bluuebunny/crossref_metadata_2025 huggingface dataset:
Pressure Dependence of Space Charge Distribution in the Cathode Fall Region of Ar Hollow Cathode Discharges
Authors: Masaki Takashi , Wada Akihide , Adachi Yukio , Hirose Chiaki
Published: July 2005

The electric field in the cathode fall region of an Ar hollow cathode discharge has been measured by the use of optogalvanic spectroscopy in a gas pressure range from 1 to 6 Torr and at a discharge current from 12 to 20 mA. The radial variation of the field strength follows the mathematical expression derived from the space charge distribution function of ρ( r) = – Ar + B, where r is the radial distance from the cathode axis. In this equation the parameters A and B have been found by curve fitting to follow the formula B = aA + b, in which a is constant at −2.57 ± 0.1 mm when A and B are expressed in units of C/m4 and C/m3, respectively, while b is directly related to the gas pressure. In addition, the current- and pressure-dependent behavior of the cathode fall voltage and the electric field at the cathode surface have been examined.
Low-Signal-Level Raman Spectroscopy with an Intensified Optical Multichannel Array Detector
Authors: Schlotter N. E. , Schaertel S. A. , Kelty S. P. , Howard R.
Published: July 2005

A conventional intensified optical multichannel array detector (I-OMA) with minor modifications can detect organic monolayers at “counting rates” as low as 0.05 photoelectrons per second per pixel. Both hardware modifications and data analysis techniques are presented that allow one to obtain maximum performance from the conventional I-OMA.
Atomic and Ionic Fluorescence in an Inductively Coupled Plasma Using Hollow Cathode Lamps Pulsed at High Currents as Excitation Sources
Authors: Masamba W. R. , Smith B. W. , Krupa R. J. , Winefordner J. D.
Published: July 2005

Hollow cathode lamps pulsed at high currents were used as atomic and ionic fluorescence sources to excite atoms and ions in an inductively coupled plasma. Atomic fluorescence was measured for Cu, Ag, Zn, Al, Cr, and Mo, while ionic fluorescence was measured for Cu, Cr, Zn, and Sr. Limits of detection for atomic fluorescence were found to be better than those obtained by a commercial atomic fluorescence instrument operated under the same conditions, and calibration curves were linear over a range of approximately 104.
Optimized Spectroscopic Signal Estimates Using Integration and Matched Filters
Authors: Bialkowski Stephen E.
Published: July 2005

This paper examines theories of signal processing as applied to peak magnitude estimation in absorption and emission spectroscopy. Signals obtained from Fourier transform, fixed wavelength, and scanning dispersive instruments are modeled in terms of the time required to obtain a spectrum. The differences between these techniques and the signal processing procedures that should be used for each technique are characterized for a Lorentzian spectral feature. Including the time required to scan over a range of optical frequencies results in optimal signal processing procedures that are different from those previously supposed. In particular, it is found that the optimal matched filter is less efficient than repetitive measurements at a single frequency. The theory developed for the Lorentzian line model is extended to include an arbitrary shaped peak.
Site-Selective Shpol'skii Spectrometry of Sulfur-, Oxygen-, and Nitrogen-Containing Aromatic Compounds in Complex Samples
Authors: Elsaiid A. E. , Walker R. , Weeks S. , D'Silva A. P. , Fassel V. A.
Published: July 2005

Laser excited Shpol'skii spectrometry (LESS) was utilized to directly determine nitrogen (N-), oxygen (O-), and sulfur (S-) heterocyclic compounds in solvent refined coal (SRC-II), petroleum crude oil, and carbon black. Characteristic quasilinear LESS excitation and emission spectra of the heterocyclic compounds are presented for the first time under site-selective conditions. Deuterated analogs of dibenzothiophene and dibenzofuran were utilized for quantitation. Site-selective fluorescence spectra of aminopyrene derivatives of polycyclic aromatic compounds (PAC) are also presented for the first time. The potential for utilizing the LESS technique in critical environment and biological studies for the direct determination of N-, O-, and S-heterocyclic compounds and substitutional derivatives of parent PAC has been demonstrated.
Forensic Drug Analysis by GC/FT-IR
Authors: Kempfert Ken
Published: July 2005

Gas chromatography Fourier transform infrared spectroscopy (GC/FT-IR) has been examined as a new forensic drug identification technique. The method is found to be specific for many closely related isomers including cocaine and pseudococaine or phentermine and methamphet-amine. Distinguishing some isomers may require spectral subtraction or examination of band positions. The useful range of GC/FT-IR sensitivities was determined to be from 5O to 500 nanograms per component.
Evaluation of an Isolated Droplet Sample Introduction System for Laser-Induced Breakdown Spectroscopy
Authors: Archontaki H. A. , Crouch S. R.
Published: July 2005

An isolated droplet generator (IDG) has been used as a novel solution sample introduction system for laser-induced breakdown spectroscopy (LIBS). The IDG converts liquid samples to equally-spaced, uniform-sized droplets. The droplets are introduced into the region where a high-powered Nd:YAG laser beam is focused. The resulting analyte emission is spectrally and temporally resolved. The dependence of analyte emission intensity on several parameters (droplet radius, droplet production frequency, etc.) is examined. A flow injection analysis (FIA) manifold has been used to introduce samples to the IDG for quantitative analysis. Performance characteristics of the FIA/IDG/LIBS method are given. Calibration curves linear over 3 orders of magnitude have been obtained for several elements. Detection limits for solutions with the FIA/IDG/ LIBS system are in the low ppm range.
Determination of Particle Size in Powders by Scatter Correction in Diffuse Near-Infrared Reflectance
Authors: Ilari J. L. , Martens H. , Isaksson T.
Published: July 2005

