bluuebunny/crossref_metadata_2025 huggingface dataset:
FT-IR Imaging of the Interface in Multicomponent Systems Using Optical Effects Induced by Differences in Refractive Index
Authors: Bhargava Rohit , Wang Shi-Qing , Koenig Jack L.
Published: October 2003

For phase-separated multicomponent polymeric systems, characterization of the interface between the components is particularly challenging. We have observed an optical effect in the infrared that can be used to image the interface specifically. This method yields images of the interfaces based on the interfaces showing apparent absorption arising from changes in refractive index at frequencies far from the specific frequencies associated with the components of the mixture. This method has been applied to multicomponent samples of polymer-dispersed liquid crystals where the nature of the interface can be specifically altered by the application of an electric potential across the sample. Effects of this optical phenomenon on spectra from such multicomponent systems are discussed, and factors that complicate quantitative analysis of data from interfacial regions have been pointed out.
Depth Profiling of Phosphorus in Photonic-Grade Silicon Using Laser-Induced Breakdown Spectrometry
Authors: Milán M. , Lucena P. , Cabalín L. M. , Laserna J. J.
Published: October 2003

Laser-induced breakdown spectrometry (LIBS) has been evaluated for depth profiling of phosphorus doping in silicon. Laser plasmas were formed by focusing a Nd:YAG laser (operating in the second harmonic, 532 nm) on the sample surface. Plasma emission was collected, dispersed, and detected with the use of a charge-coupled device (CCD). Experimental parameters, such as delay time and sample position relative to the laser focal point, were optimized to improve the signal-to-background ratio of phosphorus line emission. Diffusion profiles by LIBS of samples with different phosphorus diffusion steps are shown. Crater depth per pulse and ablated mass per pulse were measured to be 1.2 μm pulse−1 and 50 ng pulse−1, respectively. The knowledge of depth per pulse permitted the estimation of thickness of the P diffusion layer.
Temporal and Spatial Behavior of Electron Density and Temperature in a Laser-Produced Plasma from YBa2Cu3O7
Authors: Harilal S. S. , Bindhu C. V. , Nampoori V. P. N. , Vallabhan C. P. G.
Published: October 2003

Spectroscopic studies of laser-induced plasma from a high-temperature superconducting material, viz., YBa2Cu3O7 (YBCO), have been carried out. Electron temperature and electron density measurements were made from spectral data. The Stark broadening of emission lines was used to determine the electron density, and the ratio of line intensities was exploited for the determination of electron temperature. An initial electron temperature of 2.35 eV and electron density of 2.5 × 1017 cm−3 were observed. The dependence on electron temperature and density on different experimental parameters such as distance from the target, delay time after the initiation of the plasma, and laser irradiance is also discussed in detail.
Factors That Affect the Accuracy of Raman Shift Measurements on Multichannel Spectrometers
Authors: Fountain Augustus W. , Vickers Thomas J. , Mann Charles K.
Published: October 2003

Raman shift measurements have been made on cyclohexane, by using linear interpolation between bracketing neon line positions to establish Raman band wavelengths. Factors that affect the precision of these measurements have been examined in detail. These include change of slit width, grating line spacing, neon line intensity, distance of separation of neon lines, and effects of small grating movements. All these have some effect, but the last factor is particularly important. Techniques that give standard deviations of 0.03 cm−1 when measurements are made without moving the grating are degraded by about an order of magnitude when the grating is moved. This result is attributed to adventitious partitioning of signal power between adjacent detector elements. By deliberately moving the grating a small amount between otherwise replicate measurements, one can control this effect. Values for the Raman shifts for eleven cyclohexane bands, based on approximately 800 Raman spectra and an equal number of neon emission spectra, are presented. The values are compared with previous measurements. They are generally within the ±σ range of the earlier values, but the standard deviations of these results are about an order of magnitude smaller.
High-Throughput Large-Aperture Prism Prefilter for Ultraviolet Resonance Raman Spectroscopy
Authors: Kaminaka Shoji , Mathies Richard A.
Published: October 2003

For the acquisition of high-quality ultraviolet resonance Raman spectra of strongly scattering samples such as membrane protein suspensions, an f/3.5 Littrow prism prefilter has been designed, built, and characterized. This prefilter has a Czerny–Turner configuration, and its focal length is 25 cm. The apex angle of the dispersive prism (20°) was chosen to provide maximum performance in the 220 to 240 nm range. The prism prefilter significantly reduced stray background due to Rayleigh scattering and visible fluorescence, while maintaining a low dispersion of 1300 cm−1/mm at 253 nm as well as a large f/3.5 aperture. The sharpness of the transmission edge (at 242 nm, the T = 0% to 95% transition occurs in 1.3 nm) quantitates its effectiveness as a sharp-cut Rayleigh scattering filter. The total throughput of the prefilter is ∼60% at 235 nm and ∼50% at 632.8 nm. The utility of this prefilter is demonstrated by obtaining high signal-to-noise resonance Raman spectra of bacteriorhodopsin in a purple membrane suspension with 239.5 nm excitation.
Combined Near-Infrared Raman Microprobe and Laser Trapping System: Application to the Analysis of a Single Organic Microdroplet in Water
Authors: Ajito Katsuhiro
Published: October 2003

