bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of Immersion Sampling Technique in Confocal Raman Depth Profiling
Authors: Vyörykkä J. , Halttunen M. , Iitti H. , Tenhunen J. , Vuorinen T. , Stenius P.
Published: October 2003

The confocal Raman technique is widely used for the depth profiling of thin transparent polymer films. Reported depth resolutions are on the order of two micrometers. The depth resolution is worsened and the actual measurement depth is changed by the use of metallurgical “dry” objectives. Also, if the sample is strongly light scattering, the measurement depth is reduced drastically. In this work, we demonstrate how these problems can be circumvented by using an immersion technique in confocal Raman depth profiling. In the method, two different immersion fluid layers and a cover glass, which separates the two fluid layers, are used. This configuration allows the fluid that is in contact with the sample to be selected with respect to the requirements dictated by the refractive index of the sample, sample–immersion fluid interaction, Raman spectra overlapping, or fluorescence quenching properties. The use of the immersion technique results in major improvements in the depth resolution and in the depth profiling capability of the confocal Raman technique when applied to strongly light scattering materials.
Laser-Induced Breakdown Spectroscopy for Microanalysis Using Submillijoule UV Laser Pulses
Authors: Rieger G. W. , Taschuk M. , Tsui Y. Y. , Fedosejevs R.
Published: October 2003

This paper presents a study of laser-induced breakdown spectroscopy (LIBS) at low energies using KrF laser pulses of only 50–300 μJ. Very small focal spots with diameters of 5 to 20 μm are employed in order to achieve strong plasma emission. The focused intensities were in the range of 1.6 to 150 GW/cm2. The evolution of the micro-plasma progresses more rapidly in this energy range compared to conventional LIBS using mJ laser pulses. The optimum delay time for the detection of emission from minor constituent elements in aluminum is between 100 and 360 ns after the laser pulse hits the sample. The corresponding limits of detection are in the range of 2 to 450 ppm and are comparable to experiments that have used much higher laser energies. The amount of ablated material is significantly reduced using low laser energies and typical crater diameters are approximately 15–40 μm.
Hand-Held NIR Spectrometry. Part II: An Economical No-Moving Parts Spectrometer for Measuring Chlorophyll and Moisture
Authors: McClure W. F. , Moody David , Stanfield D. L. , Kinoshita Osamu
Published: October 2003

The design and performance of a low-cost no-moving-parts handheld NIR spectrometer are discussed. Dubbed the TWmeter, this device was conceived for use by researchers and others in developing countries unable to afford more costly technology found in developed countries. Two design features contribute to the novelty of this spectrometer: (1) three unfiltered light emitting diodes (LEDs) with peak emissions at 700, 880, and 940 nm for measuring chlorophyll in plant tissue and moisture in paper, and (2) a silicon intensity-to-frequency detector (a silicon detector with an integral voltage-to-frequency converter). The latter feature allows an ordinary microcomputer to obtain intensity measurements by counting for a fixed length of time, thus avoiding the need for higher-priced analog-to-digital hardware. Performance tests, using multiple linear regression for calibration, demonstrate that chlorophyll and moisture can be determined with a root mean squared standard error of prediction of 0.99 mg/cm2 of leaf surface for a range of 1–8 mg/cm2 and 1.04% (wet basis) for a range of 30–65% moisture, respectively. Development of the TWmeter (costing less than $300 US), demonstrates that spectrometry need not be costly.
ArF Laser-Induced Plasma Spectroscopy for Part-per-Billion Analysis of Metal Ions in Aqueous Solutions
Authors: Lo K. M. , Cheung N. H.
Published: October 2003

Aqueous samples containing trace amounts of metal ions in 0.8 M HCl were ablated with an ArF laser. Plasma emissions were monitored for elemental analysis. The signal-to-noise ratio was optimized when the laser fluence was about 10 J cm−2, while the detector gate delay and width were 1–2 μs and 3–4 μs, respectively. During that time, the temperature and electron density of the induced plasma were also measured spectroscopically. The temperature dropped from about 0.5 to about 0.3 eV, while the density remained fairly constant at about 3 × 1016 cm−3. Background-free spectrochemical analysis was therefore possible. The detection limits for Na, Ca, Ba, and Pb were 0.4, 3, 7, and 300 ppb, respectively. These are 20 to 1000 times better than the best achieved by non-193-nm laser-induced breakdown spectroscopy.
Near-Infrared Diode Laser Based Spectroscopic Detection of Ammonia: A Comparative Study of Photoacoustic and Direct Optical Absorption Methods
Authors: Bozóki Zoltán , Mohácsi Árpád , Szabó Gábor , Bor Zsolt , Erdélyi Miklós , Chen Weidong , Tittel Frank K.
Published: October 2003

A photoacoustic spectroscopic (PAS) and a direct optical absorption spectroscopic (OAS) gas sensor, both using continuous-wave room-temperature diode lasers operating at 1531.8 nm, were compared on the basis of ammonia detection. Excellent linear correlation between the detector signals of the two systems was found. Although the physical properties and the mode of operation of both sensors were significantly different, their performances were found to be remarkably similar, with a sub-ppm level minimum detectable concentration of ammonia and a fast response time in the range of a few minutes.
Comparative Study of an Anisotropic Polymer Layer by Infrared Spectroscopic Techniques
Authors: Hinrichs K. , Tsankov D. , Korte E. H. , Röseler A. , Sahre K. , Eichhorn K.-J.
Published: October 2003

