bluuebunny/crossref_metadata_2025 huggingface dataset:
Near-Infrared Study of the Light Liquid Alkanes
Authors: Rest A. J. , Warren R. , Murray S. C.
Published: May 2005

A cryostat cell has been designed and constructed to enable the in situ liquification of methane, ethane, and natural gas from the mains. This cell, which was operated with pathlengths of 3 mm and 62 mm, was used to study the near-infrared spectra of methane, ethane, propane, n-butane, n-pentane, n-hexane, n-heptane, liquified mains gas, and bulk storage liquid natural gas (LNG) over the range 3000 to 15,000 cm−1 with a resolution of 8 cm−1. Band positions and their extinction coefficients corresponding to overtone and combination bands have been obtained for the first time under standard conditions. It was shown that significant differences are seen between the spectra of methane and ethane, and hence their relative concentrations can be estimated in the different samples of LNG, while the concentrations of the longer chain alkanes are so small and their spectra so similar that it would be impossible to determine their individual concentrations in the LNG samples without the aid of chemometric manipulation.
Infrared Spectroscopic Investigations of the Stability of Xanthate-Mineral Interaction Products
Authors: Brienne Stéphane H. R. , Bozkurt M. M. Volkan , Rao S. R. , Xu Zhenghe , Butler Ian S. , Finch James A.
Published: May 2005

The products of the interaction of ethyl xanthate (CH3CH2OCS2−) with copper and chalcocite (Cu2S) electrodes at a controlled potential have been investigated by ex situ infrared spectroscopy. The disappearance of bands assigned to dixanthogen over time indicated that additional reactions were occurring subsequent to the initial interaction. These reactions were also followed by gas-phase infrared photoacoustic spectroscopy (PAS), which suggested the formation of CO2 and COS. The PAS technique was also employed to identify the gas-phase species produced from a variety of powdered minerals [heazlewoodite (Ni3S2), chalcocite (Cu2S), chalcopyrite (CuFeS2), pyrite (FeS2), pyrrhotite (Fe1- xS x), pentlandite ([Fe, Ni]S), galena (PbS), sphalerite ([Zn, Fe]S), and arsenopyrite ([Fe, As]S)] when treated with ethyl and isobutyl xanthates. The main species produced were COS, CO2, and H2O, with CS2 and C2H5OH being observed for ethyl xanthate in certain cases. The results show that the xanthate films decompose over time. The following decomposition pathways could account for the products observed: elimination of the triatomics from metal-xanthate complexes; decomposition of dixanthogen; formation of radicals; and pyrolysis of the xanthate complexes.
Improvements in Spectral Line Shape Reproduction from Spectrographs with CCD Detection
Authors: Sadler D. A. , John D. Little , Riley R. , Perkins C. V.
Published: May 2005

A new procedure has been developed which improves the reproduction of spectral line shapes from spectrographs with charge-coupled device (CCD) detection. The procedure, which requires that the image of the entrance aperture be slanted with respect to the columns of the CCD pixels, increases the effective spatial resolution of the instrument without the necessity for mechanical scanning of the exit focal plane and the acquisition of multiple images. A simple algorithm is described which converts the recorded two-dimensional data into a one-dimensional spectrum. The resultant spectrum lacks the stepped and angular appearance normally associated with CCD-derived spectral data. In addition, the dependence of the peak height signal with the peak center position for narrow spectral features is substantially reduced. For example, the variation in peak height signal with the intra-pixel peak position, for a spectral line with full width at half-maximum of 2.0 pixels, can be reduced from 15% to only 3%. The procedure has been implemented on an Echelle spectrograph used for inductively coupled plasma atomic emission spectroscopy (ICP-AES).
Determination of Synthetic Food Antioxidants in Multicomponent Mixtures Using UV-Visible Spectrophotometry and Partial Least-Squares Calibration
Authors: Espinosa-Mansilla A. , Salinas F. , Del Olmo M. , de Orbe Payá I.
Published: May 2005

Determination of quaternary, ternary, and binary mixtures and single determination of butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), tert-butylhydroquinone (TBHQ), and nordi-hydroguaiaretic acid (NDGA) have been made by using a partial least-squares (PLS) model. A calibration set containing between 2 to 80 μg mL−1 of BHA, TBHQ, and NDGA and 10 to 200 μg mL−1 of BHT was used, and a model was optimized by using a cross-validation process. Relative standard deviation values between 0.1 and 2.1% for BHA, between 0.2 and 2.1% for BHT, between 0.4 and 8.3% for NDGA, and between 1.2 and 1.3 for TBHQ were calculated. The resolution of quaternary mixtures was tested in sunflower oil samples.
Spatial Distribution of Radiant Intensity from Primary Sources for Atomic Absorption Spectrometry. Part II: Electrodeless Discharge Lamps
Authors: Gilmutdinov Albert Kh. , Radziuk Bernard , Sperling Michael , Welz Bernhard , Nagulin Konstantin Yu.
Published: May 2005