A combined Raman microprobe and laser trapping system using near-infrared (NIR) laser light was developed for the investigation of single organic microdroplets. The NIR laser light is noninvasive and reduces fluorescence interference in the Raman spectrum for organic molecules. The focused laser beam used for the laser trapping of a microdroplet serves simultaneously as the laser microprobe for Raman measurement. With this system, the focused laser spot is about 1 μm in diameter, which is small enough for the laser trapping of a single toluene microdroplet in water. The system also makes it possible to visualize a focused laser spot together with a laser-trapped microdroplet by using holographic notch filters. The Raman spectrum for a single laser-trapped toluene microdroplet can be obtained from below 100 cm−1 to above 3000 cm−1 with a charge-coupled device (CCD) detector. Fluorescence interference in the Raman spectrum is completely removed by using NIR laser light. The signal-to-noise ratio (SNR), defined as the ratio of the peak height to the standard deviation of the baseline noise in the spectrum, exceeded 250 for the 1003 cm−1 band of a toluene microdroplet at 1 s, which is sufficient to allow identification of the molecular species of a microdroplet.
Two-Dimensional Two-Phase Water Detection Using a Tunable Excimer Laser
Authors: Versluis Michel , Juhlin Greger , Andersson Öivind , Aldén Marcus
Published: October 2003

A method for simultaneous two-dimensional visualization of water in both gas and liquid phase is presented. This laser-based diagnostic technique uses a combination of two-photon laser-induced fluorescence (LIF) and spontaneous Raman scattering. A tunable KrF excimer laser, operating near 248 nm, was used as an excitation source. The technique was demonstrated on single water droplets and their surrounding gas-phase content. Prior to the visualization experiments, spectroscopic measurements were performed to find optimum filtering conditions.
Confocal Direct Imaging Raman Microscope: Design and Applications in Biology
Authors: Sijtsema Nanna M. , Wouters Siddi D. , De Grauw Cees J. , Otto Cees , Greve Jan
Published: October 2003

A confocal direct imaging Raman microscope (CDIRM) based on two synchronized scanning mirrors, a monochromator, and two charge-coupled device (CCD) cameras has been developed. With this system it is possible to make both Raman spectra of a small measurement volume and images of a larger sample area in one specific Raman band. The spatial resolution of the system was determined for two limiting situations: a small sphere and a thin layer. The image of a 0.282 μm sphere appeared to have a full width at half-maximum (FWHM) of 1.2 μm in the axial and 0.37 μm in the lateral direction, whereas the image of a 275 nm layer showed an FWHM of 1.4 μm in the axial direction. Confocal Raman images were made of the DNA and protein distribution in polytene chromosomes with a relatively weak Raman signal [0.1 photons/(second·pixel)]. Further, a three-dimensional Raman image of the drug distribution in a phthalocyanine-incubated fixed cell is presented. These examples show that the CDIRM can be used to image samples with a weak Raman signal and that three-dimensional images of the distribution of specific molecules in a sample can be made.
Effect of Various Treatments on Carbon Fiber Surfaces Studied by Raman Microprobe Spectrometry
Authors: Cuesta A. , Dhamelincourt P. , Laureyns J. , Martínez-Alonso A. , Tascón J. M. D.
Published: October 2003

High-modulus and high-strength carbon fibers were submitted to oxidation plus sizing and grinding treatments. Subsequent changes at the fiber surfaces were studied by Raman spectrometry. X-ray diffractograms and Raman spectra of the fresh fibers were compared with those of other carbon materials with different graphitization degrees. The industrial oxidation +sizing treatment induces disorder at the fibers surface, this being of a higher order of magnitude than that introduced by grinding. However, this disorder is different in nature from the intrinsic disorder typical for little graphitized carbon materials.
Quantitative ATR FT-IR Analysis of Surface Segregation of Polymer Blends of Polystyrene/Poly(Dimethylsiloxane)-co-polystyrene
Authors: Chen Jiaxing , Gardella Joseph A.
Published: October 2003

The surface segregation of a series of two-component polymer blends of polystyrene/poly(dimethylsiloxane)-co-polystyrene has been studied by attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy. We examined the details of calibration for quantitative ATR FT-IR. The quantitation is based on calibration of Beer's law by transmission FT-IR measurements. The effect of spectral distortion and penetration depth dependence of radiation wavelength due to ATR sampling is evaluated. ATR spectra are corrected for penetration depth dependence before being used for quantitation. The corrected ATR spectra were compared with the transmission spectra of the same samples. Peak area ratios using one peak from each component were measured for the determination of the concentration of surface poly(dimethylsiloxane). The correction and calibration procedure improves the accuracy of quantitative surface analysis in the range of micrometer sampling depth. Unlike other approaches for quantification of ATR data on polymers, this method can be used for systems with a complex, unknown concentration gradient near the surface such as the blend system reported here.
Simplified Equation for ATR Spectral Intensity of a Three-Phase System
Authors: Ekgasit Sanong , Siesler Heinz W.
Published: October 2003