Infrared spectroscopic ellipsometry (IRSE), reflection absorption IR spectroscopy (RAIRS), IR transmission spectroscopy, and best-fit calculations are applied in a cooperative study to determine the anisotropic optical properties of a thin polyimide layer in the spectral range 4000–500 cm−1. The employed anisotropic uniaxial optical layer model afforded very good agreement between the calculated and the experimental spectra obtained by the different complementary IR methods. The main advantage of IRSE is that it is possible to obtain data for the optical constants and the thickness ( d = 1.81 μm) of the polyimide layer simultaneously within one experiment. From the ellipsometric spectra it was concluded that the layer structure can be regarded as possessing uniaxial symmetry where the layer is isotropic in directions (x, y) parallel to the sample surface. A qualitative determination of the anisotropic parameters of vibrational bands is possible by calculation of the ellipsometric spectra. The evaluation procedure can be improved by evaluation of polarized reflection spectra, provided the reference standard has been calibrated by ellipsometry. The oscillator parameters are then derived more accurately from the separate s- and p-polarized reflection spectra rather than from their ratio, which is measured in ellipsometry.
Raman Spectroscopy and Factor Analysis of Tumorigenic and Non-Tumorigenic Cells
Authors: Omberg Kristin M. , Osborn Jill C. , Zhang Shuliang L. , Freyer James P. , Mourant Judith R. , Schoonover Jon R.
Published: October 2003

Raman spectra, measured for viable suspensions of M1 and MR1 cells, demonstrate spectral differences correlating with an increased protein and phospholipid content relative to DNA in the MR1 cells. The M1 and MR1 cell lines consist of rat fibroblast cells that have been transfected with a gene causing immortality, and the MR1 line has been further transfected with a gene causing tumor formation. The cell suspensions were prepared from monolayer cultures in the same phase of growth and remained viable throughout the experiment. The Raman data have been further examined by principal factor analysis with two approaches, (1) a constrained analysis to provide a relative contribution to the Raman data from cellular components, and (2) analysis of differences in the raw data files of the two cell lines. Utilizing the constrained principal factor analysis for the two cell lines analyzed separately provides a measure of the relative contribution of protein, lipid, DNA, RNA, and buffer to the cell Raman spectra. Factor analysis of M1 and MR1 Raman spectra analyzed together demonstrates that the two cell lines can be differentiated by Raman spectroscopy with no prior spectral processing.
Field and Laboratory Spectroscopic Methods for the Identification of Pigments in a Northern Italian Eleventh Century Fresco Cycle
Authors: Bruni S. , Cariati F. , Consolandi L. , Galli A. , Guglielmi V. , Ludwig N. , Milazzo M.
Published: October 2003

The pigments of an XI-century fresco cycle in a small pre-alpine church of northern Italy were characterized by means of field techniques, in particular imaging spectroscopy, and laboratory spectroscopic techniques, namely total reflection X-ray fluorescence, micro-Raman, micro-Fourier transform-Raman, and micro-Fourier transform infrared spectroscopies, thus achieving a complete identification of the ancient painter's palette. Advantages and limitations of each technique in its application to the study of fresco pigments are discussed. The artistic value of the fresco cycle and the religious role in the year 1000 of the church where it is located (S. Michele Arcangelo in Gornate Superiore, Varese, Italy) were demonstrated by the precious and elaborate materials used by the painter. Different pigments were used for different hues of the same color, e.g., azurite, carbon, and the most precious lapis-lazuli for blue, while mixtures of pigments were recognized in details having a particular tint, e.g., lapis-lazuli and minium for violet.
Sensitive and Selective Detection of Paramagnetic Species Using Cavity Enhanced Magneto-Optic Rotation
Authors: Emig Mary , Billmers Richard I. , Owens Kevin G. , Cernansky Nicholas P. , Miller David L. , Narducci Frank A.
Published: October 2003

Cavity enhanced magneto-optic rotation spectroscopy (CEMOR) is a technique that utilizes a high-finesse cavity within a traditional magnetic rotation experimental setup to realize the benefits of both cavity ringdown and magneto-optic methods simultaneously. By observing Ga atoms at their resonance line of 417.204 nm, we demonstrate that CEMOR allows selective detection of paramagnetic species with lower detection limits than can be obtained through either flame atomic absorption or magnetic rotation spectroscopies. Quantitative CEMOR measurements of Ga in an air–acetylene flame reveal a 105 sensitivity increase over conventional flame atomic absorption in our experimental setup. Sample concentration is shown to impact the temporal behavior of transmitted signals, resulting in a significant time shift in transmission of peak signal intensity. Such time shifting has not been theoretically predicted, and we report its first experimental demonstration. The work discussed herein suggests that the CEMOR technique can be used to simplify the study of species such as combustion-generated radicals, which often absorb weakly and occur in spectral regions crowded by stronger molecular absorption lines.
Application of Time-of-Flight Near-Infrared Spectroscopy to Wood with Anisotropic Cellular Structure
Authors: Tsuchikawa Satoru , Tsutsumi Shigeaki
Published: October 2003