Diffuse near-infrared reflectance spectroscopy has traditionally been an analytical technique for determining chemical compositions in a sample. We will, in this paper, focus on light scattering effects and their ability to determine the mean particle sizes of powders. The reflectance data of NaCl, broken glass, and sorbitol powders are linearized and submitted to the Multiplicative Scatter Correction (MSC), and the ensuing parameters are used in subsequent multivariate calibrations. The results indicate that particle size can, to a large degree, be determined from NIR reflectance data for a given type of powder. Up to 99% of the partical size variance was explained by the regression.
Effects of Noise, Time-Domain Damping, Zero-Filling and the FFT Algorithm on the “Exact” Interpolation of Fast Fourier Transform Spectra
Authors: Verdun Francis R. , Giancaspro Carlo , Marshall Alan G.
Published: July 2005

A frequency-domain Lorentzian spectrum can be derived from the Fourier transform of a time-domain exponentially damped sinusoid of infinite duration. Remarkably, it has been shown that even when such a noiseless time-domain signal is truncated to zero amplitude after a finite observation period, one can determine the correct frequency of its corresponding magnitude-mode spectral peak maximum by fitting as few as three spectral data points to a magnitude-mode Lorentzian spectrum. In this paper, we show how the accuracy of such a procedure depends upon the ratio of time-domain acquisition period to exponential damping time constant, number of time-domain data points, computer word length, and number of time-domain zero-fillings. In particular, we show that extended zero-filling (e.g., a “zoom” transform) actually reduces the accuracy with which the spectral peak position can be determined. We also examine the effects of frequency-domain random noise and roundoff errors in the fast Fourier transformation (FFT) of time-domain data of limited discrete data word length (e.g., 20 bit/word at single and double precision). Our main conclusions are: (1) even in the presence of noise, a three-point fit of a magnitude-mode spectrum to a magnitude-mode Lorentzian line shape can offer an accurate estimate of peak position in Fourier transform spectroscopy; (2) the results can be more accurate (by a factor of up to 10) when the FFT processor operates with floating-point (preferably double-precision) rather than fixed-point arithmetic; and (3) FFT roundoff errors can be made negligible by use of sufficiently large (> 16 K) data sets.
Analysis of Electric Field Distribution in the Cylindrical Cathode Fall Region of Ar Hollow Cathode Discharges
Authors: Hirose Chiaki , Adachi Yukio , Masaki Takashi
Published: July 2005

A theoretical model, as described in the preceding paper, has been applied to the analysis of the observed radial distribution of the electric field which was measured in the cathode fall region of Ar hollow cathode discharges under pressures from 1 to 6 Torr and discharge currents from 12 to 20 mA. The distribution of ion density was calculated from the derived parameters, confirming the monotonie increase toward the negative glow region. The derived values of the parameters are briefly discussed in relation to the conceivable physical picture of the processes taking place in the relevant region. A list of observed electric fields at various radial positions, gas pressures, and discharge currents is also given.
An Argon-Sheathed Premixed Oxygen-Hydrogen Burner for Fundamental Studies
Authors: May J. H. , Niemczyk T. M.
Published: July 2005

A laminar flow premixed oxygen-hydrogen slot burner has been designed and constructed. The design allows operation over a wide variety of oxygen-hydrogen mixtures without flashback. One of the key design criteria was ease of machining, a feature that has resulted in considerable flexibility in the dimensions of the slots and the positioning of the sheath slots relative to the flame slot. The flame produced shows high stability and distinct regions which make it ideal for fundamental combustion diagnostic studies.
Intriguing Absorption Band Behavior of IR Reflectance Spectra of Silicon Dioxide on Silicon
Authors: Wong James S. , Yen Yu-Sze
Published: July 2005

Infrared reflectance spectra of a thermally grown 30-nm SiO2 film on a Si wafer were measured as a function of incident angle and polarization. Spectra measured with s-polarized light resemble the published extinction coefficient for SiO2. The p-polarized spectra show significant distortions at all incident angles. Bands change in frequency and intensity and can even invert as the incident angle increases beyond the Brewster angle of the Si substrate. Spectral simulations using the classical electromagnetic equations reproduce these distortions.
Step Scan Interferometry in the Mid-Infrared with Photothermal Detection
Authors: Smith Matthew J. , Manning Christopher J. , Palmer Richard A. , Chao James L.
Published: July 2005

A medium resolution mid-infrared FT-IR instrument (IBM Instruments IR 44) has been modified to do step scanning; this has been done with the use of concepts previously applied to both near- and far-infrared instruments. In this paper we illustrate the method used for driving the mirror in the step scan mode and present some preliminary results from using the instrument with photothermal detection. At the current state of development, results obtained with the use of phase modulation indicate that this method produces significantly higher signal-to-noise ratios than does the use of amplitude (chopper) modulation to generate the photothermal signal.
The Use of Refractive Optics for High-Fidelity Image Transfer in Spatially Resolved Spectroscopic Measurements
Authors: Padgett Larry R. , Farnsworth Paul B.
Published: July 2005