A simplified equation for attenuated total reflection (ATR) spectral intensity in a three-phase system under a small absorption condition is derived. The spectral intensity is expressed in terms of a linear function of the bulk spectral intensities or absorption coefficients of the absorbing media. The applicability and limitation of the simplified equation are verified by comparing the spectral intensity obtained from the simplified equation to that from the exact equation.
Prototype Raman Spectroscopic Sensor for in Situ Mineral Characterization on Planetary Surfaces
Authors: Wang Alian , Haskin Larry A. , Cortez Enriqueta
Published: October 2003

Raman spectroscopy has the potential to provide definitive identification and detailed characterization of the minerals that comprise rocks and soils on planetary surfaces. We have designed a probe head for Raman spectroscopy that is suitable for use on a spectrometer deployed by a rover or a lander on the surface of a planet such as Mars, the Moon, or an asteroid. The probe head is lightweight, low power, rugged, and simple. It is based on a tiny distributed feedback diode laser and volume holographic components. A protective shell surrounds the probe head and serves as a mechanical stop for the mechanical arm of a planetary rover or lander during placement of the probe head onto the surface of a rock or soil. Pressing the shell against the rough surface of a target rock or soil also places the sampling objective of the probe head in rough focus, and the probe head is designed to be tolerant of focusing errors of ∼5 mm. A breadboard version of the probe head gave spectra of high quality on clean crystals of diamond, sulfur, calcite, quartz, and olivine. The results are qualitatively comparable to those obtained by using a conventional micro-Raman spectrometer on fine-grained travertine and on difficult specimens of basaltic lavas and impactites whose original mineralogy had been altered by reaction with water and air.
Evanescent Wave Absorption Spectroscopy by Means of Bi-Tapered Multimode Optical Fibers
Authors: Mignani Anna Grazia , Falciai Riccardo , Ciaccheri Leonardo
Published: October 2003

This paper discusses the theoretical and experimental implications of tapering a multimode optical fiber with a view to its use in evanescent wave absorption spectroscopy. Good experimental results are obtained, showing the possibility of quadruplicating the absorbance efficiency. This easy and reproducible technique for taper fabrication is suitable for the implementation of both probes for spectroscopy and chemically assisted fiber-optic sensors.
Fourier Transform Near-Infrared Monitoring of Reacting Resins Using an Evanescent Wave High-Index Fiber-Optic Sensor
Authors: Dunkers Joy P. , Flynn Kathleen M. , Huang Mitchell T. , McDonough Walter G.
Published: October 2003

In this work, a high-index silica-based fiber-optic mini-bundle sensor was constructed and implemented with a Fourier transform near-infrared spectrometer in the spectral region from 10 000 to 4500 cm−1. The refractive index of the multimode step index fiber was 1.618. This arrangement allows the propagation of waveguiding modes when the sensor is immersed in most resin systems. The reactions of a polyisocyanurate resin system and an epoxy resin system were monitored and peak assignments were made and discussed with respect to their potential for use in real-time analysis to be applied to cure control. Last, cure monitoring with this sensor was successfully demonstrated in a glass-reinforced resin transfer molded epoxy part.
Real-Time Polarization Modulation in Situ Infrared Spectroscopy Applied to the Study of Atmospheric Corrosion
Authors: Faguy Peter W. , Richmond William N. , Jackson Richard S. , Weibel Stephen C. , Ball Gail , Payer Joe H.
Published: October 2003

A new methodology for the real-time in situ monitoring of atmospheric corrosion processes is presented. The mid-infrared spectra of surface films formed on polished copper substrates exposed to humid air containing sub-ppm levels of sulfur dioxide, nitric oxide, and hydrogen chloride were obtained by using a novel surface-sensitive infrared technique: real-time polarization modulation grazing angle reflection-absorption spectroscopy. The new methodology demonstrated improved signal-to-noise ratios, by a factor of 2.5, as compared to conventional Fourier transform infrared reflection absorption spectroscopy. Molecular spectroscopic data for water- and hydroxyl-containing species present at the metal surface were obtained with no interference from water vapor. Over the spectral region 4000–800 cm−1, bands were identified and assigned to nitro and nitrito adsorbates, to sulfite ions, and to bound water on the copper surface. Analysis of the time evolution and the profile composition of these bands is possible because of the sensitivity of this new optical sampling technique.
Evaluation of a Correction for Photometric Errors in FT-IR Spectrometry Introduced by a Nonlinear Detector Response
Authors: Richardson Robert L. , Yang Husheng , Griffiths Peter R.
Published: October 2003

For strongly absorbing bands measured with a Fourier transform infrared (FT-IR) spectrometer, the effects of a nonlinear detector response must be eliminated before Beer's law linearity can be achieved. An empirical method for greatly reducing the effect of detector nonlinearity on FT-IR Beer's law spectra measured by using an FT-IR spectrometer equipped with a mercury-cadmium-telluride (MCT) detector is investigated. This first-order analytical function has been applied to correct nonlinear vapor-phase spectra and statistically evaluated for validity for spectral regions above the detector cutoff. In addition, a series of second-order functions has been evaluated to investigate the possibility that the transmittance scale is slightly nonlinear even after the first-order correction has been applied. Any improvement caused by the second-order functions was not statistically significant.
Effects of Detector Nonlinearity on Spectra Measured on Three Commercial FT-IR Spectrometers
Authors: Richardson Robert L. , Yang Husheng , Griffiths Peter R.
Published: October 2003