The newly constructed optical measurement system, which was mainly composed of a parametric tunable laser and a near-infrared photoelectric multiplier, was introduced to clarify the optical characteristics of wood with anisotropic cellular structure on the basis of the time-of-flight near-infrared spectroscopy (TOF-NIRS). The combined effects of the cellular structure of the wood sample, the wavelength of the laser beam, and the detection position of transmitted light on the time-resolved profiles were investigated in detail. The substantial optical pathlength calculated from the time-resolved profile was outstandingly larger than the sample thickness. The substance of the wood was directly related to the time delay of light propagation. In applying TOF-NIRS to the cellular structural materials, it is very important to give attention to the difference in the light scattering within the cell wall and that caused by the multiple specular-like reflections between cell walls. The newly proposed empirical equation, considering the effects of optical parameters, could well express the wavelength and sample thickness dependency of the time delay of the peak maxima. The time-resolved profile was intensively governed by the combination of light-absorbing and -scattering conditions and the degree of anisotropy. These basic data will be essential for this system to put an in-process measurement system in the wood industry to practical use.
Calibration with Empirically Weighted Mean Subset
Authors: Öjelund Henrik , Madsen Henrik , Thyregod Poul
Published: October 2003

In this article a new calibration method called empirically weighted mean subset (EMS) is presented. The method is illustrated using spectral data. Using several near-infrared (NIR) benchmark data sets, EMS is compared to partial least-squares regression (PLS) and interval partial least-squares regression (iPLS). It is found that EMS improves on the prediction performance over PLS in terms of the mean squared errors and is more robust than iPLS. Furthermore, by investigating the estimated coefficient vector of EMS, knowledge about the important spectral regions can be gained. The EMS solution is obtained by calculating the weighted mean of all coefficient vectors for subsets of the same size. The weighting is proportional to SS−ωγ, where SSγ is the residual sum of squares from a linear regression with subset γ and ω is a weighting parameter estimated using cross-validation. This construction of the weighting implies that even if some coefficients will become numerically small, none will become exactly zero. An efficient algorithm has been implemented in MATLAB to calculate the EMS solution and the source code has been made available on the Internet.
Effects of Matrix Elements on the Analyte Emission Signals in Inductively Coupled Plasma Optical Emission Spectrometry Using a Thermospray Sample Introduction System
Authors: Razpotnik P. , Budič B. , Veber M.
Published: October 2003

Matrix effects due to Ca, K, Na, and P on analyte transport rate, line intensities, and plasma excitation conditions were studied using a fused silica capillary thermospray nebulizer. Several emission lines of Ba, Cd, Co, Cr, Cu, Mg, Mn, Ni, Pb, and Zn, differing in their excitation and ionization energies, were investigated. In general, the addition of matrix elements to the analyte solution resulted in a reduction of the analyte emission signal. The greatest reductions were observed for matrices containing calcium and for the analyte emission lines with higher sum of excitation and ionization energies. A decrease in the analyte transport rate was the highest for single potassium matrix and for binary matrices containing calcium. The excitation temperature was not significantly changed in the presence of Na, K, and P, but it was depressed for single and composite matrices containing Ca. It was shown that variations in the analyte emission intensities in the presence of concomitants could be attributed to changes in the plasma as well as to changes in the analyte transport efficiency.
Mechanistic Studies of Chromium Speciation with Thermospray
Authors: Zhang Xiaohua , Koropchak John A.
Published: October 2003

Thermospray (TSP) coupled with inductively coupled plasma-atomic emission spectroscopy (ICP-AES) or inductively coupled plasma-mass spectrometry (ICP-MS) has been developed as a non-chromatographic method for chromium speciation to quantitatively separate and determine two chromium oxidation states: Cr(III) and Cr(VI). The limits of detection can reach 0.5 ng/mL with ICP-AES detection and 50 pg/mL with ICP-MS detection. The basis for this speciation method is that Cr(III) can selectively and nearly quantitatively deposit inside a thermospray system as Cr2O3, while Cr(VI) does not. To fully understand the mechanism of this deposition process, four questions were investigated: is aerosol formation necessary for the reaction to occur? Does the deposition occur in the aerosol or liquid regime? Does the deposit tend to be retained on the surface of the fused silica capillary? Can the reaction be predicted from thermodynamic calculations? These studies show that this reaction happens before solvent evaporates (i.e., the liquid regime). The high temperature inside the thermospray system is the major factor triggering this reaction. At the same time, the high pressure is important for its influence on the solvent boiling point, which affects the residence time (the time that the analyte spends in the solution before the solvent evaporates) and the kinetics of the reaction. The effects of the other parameters (vaporizer length, heating length, drawn tip, etc.) on the efficiency of the deposition reaction, represented as background residual signal (BRS), were also studied.
New Method of Modeling Infrared Spectra of Non-Cubic Single-Phase Polycrystalline Materials with Random Orientation
Authors: Mayerhöfer Thomas G.
Published: October 2003