The spatial distribution of radiant intensity from electrodeless discharge lamps (EDLs) used as radiation sources in atomic absorption spectrometry is investigated with a digital photodiode array imaging system. Intensity distribution over the radial and longitudinal sections of Pb and Hg lamps is measured for both atomic and ionic lines of the analyte and the filler gas. The plasma in the EDLs is highly structured, with metal and filler gas excited species being distributed nonuniformly but in different ways. The clouds of emitting metal and Ar atoms are spatially separated in the volume of the Pb EDL. The excited Pb atoms detected from both the resonance and nonresonance lines have the form of a thin layer concentric to the bulb walls located near the surface of the bulb (“optical skin effect”). In contrast, the emission distribution for Ar atomic lines is bell-shaped with a maximum at the center of the plasma. The spatial distribution of emitting Ar ions is more complex—there is a bulk maximum coinciding with Ar atomic emission maximum and another maximum concentric to the walls coinciding with the maximum of metal atom emission. In the Hg EDL the difference between the spatial intensity profiles of metal and filler gas (Ar) lines is less pronounced because of the use of an increased filler gas pressure in the lamp. Emitting species of both Ar and metal are primarily located in the bulk of the plasma with, however, a small depletion in the vicinity of the lamp axis. Evolution of the spatial intensity profiles during warm-up of the lamps is investigated as well. In both lamps the radial and longitudinal intensity distributions of metal lines are established during the first minutes after lamp ignition, after which there is a slow and monotonic increase of the established intensity profiles. This result implies thermal vaporization as a mechanism of analyte supply to the plasma. The spatial intensity profiles for Ar lines are established in the first seconds after lamp ignition, after which only the absolute values of the established distributions change. The approach to the steady-state intensity of Ar atomic and ionic lines is nonmonotonic; there is a clearly pronounced initial overshoot in intensity of Ar atomic lines that coincides with a decline in the intensity of Ar ion lines. An interpretation for the observed spatial intensity profiles is given on the basis of radial cataphoresis theory.
Two-Dimensional Correlation of Fourier Transform Near-Infrared and Fourier Transform Raman Spectra I: Mixtures of Sugar and Protein
Authors: McClure William Fred , Maeda Hisashi , Dong Jian , Liu Yongliang , Ozaki Yukihiro
Published: May 2005

Two-dimensional (2D) correlation of near-infrared (NIR) and Raman spectra was carried out for mixtures of protein (lysozyme) and sugar (sucrose) to investigate the potential of this technique for qualitative NIR spectral interpretation. Cross-correlation by least-squares was employed to assess changes in both sets of spectra which result from changes in the set of sample spectra. Fourier transform (FT) NIR and NIR-excited FT-Raman spectra were measured for each of the samples under the same conditions, and point-for-point 2D cross-correlation was calculated. In this technique, each wavenumber in the NIR region gives rise to a sliced Raman spectrum where each data point is correlated to the NIR wavenumber, while each wavenumber in a Raman spectrum provides a sliced NIR spectrum in which each data point is correlated to the Raman wavenumber. For example, choosing NIR wavenumbers 7272, 6960, 6324, and 4812 cm−1 gives sliced Raman spectra with features attributable to sucrose, while choosing NIR wavenumbers at 8424, 5148, 5052, and 4584 cm−1 provides slices with distinct lysozyme features. Therefore, the technique permits the determination of the most probable origin of NIR signals by connecting NIR spectra, which have rather broad and overlapped bands, to Raman spectra consisting of sharp and clearly separated bands. It is also possible to produce sliced NIR spectra of lysozyme and sucrose by properly selecting wavenumbers in their Raman spectra. The NIR slices explain which wavenumbers in the NIR region are correlated to lysozyme or to sucrose. Thus, 2D correlation spectroscopy helps explain the reasons why certain wavenumbers are selected in a chemometric calibration model.
Emission Spectrochemical Analysis of Glass Containing Li and K in High Concentrations Using a XeCl Excimer Laser-Induced Shock Wave Plasma
Authors: Kurniawan H. , Kagawa K. , Okamoto M. , Ueda M. , Kobayashi T. , Nakajima S.
Published: May 2005

A XeCl excimer laser (20 ns, 25 mJ) was focused on glass samples containing high concentrations of Li and K (10%, 15%, and 20%) in a surrounding gas of air and He. Plasma characteristics are compared in two cases: at 1 atm and at reduced pressure (1–10 Torr). It is shown that the plasma produced at 1 atm cannot be applied to the elemental analysis of solid samples because of strong background emission and self-absorption in the plasma. The spectrum width of the emission line is very wide due to strong interaction in the plasma. In contrast to this, the shock-wave-induced plasma produced at reduced pressure gives a high S/B (ratio of the intensity of the emission line to that of the background) in the measurement of analytical emission lines, and the slope of the calibration curve is near unity in a log-log plot, thus making it possible for emission spectrochemical analysis.
Fluorescence Studies of Metal-Humic Complexes with the Use of Lanthanide Ion Probe Spectroscopy
Authors: Thomason J. W. , Susetyo W. , Carreira L. A.
Published: May 2005

The acidic functional groups of humic materials are an abundant source of metal binding sites in the natural environment. Studies of metal binding to humics are of great environmental interest because the biological and physicochemical properties of metals are often changed dramatically as a result of complexation with humics. In order to understand how these heterogeneous organic macromolecules bind metals with such a large range of binding energies, lanthanide ion probe spectroscopy (LIPS) has been used to study changes in the fluorescence lifetime of the europium probe metal as it binds to these substances. A method developed by Horrocks and Sudnick for the determination of the number of water molecules bound to Eu3+ was used to calculate the coordination number of humic-bound Eu3+ from the fluorescence data. The peak shift of the Eu3+ hypersensitive emission band (616 nm) was used to calculate the change in charge of the complex. Equations based on Horrocks and Sudnick's method were also developed to calculate the distribution of metal associated with the different types of binding sites on humic substances by computer modeling of the fluorescence lifetime data.
Near-IR Reflectance Spectroscopy for the Determination of Motor Oil Contamination in Sandy Loam
Authors: Stallard Brian R. , Garcia Manuel J. , Kaushik Sumanth
Published: May 2005