The effect of the nonlinear response of mercury-cadmium-telluride (MCT) detectors has been evaluated on three commercial Fourier transform infrared (FT-IR) spectrometers. The greater the photon flux and the photon flux density, and the smaller the area of the detector on which the source image is focused, the greater are the effects of the nonlinearity. The signal-to-noise ratio (SNR) of spectra measured with an MCT detector under conditions of high photon flux and, especially, high photon flux density is significantly less than the SNR calculated by using the manufacturer's D* value. Detector nonlinearity usually leads to negative deviations in Beer's law plots. An empirical correction algorithm has been applied to Beer's law spectra acquired with the use of photoconductive MCT detectors and has been found to work well.
Origin of and Compensation for the Baseline Errors in Fourier Transform Spectra
Authors: Salomaa I. K. , Kauppinen J. K.
Published: October 2003

In Fourier transform absorbance spectroscopy, several types of baseline errors may be caused by the variations in the optical system, especially in the interferometer. The nature and causes of these errors have been studied. Furthermore, a method to eliminate the effect of these errors on multicomponent analysis is introduced. The nature of the errors has been experimentally verified, and a practical example of the use of the correction method is presented.
Overcoming the Multiplex Disadvantage by Using Maximum-Likelihood Inversion
Authors: Bialkowski Stephen E.
Published: October 2003

A maximum-likelihood estimator, derived under quantum-noise-limited measurement conditions, is used to obtain wavenumber-or-dered spectra produced by a model Michelson interferometer. The estimator is tested on a number of synthetic interferograms, and results are compared to similar spectra obtained by using the Fourier (cosine) transform. It is found that the maximum-likelihood inversion method does not result in white noise in the spectrum estimate when the spectrum is sparse. It thus may be used to circumvent the main disadvantage in multiplexed spectrometer measurements using quantum-noise-limited detectors for emission-based measurements. It is also found that maximum-likelihood inversion methods can be used to obtain spectrum estimates with greater peak-width resolution than those found by using Fourier transforms. The methods produce optical spectrum estimates that are relatively free of artifacts associated with the Fourier transform. The method is extended to include measurements with both quantum noise and additive white noise. Results obtained by using the quantum-noise-limited and normal noise maximum-likelihood spectrum estimation methods suggest that both the multiplex-disadvantage and the Gibbs phenomenon effects may be reduced by limiting the parameter space. The main problem with the maximum-likelihood method is the relatively long times required to obtain spectrum estimates.
Hybrid Calibration Models: An Alternative to Calibration Transfer
Authors: Ozdemir Durmus , Mosley Matt , Williams Ron
Published: October 2003

A new procedure for calibrating multiple instruments is presented in which spectra from each are used simultaneously during the construction of multivariate calibration models. The application of partial least-squares (PLS) and genetic regression (GR) to the problem of generating these hybrid calibrations is presented. Spectra of ternary mixtures of methylene chloride, ethyl acetate, and methanol were collected on a dispersive and a Fourier transform spectrometer. Calibration models were generated by using differing numbers of spectra from each instrument simultaneously in the calibration and prediction sets, and then validated by using a set of spectra from each instrument separately. Calibration models were found that perform well on both instruments, even when only a single spectrum from the second instrument was used during the calibration process. As a benchmark, comparison with PLS showed that GR is more effective than PLS in building these hybrid calibration models.
Crystallinity Determination of Polylactide by FT-Raman Spectrometry
Authors: Qin Deru , Kean Robert T.
Published: October 2003

The complete Raman spectra of isotropically crystalline and amorphous polylactide (PLA) have been successfully obtained with the use of a Fourier transform instrument equipped with a near-IR laser source. The Raman spectra of PLA were recorded at a resolution of 4 cm−1 from a backscattering sampling geometry. The changes in band intensity and shape of Raman spectra in the crystalline PLA samples facilitated the quantification of the crystallinity, which was primarily determined by the change in enthalpy via differential scanning calorimetry (DSC). A comparison of quantitative analysis of crystallinity by a multivariate technique, partial least-squares (PLS), and a univariate method at the carbonyl stretching band is described. Quantitative analysis of PLA crystallinity was performed after the data preprocessing with the standard normal variate (SNV) method in the combined spectral regions 3100–2800 cm−1 and 2000–200 cm−1 that were determined by the analysis of the correlation spectrum. The use of the calibration model containing mostly 1% d-PLA samples to separately analyze the samples with 1% and 5% d-PLA is discussed. Superior results obtained from the multivariate over the univariate method make PLS the preferred method of choice in quantification of crystallinity. The standard error of prediction (SEP) for the analysis of 1% d-PLA samples with the use of the calibration model described is 0.85 (—J/g), and the SEP for 5% d-PLA samples is 1.35 (—J/g) with the outliers excluded. The discrepancy in analyzing these two types of PLA samples with the use of the same calibration model is also discussed.
A Priori Estimation of the Parameters of the Method of Spectral Curve Deconvolution
Authors: Buslov Dmitrii K. , Nikonenko Nataliya A.
Published: October 2003