A new approach has been used to model optical properties of noncubic single-phase polycrystalline materials with random orientation and crystallites small compared to the resolution limit of light. This method has been applied to fresnoite (Ba2TiSi2O8) and proved to provide widely adequate results to effective medium approximation (EMA) and an excellent correspondence between simulated and measured spectra. In contrast to EMA, the new theory predicts that the deviation between damping constants of polycrystalline and single crystal fresnoite can be adjusted by one common factor for all damping constants. Based on EMA and the new model, much smaller damping constants have been determined for polycrystalline fresnoite compared to conventional dispersion analysis; the latter is able to provide a relevant dielectric function, but seems to be of little reliability concerning the determination of meaningful oscillator parameters due to the implicit assumption of an arithmetic average of the principal dielectric functions. This approximation, which can be derived in a similar form from EMA and is of widespread use, is shown to be inferior to an approximation based on the arithmetic average of the principal refractive indices.
Improved Myoglobin Saturation Measurement Made by Partial Least-Squares Analysis of Optical Reflectance Spectra
Authors: Schenkman Kenneth A. , Ciesielski Wayne A.
Published: October 2003

Accurate myoglobin oxygen saturation determination from tissue using optical spectral analysis has been limited by overlap in spectral features between myoglobin and hemoglobin. Partial least-squares analysis of reflectance spectra has been successfully used to predict myoglobin oxygen saturation from blood perfused hearts, although uncertainty remains as to how much error in the myoglobin saturation estimate occurs due to hemoglobin contamination. This study was undertaken to quantify the error due to hemoglobin in the partial least-squares estimate of myoglobin saturation. Calibration spectra were developed by mathematical addition of individually acquired in vitro reflectance spectra from various absorbing species in scattering media. The isolated perfused guinea pig heart model was used to allow for switching between crystalloid and red blood cell perfusion in a beating heart. Inclusion of cytochrome c and cytochrome oxidase in a calibration set containing hemoglobin and myoglobin improved the accuracy of the partial least-squares analysis of myoglobin saturation. Both the Mahalanobis distance test and the residual ratio test demonstrated improved representation of spectra obtained from the heart using a calibration set that included both cytochromes. A 4.3% error in myoglobin oxygen saturation measurements was determined.
Analysis and Application of the Transmission Spectrum of a Composite Optical Waveguide
Authors: Qi Zhi-Mei , Matsuda Naoki , Takatsu Akiko , Kato Kenji , Itoh Kiminori
Published: October 2003

A composite optical waveguide (OWG) was fabricated by use of the masked sputtering method to deposit a tapered TiO2 film onto a single-mode potassium ion-exchanged (PIE) planar waveguide. Using the slab OWG spectroscopy apparatus, including a xenon lamp and a charge-coupled device (CCD) spectrometer, transmission spectra of the composite OWG with different superstrates were measured in the wavelength range 400 to 900 nm. The findings show that the composite OWG transmission spectrum is sensitive to the refractive index of the liquid overlaid on the TiO2 film. The sensing mechanism is considered to be the liquid-index-induced change in surface-scattering loss for the guided mode coupled adiabatically from the PIE layer into the TiO2 film. The composite OWG transmission spectrum and its response to liquid index exhibit strong polarization dependence due to large differences in properties between the TE0 and TM0 modes in the TiO2 film. The composite OWG transmission spectroscopy as a new refractometry was analyzed experimentally and theoretically.
Mössbauer Spectroscopy Investigation of the Properties and Stability of Dollar Bank Note Pigments
Authors: Rusanov V. , Chakarova K. , Madolev T.
Published: October 2003

Two groups of “high quality” counterfeit United States currency bank notes from the old and new 100 USD bank note bill, respectively, are investigated by means of Mössbauer spectroscopy, and their Mössbauer parameters are compared to genuine 100 USD bank note parameters. The dispersion of the distribution of the Mössbauer parameter values for 54 genuine bank notes is discussed. The most unstable spectra appear to be those of the green pigment. The instability of pigment properties is due to the different thermal conditions at which the different manufacturers have synthesized the pigment. The ability to use Mössbauer spectroscopy in forensic studies has been tested and the hypothesis of one and the same source of dissemination of the forged bank notes has been confirmed.
Diffusion of Binary Non-Solvent Mixtures in Polymers: Aqueous Ethanol Solutions in Poly(Vinyl Acetate)
Authors: Rafferty Denise Wade , Koenig Jack L.
Published: October 2003

The diffusion of binary non-solvent mixtures of ethanol and deuterium oxide (D2O) into poly(vinyl acetate) (PVAc) was studied by FT-IR imaging. Initial diffusion rates were calculated for all mixtures from the concentration profiles, and a positive deviation from ideal behavior was observed; higher initial diffusion rates and greater degrees of swelling were observed for the solvent mixtures than for the pure liquids. PVAc swells to various extents in pure deuterium oxide, 20, 30, and 40 weight percent (wt %) ethanol, and pure ethanol. Dissolution of PVAc occurs for 50, 60, 70, 80, 90, and 95 wt % ethanol–water mixtures. The lowest initial diffusion rate occurred for pure deuterium oxide and the highest initial rate for 80 wt % ethanol. The spectral data suggest that ethanol and water form a complex that solvates PVAc more effectively than either pure liquid. Furthermore, the data indicate that sufficient quantities of this complex for effective dissolution are formed above 40 wt % ethanol, while optimum quantities occur between 70 and 90 wt % (50 to 80 mole %) ethanol.
In-Line Monitoring of Polymer Processing. II: Spectral Data Analysis
Authors: Apruzzese Francesca , Reshadat Ramin , Balke Stephen T.
Published: October 2003