We have investigated the application of near-IR reflectance spectroscopy to the determination of motor oil contamination in sandy loam. Although the present work is concerned with a specific case of contamination, we discuss the possibility of applying the method to other organic contaminants and other types of soil. The spectral region considered was 1600–1900 nm, which contains the first overtone of the CH stretch. Using a commercial Fourier transform spectrometer together with cross-validated partial least-squares data analysis, the one-sigma precision for the determination of motor oil in sandy loam was 0.17 wt % (0.13 to 0.26 wt % at the 95% confidence level). The largest contribution to the precision of the determination was sampling error, or inhomogeneity in each sample. Given the precision limit imposed by the sampling error, we found that the performance of the spectrometer could be lowered without affecting the overall precision. In a modeling exercise, adequate performance was obtained with a spectrometer having only seven spectral channels with a spectral resolution of 10 nm and a spectral noise level of 10−3 absorbance units. A design for an inexpensive miniature instrument is presented.
Density Mapping in Poly(Ethylene Terephthalate) Using a Fiber-Coupled Raman Microprobe and Partial Least-Squares Calibration
Authors: Everall Neil , Davis Kevin , Owen Harry , Pelletier M. J. , Slater Joe
Published: May 2005

Partial least-squares (PLS) analysis has been used to calibrate Raman microprobe spectra of poly(ethylene terephthalate) films in terms of density, in order to give insight into changes in crystallinity through the film thickness. The microprobe utilizes a static multiplexed holographic grating to obtain the entire Raman spectrum (-1600-4000 cm-1) in a “single-shot” at ∼ 5-cm−1 resolution. Because there are no moving parts, frequency registration and repeatability are excellent and ideally suited for multivariate calibration. In addition, the high spectral throughput allows the whole spectrum to be collected in a few seconds with high signal-to-noise ratio. With this equipment, cross-validated calibration precisions as low as - 0.0021 g cm−3 were achieved.

In this work we considered two ways of removing fluorescence backgrounds prior to carrying out multivariate calibration. The first involved manually fitting a baseline using a polynomial curve and subtracting it. The second approach simply takes the second derivative of the spectrum to attenuate the low-frequency components (i.e., the curved baseline). It was found that either pretreatment gave good calibration precision provided that the resultant spectra were intensity-normalized to correct for variations in laser power, sample alignment, and so on. Surprisingly, it was found that the best precision was obtained by grouping the spectral resolution elements into blocks of eight data points, thereby improving the signal-to-noise but effectively degrading the spectral resolution by a factor of three. This was especially important for the derivative spectra. Alternatively, Savitsky-Golay smoothing of the second derivative data was applied to the same effect but also at the expense of degrading spectral resolution. The implication of this work is that instruments intended for multivariate calibration applications could perhaps be designed to work at rather lower spectral resolutions (but higher signal-to-noise) than might otherwise be considered.
Fluorescence Measurement of Tetracycline in Model Fermentation Media Samples Containing Streptomyces Aureofaciens Cell Mass
Authors: Horvath John J. , Glazier Scott A.
Published: May 2005

This study describes fluorescence measurements made with a fiber-optic probe on model fermentation media samples containing natural media components, high densities of Streptomyces aureofaciens cell mass, and varying concentrations of tetracycline. Tetracycline, produced commercially from S. aureofaciens, is a highly fluorescent antibiotic, and these measurements were conducted to determine the correlation between the tetracycline content in the media and the observed fluorescence of the samples. Seven separate types of media samples were examined for this study. Each medium contained a nonfluorescent base of nutrients and salts along with one of seven different natural feedstocks at a concentration of 50 g/L. In addition, the samples contained S. aureofaciens cell mass densities of 50 g/L (based on dry cell mass). Excitation wavelengths of 290 nm, 390 nm, and 413 nm were used to probe the fluorescence of the samples, and emission spectra were obtained over the wavelength ranges of 320–360 nm, 420–600 nm, and 440–600 nm, respectively. Background fluorescence observed in the region of 320–360 nm upon 290-nm excitation in the samples was due to tryptophan fluorescence contained in the S. aureofaciens cell mass and was found to decrease dramatically as tetracycline levels increased from 0 to 8000 μg/mL. Plots of fluorescence intensity at a number of emission wavelengths versus tetracycline concentration in the samples clearly revealed strong correlations.
Design and Performance of a New Infrared Reflection Accessory for Spectroelectrochemical Studies
Authors: Faguy Peter W. , Marinković Nebojša S.
Published: May 2005

A novel spectroelectrochemical cell based on a hemispherical window which fits in the sample compartment of a center-focus FT-IR spectrometer is described. The ZnSe hemisphere serves to collimate the beam, provide near-critical angle reflection, lower first-surface reflection losses, and reestablish the instrument focal point. The optics of the spectroelectrochemical accessory include only two folding mirrors, the IR polarizer, the ZnSe window, and the electrode. The optimum angle of incidence for the reflection experiment is determined from calculated mean-squared electric field strengths. Typical potential difference spectra are presented for varying degrees of signal optimization, and the gains in signal-to-noise ratios are reported.
Separation of Additive Mixture Spectra by a Self-Modeling Method
Authors: Volkov Vladimir V.
Published: May 2005