A method is proposed for estimating the parameters used in the deconvolution technique. The proposed method is based on the use of the Fourier transform modulus of the spectrum being treated with the purpose of obtaining information about the characteristics of the spectral bands and random measurement errors. Formulas are given that permit estimation of the values of noise variance in the experimental spectrum, the low-pass filter passband, and the contour half-width of the high-pass filter. Results are considered for the application of the proposed formulas for determining the parameters used with the deconvolution of synthetic and experimental spectra. It has been concluded that practical use of the proposed method of a priori estimation of the parameters permits, to a certain extent, the optimization of the process of deconvolution of spectral curves.
Simple Approach to Determining Absolute Raman Cross Sections Using an Optical Parametric Oscillator
Authors: Biswas Nandita , Umapathy Siva
Published: October 2003

In the present investigation, it is shown that use of commercial optical parametric oscillators (OPOs) has allowed for a simple method of determining the absolute Raman cross sections utilizing the measurement of integrated intensity ratios. Standard curves for the absolute Raman cross sections of the commonly used internal standards (viz., acetonitrile 918 cm−1 peak and nitrate 1045 cm−1 band) have been developed from the relative Raman intensities measured in the wavelength range 450–650 nm. The absolute intensities are fitted to the A-term frequency dependence and found to be consistent with the available literature data. We have demonstrated that, using an OPO, one can develop a standard curve for any internal standard, in order to accurately determine absolute Raman cross sections for a given system. This approach, in general, avoids the use of precalibrated lamps or external standard methods which are cumbersome, in comparison to measuring the integrated intensity changes with respect to an internal standard.
Evaluation of a Solid-Phase Extraction Membrane as a Surface-Enhanced Raman Substrate
Authors: Szabo Nancy J. , Winefordner James D.
Published: October 2003

A commercially available solid-phase extraction membrane was evaluated as a substrate suitable for routine analysis by surface-enhanced Raman spectrometry (SERS). The material was silver coated in-house via chemical reduction. Because the material has chromatographic capabilities, the use of SERS as a detection method for thin-layer chromatography (TLC) was considered by separating, then detecting, a mixture of commonly used sulfonamides from the bare and coated material. While the mobilities of the sulfa drugs were not strongly affected by the silver, the SER response was weak and analyte degradation was apparent. Some signal improvement was gained by dampening the surface with water in a simple surface modification. General substrate performance in both dry and in the modified dampened states was evaluated by using the model, crystal violet. The resulting analytical curves were linear across 1–2.5 orders of magnitude with limits of detection in the subnanogram range (total analyte applied). Under routine preparation and analysis procedures, reproducibility was <30%, but improvement to ∼10% was possible when great care was used. Typical spectra for two compound series having a variety of functional groups were obtained and showed general trends for response dependence on functional group.
Quantitative Assay of Bucindolol in Gel Capsules Using Infrared and Raman Spectroscopy
Authors: Niemczyk T. M. , Delgado-Lopez M. , Allen F. S. , Clay J. T. , Arneberg D. L.
Published: October 2003

The methods most commonly employed to determine active ingredient content in solid drug formulations involve dissolution of the sample. While these methods are capable of accurate and precise performance, the sample preparation required limits their use in quality-control applications to an occasional sample. There is a need for nondestructive methods capable of rapidly determining the active ingredient content in drug formulations. Spectroscopic methods of analysis have the potential for making the determinations with little or no sample preparation; hence these methods might be applied as at-line product quality monitors. We have investigated the use of diffuse reflectance infrared and Raman spectroscopies for the determination of bucindolol content in solid drug formulations. In experiments on formulations containing 0 to 100 mg of the active ingredient, the standard error of prediction with the use of either spectroscopic method was about 2.0 mg. The Raman spectroscopic method involved virtually no sample preparation, and the spectroscopic data can be collected rapidly; hence Raman spectroscopy shows very good potential as an at-line quality control monitor.
UV-Vis, FT-Raman, and 1H NMR Spectroscopies of cis-trans Carotenoids from Saffron (Crocus sativus L.)
Authors: Assimiadis Manolis K. , Tarantilis Petros A. , Polissiou Moschos G.
Published: October 2003

Stigmata of Crocus sativus L. were extracted in water, and the extract was analyzed by using a high-pressure liquid chromatography (HPLC) method. The carotenoids of saffron [ cis and trans glycosyl esters of crocetin or crocins (CRCs)] were isolated, and the two major isomer compounds (all- trans-digentiobiosyl crocetin and 13- cis-digentiobiosyl crocetin) were characterized spectroscopically with ultraviolet-visible (UV-vis), Fourier transform (FT)-Raman, and 1H NMR spectroscopies. The 13 -cis compound showed in a UV-vis spectrum an additional peak at 330 nm, in an FT-Raman spectrum the presence of a peak at 1138 cm−1, and in the 1H NMR downfield shifts of protons 12 and 15 and an uptield shift of proton 14, with respect to the all-trans isomer, according to differences in their skeletal structures. These features are shown also by the profile of their two-dimensional spectra.
UV-Visible and Inelastic Electron Tunneling Spectroscopies of Brevetoxins
Authors: Brousseau J.-L. , Vibet N. , Leblanc R. M. , Rein K. S. , Baden D. G.
Published: October 2003