The objective of this work was to examine the application of various multivariate methods to determine the composition of a flowing, molten, immiscible, polyethylene–polypropylene blend from near-infrared spectra. These spectra were acquired during processing by monitoring the melt with a fiber-optic-assisted in-line spectrometer. Undesired differences in spectra obtained from identical compositions were attributed to additive and multiplicative light scattering effects. Duplicate blend composition data were obtained over a range of 0 to 100% polyethylene. On the basis of previously published approaches, three data preprocessing methods were investigated: second derivative of absorbance with respect to wavelength (d2), multiplicative scatter correction (MSC), and a combination consisting of MSC followed by d2. The latter method was shown to substantially improve superposition of spectra and principal component analysis (PCA) scores. Also, fewer latent variables were required. The continuum regression (CR) approach, a method that encompasses ordinary least squares (OLS), partial least squares (PLS), and principle component regression (PCR) models, was then implemented and provided the best prediction model as one based on characteristics between those of PLS and OLS models.
UV Raman Spectroscopy of Oilsands-Derived Bitumen and Commercial Petroleum Products
Authors: Shoute L. C. T. , Schmidt K. J. , Hall R. H. , Webb M. A. , Rifai S. , Abel P. , Arboleda P. H. , Savage A. , Bulmer J. T. , Loppnow G. R.
Published: October 2003

Raman and resonance Raman spectroscopy with ultraviolet excitation were performed on several sample types of oilsands-derived bitumen, highly heterogeneous mixtures of hydrocarbons, and commercial gasoline samples. Only excitation wavelengths below ∼240 nm successfully yielded fluorescence-free Raman spectra on all of the samples tested. The spectra were surprisingly simple in the 800–1800 cm−1 region, with most of the samples yielding spectra containing only 2 bands. The results presented here tentatively suggest that ultraviolet (UV) Raman spectroscopy in the “fingerprint” spectral regions will be useful for the qualitative identification of saturate, mono-, bi-, tri-, and polycyclic aromatic hydrocarbons. Tentative marker bands for total aromatic, saturate, mono-, and bicyclic (or higher) aromatic hydrocarbons are clearly observed at ∼1600, <900, 1036, and ∼1380 cm−1, respectively. Observed relative intensities vary with the excitation wavelength from 220 to 234 nm, suggesting that some selectivity is achievable by wavelength tuning. Preliminary investigations of commercial gasoline samples indicate that UV Raman spectroscopy can be used for refinery/vendor identification of unknown gasoline samples.
Pigment Identification by Fiber-Optics Diffuse Reflectance Spectroscopy
Authors: Dupuis Guillaume , Elias Mady , Simonot Lionel
Published: October 2003

Fiber-optics reflectance spectroscopy is used to identify pigments in pictorial layers of works of art thanks to a spectra database of dry powdered mineral pigments. Measurements are noninvasive, without any contact, and can be implemented in situ, without moving the work of art under investigation from its conservation place. The experimental device, using the special back-scattering configuration, is briefly presented. The protocol leading to the constitution of the spectra database of dry mineral pigments is described. Unlike other studies, this protocol has been developed to emphasize multiple scattering of light by elementary pigments in comparison with specular reflection on the surface of the sample. In these conditions, the diffuse reflectance spectrum is the label of the mineral pigment. The numerical processing of pigment identification is detailed. Both the influences of the roughness of the studied surface and of a possible varnish layer are taken into account when numerical identification is implemented. Several applications on patrimonial works of art are reported.
Molecular Orientation Study of the Drying of Latex in Real Time Using the Variable-Angle Attenuated Total Reflectance Technique
Authors: Shin Eun-Mi , Koenig Jack L.
Published: October 2003

The changes in orientation of polymer chains during the drying of latex have been studied. The Fourier transform infrared spectroscopy-attenuated total reflectance (FT-IR ATR) technique was used to obtain dichroic ratios. The variable-angle ATR technique was used to profile the dichroic ratio changes at different depths in the films. Using the dichroic ratio and the Hermans orientation function, it was possible to monitor the orientation changes of the polymer chains during latex drying in real time. New insights into the film formation process during the different stages of drying and condensation were obtained.
Surface-Enhanced Infrared Absorption Spectroscopy of p-Nitrothiophenol on Vapor-Deposited Platinum Films
Authors: Bjerke Amy E. , Griffiths Peter R.
Published: October 2003

Surface-enhanced infrared absorption (SEIRA) has been observed by transmission spectroscopy on a vapor-deposited platinum substrate. Monolayers of p-nitrothiophenol ( p-NTP) adsorbed on thin island films of platinum were used to probe the enhancement and distortion of the absorption bands of p-NTP. The greatest enhancement was accompanied by distortion of the strongest band in the spectrum of p-NTP into a bipolar shape. The magnitude of enhancement was dependent on the size of the metal islands and their proximity to each other. The applicability of the surface selection rule to SEIRA was confirmed by the weakness of the antisymmetric NO2 stretching band in the spectra of the self-assembled monolayers. Although these preliminary transmission studies show only modest (∼10×) enhancement when p-NTP is vapor-deposited onto platinum films, the potential of SEIRA for transmission studies on platinum island films has been established.
Multiplex Infrared-Visible Sum-Frequency Spectrometer with a Phase-Conjugated Pulse Mixing Device for Narrow-Bandwidth Visible Probe Generation
Authors: Ishibashi Taka-Aki , Onishi Hiroshi
Published: October 2003