Measurements of emission intensities from spatially inhomogeneous sources often require faithful image reproduction at the entrance slit of a monochromator or spectrograph, or at some intermediate aperture. In fundamental studies, the spatial variations in intensity contain information about the basic nature of the source. For analytical measurements, the spatial resolution is required for the selection of a region in the source which exhibits the optimum analytical characteristics. Refractive optics can be used for this type of image transfer, but only if proper attention is given to the minimization or elimination of lens aberrations. We have developed a simple lens system that allows for the elimination of chromatic aberration and the control of spherical aberration. Two plano-convex fused-silica lenses with nominal focal lengths of 300 mm are mounted on translation stages that are driven in opposite directions by a right-hand/left-hand leadscrew. The performance of this system will be discussed and compared with that predicted by ray-tracing calculations. The magnitudes of various lens aberrations will be compared, and their effect on spatially resolved measurements of emission from an inductively coupled plasma will be examined.
Reaction of Nitrogen Oxides with Black Carbon: An FT-IR Study
Authors: Smith D. M. , Welch W. F. , Graham S. M. , Chughtai A. R. , Wicke Brian G. , Grady Karen A.
Published: July 2005

Qualitative and quantitative studies of the reaction of black carbon with the oxides of nitrogen, including NO, NO2/N2O4, N2O, and N2O3, have been carried out with the use of Fourier transform infrared spectroscopy (FT-IR). The active reactant is shown to be NO2, whether it acts as a disproportionation product or as an impurity in the gas under study. FT-IR spectra of the surface species identify them as resulting from reaction of carbon with NO2. For paraffin candle soot which was exposed simultaneously to oxygen atoms, and nitric oxide at 298 K, the surface species also are due to NO2, formed by oxidative adsorption of NO on the soot surface.
A Low-Power Surfatron Source for the Atomic-Emission-Spectrometric Detection of Nonmetals in Aqueous Solution
Authors: Galante Leonard J. , Selby Mark , Hieftje Gary M.
Published: July 2005

Emission spectra in the UV-visible and near-infrared (NIR) spectral regions are presented for several nonmetals introduced as aqueous solutions by a glass-frit nebulizer. Detectability improves dramatically for some nonmetals with the use of a desolvation system to reduce the amount of water vapor entering the plasma. Detection limits for P, I, S, Cl, Br, and C are in the low- to sub-ppm range. Good precision (RSD <5%) and a dynamic range of 2–3 decades were observed for I and P. Easily ionizable elements such as K, Na, and Li can enhance nonmetal emission by as much as 30%.
A Spatial Study of the Influence of Plasma Length on Interference Effects in a Six-Electrode, Direct-Current, Variable-Length Plasma
Authors: Shields James P. , Piepmeier Edward H.
Published: July 2005

Vertical spatial profiles of a six-electrode, direct-current plasma emission source were used to study the influence of plasma length on the interference of Na on Ca and Zn and P on Ca. For the shortest plasma (11.5 mm), depression of the Ca atom line is observed in the region up to 10 mm above the tip of the sample bullet when Na is present. A cross-over to enhancement occurs for higher regions. This is directly opposite to the observations in the ICP for the Na interference on Ca. Increasing the plasma length causes downward shifts in the cross-over point which are not a simple effect of the lowering of the sample bullet. When P is present, the Ca atom emission is initially depressed in the region directly above the sample bullet. At higher observation heights, little effect is observed. Similar behavior is observed for the Ca ion line in the presence of P, suggesting the possibility of a classical vaporization-type interference mechanism. The interference effects studied here can be virtually eliminated by careful selection of plasma length and observation height.
Excimer Laser Pumped Dye Laser for Fluorescence Decay Time Measurement
Authors: Bor Zs. , Raksi F. , Kovacs G. , Rácz B.
Published: July 2005

A simple method is proposed for short fall-time dye laser pulse generation. The pulse tailoring is demonstrated by an excimer laser pumped double cavity dye laser. The achieved fall time is 280 ps with the use of a 7 ns long pump pulse.
Spectroscopic Quantitative Analysis of Strongly Interacting Systems: Human Plasma Protein Mixtures
Authors: Nyden Marc R. , Forney Glenn P. , Chittur Krishnan
Published: July 2005

Blood plasma protein infrared spectra, while qualitatively very similar, display subtle differences in the frequencies and intensities of absorption bands. These small differences are sufficient to permit an accurate quantitative analysis of mixtures of these proteins. In this paper we examine the performance of some alternative methods of spectroscopic quantitative analysis in determining the concentrations of proteins in aqueous solutions. The widely-used K matrix method, using sloping baselines and intercept functions, was found to be inadequate for these determinations. In contrast, a method based on the little-known Q matrix approach, augmented by a robust equation solver, yielded results with a sufficient degree of accuracy to make it a viable tool for use in the study of proteins at solid interfaces and for more general applications in the field of protein chemistry.
A Six-Electrode, Direct-Current, Variable-Length Plasma Source for Atomic Emission Spectroscopy
Authors: Shields James P. , Lee Gae Ho , Piepmeier Edward H.
Published: July 2005