A method for the separation of additive spectra of complex mixtures is developed on the basis of a linear algebra technique and nonlinear optimization algorithms. It is shown to be possible, under certain conditions, to uniquely separate a set of complex spectral curves consisting of the same components, but with different proportions, into the unknown spectra of the pure constituents and to give their respective relative concentrations. The method proposed is a variant of the self-modeling curve-resolution approach based on the singular value decomposition of the data matrix formed by the set of digitized spectra of mixtures. The spectra of components are calculated as linear combinations of left-side singular vectors of the data matrix provided that both individual spectra and their concentrations are nonnegative and the shapes of the spectra are as dissimilar as possible. The technique provides a unique decomposition if each fundamental spectrum has at least one wavelength with zero intensity and the other pure spectra are nonzero at this wavelength. The algorithm is evaluated on an artificial data set to clearly demonstrate the method. The approach described in this paper may be applied to any experiment whose outcome is a continuous curve y( x) that is a sum of unknown, nonnegative, linearly independent functions.
Fourier Transform Infrared Microspectroscopy of Plant Tissues
Authors: Stewart Derek
Published: May 2005

Fourier transform infrared (FT-IR) microspectroscopy was applied to three distinct types of plant tissue. Reflectance microspectroscopy of nutshells highlighted the differences between the chemistries of the inner and outer surfaces and the tissue as a whole. The outer surfaces were suberized, while the inner surfaces contained absorbances indicative of lignin or tannins or both. Transmission microspectroscopy was used to follow the changes in cell wall structure and composition of flax epidermal cells during development and showed that initial development was accompanied by suberin and lignin deposition, which was followed by polysaccharide deposition characteristic of secondary cell wall formation. These results were compared with those obtained from bamboo. Transmission microspectroscopy was also used to study the infection of potato tubers by Erwinia carotovora ssp. carotovora in aerobic and anaerobic conditions. The spectra suggested that both infective conditions produced cell wall degradation, whereas anaerobic infection was accompanied by extensive breakdown of starch and plasma membrane.
Important Aspects concerning the Quantification of Biomolecules by Time-of-Flight Secondary-Ion Mass Spectrometry
Authors: Muddiman David C. , Nicola Anthony J. , Proctor Andrew , Hercules David M.
Published: May 2005

Fundamental aspects regarding the use of time-of-flight secondary-ion mass spectrometry (TOF-SIMS) as a quantitative tool for the analysis of organic compounds are reported. The following factors are discussed: (1) the use of Poisson's law to correct for dead-time in single-ion data collection; (2) practical considerations concerning the analysis of “real world” samples; and (3) the effect of the etching process on the reproducibility of the intensity ratio (analyte/internal standard) of Ag-cationized species. To evaluate the importance of these factors, we used cocaine and cyclosporin A (CsA) as analytes because they show protonated and Ag-cationized species, respectively, in their SIMS spectra. Correction for detector dead-time using Poisson's law of single-ion counting expanded the dynamic range for cocaine by ∼2 orders of magnitude. For analyses requiring only a small dynamic range (i.e., CsA), the correction improved the % RSD of the slope from 2.43 to 0.87%. The maximum secondary-ion (SI) yield of CsA (Ag-cationized species) occurs at a CsA concentration ∼3 orders of magnitude higher than the therapeutic levels in blood (25–2000 ng/mL). It is discussed how this problem should be addressed. Analysis of variance (ANOVA) indicates that Ag substrates must be etched under identical conditions to obtain quantitative results when species requiring cationization are being analyzed.
Spectroscopic and Binding Properties of Near-Infrared Tricarbocyanine Dyes to Double-Stranded DNA
Authors: Davidson Yolanda Y. , Gunn Bonnie M. , Soper Steven A.
Published: May 2005

The noncovalent binding and spectroscopic properties of several near-infrared tricarbocyanine dyes with respect to sonicated calf-thymus DNA are reported. The dyes investigated were diethylthiatricarbocyanine iodide (DTTCI), diethyloxatricarbocyanine iodide (DOTCI), and 1,1',3,3,3',3'-hexamethylindotricarbocyanine iodide (HITCI), which are cationic and possess absorption maxima at 772, 695, and 750 nm, respectively, in DMSO. In buffered aqueous solutions, these dyes demonstrated extensive ground-state aggregation in aqueous solvents when compared to DMSO. In the presence of double-stranded DNA (dsDNA), the fluorescence emission spectra revealed enhancement ratios of bound-to-free dye ranging from 4.5 for DOTCI to 128 for DTTCI. Spectrophotometric titrations and Scatchard analyses of the dye-dsDNA complexes yielded nonlinear plots, suggestive of possible multiple binding sites on the DNA. Viscometric titrations of the complexes showed increased solution viscosities for DTTCI, consistent with an unraveling and lengthening of the dsDNA upon complexation. Fluorescence lifetime data of the dye-dsDNA complexes showed longer lifetimes exhibited by these dyes in the presence of the dsDNA compared with those in solutions with no DNA.
Simultaneous Measurements of Glucose, Glutamine, Ammonia, Lactate, and Glutamate in Aqueous Solutions by Near-Infrared Spectroscopy
Authors: Chung Hoeil , Arnold Mark A. , Rhiel Martin , Murhammer David W.
Published: May 2005