We have constructed a multiplex infrared-visible sum-frequency (SF) spectrometer. Picosecond narrow-bandwidth visible laser light (full width at half-maximum (FWHM) ∼8 cm−1, 400 nm) was obtained by sum-frequency mixing of a pair of phase-conjugated broad-bandwidth pulses generated from femtosecond laser light (∼110 fs, 800 nm). Femtosecond broad-band infrared laser light (FWHM ∼280 cm−1, 3.4 μm) was obtained as a difference frequency mixing output of the signal and idler lights of an optical parametric amplifier pumped by the femtosecond laser light. Broad-bandwidth sum-frequency signal light (FWHM ∼280 cm−1) was generated by focusing the broad-bandwidth femtosecond infrared laser light and the narrow-bandwidth picosecond visible laser light onto a sample surface. The generated light was dispersed by a spectrograph and analyzed with a multichannel detector. An SF spectrum with a high signal-to-noise ratio over a 400 cm−1 spectral region with an ∼8 cm−1 resolution was obtained from an octadecanethiol self-assembled monolayer with a 60 s exposure time.
Simple Multivariate Approach for the Monitoring of Vinylation Reactions Using FT-Raman Spectroscopy
Authors: Hutsebaut Didier A. A. , Vercaemst Carl , Hugelier Chris , Verpoort Francis
Published: October 2003

Catalysts are major partners in industrial reactions. They arrange a higher selectivity, higher specificity, and lower production costs. The development of catalysts is therefore of major importance but the characterization is often time consuming since several analytical techniques are needed to obtain an insight into the process. This paper describes a simple multivariate approach for the acquisition of kinetic data resulting in a decrease of noise in the calibration using FT-NIR Raman spectroscopy. The latter has great potential to replace the classical analytical techniques since they may offer the catalyst-developing scientist a large variety of kinetic and structural information in a simple way. This paper reports on the application of multivariate calibration to extracting kinetic information out of the Raman spectra. Based on an experimental design, a calibration model has been calculated for the monitoring of a vinylation reaction. Due to appropriate data preprocessing, changes in sample position, variations in temperature, and laser fluctuations were corrected. The calculated calibration model was validated using leave-one-out cross validation and resulted in an RMSECV value of 0.013838 M. Based on the calibration model, the conversion for the vinylation was calculated and reported in this work.
Virtual Enantiomers as the Solution of Optical Activity's Deterministic Offset Problem
Authors: Hug W.
Published: October 2003

Deterministic offsets have remained one of optical activity's most intractable problems. To the extent that the mechanisms by which they are produced do not depend on the chiroptical properties of the sample, they can be eliminated by the subtraction of measurements done on both enantiomers. We show that it is possible to create, by purely optical means, by the sole use of half-wave retarders, the optical antipode of a chiral molecule, to measure the chiroptical properties of the molecule and of its optically generated antipode, and to recover, by subtracting the measurements, the offset-free data of the enantiomer which is physically present. We moreover show that it is possible to do the measurements in a way that eliminates offsets that might occur through the influence of the differing chiroptical properties of the two antipodes. The procedure can be repeated, and by doing so, an almost arbitrarily high precision can be reached. The method is demonstrated by offset-free Raman optical activity back-scattering spectra measured in the so-called scattered circular polarization mode, one of optical activity's so far largely unsolved measurement problems. Such measurements can now be done with 2 mg of substance, in throw-away capillary cells, and on compounds sealed in cylindrical vials.
Classification of Fourier Transform Infrared Microscopic Imaging Data of Human Breast Cells by Cluster Analysis and Artificial Neural Networks
Authors: Zhang Lin , Small Gary W. , Haka Abigail S. , Kidder Linda H. , Lewis E. Neil
Published: October 2003

Cluster analysis and artificial neural networks (ANNs) are applied to the automated assessment of disease state in Fourier transform infrared microscopic imaging measurements of normal and carcinomatous immortalized human breast cell lines. K-means clustering is used to implement an automated algorithm for the assignment of pixels in the image to cell and non-cell categories. Cell pixels are subsequently classified into carcinoma and normal categories through the use of a feed-forward ANN computed with the Broyden–Fletcher–Goldfarb–Shanno training algorithm. Inputs to the ANN consist of principal component scores computed from Fourier filtered absorbance data. A grid search optimization procedure is used to identify the optimal network architecture and filter frequency response. Data from three images corresponding to normal cells, carcinoma cells, and a mixture of normal and carcinoma cells are used to build and test the classification methodology. A successful classifier is developed through this work, although differences in the spectral backgrounds between the three images are observed to complicate the classification problem. The robustness of the final classifier is improved through the use of a rejection threshold procedure to prevent classification of outlying pixels.
New Method for Pollen Identification by FT-IR Spectroscopy
Authors: Pappas C. S. , Tarantilis P. A. , Harizanis P. C. , Polissiou M. G.
Published: October 2003