A variable-length plasma source has been developed for analytical atomic emission spectroscopy. The length of the plasma, adjustable during plasma operation, provides a means of adjusting the sample residence time in the plasma. The plasma operates from three compact, simple, and inexpensive direct-current power supplies. Three concentric quartz tubes supply argon and sample aerosol to the plasma. The modular design allows the quartz tubing to be easily replaced and a variety of electrode distances to be established. The argon consumption, typically 7.4 L/min, is comparable to, or less than, that for commercial DCP and ICP systems. Many of the vertical spatial characteristics of the plasma described here are similar to those documented for the ICP. Changes in the nebulizer gas flow rate produced spatial shifts in the maximum of the vertical, spatial analyte emission profiles of Mg. Increases in the signal-to-background ratios at common analytical wavelengths were observed with increasing plasma length. The movement of the region of maximum emission to positions below the top of the outer quartz tube, which occurs as a result of increasing the plasma length, is thought to be the main reason for the worse detection limits. The addition of 10% nitrogen to the outer argon gas flow caused a 35% enhancement in the Ca ion and a 28% decrease in the Ca atom signal-to-background ratios.
High-Precision Fluorimetry with a Light-Emitting Diode Source
Authors: Smith B. W. , Jones B. T. , Winefordner J. D.
Published: July 2005

A simple fluorimeter which uses a light-emitting diode as a source of excitation and a photodiode as a detector has been constructed and evaluated. The exceptional stability of both the detector and the source make it possible to make concentration measurements by fluorimetry with a precision of at least 0.002%. Furthermore, the system exhibited excellent linear dynamic range and a limit of detection of 20 ng/L for the dye Oxazine 720 in methanol.
Detection of Subpopulations in Near-Infrared Reflectance Analysis
Authors: Lodder Robert A. , Hieftje Gary M.
Published: July 2005

In typical near-infrared multivariate statistical analyses, samples with similar spectra produce points that cluster in a certain region of spectral hyperspace. These clusters can vary significantly in shape and size due to variation in sample packings, particle-size distributions, component concentrations, and drift with time. These factors, when combined with discriminant analysis using simple distance metrics, produce a test in which a result that places a particular point inside a particular cluster does not necessarily mean that the point is actually a member of the cluster. Instead, the point may be a member of a new, slightly different cluster that overlaps the first. A new cluster can be created by factors like low-level contamination or instrumental drift. An extention added to part of the BEAST (Bootstrap Error-Adjusted Single-sample Technique) can be used to set nonparametric probability-density contours inside spectral clusters as well as outside, and when multiple points begin to appear in a certain region of cluster-hyperspace the perturbation of these density contours can be detected at an assigned significance level. The detection of false samples both within and beyond 3 SDs of the center of the training set is possible with this method. This procedure is shown to be effective for contaminant levels of a few hundred ppm in an over-the-counter drug capsule, and is shown to function with as few as one or two wavelengths, suggesting its application to very simple process sensors.
The History of Baird Corporation: A Broad Perspective on the Progress of Industrial Spectroscopy
Authors: Walsh David F.
Published: July 2005

Looking back on more than fifty years of independent innovation in spectrochemical instrumentation, Baird Corporation has now combined forces with Imo Delaval Inc. to ensure that its practical pioneering continues. Sophisticated analytical systems now apart of the company's product line provide advanced automation and software integration not only in the laboratory, but for many industrial processes and controls.
Evaluation of the Mini-Hollow Cathode Emission Source for the Analysis of Microsamples
Authors: Ryu Jong Yol , Davis Ray L. , Williams J. C. , Williams James C.
Published: July 2005

The analysis of very small samples by atomic emission from a hollow cathode discharge source is investigated. Subpicogram detection limits of 0.88, 0.72, 0.38, and 0.70 pg are reported for Li, Na, K, and Ca, respectively, by viewing the excitation from a very small hollow with a custom-built multichannel spectrometer. These detection limits are comparable to those from electrothermal atomic absorption, with the additional advantage of the ability to analyze nonmetals. The technique has adequate sensitivity for the analysis of microsamples of physiological fluids for Na, K, and Ca; similar methods may be successful for Mg, P, and Cl, which are of significant physiological interest. Literature of applications of the hollow cathode as an emission source is reviewed. Instrumentation, operation, and sample preparation procedures are described. Temporal profiles of the emission from very small samples deposited in the hollow and working curves are given.
Raman Spectroscopy over Optical Fibers with the Use of a Near-IR FT Spectrometer
Authors: Archibald D. D. , Lin L. T. , Honigs D. E.
Published: July 2005

A commercial Fourier transform infrared (FT-IR) spectrometer was modified for remote near-IR Raman spectroscopy. In one configuration, a single optical fiber was used to guide the excitation light to the specimen and to collect scattered light from the specimen. In an alternative configuration, separate fibers were used for excitation and collection. The optical fiber probes were used to record the Raman spectra of both liquid and solid specimens. The Raman scattering of the optical fibers interfered with the analyte signal. This fiber interference was affected by the optical properties of the specimen and the optical sampling configuration. These interferences were partially removed by subtracting a background spectrum. Potential applications and improvements are discussed.
A Monte Carlo Study of the Effect of Noise on Wavelength Selection during Computerized Wavelength Searches
Authors: Mark Howard
Published: July 2005

