bluuebunny/crossref_metadata_2025 huggingface dataset:
FT-Raman Spectroscopic Investigations on the Organic Crosslinking in Hybrid Polymers. Part I: Model Reactions of Simple Epoxides
Authors: Riegel B. , Kiefer W. , Hofacker S. , Schottner G.
Published: October 2003

Epoxypropane and epoxyhexane are used in model reactions to analyze the ring opening in epoxy silane-based sol-gel-derived hybrid polymers by means of Fourier transform (FT)-Raman and 13C NMR (nuclear magnetic resonance) spectroscopy. The reactions with sodium methylate yield the methyl ethers. The behavior during the sol-gel process is analyzed by using a mixture of epoxyalkane, tetramethoxysilane, and aluminum sec-butylate. The reaction product depends on the molar ratio of methanol and water during the reaction. Assignments for Raman and NMR bands of some products are given.
Assessing the Extent of Degradation in the UV Radiation and Heat-Catalyzed Oxidized Whole Milk Powder: The UV Photoacoustic and Diffuse Reflectance Spectroscopies versus the Peroxide Value
Authors: Dóka Ottó , Ajtony Zsolt , Bicanic Dane , Koehorst Rob
Published: October 2003

The extent of quality loss caused by enzymatic and nonenzymatic browning reactions in milk powders is usually assessed by the chemical methods, among which the determination of peroxide value (PV) is a widely used approach. In this paper, peroxide values obtained from deliberately oxidized (UV irradiation combined with the thermal stress) whole milk powders are compared to the results of photoacoustic spectroscopy (PAS) and diffuse reflectance spectrometry (DRS) in the ultraviolet and visible region. The same samples were also investigated by various methods in the near-infrared (NIR) region. The experimental data suggest a good degree of correlation between the PV and the PAS and DRS data collected at 335 nm.
Steel Analysis with Laser-Induced Breakdown Spectrometry in the Vacuum Ultraviolet
Authors: Sturm V. , Peter L. , Noll R.
Published: October 2003

Laser-induced breakdown spectrometry (LIBS) with multiple pulse excitation has been applied for the multielemental analysis of steel samples in the vacuum ultraviolet. The emission of the induced plasma was coupled into a Paschen-Runge spectrometer equipped with photomultipliers linked to high-speed multichannel signal electronics. Time-resolved signal evaluation yields a significantly improved signal-to-noise ratio for the plasma emission periods after a multi-pulse excitation. Reference materials for low-alloy steel grades were used to calibrate the measurements. The investigations concentrated on the light elements phosphorus, sulfur, and carbon using emission wavelengths in the range from 178.28 nm to 193.09 nm. For the first time, limits of detection below 10 μg/g were achieved for the light elements phosphorus, sulfur, and carbon using LIBS. With these results the basis is established for future on-line applications of LIBS in the steel industry.
Mixed Gas Helium/Argon Low-Power/Reduced-Pressure ICP as a Tunable Ionization Source for the Mass Spectrometric Detection of Organotin Compounds
Authors: Milstein Lisa S. , Waggoner Joseph W. , Sutton Karen L. , Caruso Joseph A.
Published: October 2003

Quantitative and qualitative mass spectrometric results have been obtained for organotin compounds introduced into a mixed gas He/Ar low-power/reduced-pressure (LP/RP) inductively coupled plasma (ICP). Molecular fragmentation of 10 mg kg−1 of tetraethyltin (TET), introduced by gas chromatography (GC), with respect to pressure and mixed gas composition of the LP/RP-ICP was observed. Detection limits for the organotin compounds introduced into an LP/RP-He/Ar ICP at the pressure producing the optimum analyte signal were in the low picogram range. The source demonstrated “tunable” fragmentation with variation in the helium/argon mixed gas ratio. In addition, tunable fragmentation with pressure variations similar to that achieved previously with helium radio-frequency glow discharge (He-rf-GD) was observed with the LP/RP-He ICP.
Determination of Rate Constants in Second-Order Kinetics Using UV-Visible Spectroscopy
Authors: Bijlsma Sabina , Boelens Hans F. M. , Smilde Age K.
Published: October 2003