We have studied the UV-vis and vibrational spectra of the brevetoxins PbTx-2, PbTx-3, PbTx-9, and 2, 3, 27, 28, 41, 43-hexahydro-(reduced) PbTx-3. The absorption at 194 nm (ε ≈ 18 000 L mol−1 cm−1) of PbTx-2 and PbTx-3 is assigned to the Π–Π* transition of the lactone conjugated double bonds. The n-Π* transition of the lactone is seen at 239 nm (∈ ≈ 2 800 L mol−1 cm−1). The absorption band at 208 nm for PbTx-2 is assigned to the conjugated double bonds of the aldehyde function located on the K-ring side chain. The inelastic electron tunneling spectra of PbTx-2, PbTx-3, PbTx-9, and fully reduced PbTx-3 are presented and the vibrational bands are assigned. We show that inelastic electron tunneling spectroscopy can be used to monitor and measure the vibrational fingerprint of the brevetoxins at a level as low as 1 ng.
Source-Corrected Two-Photon Excited Fluorescence Measurements between 700 and 880 nm
Authors: Fisher W. G. , Wachter E. A. , Lytle Fred E. , Armas Michael , Seaton Colin
Published: October 2003

Passively mode-locked titanium:sapphire (Ti:S) lasers are capable of generating a high-frequency train of transform-limited subpico-second pulses, producing peak powers near 105 W at moderate average powers. The low energy per pulse (<20 nJ) permits low fluence levels to be maintained in tightly focused beams, reducing the possibility of saturating fluorescence transitions. These properties, combined with a wavelength tunability from approximately 700 nm to 1 μm, provide excellent opportunities for studying simultaneous two-photon excitation (TPE). However, pulse formation is very sensitive to a variety of intracavity parameters, including group velocity dispersion compensation, which leads to wavelength-dependent pulse profiles as the wavelength is scanned. This wavelength dependence can seriously distort band shapes and apparent peak heights during collection of two-photon spectral data. Since two-photon excited fluorescence is proportional to the product of the peak and average powers, it is not possible to obtain source-independent spectra by using average power correction schemes alone. Continuous-wave, single-mode lasers can be used to generate source-independent two-photon data, but these sources are four to five orders of magnitude less efficient than the mode-locked Ti:S laser and are not practical for general two-photon measurements. Hence, a continuous-wave, single-mode Ti:S laser has been used to collect a source-independent excitation spectrum for the laser dye Coumarin 480. This spectrum may be used to correct data collected with multimode sources; this possibility is demonstrated by using a simple ratiometric method to collect accurate TPE spectra with the mode-locked Ti:S laser. An approximate value of the two-photon cross section for Coumarin 480 is also given.
Analysis of Discolored Aluminum Foil by Laser Ablation Inductively Coupled Plasma Mass Spectrometry and Scanning Electron Microscopy
Authors: Yuzefovsky Alexander I. , Miser Donald E.
Published: October 2003

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was employed for the characterization of the elemental composition of discolored areas of thin (50 μm) aluminum foil samples. The spatial distribution of the impurities, which included 11 elements present in the foil material at ppm and ppb levels, was analyzed. Elevated concentrations of almost all studied elements were found in the discolored regions with respect to the nondiscolored regions of the foil. In particular, the difference in the elemental yield observed for iron was approximately 6 to 25 times higher in the discolored regions of the foil. In addition, an elevated level of oxygen was detected in the discolored regions of the sample by the use of scanning electron microscopy with a wavelength-dispersive spectroscopy (SEM-WDS) system. Thus, the elevated levels of iron and oxygen in the same discolored regions of the foil, according to the authors' opinion, strongly indicated the development of a corrosion process within the samples. The discoloration itself was most likely a result of the formation of metal oxide compounds as products of the corrosion process, with iron oxide contributing the yellowish color in the affected areas.
Analysis as a Function of Temperature of the Dynamic Linear Infrared Dichroism Spectra of Isotropic and Cold-Drawn High-Density Polyethylene
Authors: Lagarón José M. , Steeman Paul A. M. , Kip Bert J.
Published: October 2003

A dynamic linear infrared dichroism (DLIRD) study was carried out as a function of temperature on isotropic and cold-drawn high-density polyethylene (HDPE) with the use of a rapid-scan setup. The dynamic in-phase dichroic spectrum and its components (parallel and perpendicular polarized spectra) were analyzed. From the results, it turned out that, in addition to molecular orientation effects, other effects such as frequency shifts are clearly identified in the dynamic signals, which furthermore were in agreement with previously reported results on polyethylene under stress from the use of conventional infrared spectroscopy. Moreover, the frequency shifts were more apparent at the lowest temperatures and in the cold-drawn material, i.e., with increasing sample moduli. A revision of the interpretation of the results published earlier, in which the dynamic signals were solely attributed to molecular orientations, is also carried out in view of our results. From our results it seems that indeed an orientation of the crystallographic b axis parallel to the applied strain is suggested from the –CH2–bending and rocking ranges of the isotropic sample. However, an orientation of the crystallographic a axis of the unit cell perpendicular to the strain direction as suggested from previous studies is questioned, as well as the assignment of a certain dynamic signal to a reorientation of chains in the amorphous phase. Besides these results, the behavior of the –CH2– wagging at 1176 cm−1, assigned to the crystalline phase, suggests an orientation of the crystallographic c axis of the unit cell parallel to the strain direction. As a consequence, two conclusions are made: (1) a more complex orientation motion occurs in the crystals than has been reported so far, and (2) a more thorough study of the DLIRD signals has to be carried out in which other factors such as thickness variations and instrumental artifacts need to be addressed.
Dryer Effluent Monitoring in a Chemical Pilot Plant via Fiber-Optic Near-Infrared Spectroscopy
Authors: Coffey Charity , Predoehl Alex , Walker Dwight S.
Published: October 2003