The process of selecting wavelengths for performing quantitative analysis in the near-infrared is notorious for its instability. A Monte Carlo technique was used to investigate the sensitivity of the wavelength selection process to the noise content of the spectra. The random nature of the noise causes the wavelengths to be selected at random; this seems to be sufficient to explain the instability of the selection process. The statistics of the selection process are insensitive to error in the dependent variable, and, within limits, also insensitive to the amount of noise in the spectral data. The statistics are sensitive to the number of samples in the data set and to the nature of the distribution of the noise.
Near-Infrared Surface-Enhanced Raman Spectroscopy. Part I: Copper and Gold Electrodes
Authors: Angel S. M. , Katz L. F. , Archibald D. D. , Lin L. T. , Honigs D. E.
Published: July 2005

Surface-enhanced Raman spectra of pyridine on copper and gold electrodes in the near-infrared were obtained with a Fourier transform Raman spectrometer. Surface-enhanced Raman spectra were observed for pyridine adsorbed on copper and gold electrodes while a Nd:YAG laser (1.064/μm) was used for excitation. Good-quality spectra were recorded for 0.08 mM pyridine on a copper electrode with a single oxidation-reduction cycle, whereas for a gold electrode, several ORCs were necessary. A very intense low-energy Raman band was observed on both metals at positive potentials, which may be due to a metal-oxide vibrational mode.
Simultaneous Dual-Window Measurements with a Linear Photodiode Array Detector
Authors: Zhu Jianxiong , Mann Charles K. , Vickers Thomas J.
Published: July 2005

A generally applicable method is described for simultaneous measurement of reference and analyte spectral features which would not otherwise fall within the range covered by a single linear diode array detector. The method employs dual entrance slits on the spectrometer to cause two spectral windows to overlap on the detector. The method is demonstrated for fluorescence measurement of Rhodamine B in ethanol. Recovery of the spectral information from the overlapped spectra using a least-squares fitting procedure is demonstrated. The simultaneously recorded reference measurements are shown to be effective in correcting for excitation source intensity variation by comparing corrected and uncorrected excitation spectra and calibration curve data.
Total Reflection Prisms as Achromatic IR Retarders
Authors: Korte E. H. , Jordanov B. , Kolev D. , Tsankov D.
Published: July 2005

Retarders based on total internal reflections are discussed. Quarterwave retardation can be obtained by a single reflection when one is using material of high refractive index (≥2.4), as it is available for the IR range. Alternatively, the influence of the beam divergence can be efficiently compensated for. Several optical designs and first results are presented.
Provenance Study of Venezuelan Pre-Columbian Ceramics Employing Radioisotope X-Ray Fluorescence
Authors: Labrecque J. J. , Vaz J. E. , Tarble K. , Rosales P. A.
Published: July 2005

Radioisotope x-ray fluorescence analysis was performed to determine normalized elemental intensities for pre-Columbian sherds and roller stamps from different archaeological sites in the Middle Orinoco region of Venezuela. These normalized intensities were used to construct three-component (Triangle) graphs separating the sherds into three groups based on their known origin. The three-component graphs were: (Zn, Sr, Zr), (Rb, Sr, Zr), and ( A, Sr, Zr), where A = Cu + Zn + Pb normalized intensities. The total precision was shown to be better than 5% absolute for all cases studied. It was concluded that two of the roller stamps found at one site were probably manufactured in a different source area. This lends support to the notion that the roller stamps were a trade item in late pre-Columbian times (1000–1400 A.D.). The method applied in this study using a 109Cd (2 mCi) source seems to be appropriate for provenance studies of archaeological ceramics where many samples are processed, because it has the inherent advantages of being simple, economical, and rapid.
Modulation Transfer Function Evaluation of a Hadamard Transform Photothermal Deflection Imaging System with Beam Condensing Optics
Authors: Treado Patrick J. , Morris Michael D.
Published: July 2005

The modulation transfer function of a source-encoded Hadamard transform imaging system including beam condensing optics is derived. The effects of diffraction, convolution with the encoding apertures, mask motion, and focus errors are considered explicitly. The derived equations are shown to describe resolution of Hadamard transform photothermal deflection imagers with up to 30 × condensing optics.
Polycyclic Aromatic Hydrocarbon Solute Probes: Effect of Solvent Polarity on the Ovalene and Benzo[ghi]perylene Fluorescence Emission Fine Structures
Authors: Waris Riaz , Rembert Michael A. , Sellers David M. , Acree William E. , Street Kenneth W. , Poole Colin F. , Shetty Prabhakara H. , Fetzer John C.
Published: July 2005

Fluorescence properties of benzo[ghi]perylene (BPe) and ovalene (Ov) dissolved in 25 solvents of varying polarity are reported. Measurements indicate that emission intensities depend on solvent polarity. The BPe and Ov solvent polarity scales are defined as the ratio of the fluorescence emission intensities of bands I and III of the vibronic spectra. Benzo[ghi]perylene and ovalene solute probes enable fluorescence measurements to be made in spectral regions less prone to solvent inner filtering and other artifacts which have hampered the use of pyrene (Py) as a polarity probe molecule.
A Compact Surface Plasmon Resonance Sensor for Measurement of Water in Process
Authors: Matsubara K. , Kawata S. , Minami S.
Published: July 2005