A general method for estimating reaction rate constants of chemical reactions using ultraviolet-visible (UV-vis) spectroscopy is presented. The only requirement is that some of the chemical components involved be spectroscopically active. The method uses the combination of spectroscopic measurements and techniques from numerical mathematics and chemometrics. Therefore, the method can be used in cases where a large spectral overlap of the individual reacting absorbing species is present. No knowledge about molar absorbances of individual reacting absorbing species is required for quantification. The reaction rate constants and the individual spectra of the reacting absorbing species of the two-step consecutive reaction of 3-chlorophenylhydrazonopropane dinitrile with 2-mercaptoethanol were estimated simultaneously from UV-vis recorded spectra in time. The results obtained were excellent.
Optical Bleaching in Continuous Laser-Excited Photothermal Lens Spectrometry
Authors: Chartier Agnès , Bialkowski Stephen
Published: October 2003

This paper presents methods for measuring and modeling optical bleaching that occurs, by using continuous laser sources for solution-phase organic dye molecule spectrometry. Photothermal lens experiments are used to measure the nonlinear optical absorption coefficients of eosin Y, erythrosin B, and pseudo-isocyanine iodide dyes in ethanol as a function of excitation irradiance. Excitation irradiance-dependent photothermal lens data are subsequently interpreted in terms of the photophysics and excited-state relaxation dynamics of the condensed-phase dye molecules under study. The model uses first-order kinetics for excitation and subsequent metastable-state relaxation back to the ground state and accounts for both ground- and metastable-state absorption. The measurement model accounts for thermal lens formation and apparatus configuration. Nonlinear absorption measurements are fit to the model with nonlinear regression. The resulting parameters allow calculation of triplet-state absorption coefficients and triplet to ground singlet state-relaxation rate constants.
Detection of Density Jump in Laser-Induced Shock Wave Plasma Using a Rainbow Refractometer
Authors: Kurniawan Hendrik , Lahna Kurnia , Lie Tjung Jie , Kagawa Kiichiro , Tjia May On
Published: October 2003

A special interferometric technique with high sensitivity has been devised on the basis of rainbow refractometry without the use of an additional and delicate amplitude-splitting setup. This new technique was used for the characterization of shock wave plasma induced by a Q-switched Nd:YAG laser on various metal samples under reduced surrounding gas pressures. An unmistakable signal of the density jump was detected simultaneously with the observation of the emission front signal. It proved that the emission front and the front of the blast wave coincided and moved together with time at the initial stage of the secondary plasma expansion. However, at a later stage, the emission front began to separate from and left behind the blast wave front propagating in the surrounding gas at low pressures. With the use of Cu and Zn samples, the experimental results showed that the separation of the emission front and blast wave front took place at about 5 mm above sample surface for laser energy of 140 mJ.
Estimation of the BII Conformer Substate Population in Nonoriented Hydrated B-DNA via Curve Resolution of Infrared Spectra
Authors: Pichler Arthur , Rüdisser Simon , Winger Rudolf H. , Wellenzohn Bernd , Flader Wolfgang , Liedl Klaus R. , Hallbrucker Andreas , Mayer Erwin
Published: October 2003

Hydrated films of the self-complementary B-type d(CGCGAATTCGCG)2 dodecamer, with 13 or 14 water molecules per nucleotide, were studied by Fourier transform infrared (FT-IR) spectroscopy either as equilibrated samples between 290 and 260 K or, after quenching into the glassy state, as nonequilibrated films isothermally at 200 K. IR spectral changes on isothermal relaxation at 200 K revealed that difference spectra are caused by interconversion of B-DNA's conformer substates, BI converting into BII. Curve resolution of IR spectra in the spectral region containing the symmetric stretching vibration of the ionic phosphate group, with a composite band centered at 1087 cm−1 for BI and at 1109 cm−1 for BII, gives the BI/BII conformer substate population ratio and its dependence on temperature between 290 and 260 K, and on time for isothermal relaxation at 200 K. Curve resolution of the overlapping composite band profile was optimized by comparison of second-derivative and of difference curves, aiming thereby for optimal correspondence between experimental and curve-fitted bands as a criterion for goodness-of-fit. The spectroscopic aspects relevant for reliable curve resolution of the overlapping composite band profile are reported and discussed in detail.
Detection of Hydrocarbons in Water by MIR Evanescent-Wave Spectroscopy with Flattened Silver Halide Fibers
Authors: Hahn P. , Tacke M. , Jakusch M. , Mizaikoff B. , Spector O. , Katzir A.
Published: October 2003