Calibration models are generated and evaluated for the measurement of five different components in synthetic mixtures prepared in aqueous solutions. Mixtures of glucose, glutamine, ammonia, lactate, and glutamate were prepared to simulate concentration levels expected during routine bioreactor fermentation processes. Near-IR spectra were collected from these solutions over the spectral range from 5000 to 4000 cm−1. This spectral information was used to build individual multivariate calibration models for each analyte. Models were constructed on the basis of partial least-squares regression of raw and Fourier filtered absorbance spectra. Each analyte could be detected selectively with mean percent errors of prediction ranging from 4 to 8%.
Depth-Resolved Near-Infrared Spectroscopy
Authors: Nerella Nadhamuni G. , Drennen James K.
Published: May 2005

While there is substantial evidence proving the success of transdermal drug delivery, there have been few accomplishments in the area of depth-resolved prediction of drug concentration during diffusion through a matrix. Such a method for noninvasive quantification of a diffusing species could assist in the development of new drugs, dosage forms, and penetration enhancers. Near-infrared depth-resolved measurements were accomplished by strategically controlling the amount of reflected light reaching the detectors using a combination of diaphragms with different-diameter apertures. Near-IR spectra were collected from a set of cellulose and Silastic® membranes to prove the possibility of depth-resolved near-IR measurements. Principal component regression was used to estimate the depth resolution of this method, yielding an average resolution of 31 μm. Further, to demonstrate depth-resolved near-IR spectroscopy in a practical in vitro system, we determined concentrations of salicylic acid (SA) in a hydrogel matrix during diffusion experiments carried out for up to three hours. An artificial-neural-network-based calibration model was developed which predicted SA concentrations accurately ( R2 = 0.993, SEP = 123 μg/mL).
Solid-State Matrix Effects on Near-Infrared Spectra: Interactions of Glucose and Sucrose with Amylose, Amylopectin, Cellulose, and Starch—Implications for Near-Infrared Calibrations
Authors: Reeves James B.
Published: May 2005

The objective of this work was to explore the question of how the interactions between carbohydrate monomers and polymers affect near-infrared spectra and to evaluate the implications of such effects with respect to the development of near-infrared calibrations. The effects of the presence of amylopectin, amylose, cellulose, and starch during the drying of glucose and sucrose on the resulting spectra were investigated. Sugars in various molar ratios with polymers were dried in a rotating mixer and then reground, and spectra from 10,000 to 4000 cm−1 were taken. In addition, spectra of identical mixtures prepared by mixing previously ground sugars and polymers were taken for comparison. Results on samples prepared either by simple mixing of sugars and carbohydrate polymers or by grinding mixtures produced by drying sugars in the presence of polymers indicated that interactions occur between the substances in question. Although simple mixtures of sugars with cellulose, amylose, amylopectin, or starch showed some spectral changes in the spectra of the sugars, in general, the spectra obtained by spectral subtraction were considerably more similar to those of the pure sugars than were those obtained for materials dried together.
Detection of Ambient NO by Laser-Induced Photoacoustic Spectrometry Using A2Σ+ − X2Π (0,0) Transitions Near 226 nm
Authors: Williamson C. K. , Pastel R. L. , Sausa R. C.
Published: May 2005

Trace concentrations of NO are detected under ambient conditions by laser-induced photoacoustic spectroscopy. NO is excited via its A2Σ+-X2π (0,0) band with radiation near 226 nm, and the subsequent heat released is monitored by a microphone. Rotationally resolved photoacoustic spectra are recorded and fit with the use of a multiparameter computer simulation based on a Boltzmann distribution. Transition probabilities and rotational energies are used as input parameters. The effect of buffer gas pressure, buffer gas, laser energy, and NO concentration on the PA signal is investigated both experimentally and by model calculations. Limits of detection (LODs) of 1.2, 2.8, and 4.9 ppm are obtained for NO in Ar, N2, and air, respectively. The ultimate sensitivity of this approach is greater with LODs projected in the low-ppb range by utilizing higher laser energies and an improved system design. The results are compared with those of previous studies using complementary laser-based spectroscopic techniques.
Thermal Lens Spectrophotometry in Agarose Gels
Authors: Briggs Michael W. , Long George R.
Published: May 2005

In this study, the application of thermal lens spectroscopy to detection of analytes in agarose gels was examined. It was found that a long-term refractive index gradient is produced in the sample, in addition to the thermally induced refractive index gradient, and gives rise to a long-term thermal lens signal. It is argued that the most likely source of the long-term signal is a concentration gradient formed in the sample. The long-term refractive index gradient results in a focusing lens, and is thus opposite to the thermal gradient. The formation of this gradient requires as much as 500 s to reach equilibrium during constant irradiation. The existence of the long-term refractive index gradient is verified by time-resolved Z-scan experiments. The signal resulting from this gradient is termed the long-term thermal lens and is shown to depend on temperature, is observed only for gelled agarose solutions, and is sensitive to anisotropies in the sample.
Optically Induced Analytical Error in Glow Discharge Optical Emission Spectrometry
Authors: Winchester Michael R.
Published: May 2005