An optical sensor based on surface plasmon resonance (SPR) for water measurement in process has been developed. The optical setup of this sensor is made in a simple and compact way, by the use of a laser diode as a point light source, providing an angularly spread (convergent) beam incident to the sensing part with imaging optics. Multichannel detection by a photodiode array and the Fourier transform optical setup eliminates the need for a mechanical angle scanner or a rotary stage in the system, resulting in a reduction in the size, the weight, and the cost of the sensor. Water concentrations in ethanol were measured by this sensor. Water concentrations of from 0.3% to 10% were obtained. Temperature dependence of the sensor and the method for compensation are discussed.
Identification and Assay of an Organosilicon Contaminant in Unleaded Gasolines
Authors: Carduner K. R. , Carter R. O. , Westwood L. C.
Published: July 2005

Inductively coupled plasma-atomic emission spectroscopy is used to determine the concentration of a silicon impurity that appeared in some samples of unleaded fuel from a metropolitan area in 1984 and 1985. Silicon-29 NMR is used to identify the contaminant as the cyclic silicone, octamethylcyclotetrasiloxane. This silicone tetramer is also observed in the NMR of a commercial coating, a xylene solution of linear and cyclic silicones, used as a moisture barrier in the electronics industry.
Grazing Angle Metal-Overlayer Infrared ATR Spectroscopy
Authors: Ishino Yuichi , Ishida Hatsuo
Published: July 2005

The most sensitive reflection spectroscopic technique has been developed for studying the structure of thin films between a semiconductor and a metallic film. In this study, a metal-overlayer ATR technique was applied to measure the infrared spectra of interfacial layers. According to optical theory, this technique requires a high angle of incidence near the grazing angle in order to obtain optimum sensitivity. On the basis of the theoretical prediction, an optimized prism was designed. Our prism/thin film/ metal configuration yields an S/N ratio 5 times better than that achieved by the conventional reflection-absorption spectroscopy. This enhancement is not due to the so-called metal island effect, but is due instead to the high refractive index of the semiconductor prism.
Pulsed High-Pressure Liquid Injection of Biological Molecules into Supersonic Beam/Mass Spectrometry with Resonant Two-Photon Ionization Detection
Authors: Pang Ho Ming , Sin Chung Hang , Lubman David M.
Published: July 2005

Pulsed high-pressure liquid injection is used as a means of introducing thermally labile biological species into a time-of-flight mass spectrometer (TOFMS) system. The analyte species are then ionized by resonant two-photon ionization (R2PI) in the near ultraviolet. This method serves as a means of producing soft ionization or extensive fragmentation on the basis of the laser power and wavelength, without physical separation of the analyte from the effluent jet expansion. In addition, the pulsed liquid injection method allows introduction of the sample in methanol at 80°C without the extensive clustering that normally occurs in continuous expansions unless much higher temperature is utilized. With the use of this method the R2PI of catecholamines and indoleamines, as well as their metabolites, is studied in a TOFMS. The ability to obtain some spectral selectivity from jet expansions of liquid methanol is also demonstrated.
Spatial Mapping of Analyte Distribution within a Graphite Furnace Atomizer
Authors: Huie Carmen W. , Curran Charles J.
Published: July 2005

A versatile diagnostic scheme based on the combination of the unique properties of a laser, such as collimation and monochromaticity, together with absorption spectroscopy and subsequent computer extraction of quantitative information from a video signal has been applied to acquire spatially and temporally resolved information in a graphite tube atomizer. Spatially resolved concentration profiles with a 256 × 240 array of intensities can be obtained in 1/60 second. This capability has been demonstrated in the study of sodium atom distribution within a graphite furnace. Spatially and temporally resolved absorbance profiles taken within the furnace show extreme nonuniformities throughout the lifetime of the sodium atom plume. Early in the absorbance signal, the distributions show absorbances which decrease in going from the bottom, where the sample was initially deposited, to the top of the furnace. A more uniform distribution of the free atoms can be seen after a majority of the analyte has been released from the surface of the graphite tube, i.e., after the absorbance peak.
Degradation of Polystyrene on Silver Substrates during Surface-Enhanced Raman Scattering
Authors: Venkatachalam R. S. , Boerio F. J. , Carnevale M. R. , Roth P. G.
Published: July 2005

Surface-enhanced Raman scattering (SERS) by films of polystyrene adsorbed onto silver island films was investigated. Films that were only a few tens of angstroms in thickness degraded rapidly during laser irradiation to form graphite-like species at the silver surface. However, no degradation was observed while Raman spectra of the solid polymer were obtained, indicating that the graphitization was probably induced by laser heating of the substrate and catalyzed by silver. For thin films of polystyrene, the rate of graphitization was high and was proportional to laser power. However, the degradation reaction was inhibited for thick films or for thin films overcoated with thick films of a second polymer. The Raman spectra were similar for all films thicker than approximately a hundred angstroms, even those overcoated with a thick film of a second polymer having a large Raman scattering cross section, indicating that most of the observed scattering originated from polymer molecules within a few tens of angstroms of the silver surface. It was concluded that SERS can be used to probe the molecular structure of polymer/metal interfaces without interference by scattering from the bulk of the polymer.
Evaluation of Line and Continuum Sources for Atomic Fluorescence Spectrometry Using a Low-Powered Argon Microwave-Induced Plasma
Authors: Perkins Larry D. , Long Gary L.
Published: July 2005