A new methodology for identification of pollen was developed based on FT-IR spectroscopy. Pollen samples of twenty different plant species were collected and the diffuse reflectance infrared Fourier transform (DRIFTS) and KBr pellet spectra were recorded. Libraries of spectra were created. Spectra of unknown plant origin pollen were recorded and compared with those of the corresponding pollen library and the match value was measured automatically using the appropriate software (OMINC ver. 3.1). From the same pollen samples, microscopic slides were prepared and the photographs of the pollen grains were used as a second comparison method. Using light microscopy, the pollen identification is usually limited to the family or generic name, while FT-IR spectroscopy can distinguish species belonging to the same genus. This method is simple and fast, and when the DRIFTS technique is used the sample is not destroyed.
Use of the Orthogonal Projection Approach (OPA) to Monitor Batch Processes
Authors: Gourvénec S. , Lamotte C. , Pestiaux P. , Massart D. L.
Published: October 2003

The orthogonal projection approach (OPA) and multivariate curve resolution (MCR) are presented as a way to monitor batch processes using spectroscopic data. Curve resolution allows one to look within a batch and predict on-line real concentration profiles of the different species appearing during reactions. Taking into account the variations of the process by using an augmented matrix of complete batches, the procedure explained here calculates some prediction coefficients that can afterwards be applied for a new batch.
Preparatory Study for Detection of Nickel in Industrial Flue Gas by Excimer Laser-Induced Fragmentation Fluorescence Spectroscopy
Authors: Gottwald U. , Monkhouse P.
Published: October 2003

The purpose of this work is to survey possibilities for detecting molecular nickel species in industrial flue gas using excimer laser-induced fragmentation fluorescence (ELIF), in particular to establish suitable detection schemes and to obtain a sensitivity estimate for Ni detection. Investigations were conducted in a heated laboratory cell under defined conditions of temperature and pressure, using NiCl2 as the precursor molecule. An ArF excimer laser (193 nm) was used for excitation and Ni atomic emission spectra were recorded in the range 300 to 550 nm. The dependence of ELIF signal on laser fluence was quadratic in the range of laser intensities investigated, as expected for a two-photon excitation process. The temporal behavior of the ELIF signals gave lifetimes significantly longer than the known natural lifetimes. This result and the energetics of the system suggest a Ni* production mechanism involving the formation of Ni+ and subsequent ion–electron recombination. The temperature dependence of the ELIF signal, determined in the range 773 to 1223 K, was found to follow the vapor-pressure curve (Antoine equation) known from the literature. Finally, quenching effects were investigated by measuring ELIF signals and lifetimes in nitrogen or air up to 1 atm. On the basis of the results so far, detection limits for Ni in practical combustion applications in the range of tens of ppb should be achievable, which will be sufficient for regulatory measurements in incinerators and power plants.
Near-Infrared Spectroscopy: A Tool for Monitoring Submerged Fermentation Processes Using an Immersion Optical-Fiber Probe
Authors: Tamburini E. , Vaccari G. , Tosi S. , Trilli A.
Published: October 2003

Near-infrared (NIR) spectroscopy has been developed as a noninvasive tool for the direct, real-time monitoring of glucose, lactic acid, acetic acid, and biomass in liquid cultures of microrganisms of the genera Lactobacillus and Staphylococcus. This was achieved employing a steam-sterilizable optical-fiber probe immersed in the culture (In-line Interactance System®). Second-derivative spectra obtained were subjected to partial least-squares (PLS) regression and the results were used to build predictive models for each analyte of interest. Multivariate regression was carried out on two different sets of spectra, namely whole broth minus the spectral subtraction of water, and raw spectra. A comparison of the two models showed that the first cannot be properly applied to real-time monitoring, so this work suggests calibration based on non-difference spectra, demonstrating it to be sufficiently reliable to allow the selective determination of the analytes with satisfactory levels of prediction (standard error of prediction (SEP) < 10%). Direct interfacing of the NIR system to the bioreactor control system allowed the implementation of completely automated monitoring of different cultivation strategies (continuous, repeated batch). The validity of the in-line analyses carried out was found to depend crucially on maintaining constant hydrodynamic conditions of the stirred cultures because both gas flow and stirring speed variations were found to markedly influence the spectral signal.
Accurate Wavelength Measurements of a Putative Standard for Near-Infrared Diffuse Reflection Spectrometry
Authors: Isaksson Tomas , Yang Husheng , Kemeny Gabor J. , Jackson Richard S. , Wang Qian , Alam M. Kathleen , Griffiths Peter R.
Published: October 2003

The diffuse reflection (DR) spectrum of a sample consisting of a mixture of rare earth oxides and talc was measured at 2 cm−1 resolution, using five different accessories installed on five different Fourier transform near-infrared (FT-NIR) spectrometers from four manufacturers. Peak positions for 37 peaks were determined using two peak-picking algorithms: center-of-mass and polynomial fitting. The wavenumber of the band center reported by either of these techniques was sensitive to the slope of the baseline, and so the baseline of the spectra was corrected using either a polynomial fit or conversion to the second derivative. Significantly different results were obtained with one combination of spectrometer and accessory than the others. Apparently, the beam path through the interferometer and DR accessory was different for this accessory than for any of the other measurements, causing a severe degradation of the resolution. Spectra measured on this instrument were removed as outliers. For measurements made on FT-NIR spectrometers, it is shown that it is important to check the resolution at which the spectrum has been measured using lines in the vibration-rotation spectrum of atmospheric water vapor and to specify the peak-picking and baseline-correction algorithms that are used to process the measured spectra. The variance between the results given by the four different methods of peak-picking and baseline correction was substantially larger than the variance between the remaining five measurements. Certain bands were found to be more suitable than others for use as wavelength standards. A band at 5943.13 cm−1 (1682.62 nm) was found to be the most stable band between the four methods and the six measurements. A band at 5177.04 cm−1 (1931.61 nm) has the highest precision between different measurements when polynomial baseline correction and polynomial peak-picking algorithms are used.
Trace Explosive Detection in Aqueous Samples by Solid-Phase Extraction Ion Mobility Spectrometry (SPE-IMS)
Authors: Buxton Tricia L. , Harrington Peter De B.
Published: October 2003