It is shown that the common practice of imaging the plasma directly onto the spectrometer entrance slit in analytical glow discharge optical emission spectrometry (GDOES) may induce analytical error when used with samples which are chemically heterogeneous. An alternative method for transferring the source emission to the entrance slit is demonstrated to eliminate the potential error, suggesting its routine use in analytical GDOES.
Mathematical Alignment of Wavelength-Shifted Optical Spectra for Qualitative and Quantitative Analysis
Authors: Booksh Karl S. , Stellman Christopher M. , Bell Wendy C. , Myrick Michael L.
Published: May 2005

A multivariate method for aligning Raman spectra that suffer from spectral shifts resultant from diode laser mode-hopping is presented. This alignment method permits accurate alignment without necessitating a consistent reference peak while avoiding the uncertainties of estimating the maxima of broad or noisy peaks. This method differs from multivariate standardization methods in that the training set needs to be measured only once. The spectra are not compared to the spectra of a separate instrument. It is shown that the alignment enhances the performance of Raman spectroscopy for quantitative and qualitative applications. This evidence is supported by Monte Carlo simulations, quantitation of a mixture of aromatics by Raman spectroscopy, and imaging of a polymer surface by a Raman microscope.
Detection of Metals in the Environment Using a Portable Laser-Induced Breakdown Spectroscopy Instrument
Authors: Yamamoto Karen Y. , Cremers David A. , Ferris Monty J. , Foster Leeann E.
Published: May 2005

A portable instrument, based on laser-induced breakdown spectroscopy (LIBS), has been developed for the detection of metal contaminants on surfaces. The instrument has a weight of 14.6 kg, fits completely into a small suitcase (46 × 33 × 24 cm), and operates from 115 V ac. The instrument consists of a sampling probe connected to the main analysis unit by electrical and optical cabling. The hand-held probe contains a small laser to generate laser sparks on a surface and a fiber-optic cable to collect the spark light. The collected light is spectrally resolved and detected with the use of a compact spectrograph/CCD detector system. The instrument has been evaluated for the analysis of metals in the environment: Ba, Be, Pb, and Sr in soils; Pb in paint; and Be and Pb particles collected on filters. Detection limits in ppm for metals in soils were 265 (Ba), 9.3 (Be), 298 (Pb), and 42 (Sr). The detection limit for Pb in paint was 0.8% (8000 ppm), corresponding to 0.052 mg/cm2. The higher limit obtained for Pb in paint is attributed to the use of the 220.35-nm Pb(II) line instead of the stronger 405.78-nm Pb(I) line used for soils. Spectral interferences prevented use of the 405.78-nm line to determine Pb in paint. The surface detection limit for Be particles on filters was dependent on particle size and ranged from 21 to 63 ng/cm2. The detection limit for Pb particles on filters was 5.6 μg/cm2.
Dielectric Filter for Highly Sensitive Raman Spectroscopy
Authors: Futamata Masayuki
Published: May 2005

A filter spectrometer using dielectric bandpass filters eliminates Rayleigh scattering down to 10-5 while passing more than 90% of Raman signal from 50 to 2000 cm−1. It improves the optical throughput about 8–9 times in comparison to a double-stage subtractive monochromator, and about 20% in comparison to a holographic notch filter. Moreover, transmittance of the filter spectrometer does not depend on polarization of the incident light at the optimum angle. Raman spectra from powder sample of bismuth oxide and copper phthalocyanine and liquid sample of carbon tetrachloride in a glass capillary were easily observed down to 50 cm−1 with the use of the filter spectrometer combined with a single-stage monochromator.
Characteristics of a Rubidium Metal Vapor Filter for Laser Scatter Rejection in Single Molecule Detection
Authors: Guenard Robert D. , Lee Yuan-Hsiang , Bolshov Mikhail , Hueber Dennis , Smith Benjamin W. , Winefordner James D.
Published: May 2005

The characteristics of a rubidium metal vapor filter (MVF) for its use as a laser scatter filter for single molecule detection (SMD) were investigated. This investigation was done by a simulation along with experimental observation. A monochromator was used to elucidate the spectral components of the background in SMD. The major contributors to the background were laser transmission and fluorescence of the rubidium vapor. Experiments on the filter's performance under varying conditions such as MVF temperature, MVF pressure, and laser power were done. It was found that the integrated transmission intensity decreased with increasing pressure and temperature while it increased for increasing laser powers. The computer simulation modeled the experimentally observed profiles very well. Through the simulation, it was determined that the limitation on the attenuation by the MVF was due to the transmission of the broad-band stimulated emission “wings” of the Ti:sapphire laser.
FT-IR Study of the Electric Field Modulation of Liquid Crystalline 5CB
Authors: de Bleijser J. , Leyte-Zuiderweg L. H. , Leyte J. C. , van Woerkom P. C. M. , Picken S. J.
Published: May 2005

The dynamic IR spectra of electrically modulated liquid crystalline 5CB (4-pentyl-4'-cyanobiphenyl) are determined to be due to the director reorientation. In the absence of dc fields, the IR response is mainly at two times the modulation frequency. IR signals at the modulation frequency may be induced by application of additional dc fields. These signals at the modulation frequency are caused by the creation of polar orientation due to the static field. No difference in dynamic response has been found between the rigid aromatic core and the pentyl chain of 5CB. Expressions are given for the in-phase and in-quadrature signals at the modulation frequency and at twice its value. It is shown that the frequency-domain dynamic IR experiment mainly probes the transition range between the uniform planar to the homeotropic regions in the sample. The different probing of the sample by time-domain experiments is briefly discussed.
Portable, Battery-Powered, Tungsten Coil Atomic Absorption Spectrometer for Lead Determinations
Authors: Sanford Caryn L. , Thomas Susan E. , Jones Bradley T.
Published: May 2005