The monitoring of the effluent of a rotary dryer has been developed and implemented. The vapor stream between the dryer and the vacuum is monitored in real time by a process fiber-optic coupled near-infrared (NIR) spectrometer. A partial least-squares (PLS) calibration model was developed on the basis of solvents typically used in a chemical pilot plant and uploaded to an acousto-optic tunable filter NIR (AOTF-NIR). The AOTF-NIR is well suited to process monitoring as it electrically scans a crystal and hence has no moving parts. The AOTF-NIR continuously fits the PLS model to the currently collected spectrum. The returned values can be used to follow the drying process and determine when the material can be unloaded from the dryer. The effluent stream was monitored by placing a gas cell in-line with the vapor stream. The gas cell is fiber-optic coupled to a NIR instrument located 20 m away. The results indicate that the percent vapor in the effluent stream can be monitored in real time and thus be used to determine when the product is free of solvent.
On-Line Monitoring of Powder Blending with Near-Infrared Spectroscopy
Authors: De Maesschalck R. , Sánchez F. Cuesta , Massart D. L. , Doherty P. , Hailey P.
Published: October 2003

Powder blending was monitored on-line by taking near-infrared measurements at regular time intervals during the mixing process. The average standard deviation between the measurements taken at each time and the dissimilarity between each mixture spectrum and the ideal mixture spectrum were used to monitor the changes in the powder blend over time. The distribution of the pure compounds in the blend can be investigated by looking at the score plot for the first two principal components (PCs), the contribution of each variable to the dissimilarity and, in particular, the contrasts between two characteristic wavelengths for each compound. Statistical process monitoring charts were used to determine the blending time at which the mixture was within (spectroscopic) specifications. Shewhart charts monitor the blend at characteristic wavelengths for each substance separately. The Hotelling's T2 test defines a multivariate confidence interval. For spectral data, feature reduction is needed. This procedure is accomplished by using characteristic wavelengths for the pure compounds or the significant PCs after performing principal components analysis (PCA).
Transfer of Calibrations of Near-Infrared Spectra Using Neural Networks
Authors: Despagne Frédéric , Walczak Beata , Massart Desire-Luc
Published: October 2003

A new approach for multivariate instrument standardization is presented. This approach is based on the use of neural networks (NNs) for modeling spectral differences between two instruments. In contrast to the piecewise direct standardization (PDS) method to which it is compared, the proposed method builds a single transfer model for all spectral windows. The apparently incompatible requirements for a high number of training objects and a low number of standardization samples are addressed by truncating spectra in finite-size windows and assessing a position index to each window. Each spectral window with the corresponding position index constitutes a training object. No prior background correction is required with this method. Both the proposed method and PDS were applied to some real and simulated data sets, and results were evaluated for reconstruction and subsequent calibration. On the studied data sets, the neural network approach was found to perform at least as well as PDS for both reconstruction and calibration.
Fluorescence Detection in Hydrodynamically Focused Sample Streams: Reduction of Diffusional Defocusing by Association of Analyte with High-Molecular-Weight Species
Authors: Demas J. N. , Wu Ming , Goodwin Peter M. , Affleck Rhett L. , Keller Richard A.
Published: October 2003

Fluorescence methods have been developed for ultra-low-level detection down to the single molecule level. In ultra-low-level analysis, one successful approach to background reduction is to use hydrodynamically focused sample streams coupled with focused laser excitation to reduce detection volumes. However, low-molecular-weight analytes such as fluorescent dyes or fluorescently tagged nucleotides can diffuse radially out of the sample stream before detection, which can cause a significant reduction in the detection efficiency. Diffusional spreading can cause sample stream mixing in multiplexed analyses. Also, axial diffusion can cause misordering of analyte molecules in DNA sequencing at high analysis rates. A new method is presented for reducing diffusion effects by incorporating a high-molecular-weight species that has a strong binding affinity for the analyte (anchor) into the sheath fluid. As the analyte starts to diffuse out of the sample stream, it associates with the anchor and effectively assumes the anchor's molecular weight. This association reduces the analyte's mobility to that of the anchor. Consequently, both radial and axial diffusion are reduced. Further, in favorable cases, this adduct can have significantly increased luminescence yields and photostability compared to the free analyte. Examples of several dye polymer combinations involving electrostatic and other binding modes are given that show the very beneficial effects of this approach. Extension to other systems is described.
Use of Internal Standardization to Compensate for a Wide Range of Absorbance in the Analysis of Glasses by UV Laser Ablation Inductively Coupled Plasma Atomic Emission Spectrometry
Authors: Kanicky Viktor , Otruba Vitezslav , Mermet Jean-Michel
Published: October 2003