IR transmitting AgCl xBr1- x, fibers were used as internal reflection elements for the spectroscopic detection of hydrocarbons that are dissolved in water in an attenuated total reflection (ATR) type of setup. The fibers were partly flattened by pressing and then coated with an analyte-enriching organic polymer in order to increase the sensor sensitivity. A portable tunable diode laser spectrometer served as a spectrometric unit. The dependence of the sensitivity on coupling conditions was investigated and lead to an optimized coupling. It is shown that the sensitivity of the flattened waveguide with a thickness of 170 μm can be enhanced by a factor of 5 compared to a fiber with 900 μm diameter. Aqueous toluene solutions with concentrations in the parts-per-million range were used to characterize the sensor system that showed a linear response with regard to analyte concentration. The noise equivalent concentration (NEC) was on the order of 1 ppm.
High-Pressure Measuring Cell for Raman Spectroscopic Studies of Natural Gas
Authors: Hansen S. Brunsgaard , Berg R. W. , Stenby E. H.
Published: October 2003

A system for obtaining Raman spectra of gases at high pressure has been constructed. In order to ensure that a natural gas sample is totally representative, a high-pressure gas-measuring cell has been developed, built up by stainless steel fittings and a sapphire tube. The design and construction of this cell are described. A perfect pressure seal has been demonstrated up to 15.0 MPaA (MPa absolute). The cell has been successfully used to obtain Raman spectra of natural gas samples. Some of these spectra are presented and assigned. The most remarkable observation in the spectra is that it is possible to detect hydrogen sulfide at concentrations of 1–3 mg H2S/Nm3. An attempt to make a quantitative analysis of natural gas by the so-called “ratio method” is presented. In addition to this, the relative normalized differential Raman scattering cross sections for ethane and i-butane molecules at 8.0 MPaA and 10.2 MPaA have been determined.
Influence of Wavelength Selection and Data Preprocessing on Near-Infrared-Based Classification of Demolition Waste
Authors: de Groot P. J. , Postma G. J. , Melssen W. J. , Buydens L. M. C.
Published: October 2003

The separation of demolition waste into three fractions-wood (required purity >90%), plastic (required purity >80%), and stone (no requirement)—has been investigated. The materials are measured with diffuse near-infrared reflectance spectroscopy and classified with linear discriminant analysis (LDA). To speed up the classification, simulated annealing extracts the six most discriminating wavelength regions for each preprocessing technique. For improvement in the classification results, several preprocessing techniques are investigated. Both the reflectance R and log 10(1/ R) are investigated. The influence of the so-called wavelength shift (radiation that does not pass a filter perpendicular and shifts maximally 6 nm to lower wavelength) is accounted for during wavelength selection. Preprocessing methods that remove spectral offset differences and remove differences in peak heights give the best classification improvement. Modified standard normal variate (SNV) preprocessing, applied on the reflectance R, is the best preprocessing technique. The modification is the addition of the mean spectral value after the application of standard SNV preprocessing. The mean spectral value contains some additional information that is used by the (LDA) algorithm to improve the classification performance. The influence of the so-called wavelength shift effect is minimal.
Hand-Held NIR Spectrometry: Part I: An Instrument Based upon Gap-Second Derivative Theory
Authors: Morimoto Susumu , McClure William F. , Stanfield Donald L.
Published: October 2003

A hand-held near-infrared (NIR) meter (called the Gmeter), based upon gap-second derivative (GSD) theory, was designed, constructed, and performance-tested. The design incorporated narrow-band interference filters for isolating the three wavelengths required by the GSD calculations. A microprocessor was included in the design to facilitate both stand-alone and personal computer (PC) operation. The Gmeter was mounted in a caddy for making measurements within the laboratory. Performance of the Gmeter was compared with the performance of a FOSS NIRSystems Model 6500 spectrophotometer for measuring protein in soy-protein/sugar mixtures and for measuring nitrogen in fescue grass tissue. Two calibrations were developed on both instruments: (1) single-term GSD equations and (2) three-term (log 1/ R) multiple linear regression (MLR) equations. Second-derivative calibration experiments on the Model 6500 spectrophotometer formulated the basis for selecting the three filters in the Gmeter. Model 6500 data indicated that the GSD calibration [coefficient of variation (CV) = 5.14%] performed better than a three-term MLR equation (CV = 8.0%). In addition, the Gmeter performed almost as well (CV = 6.30%) as the Model 6500 (CV = 5.14%) for measuring protein in the mixtures using single-term GSD equations. An exciting extra in this study was the fact that measurements from the same three filters selected for determining protein in protein/sugar mixtures could be used for determining nitrogen (CV = 17.2%) in dry-grass tissue.
Gas-Oil Ratio of Live Crude Oils Determined by Near-Infrared Spectroscopy
Authors: Mullins Oliver C. , Daigle Tim , Crowell Chris , Groenzin Henning , Joshi Nikhil B.
Published: October 2003