A compact, inexpensive atomic absorption spectrometer has been designed, constructed, and evaluated for the determination of lead at the μg/L level. The new device is made feasible by the combination of a reliable tungsten coil atomizer, a miniature spectrometer/charge-coupled device combination mounted on a PC card, and a near-line background-correction method. The finished spectrometer can be powered by a normal 12-V car battery, controlled with a laptop computer, and transported in any automobile. The overall dimensions of the original prototype system are 19 in. × 8 in. × 3 in. (excluding the computer), and it has no moving parts. The total estimated cost of the system including the computer is less than $6000. The limit of detection for Pb is 20 pg (20-μL sample volume), the linear dynamic range is two orders of magnitude, and the precision for the technique is 5% RSD at concentrations ten times greater than the detection limit. The accuracy of the technique was determined with the use of NIST SRM #1579a “Powdered Lead-Based Paint” containing 11.995 wt % Pb and NIST SRM 955a “Lead in Blood” containing 54.43 μg/dL Pb. The accuracy for the paint sample was 95.1% (11.41 wt % found) with the use of the calibration curve method (aqueous standards) and 97.2% (11.66 wt % found) with the method of standard additions. The accuracy for the blood sample was 93.5% (50.9 μg/dL found) with the calibration curve method and 96.6% (56.3 μg/dL found) with the method of standard additions. The limiting source of noise for the instrument is detector noise, so that the performance of the device can be improved by increasing the optical throughput of the system.
High-Fidelity Fourier Transform Infrared Spectroscopic Imaging of Primate Brain Tissue
Authors: Lewis E. Neil , Gorbach Alexander M. , Marcott Curtis , Levin Ira W.
Published: May 2005

We demonstrate a new mid-infrared and near-infrared imaging approach which is ideally suited to microscopic applications. The method employs an indium antimonide (InSb) focal-plane array detector and a commercially available step-scan Fourier transform infrared spectrometer (FT-IR). With either a KBr or a CaF2 beamsplitter, images from 1 to 5.5 μm (10,000-1818 cm−1) can be rapidly acquired with the use of all the available pixels on the detector. The spectral resolution for each image is easily varied by changing the number of acquired images during the interferometer scan. We apply this technique to noninvasively generate image contrast in sections of monkey brain tissue and to relate these data to specific lipid and protein fractions. In addition, we describe several computational methods to highlight the spatial distributions of components within a sample.
Synthetic Calibration and Quantitative Analysis of Gas-Phase FT-IR Spectra
Authors: Griffith David W. T.
Published: May 2005

A method for the quantitative analysis of gas-phase infrared spectra is described in which calibration spectra are calculated from a database of absorption line parameters rather than measured in a real spectrometer. The synthetic calibration spectra are computed with the use of the program MALT (Multiple Atmospheric Layer Transmission), including environmental (pressure, temperature, pathlength, etc.) and instrumental (resolution, line shape, wavenumber shift) effects in the calculation, so that the calculated spectra closely approximate real measured spectra. The synthetic calibration spectra are then used in quantitative analysis as if they were real spectra. In conventional laboratory studies, the method circumvents the need for time-consuming collection of large sets of laboratory calibration spectra often required when many absorbing gases must be analyzed. It is particularly useful in long open-path and solar FT-IR spectroscopy when no sample cell is available for recording calibration spectra. Examples are presented from conventional laboratory spectra in a closed-cell, open-path FT-IR spectra used to determine trace gas fluxes in an open field, and solar absorption spectroscopy using ground-based FT-IR spectrometers.
Maximum Entropy Methods Applied to Simulated and Observed Raman Spectra
Authors: Craggs C. , Galloway K. P. , Gardiner D. J.
Published: May 2005

One- and two-channel maximum entropy methods (MEMs) have been applied to simulated and experimental Raman spectra of both single and double (overlapping) bands. The extent to which signal recovery is affected by signal-to-noise ratios has been determined with the use of measures based on the mean sum of squared residuals, loss of band intensity, and band area reduction. The analysis demonstrates that the two-channel approach results in improved signal recovery, especially at high signal-to-noise ratios.
Energy-Gap Law and Room-Temperature Phosphorescence of Polycyclic Aromatic Hydrocarbons Adsorbed on Cyclodextrin/Sodium Chloride Solid Matrices
Authors: Ramasamy S. M. , Hurtubise R. J.
Published: May 2005

The energy-gap law was shown to be applicable to the room-temperature solid-matrix phosphorescence of polycyclic aromatic compounds adsorbed on cyclodextrin/salt matrices. No heavy atom was used to enhance the phosphorescence signals. As the energy gap between the lowest excited triplet state and ground state increased, the phosphorescence lifetime of the phosphor increased. The changes in the phosphorescence lifetimes were correlated with the magnitude of the nonradiative rate constants which, in turn, were related to the energy gap between the excited triplet state and ground state. With the correlations developed, it is possible to predict which polycyclic aromatic hydrocarbons will give strong solid-matrix phosphorescence.
Application of Near-Infrared Attenuated Total Reflectance Spectroscopy for Monitoring Epoxy Resin/Amine Cure Reactions
Authors: Xu Lisheng , Schlup John R.
Published: May 2005