An atomic fluorescence spectrometry system employing a low-powered, highly efficient MIP as the atom cell (MIP-AFS) has been developed and is evaluated with the use of direct aqueous nebulization. The MIP-AFS system employs hollow cathode lamp and Xe-arc lamp excitation sources. Detection limits of 14 elements were studied and compared to results for ICP-AFS. Linear working ranges of at least 5 orders of concentration magnitude were found. Interelement effects (i.e., vaporization, ionization, and scatter interferences) were also investigated.
Attenuated Total Reflection FT-IR Spectroscopy to Measure Interfacial Reaction Kinetics at Silica Surfaces
Authors: Parry D. B. , Harris J. M.
Published: July 2005

Attenuated total reflection (ATR) FT-IR spectroscopy has been adapted to measure the rates of chemical modification reactions at silica surfaces. In this method, a silicon ATR crystal is oxidized at 1000°C under dry O2 to produce a silicon dioxide layer on the crystal surface, the thickness of which can be measured using ellipsometry. The oxidized silicon layer is then used as a model silica surface in measurements of the rates of chemical modification. A flow cell is filled with a solution of a surface active reagent. ATR infrared spectra are obtained at regular time intervals, where confinement of the intensity to the interface by total internal reflection provides a measure of local changes in concentration of species which adsorb or bind to the surface. The effect of the silicon dioxide layer on the sensitivity of measuring absorbance at the silica-solution interface is investigated. A model reaction study is carried out to determine the binding kinetics diphenylchlorosilane to silica from carbon tetrachloride solution. The technique yields both in situ kinetic and structural information about the reaction of this reagent with silica surfaces.
A Simple Torch Design for a Microwave-Induced Plasma
Authors: Sobering G. S. , Bailey T. D. , Farrar T. C.
Published: July 2005

This paper describes a simple torch design for use with a microwave-induced plasma (MIP). The torch is constructed from commonly available components with an absolute minimum of machining. The basic torch may be constructed with the use of only hand tools and a drill press. The design is adaptable to a variety of configurations, including a tangential flow torch.
New Design Concepts for Direct Reader Measurement Electronics
Authors: Karanassios V. , Horlick G.
Published: July 2005

A dual-processor, distributed-intelligence approach toward the computerization of a direct-reading polychromator for atomic emission spectrometry is described. Emphasis is placed on a “zero based design” of the PMT current integration electronics of a direct-reader channel using microprocessor bus architectures, programmable support chips, data domain conversion integrated circuits, and inexpensive single-board microcomputers. Traditional analog integration of the current signal is replaced by domain conversion of the current to a frequency, and integration/digitization is achieved with the use of single chip software programmable counters. Each channel can be independently addressed, configured, cleared, preset, and read, as the channels are autonomous units on the bus of the data acquisition and control microcomputer.
The Influence of the Optical Viewing Axis on the Performance of the Microwave-Induced Plasma GC Detector
Authors: Goode Scott R. , Kimbrough L. Keith
Published: July 2005

The choice of viewing axis influences the sensitivity and selectivity of the GC-MIP detector. Axial (end-on) viewing provides higher sensitivity, but lateral (side-on) viewing yields improved selectivity.
Optogalvanic Spectroscopy in a Microwave-Induced Active Nitrogen Plasma
Authors: Seltzer M. D. , Piepmeier E. H. , Green R. B.
Published: July 2005

Optogalvanic spectra have been obtained for a microwave-induced active nitrogen plasma. The spectra originated from laser-excited transitions belonging to the second positive system of nitrogen. As the ultraviolet (UV) laser wavelength was scanned through the regions of interest, the laser-induced ionization signal was monitored. A laboratory-constructed etalon system of very low finesse was used to provide an interferometric wavelength reference. Calibration of the laser wavelength allowed the accurate identification of a series of selected nitrogen transitions.
Glow Discharge Sputter Atomization for Atomic Absorption Analysis of Nonconducting Powder Samples
Authors: Winchester Michael R. , Marcus R. Kenneth
Published: July 2005

A methodology has been developed for the analysis of nonconducting (oxide) powder samples by glow discharge atomization-atomic absorption spectrometry (GDA-AAS). The mixing of an oxide powder with a copper host matrix (1:9) allows pressing of a disk sample for glow discharge sputtering. Sample-to-sample precisions are on the order of 3–4% for iron in a geological specimen. The ability to generate analytical working curves is demonstrated for the analysis of iron by mixing Fe (III) and Al (III) oxides in the copper matrix material. The possible utility of the methodology is illustrated by the analysis of iron in an NBS geological reference material. The ability to perform analyses of these sample types suggests its applicability to such matrices as ceramics, glasses, and refractory-based catalysts.
Fluorescence Lifetime Selectivity in Multifrequency Phase-Resolved Fluorescence Spectroscopy
Authors: McGown Linda B. , Millican David W.
Published: July 2005