The gas-oil ratio (GOR) of crude oil has a tremendous impact on the processes used for oil production from subsurface formations. Determination of GOR thus becomes of central importance to oil operating companies. Here, it is shown that near-infrared (NIR) spectral measurements on single-phase crude oils (with dissolved gas) can be used to obtain a reliable estimate of the GOR. A simple theoretical formulation accurately accounts for the data. Furthermore, the NIR measurement is shown to be compatible with process flow streams at elevated temperatures and pressures.
Optical Properties of Gaseous 2,4,6-Trinitrotoluene in the Ultraviolet Region
Authors: Usachev Alexandre D. , Miller Tracy S. , Singh Jagdish P. , Yueh Fang-Yu , Jang Ping-Rey , Monts David L.
Published: October 2003

The absorption spectrum of gaseous 2,4,6-trinitrotoluene (TNT) was recorded by conventional absorption spectroscopy (AS) as well as cavity ringdown spectroscopy (CRDS) methods in the spectral regions 195–300 and 225–235 nm, respectively. These spectra were normalized by using the saturated TNT vapor-number density for the measured cell temperature to obtain the absorption cross section of TNT. No spectral features were found in the spectra; this result is consistent with a repulsive electronic excited state of TNT. The temperature dependence of the absorption coefficient of saturated TNT vapor was measured within the temperature range 5–110 °C. The limit of detection of TNT vapor by CRDS is less than 1 ppb. Real-time CRDS measurements of the TNT vapor density at 21 and 37 °C are presented. The TNT evaporation rates were found to be 7 × 108 and 4 × 1010 molecules/cm2 × s at 21 and 37 °C, respectively.
In Situ Raman Spectroscopy of the Decomposition of Tertiary Butyl Peroxy Pivalate under High Pressure and High Temperature
Authors: Freitag Detlef , Götz Christian , Luft Gerhard , Van Der Pol André , Wierda Klaas
Published: October 2003

The decomposition of tertiary butyl peroxy pivalate (TBPPI), in n-hexane, under a pressure of 1900 bar and at a temperature of 100 °C, was studied in situ with the use of a transportable high-throughput fiber-optic Raman spectrometer. The Raman probe was conveniently coupled to an optical high-pressure cell containing the TBPPI. Time-resolved experiments with a 10 wt % solution of TBPPI in n-hexane were carried out, and information on the mechanism of decomposition and the (first-order) kinetics was obtained. It is shown that the main decomposition products of TBPPI are CO2 and t-butanol. From first-order kinetic fits, of the Raman profiles of intensity vs. time of reactants and products, the rate constant for the decomposition of TBPPI and the formation of CO2 is found to be 1.65·10−3s−1 (half-life time for TBPPI of approximately 420 s). t-Butanol formation occurs at a slower rate of approximately 1.22·10−3s−1 (characteristic time of 566 s).
Characterization of a Noncolinear Acousto-Optic Tunable Filter and its Resolution Enhancement as a Near-Infrared Spectrometer
Authors: Cheng Andrew Y. S. , Zhu Jianhua , Pau Michael C. Y.
Published: October 2003

An automatic near-infrared (NIR) spectrometer based on a noncolinear acousto-optic tunable filter (AOTF) is constructed for high-speed spectrometry. Its initial spectral characteristics are studied systematically for application. The AOTF is a solid-state, rugged, compact, and high-speed device and can be readily used for spectral measurement applications, but some broadening and overlapping effects will occur when it is used for the measurement of a narrow-band spectrum. In order to correct the spectral distortion and obtain a fine spectrum, a new resolution enhancement procedure, which combines conventional Fourier self-deconvolution (FSD) with our optimized evaluation function and objective parameters determination, is used to resolve the band-broadened and band-overlapped spectral lines. The self-deconvolved spectrum is in good agreement with the fine spectrum measured by a high-resolution grating spectrometer. This is, to our knowledge, the first resolution enhancement of an AOTF spectrum by analytical and numerical operation.
Quantitative Determination of CaCO3 in Cement Blends by FT-IR
Authors: Legodi M. A. , De Waal D. , Potgieter J. H.
Published: October 2003