A frequency-tripled Q-switched Nd:YAG laser (355 nm, 10 Hz, 5 mJ per shot, Surelite, Continuum) was used for the ablation of glasses as direct solid sampling for inductively coupled plasma atomic emission spectrometric multichannel detection. The colored and transparent glasses were glass standards used for calibration in X-ray fluorescence spectrometry and exhibited a 0.15–3.5 absorbance range at 355 nm. Translation of the target (1 mm s−1) with respect to the laser beam was used over a length of 16 mm. The depths and widths of the corresponding patterns were not related to the absorbance of the samples. However, the analytical line intensities were efficiently compensated for by using the Si(I) 251.611 nm line as an internal standard. The repeatability was therefore improved for Na, K, Ca, Mg, Sr, Ba, Zn, Pb, Al, Fe, and Sb, as well as the correlation coefficients of the regression and the centroid uncertainties of the calibration graph. Preliminary investigations were carried out to evaluate the acoustic signal emitted by the microplasma as external standardization. However, a negative correlation was found with the line intensity signals under our operating conditions.
Program Considerations for Simplex Optimization of Ion Lenses in ICP-MS
Authors: Sartoros Christine , Goltz Douglas M. , Salin Eric D.
Published: October 2003

The performance of an inductively coupled plasma mass spectrometer (ICP-MS) is dependent on the ion optic bias potentials. A discussion of the multielement optimization of the ICP-MS ion optics bias potentials using a Simplex algorithm is presented. Three objective functions were tested: a function developed by Leary; the combined ratio method (CRM); and the Euclidean distance from multicriteria target vector optimization. Both the Leary and the target vector optimization's performances were comparable, whereas the CRM optimizations placed an emphasis on obtaining similar signal intensities. Experiments determined that an initial Simplex starting size of 20% of the parameter space was optimal. A method for the selection of an appropriate target vector by predicting analyte signal intensity was also investigated. Signal intensities for all elements could be predicted with an acceptable margin of error (10–30%), provided that the same conditions were used. Comparisons of optimizations using a single mid-mass element vs. multielement optimizations revealed that the multielement approach is only slightly better. If the analyst wished to optimize lens settings to favor heavy or light elements, then an average mass was better than a mid-mass optimization.
Slurry Sampling Electrothermal Atomic Absorption Spectrometry for the Analysis of Aluminum-Based Ceramic Powders
Authors: Lucic M. , Krivan V.
Published: October 2003

A slurry sampling electrothermal atomic absorption spectrometry method for the determination of Ca, Cr, Cu, K, Fe, Mg, Mn, Na, Ni, and Zn in aluminum oxide and aluminum nitride powders is described. For each analyte, the experimental conditions including atomization temperature, internal gas flow during atomization, and pyrolytic re-coating of the graphite tube were optimized with respect to the sensitivity and background absorption. Quantification was performed by means of calibration curves recorded with the use of aqueous standards. The achievable limits of detection are between 5 ng/g (K) and 130 ng/g (Fe). The accuracy was checked by comparison of the results with those obtained by instrumental and radiochemical neutron activation analysis and other methods.
Raman Spectrum of Ultrafine Anatase Powders Derived from Hydrolysis of Alkoxide
Authors: Iida Yasuo , Furukawa Masamichi , Aoki Tsutomu , Sakai Tadao
Published: October 2003

Ultrafine, nanometer-sized anatase particles were prepared by the hydrolysis of titanium isopropoxide. Their Raman spectra are discussed in view of the finite size effects. The crystallite size D estimated by the X-ray diffraction peaks (Scherrer method) was found to be correlated with the Raman peak width Γ. The relationship could be expressed in the empirical equation, Γ = Γ0 + kD−α with the scaling exponent α of 1.5. Because the anatase crystal spans a three-dimensional network, the result demonstrates that 2× α is equal to the dimensionality of the sample. In addition, the anatase powders prepared by different hydrolysis schemes regressed into curves with different constant terms γ0 and k. The amount of organic residue was mainly affected by the hydrolysis scheme, and the organic residue caused the formation of defects in the crystalline particle by the following heat treatment. Therefore, it is obvious that the variation in Γ0 and k has a close relation to the defect density of the crystalline particles. The defect densities were estimated by using the correlation between the X-ray diffraction and the Raman data.
Optical Sectioning Fluorescence Spectroscopy in a Programmable Array Microscope
Authors: Hanley Quentin S. , Verveer Peter J. , Jovin Thomas M.
Published: October 2003

We report the use of a programmable array microscope (PAM) for the acquisition of spectrally resolved and high-throughput optical sections. The microscope is based on the use of a spatial light modulator for defining patterns of excitation and/or detection of fluorescence. For obtaining optically sectioned spectral images, the entrance slit of an imaging spectrograph and a line illumination pattern defined with a spatial light modulator are placed in conjugate optical positions. Compared to wide-field illumination, optical sectioning led to greater than 3× improvement in the rejection of out-of-focus fluorescence emission and nearly 6× greater peak-to-background ratios in biological specimens, yielding better contrast and spectral characterization. These effects resulted from a reduction in the artifacts arising from spectral contributions of structures outside the region of interest. We used the programmable illumination capability of the spectroscopic system to explore a variety of excitation/detection patterns for increasing the throughput of optical sectioning microscopes. A Sylvester-type Hadamard construction was particularly efficient, performing optical sectioning while maintaining a 50% optical throughput. These results demonstrate the feasibility of full-field highly multiplexed confocal spectral imaging.