Law enforcement agencies use ion mobility spectrometers for the detection of explosives, drugs of abuse, and chemical warfare agents. Ion mobility spectrometry (IMS) has the advantages of short analysis times, detections in the parts per billion concentrations, and high sensitivity. On-site environmental analysis of explosives or explosive residues in water is possible with ion mobility spectrometers. Unfortunately, the direct analysis of low levels of explosives in water is difficult. Extraction provides a method for pre-concentrating the analytes and removing interferents. Coupling solid-phase extraction (SPE) with IMS is useful for the identification of trace amounts of explosives in water. Commercially available SPE disks were used. After extraction, the sample disk is inserted into the ion mobility spectrometer, where the analytes are thermally desorbed from the disk. Concentrations as low as one part per trillion were detected with a Barringer Ionscan® 350. An external computer and acquisition software (LabVIEW™, National Instruments) were used to collect data. SIMPLISMA (SIMPLe-to-use-Interactive Self-modeling Mixture Analysis) was applied to the data to resolve features that vary with respect to time.
Monitoring of Itaconic Acid Hydrogenation in a Trickle Bed Reactor Using Fiber-Optic Coupled Near-Infrared Spectroscopy
Authors: Wood Joseph , Turner Paul H.
Published: October 2003

Near-infrared (NIR) spectroscopy has been applied to determine the conversion of itaconic acid in the effluent stream of a trickle bed reactor. Hydrogenation of itaconic to methyl succinic acid was carried out, with the trickle bed operating in recycle mode. For the first time, NIR spectra of itaconic and methyl succinic acids in aqueous solution, and aqueous mixtures withdrawn from the reactor over a range of reaction times, have been recorded using a fiberoptic sampling probe. The infrared spectra displayed a clear isolated absorption band at a wavenumber of 6186 cm−1 (wavelength 1.617 μm) resulting from the =C–H bonds of itaconic acid, which was found to decrease in intensity with increasing reaction time. The feature could be more clearly observed from plots of the first derivatives of the spectra. A partial least-squares (PLS) model was developed from the spectra of 13 reference samples and was used successfully to calculate the concentration of the two acids in the reactor effluent solution. Itaconic acid conversions of 23–29% were calculated after 360 min of reaction time. The potential of FT-NIR with fiber-optic sampling for remote monitoring of three-phase catalytic reactors and validation of catalytic reactor models is highlighted in the paper.
Practical Algorithm for Reducing Convex Spike Noises on a Spectrum
Authors: Katsumoto Yukiteru , Ozaki Yukihiro
Published: October 2003

Quantitative data analysis and high-sensitivity measurements by use of Raman and infrared spectroscopy often suffer from noisy spikes such as those due to cosmic rays and water vapor. Since these spikes are unidirectional and isolated, the conventional smoothing techniques do a poor job of removing them. However, a small modification can improve these smoothing techniques significantly. In this paper, we present a simple denoising technique for a single-scan spectrum that is corrupted by convex spikes. In general, the noisy spikes arising from cosmic rays or water vapor have a much narrower bandwidth compared with target “informative” bands in Raman and infrared spectra. This means that these noisy spikes can be separated from the target bands by means of the difference in the bandwidths. The proposed method employs the moving window averaging procedure to distinguish and separate the convex spike. The proposed algorithm allows us to take away the convex spikes from measured spectra without preparing multiply recorded spectra and (much) biasing the measured spectrum.
Study of Complexation in Methanol/Water Mixtures by Infrared and Raman Spectroscopy and Multivariate Curve Resolution—Alternating Least-Squares Analysis
Authors: Holden Carol A. , Hunnicutt Sally S. , Sánchez-Ponce Raymundo , Craig John M. , Rutan Sarah C.
Published: October 2003

The structure of the mobile phase in liquid chromatography plays an important role in the determination of retention behavior on reversed-phase stationary materials. One of the most commonly employed mobile phases is a mixture of methanol and water. In this work, infrared and Raman spectroscopic methods were used to investigate the structure of species formed in methanol/water mixtures. Chemometric methods using multivariate curve resolution by alternating least-squares analysis were used to resolve the overlapped spectra and to determine concentration profiles as a function of composition. The results showed that the structure of these mixtures could be described by a mixture model consisting of four species, namely, methanol, water, and two complexes, methanol/water (1:1) and methanol/water (1:4). The spectral frequencies and concentration profiles found from the Raman and infrared measurements were consistent with one another and with theoretical calculations.