Fourier transform infrared (FT-IR) spectra have been recorded of cement blends containing between 0 and 25% limestone, as well as for 100% limestone. Integrated intensity of the out-of-plane vibration of the carbonate ion was used in relation to the integrated intensity of a peak remaining fairly constant in the cement blends itself. Calibration curves were set by using five measurements of each particular sample. The results are compared to ordinary weight loss measurements. FT-IR is found to be a quick and accurate method for the quantitative analysis of limestone in cement blends.
Raman Chemical Imaging of Microcrystallinity in Silicon Semiconductor Devices
Authors: Schaeberle Michael D. , Tuschel David D. , Treado Patrick J.
Published: October 2003

Silicon integrated circuits are fabricated by the creation of complex layered structures. The complexity of these structures provides many opportunities for impurities, improperly annealed dopants, and stress effects to cause device contamination and failure. Nondestructive metrology techniques that rapidly and noninvasively screen for defects and relate silicon device structure to device performance are of value. We describe the first use of a liquid crystal tunable filter (LCTF) Raman chemical imaging microscope to assess the crystallinity of silicon semiconductor integrated circuits in a rapid and nondestructive manner without the need for sample preparation. The instrument has demonstrated lateral spatial resolving power of better than 250 nm and is equipped with a tunable imaging spectrometer having a spectral bandpass of 7.6 cm−1. The instrument rapidly produces high-definition Raman images where each image pixel contains a high-quality Raman spectrum. When combined with powerful processing strategies, the Raman chemical imaging system has demonstrated spectral resolving power of 0.03 cm−1 in a test silicon semiconductor wafer fabricated by using ion implantation. In addition, we have applied Raman chemical imaging for volumetric Raman imaging by analyzing the surface distribution of polycrystalline thin film structures. The approaches described here for the first time are generally applicable to the nondestructive metrology of silicon and compound semiconductor devices.
Selective Determination of Europium(III) Oxide and Hydroxide Colloids in Aqueous Solution by Laser-Induced Breakdown Spectroscopy
Authors: Yun Jong-Il , Bundschuh Tobias , Neck Volker , Kim Jae-Il
Published: October 2003

Laser-induced breakdown spectroscopy (LIBS) was applied to selectively analyze the aqueous suspension of Eu2O3(s) particles in the presence of the Eu3+ aquo ion. A plasma was generated by focusing a pulsed Nd:YAG laser beam (λ = 532 nm) into the sample. The light emission from the plasma was detected by a spectrograph equipped with a gated intensified charge-coupled device (ICCD) in the wavelength range of 275–525 nm. The atomic emission intensity of the Eu2O3(s) suspension was about two orders of magnitude higher than that of the Eu3+ aquo ion. The detection limits for Eu3+(aq) and Eu2O3(s) were found to be 3.3 × 10−5 mol/L and 2.0 × 10−7 mol/L, respectively. Such a difference allows the selective determination of colloidal europium particles. This capability of LIBS was used to study the formation of Eu(OH)3(s) colloids in the aqueous Eu3 solution by varying pH until the solubility limit was exceeded. The appraisal of the threshold pH for the solubility limit led to the determination of the solubility product of colloidal Eu(OH)3(s), which was then calculated to be log K0sp= −25.5 ± 0.4.
Some Comparisons of LIBS Measurements Using Nanosecond and Picosecond Laser Pulses
Authors: Eland Kristine L. , Stratis Dimitra N. , Lai Tianshu , Berg Mark A. , Goode Scott R. , Angel S. Michael
Published: October 2003

