergo excitation resulting in complex emission spectra of appreciable intensity. Serious spectral interferences arise for several metal elements, from molecular emission bands associated with the stable CN radical and other polyatomic species. Failure to account for these interferences can significantly degrade accuracy particularly at low flue gas metal concentrations. Reported here is an effective method for measurement and correction of CN spectral interferences affecting the on-line detection of hazardous air pollutant metals that incorporates conventional polychromator hardware and existing instrument software capabilities. A demonstration of the ability of this method to achieve virtually complete correction of these interferences under both laboratory and field conditions is presented.
Elemental Analysis Using Microwave Digestion and an Environmental Evaporation Chamber
Authors: Rhoades Charles B. , Levine Keith E. , Salido Arthur , Jones Bradley T.
Published: October 2003

A major concern in laboratories performing trace element determinations is sample contamination. Sensitivity can be enhanced for trace elements by using larger samples, but this approach may increase the risk of contamination due to the need for more involved preparation techniques. With the isolation of the sample from the laboratory environment, the potential for contamination is greatly reduced during sample decomposition. In this investigation, an environmental evaporation chamber (EEC) placed in a microwave digestion system was used for predigestion of biological and botanical samples prior to closed-vessel digestion. The EEC was also used for the evaporation of residual acid after completion of the digestion procedure. Data are presented for the analysis of standard reference materials along with detection limits and the results of a cross-contamination study for the described method. Index Headings: Inductively coupled plasma optical emission spectrometry; Biological samples; Botanical samples; Environmental evaporation chamber; Microwave digestion.
Reducing Polyatomic Interferences in the ICP-MS Determination of Chromium and Vanadium in Biofluids and Tissues
Authors: Krushevska Antoaneta , Waheed Shahida , Nóbrega Joaquim , Amarisiriwardena Dulasiri , Barnes Ramon M.
Published: October 2003

The suitability of inductively coupled plasma quadrupole mass spectrometry (ICP-MS) for the determination of Cr and V in biofluids and tissues has been studied. High-pressure thermal and moderate-pressure microwave sample preparation with vapor-phase acid digestion successfully minimized blanks and carbon and chloride interferences. The remaining ArC+ interferences on 52Cr were corrected mathematically. Analysis of standard reference materials verified the accuracy of the method.
Quantitation of Asbestos Using Diffuse Reflection Infrared Spectroscopy
Authors: Lang Patricia L. , Chu Vir-Vir , McCune Karen , Franssen Susan , Goodnight-Schmidt Michelle , Mendenhall Ron , Conner Wendi
Published: October 2003

The use of diffuse reflection infrared spectroscopy for the quantitation of asbestos is investigated. The highly absorbing matrices that are typically present in an asbestos sample are addressed by the incorporation of an ashing technique that separates the asbestos from any cellulose matrix. The details for recovering microgram amounts of asbestos from the crucible after ashing are also described. About 0.01% by weight of amosite asbestos in cellulose can be detected. In addition, a curve-fitting program is used to assist in quantitation of two-component asbestos mixtures and in the quantitation of asbestos in the presence of china clay, a silicate commonly associated with asbestos insulation. The method shows that about 3 μg of amosite can be detected in a matrix composed of four times this mass in chrysotile and four times in kaolin.
Role of Scattering Coefficients in Extended Near-Infrared Diffuse Reflection Spectrometry
Authors: Chaffin Nathan C. , Griffiths Peter R.
Published: October 2003

The role of the bulk scattering coefficient in extended near-infrared diffuse reflection (DR) spectrometry of materials with similar or identical absorption coefficients is demonstrated. Spectral differences that arise from intraclass variation in scattering coefficient strongly affect the ability to interpret certain spectral regions. Profound intraclass differences in both band intensities and band shapes in the DR spectra of both polyethylene and polystyrene samples are shown. The effects of saturation and Fresnel reflection are discussed. The enhancement of absorption by the matrix and other analytes in DR spectrometry through the addition of a liquid with an index of refraction which matches that of the matrix is also demonstrated.
Real-Time Pursuit of Crystal Growth by Millisecond Time-Resolved Multichannel Fourier Transform Infrared Spectroscopy
Authors: Hashimoto Mamoru , Hamaguchi Hiro-O
Published: October 2003

The surface (about 130 molecular layers) of an oriented thin crystal of decanoic acid was subjected to sudden melting by a laser-induced temperature jump (T-jump), and the process of subsequent crystal re-growth was monitored by millisecond time-resolved multichannel Fourier transform infrared spectroscopy. The gauche–trans structural change of the alkane part of the molecule has been probed by the CH stretch bands in the 2800–3000 cm−1 region. The change in the molecular orientation has been detected by the OH stretch band around 3065 cm−1. The recovery curves for the CH2 antisymmetric stretch and the OH stretch bands are markedly different from each other in the first 200 ms, suggesting that the gauche–trans structural changes precedes the crystal re-growth. After 500 ms, the recovery curves become identical. This result means that the rate of the gauche to the trans structural change is equal to the rate of the recovery of the molecular orientation. It is highly likely that a fast equilibrium is attained between the gauche and the trans conformations in the liquid phase after 500 ms from the sudden melting and that the crystal re-growth takes place solely via the all-trans structure in the liquid phase.
Generation of Synthetic Background Spectra by Filtering the Sample Interferogram in FT-IR
Authors: Espinoza Luis H. , Niemczyk Thomas M. , Stallard Brian R.
Published: October 2003