Theoretical aspects of the implementation of fluorescence lifetime selectivity in multifrequency phase-resolved fluorescence spectroscopy (PRFS) are discussed. The dependence of phase-resolved fluorescence intensities on the dynamic instrumental parameters of excitation modulation frequency and detector phase angle, as well as on fluorescence lifetime, is described. The different types of fluorescence lifetime “filtering” that can be effectively achieved include longpass, shortpass, and bandpass functions. The ability to continuously scan both modulation frequency and detector phase angle greatly increases the potential of PRFS for fluorimetric analysis.
Characterization of a Gas-Stabilized Arc Plasma in an ExB Magnetic Field Configuration
Authors: Trivedi Ketan , Coll David , Sacks Richard
Published: July 2005

A magnetic field of about 200 gauss oriented normal to the electric field in a 9 amp gas-stabilized dc arc is used to control the position of the plasma current channel. The presence of the magnetic field results in a drift motion of plasma electrons in the direction normal to the plane containing the electric and magnetic field vectors. The current channel can be displaced vertically upward or downward depending on the direction of the external magnetic field. With the field strengths used, displacements of several millimeters are observed. Spatially resolved radiation measurements show that radiation from the Ar plasma gas responds differently to the magnetic field than does radiation from the tungsten electrode material. When the magnetic field is generated by a 60-Hz ac current in the electromagnet, the plasma current channel undergoes periodic displacements at the magnetic field oscillation frequency. A phase shift between the field strength and the current channel displacement is observed.
Application of Principal Component Analysis on NIR Spectral Collection after Elimination of Interference by a Least-Squares Procedure
Authors: Devaux M. F. , Bertrand D. , Robert P. , Qannari M.
Published: July 2005

In NIR spectroscopy, multidimensional analyses such as Principal Component Analysis (PCA) may be applied to examine the similarity between spectra of natural products. However, such an approach is often limited by the effect of spectral interference due to water or particle size distribution of the samples. In the present work, the advantage of the elimination of such spectral interference before performing PCA was investigated. Unwanted component spectra were eliminated by a least-squares procedure. They were first orthogonalized and normalized by the Gram-Schmidt orthogonalization method. The subtraction coefficients were then assessed, similarly to principal component (PC) scores, by projection of the NIR spectra on the orthogonalized component spectra, and PCA was performed on the corrected spectra. This method was applied on an illustrative collection of wheat semolina conditioned in three levels of water content. Water was the component to be eliminated and had been previously modeled by two spectral patterns. These spectral patterns were used as the unwanted component spectra. PCA was applied independently before and after spectral correction of the collection of spectra and graphs obtained by the two procedures were compared. The squared correlation coefficient of the 3 first PC scores with water content was 0.979 before correction, with the 3 groups of water content appearing clearly on PCA graphs. After correction, the corresponding squared correlation coefficient for the 7 first PC scores was 0.016. PCA graphs obtained with corrected spectra also showed that the water effect was completely eliminated. At this moment, samples were separated according to their technological nature. The procedure developed may be useful in pattern recognition study and for automatic clustering of NIR spectra. It may also be applied in fields other than NIR spectroscopy.
Prediction and Identification of Multiple-Photon Resonant Ionization Processes
Authors: Smith D. H. , McKown H. S. , Young J. P. , Shaw R. W. , Donohue D. L.
Published: July 2005

Many single-color, multiple-photon transitions leading to ionization are observed for lanthanide and actinide elements in experiments using resonance ionization mass spectrometry (RIMS). It is desirable both to identify the energy levels involved in observed transitions and to be able to predict in advance their location. A computer code, ETRANS, has been written to perform these functions. Examples of both types of operation are given.
The SCO (OCS) edward—lemieux effect is controlled by a P‐orbital on oxygen. Evidence from electron momentum spectroscopy, photoelectron spectroscopy, X‐ray crystallography, and density functional theory
Authors: Wolfe Saul , Shi Zheng
Published: July 2005

The nature of the lone pairs in the series of molecules methyl propyl sulfide, dimethylthiomethane, methyl thiomethyl ether (MTME), dimethoxy‐methane, and methyl propyl ether has been examined experimentally by the techniques of electron momentum spectroscopy and photoelectron spectroscopy. Although the HOMO of MTME is found to be a p‐orbital on sulfur, it is the p‐orbital on oxygen that controls the Edward—Lemieux effect (the anomeric effect) in this molecule through a combination of both stabilizing and destabilizing interactions with C–S orbitals.
Catch and Harvest by Fishing Guides Compared with Other Anglers in Five Central Minnesota Lakes
Authors: Knapp Michael L. , Goeman Timothy J.
Published: July 2005

Popular opinion assumes that guides and guided anglers are more successful in catching and harvesting fish than other anglers are. Using creel survey data obtained during 1999–2000, we compared the fishing success of guides and their clients with that of other anglers targeting walleyes Sander vitreus on five lakes managed for walleyes near Brainerd, Minnesota. Effort from guided trips ranged from 1.0% to 4.6% of the total angler-hours in each lake, resulting in 5.2–22.6% of the total walleye harvest. Guided-trip catch rates were 2.6– 4.7 times greater than catch rates of unguided trips made by walleye anglers, and harvest rates for guided trips were 2.5–5.8 times greater than those of unguided trips. The consequences of guided harvest on these fisheries are unknown at this time, but this study provides insight into the success of guided trips and the potential effects exerted by a relatively small segment of the angling population.