Laser-induced breakdown spectra were measured by using a 1.3 ps laser pulse on glass, steel, and copper. Material ablation with the use of picosecond excitation is very precise with well-formed sharp-edged craters. The spectra obtained with 570 nm, 1.3 ps excitation decay more quickly and show significantly lower background emission than those that use 1064 nm, ∼ 7 ns excitation. The background was low enough that excellent laser-induced spectroscopy (LIBS) spectra were obtained on the three samples by using a single 1.3 ps laser pulse and a nongated detector. Similar results were obtained by using nanosecond excitation but with higher relative background signals. The radiance was similar with the use of pico- or nanosecond excitation; however, the radiant intensity was larger with nanosecond excitation because of the larger plasma.
Intensity Considerations in Liquid Core Optical Fiber Raman Spectroscopy
Authors: Altkorn Robert , Malinsky Michelle Duval , Van Duyne Richard P. , Koev Ilia
Published: October 2003

This paper develops expressions for the Raman power emitted by liquid core optical fiber (LCOF) sample cells in six simple excitation/collection geometries and the fraction of that power that can be utilized in a conventional Raman spectrometer. From these expressions a “figure of merit” is developed that can be used to predict the relative intensity enhancement provided by LCOFs having different inside diameters and loss characteristics. For the apparatus used here, we show theoretically and experimentally that the figure of merit takes the simple form (α d)−1 where α and d are, respectively, the loss coefficient and inside diameter of the LCOF. Given the varying optical quality of Teflon®-AF LCOFs currently in use, the analysis presented here should be useful in optimizing the performance of LCOF accessories in Raman and related spectroscopic applications.
Development of Electrode-Less Plating Method for Silver Film Preparations for Surface-Enhanced Infrared Absorption Measurements
Authors: Yang Jyisy , Chen Sheng-Hsi
Published: October 2003

A method based on the electrode-less deposition of silver islands on an infrared substrate is proposed and examined for surface-enhanced infrared (SEIR) measurements. The simplicity of this metal island-forming method can largely reduce the cost of surface preparation. Meanwhile, this preparation method also provides the advantage of being applicable to substrates with nonplanar surfaces. The influence of formula and reaction time on silver ion reduction was studied to obtain optimum conditions for island formation suitable for SEIR measurements. The morphologies of the forming silver islands or clusters were examined by a scanning electron microscope and correlated with the level of the enhancement effect. Small silver clusters (∼ 40 nm) with a round to rod shape produced the greatest surface enhancements. Large silver crystals (or clusters) of around a few micrometers were formed during long reaction times. These crystals showed no effect on surface enhancement and only served to block IR energy. Precisely controlled reaction times were critical to prevent the stacking of unwanted silver clusters. Both formula and concentration of reactants influenced the reduction rates of silver ions; hence the IR enhancement. With an increase of the concentration of reduction agents, the formed silver surface provided higher enhancement effect. With the use of the optimized reaction conditions, the silver films deposited by electrode-less solution provided levels of enhancement similar to those for to metallic surfaces prepared by conventional physical vapor deposition.
Confocal Raman Microspectroscopy through a Planar Interface
Authors: Baldwin K. J. , Batchelder D. N.
Published: October 2003

We have developed a model to describe the effect of refraction through a planar interface on the collection efficiency and depth of focus when performing confocal Raman microspectroscopy. The planar interface introduces spherical aberration, which can substantially degrade the performance of the microscope, especially for large-numerical-aperture microscope objectives. This spherical aberration will increase the range of focal depths spanned by the paraxial and marginal rays of the illuminating laser beam within the sample. In the collection path, it will also distort the scattering volume defined by the confocal aperture; this results in a dramatic fall in the collected light intensity with increasing depth. We demonstrate that there is an optimum numerical aperture for collected light intensity at a given depth. The prediction of this theoretical model is compared to empirical results obtained by mapping the stress distribution within the diamond anvil of a high-pressure cell. Both the collected Raman intensity and the effective depth of focus are compared to the predictions from the theory.
Evaluation of a Principal Components-Based Searching Algorithm for Raman Spectroscopic Identification of Organic Pigments in 20th Century Artwork
Authors: Vandenabeele Peter , Hardy An , Edwards Howell G. M. , Moens Luc
Published: October 2003