The calculation of an absorbance spectrum depends on the measurement of a blank, or background spectrum. In many cases, such as the determination of atmospheric constituents with the use of open-path Fourier transform infrared spectroscopy (FT-IR) or the determination of water vapor in a gaseous sample, it is very difficult to obtain a good background spectrum. The difficulty is due to the fact that it is nearly impossible in these situations to measure a spectrum with no analyte features present. We present a method of generating a background spectrum based on filtering the analyte features from the sample spectrum. When the filtering method is used, the accuracy of the results obtained is found to be dependent upon the analyte peak width, peak height, and type of filter employed. Guidelines for the use of this background generation technique for quantitative determinations are presented.
Experimental Studies for a New Family of Infrared Four-Wave Mixing Spectroscopies
Authors: Chen Peter C. , Hamilton James P. , Zillan Arne , Labuda Mitchell J. , Wright John C.
Published: October 2003

Vibrationally enhanced infrared and vibrationally enhanced Raman four-wave mixing spectroscopy are experimentally explored with the use of several model systems. Studies involving a mixture of chlorobenzene, dichlorobenzene, and deuterobenzene were performed to see whether a simultaneous resonance of a combination band could enhance the Raman ring breathing mode. The results show strong interference effects that may be responsible for a suppression of the Raman resonances. Studies were also carried out in systems of chloroform/deuterobenzene and hexane/deuterobenzene. The latter samples showed intensity increases and line-shape changes that are consistent with vibrational enhancement. The discovery of these enhancements form the basis for developing infrared four-wave mixing as a method for extracting new information about molecular vibrations.
Characterization of pH Variation in Lysed Blood by Near-Infrared Spectroscopy
Authors: Alam M. Kathleen , Franke James E. , Niemczyk Thomas M. , Maynard John D. , Rohrscheib Mark R. , Robinson M. Ries , Eaton R. Philip
Published: October 2003

Near-infrared spectra (1300–2500 nm) collected from lysed blood solutions were shown to correlate with the pH of the solutions measured potentiometrically. Cross-validated partial least-squares (PLS) models were developed from these spectral data, which provided standard error of prediction (SEP) values below 0.05 pH units for a pH range of 1.0 (6.8–7.8). Experiments were designed to eliminate possible correlation between pH and other components in the blood in order to ensure that variations in the spectral data correlated to pH were due to hydrogen ion changes only. Further work was performed to discern the primary source of pH information in the lysed blood spectra by using spectra collected from plasma and histidine solutions. The blood, plasma, and histidine data sets were compared with the use of loading vectors from principal component analysis (PCA). These loading vectors show that variations in the spectra of the titrated amino acid histidine mimic those seen in lysed blood, but not those seen in plasma. These results suggest that histidine residues of hemoglobin are providing the spectral variation necessary for pH modeling in the lysed blood solutions. It is further shown that the observed pH-sensitive histidine bands do not arise from the exchangeable proton on the imidazole ring of histidine; rather they arise from the variation in the C–H bonds of the C2 and/or the C4 carbons of the imidazole ring as they are influenced by the titration of the nitrogen-bound proton of the imidazole ring.
Optimization and Comparative Study of the Room-Temperature Phosphorescence of Acenaphthene in β-Cyclodextrin in the Presence of Two Bromoalcohols
Authors: Carretero A. Segura , Blanco C. Cruces , Gutiérrez A. Fernández , Peña A. Muñoz De La
Published: October 2003

A multivariate optimization approach, using a central composite blocked cube-star design, has been carried out to optimize the room-temperature phosphorescence (RTP) of a ternary complex between a polycyclic aromatic hydrocarbon (acenaphthene), β-cyclodextrin, and two bromoalcohols (2-bromoethanol and 2,3-dibromopropanol). A comparative study of the effect of the two bromoalcohols in the phosphorescence response has shown that the highest RTP emission from acenaphthene included in β-CD is obtained with 2,3-dibromopropanol. An RTP determination method for acenaphthene has been proposed. Calibration graphs range between 50 and 250 ng mL−1, and a detection limit of 24 ng mL−1 has been established.
207Pb NMR Chemical-Shift Tensors of the Lead (II) Halides and the Lead (II) Hydroxyhalides
Authors: Dybowski Cecil , Smith Matthew L. , Hepp Mark A. , Gaffney Edward J. , Neue Guenther , Perry Dale L.
Published: October 2003

The NMR properties of the solid lead (II) halides and the lead (II) hydroxyhalides are reported. The analysis shows extremely wide powder patterns in all cases except the lead (II) iodide. The results indicate that one should be able to distinguish the lead (II) halide from the corresponding lead (II) hydroxyhalide in a mixture.
Laser-Induced Breakdown Spectroscopy of Liquids: Aqueous Solutions of Nickel and Chlorinated Hydrocarbons
Authors: Berman Leonard M. , Wolf Paul J.
Published: October 2003

Spectrochemical analyses of aqueous solutions containing nickel or the chlorinated hydrocarbons (CHCs) C2Cl4, CCl4, CHCl3, and C2HCl3 were performed with the use of laser-induced breakdown spectroscopy. A Nd:YAG laser operating at 60 mJ/pulse was focused onto the surface of the liquid. Elemental line intensities were monitored in the laser-produced plume as a function of analyte concentration to determine detection limits. The limits of detection for nickel in water were 36.4 ± 5.4 mgAL and 18.0 ± 3.8 mg/L for laser irradiation at 1.06 μm and 355 nm, respectively. Ablation of pure CHCs at 355 nm produced extremely intense plasma emissions that primarily consisted of spectroscopic features attributed to CN, C3, H, N, and Cl. The spectra were structurally identical for all the CHCs except for differences in the intensities of various emission lines. With the use of emission from neutral atomic chlorine as an identifier for CHC contamination of water, no detectable traces of these elements were observed in saturated aqueous solutions. The detection limits for the CHCs were well above the saturation limits of CHC in water.