Product quality in composite processing will be improved by dependable methods for monitoring the process. In this paper, the feasibility of using near-infrared attenuated total reflection (NIR ATR) spectroscopy as a sensor for monitoring epoxy resin cure is demonstrated. An ATR crystal serves as a contact sensor, which has several potential advantages over embedded optic fiber techniques previously reported. NIR ATR spectra obtained from several epoxy/amine systems show that both primary amine and epoxy functional groups have well-isolated absorption peaks in the near-infrared region. The utility of NIR ATR spectroscopy for in situ cure monitoring is demonstrated by following the reaction between phenyl glycidyl ether and butylamine at ambient temperature.
Gas/Aerosol Chemical Reactions in the NaOH-SO2-H2O System
Authors: Aardahl Christopher L. , Davis E. James
Published: May 2005

The hydrolysis of a solid NaOH microparticle in humid nitrogen and the chemical reaction between the resulting NaOH solution microdroplet and SO2 gas have been studied with the use of elastic and inelastic (Raman) light scattering. A single solid NaOH particle was levitated electrodynamically in a reaction chamber and exposed to water vapor. After hydrolysis/deliquescence, the resulting solution droplet was exposed to SO2 gas. Raman spectra and elastic resonance spectra collected during the reactions indicate that low SO2 concentrations in the gas phase yield NaHSO3 while high SO2 concentrations result in Na2SO3 as the product. These results indicate that the reversibility of the key reactions becomes important when the SO2 concentration is low.
FT-IR Microspectroscopic Investigation of the Interphase of Epoxy Resin-Glass Fiber-Reinforced Composites
Authors: Arvanitopoulos Constantinos D. , Koenig Jack L.
Published: May 2005

Glass fiber-epoxy with composites were analyzed with the use of FT-IR microspectroscopy. With the use of spectral subtraction along with two-dimensional mapping experiments, spectral features characteristic of the interfacial region were revealed. Different types of glass fibers were used in order to observe spectral differences at the interphase. When as-received and heat-cleaned glass fibers were used, certain similarities were observed, although an inhibition of the curing seems to be taking place at the interfacial region of epoxy-heat-cleaned glass fibers. When the glass fibers were treated with an aminosilane coupling agent (γ-APS), there was spectral evidence that the glass surface was modifying the epoxy-glass fiber interphase.
Near-Infrared Spectroscopic Determination of Acetate, Ammonium, Biomass, and Glycerol in an Industrial Escherichia Coli Fermentation
Authors: Hall Jeffrey W. , McNeil Brian , Rollins Malcolm J. , Draper Indira , Thompson Brad G. , MacAloney Graeme
Published: May 2005

By use of near-infrared (NIR) spectroscopy, simultaneous, multiple-constituent estimation of important bioprocess parameters can be obtained in a time frame (<1 min assay) that was previously unattainable. Therefore, with NIR spectroscopy the opportunity exists to incorporate real-time chemical information into bioprocess monitoring or control strategies which will lead to significant bioprocess improvements. The NIR spectroscopic analysis of unmodified whole broth samples for acetate, ammonium, biomass, and glycerol is described for an industrial Escherichia coli fed-batch fermentation bioprocess. For acetate and glycerol, suitable results were obtained from multiple linear least-squares regression (MLR) analysis. A more sophisticated partial least-squares (PLS) regression analysis was necessary to adequately model ammonium and biomass. The respective prediction errors (1σ) of 0.7 g/L, 1.4 g/L, 0.7 g/L, and 7 mmol/L for acetate, biomass, glycerol, and ammonium compare well with the error of the wet chemical reference methods used to derive the calibration algorithms.
Sample Retention in the Transport Tubing between an Electrothermal Vaporizer and an Inductively Coupled Plasma Mass Spectrometer
Authors: Sparks Christopher M. , Holcombe James A. , Pinkston Thomas L.
Published: May 2005

The transport tube between a commercial electrothermal vaporizer (ETV) and the torch for an inductively coupled plasma mass spectrometer ICPMS) was analyzed for sample that had been vaporized. A common analyte carrier, NaCl, and Ag were the primary samples analyzed. It was found that approximately 10% of the sample was retained in the transport tubing. This percentage could be varied by changing the total mass of sample vaporized, probably because of the smaller particles being formed. A temperature distribution of the argon gas in the transport tube was also obtained for maximum power heating of the ETV, for a one-second vaporization step, and for various flow rates.
Solid-Matrix Luminescence from Trace Organic Compounds in Glasses Prepared from Sugars
Authors: Wang Jiangshan , Hurtubise Robert J.
Published: May 2005

A new kind of solid matrix, glasses from sugars, was developed for trace organic analysis. Clear glasses of glucose and trehalose were prepared by evaporating the sugar solutions onto solid supports. It was determined that the ratio of methanol to water was very important in forming a clear glass. Also, glasses made from pure trehalose often cracked. However, with the addition of 8–10% NaCl to the trehalose, no cracks were formed. Clear and rigid glasses of both glucose and trehalose/NaCl were obtained on quartz plates. Strong room-temperature fluorescence (RTF) and room-temperature phosphorescence (RTP) were obtained from benzo[ f]quinoline (B[ f]Q), 4-phenylphenol (4-PP), (tetrol I-1), triphenylene, and phenanthrene. The limits of detection (LODs) of both the RTF and RTP for 4-PP and B[ f]Q in the glasses were in the subnanogram milligram range.