The characterization of artists' materials is of great importance for the conservation and restoration of 20th century paintings, and it provides information which is of art-historical interest. The identification of modern organic pigments by Raman spectroscopy is hampered by the large amount of different synthetic materials that exist. Therefore, an extended database of reference spectra is needed. Besides this spectral library, there is need for an accurate and fast-searching algorithm for selecting the reference spectrum that best corresponds with the unknown spectrum. A principal components-based spectral searching algorithm is proposed that largely reduces the number of data points for each spectrum. By subsequent measurement of the Euclidian distance between the unknown and the reference spectra in the principal components space, the corresponding reference can be selected. The algorithm is tested by using the results of the Raman spectroscopic analysis of different colored pencils. Different qualities of matches for the identification protocol could be distinguished. The synthetic organic pigments in micro-samples of the painting “Faubourg” by Paul Delvaux could be identified by the proposed algorithm.
Authentication and Quantification of Extra Virgin Olive Oils by Attenuated Total Reflectance Infrared Spectroscopy Using Silver Halide Fiber Probes and Partial Least-Squares Calibration
Authors: Küpper Lukas , Heise H. Michael , Lampen Peter , Davies Antony N. , McIntyre Peter
Published: October 2003

Infrared attenuated total reflectance spectroscopy has been assessed for the analysis of extra virgin olive oil samples from various Mediterranean sites and their adulteration by sunflower oil. In this study two different silver halide fiber-optic probes were separately tested for the mid-infrared spectroscopic measurement of pure olive oil samples and these same oils adulterated with sunflower oil. One fiber-optic probe contained an exchangeable U-shaped section of the silver halide fiber, whereas the second probe consisted of a fiber-coupled diamond crystal, which performed slightly less well than the whole fiber probe. The optimum standard error of prediction for the sunflower oil concentrations in spiked olive oil samples, obtained by optimized partial least-squares (PLS) calibration models and leave-one-out cross-validation, was 1.2% by weight with the use of a special variable selection strategy based on a pairwise consideration of significant respective minima and maxima of the optimum PLS regression vector, calculated for broad spectral intervals. Calibration robustness was proven by also using packages of 10 randomly selected samples within a further cross-validation for calculating independent prediction values. The implications for product monitoring are discussed.
Precision and Noise in Inductively Coupled Plasma Atomic Emission Spectroscopy with Charge-Injection Device Detection
Authors: Pennebaker Frank M. , Denton M. Bonner
Published: October 2003

An inductively coupled plasma (ICP)-echelle optical system coupled with a charge-injection device (CID) detector was evaluated for precision and noise. Simultaneous collection of analyte wavelengths and simultaneous background correction have invalidated underlying assumptions in some traditional models. Signal flicker noise, a major limitation in single-channel detection, was eliminated by the time correlation of analyte and internal standard wavelengths. Once flicker noise was eliminated, most fluctuation was found to be caused by slight wavelength shifts along the axis of the detector, rather than by the theoretically predicted signal shot noise. This fluctuation can be corrected by increasing center subarray sizes or by employing well-matched internal standard lines. In either case, precision of 0.3 to 0.18% relative standard deviation (RSD) was achieved over a time span of 7 h. Background flicker noise was also eliminated by simultaneous background correction, demonstrating a multichannel advantage of ICP detection using charge-transfer devices. In this work, theoretical expressions were developed to incorporate major sources of noise based on the specific readout characteristics of an array detector. These expressions match experimental data extremely well for measurement of relative standard deviation in background (RSDB) and detection limits. These data have then been compared to the single-channel case, which describes photomultiplier tube (PMT) detection, as well as the theoretical limit dictated by background shot noise.
Ultraviolet Quartz Acousto-Optic Tunable Filter Wavelength Selection for Inductively Coupled Plasma Atomic Emission Spectrometry
Authors: Gillespie Stacey R. , Carnahan Jon W.
Published: October 2003

A quartz acousto-optic tunable filter (AOTF) is utilized as a wavelength selection device for inductively coupled plasma atomic emission spectrometry (ICP-AES). System design is detailed. Fundamental characterizations indicate that the useful spectral range exceeds the 206 to 405 nm range. Wavelength calibration is extremely accurate with the correlation coefficient of the ICP atomic emission wavelength/inverse frequency plot exceeding 0.999999. Bandpasses were measured as 0.06 nm at 226 nm and 0.36 nm at 405 nm. These values are comparable to those of a moderate-resolution monochromator. The system was characterized with 12 metals: Ag, Ba, Ca, Cd, Cr, Cu, Eu, Fe, Hg, Mg, Mn, and Pb. Detection limits are in the single to tens of ng/mL range for many metals. Linearity is demonstrated from lower concentration ranges near the detection limit.
Infrared Spectroscopic Studies of Major Cellular Components. Part I: The Effect of Hydration on the Spectra of Proteins
Authors: Pevsner Alex , Diem Max
Published: October 2003

The infrared absorption spectra of two sample proteins as dry, lyophilized powders in KBr pellets, as hydrated proteins in KBr pellets, as hydrated or dehydrated films, and in solution phase are reported. We find an enormous increase in the absorption intensities of the amide I and amide II vibrations between the dry and the hydrated phases. This intensity enhancement was observed for hydration by both H2O and D2O. Furthermore, we observe significant changes in the amide I/amide II intensity ratios when comparing solution spectra acquired in transmission and attenuated total reflection (ATR) modes. Observed intensity changes between dry and hydrated protein samples were interpreted in terms of variations in the dielectric constant of the immediate surroundings of the peptide linkages.
Analytic Solution to the Autocorrelation Function for Lateral Diffusion and Rare Strong Adsorption
Authors: Wirth Mary J. , Ludes Melody D. , Swinton Derrick J.
Published: October 2003

An analytic expression is derived to describe the autocorrelation function for fluorophors interacting with heterogeneous chemical interfaces, where both lateral diffusion and reversible strong adsorption occur. The expression is accurate when the rate of strong adsorption is low compared to the rates of both diffusion and desorption, enabling analysis by nonlinear regression. Simulations of single molecules are employed to investigate the applicability of the analytic equation for interpretation of chemical equilibrium and kinetics of single fluorescent molecules undergoing both lateral diffusion and varying amounts of specific adsorption at chemical interfaces. The simulations show that the analytic equation accurately describes the autocorrelation decay, and the equation begins to deviate, as expected, when the adsorption rate becomes large. The results show that a smaller beam size enhances the ability to extract sorption kinetics from the autocorrelation decay, and that a larger beam size enhances the ability to obtain information about the diffusion coefficient with minimal interference from sorption processes. The expression provides a tool for choosing between fluorescence correlation spectroscopy and single-molecule sorting in studies of heterogeneous surfaces.
Multiple Time-Gate Module for Fluorescence Lifetime Imaging
Authors: de Grauw C. J. , Gerritsen H. C.
Published: October 2003

A versatile multiple time-gate fluorescence lifetime acquisition module is presented. The module is used as an add-on to a two-photon scanning laser microscope equipped with pulsed excitation for fluorescence lifetime imaging. It enables the recording of fluorescence lifetimes by capturing the intensity decay in four or eight time gates. The module allows fluorescence lifetime imaging at high count rates and with a high efficiency. The module is equipped with computer-controlled variable-delay lines for setting the gate widths. Decay times can be accurately measured in the 0.5 ns-1 μs range. Fluorescence lifetime imaging experiments on a number of single dye solutions with different (mono-exponential) fluorescence lifetimes are in excellent agreement with the reference values obtained with time-correlated single photon counting. Measurements on a test specimen exhibiting a bi-exponential decay demonstrate that the two decay components can be quantified with high accuracy. In a specimen containing six different lifetimes, in the range 2.8 to 12 ns, all lifetimes could be well distinguished. As an example, the results of a pH imaging experiment on oral biofilm using carboxyfluorescein are presented. Here, fluorescence lifetime imaging is used both to separate the short-lifetime autofluorescence from the carboxyfluorescein fluorescence and to determine the pH in the biofilm.
Reduction of Model Complexity by Orthogonalization with Respect to Non-Relevant Spectral Changes
Authors: Ferré Joan , Brown Steven D.
Published: October 2003

A method is presented to remove changes in the calibration spectra that are known to be not related to the property of interest. This can lead to multivariate calibration models that require fewer latent variables and are easier to interpret. This method requires the spectra of a sample to be measured under the different conditions that modify the spectra (for example, at different temperatures). These variations are not related to the concentration of the analyte and can therefore be removed before modeling with an orthogonalization step. The method has been used to remove the effect of temperature in the determination of NaOH in aqueous solutions by using near-infrared (NIR) spectra and partial least-squares (PLS) regression. This approach reduced the number of latent variables of the final model and made the interpretation of the PLS scores simpler.
Infrared Study of the Hydrogen Bonding Association in Polyamides Plasticized by Benzenesulfonamides. Part I: Self-Association in Amide and Sulfonamide Systems; Part II: Amide—Sulfonamide Interaction
Authors: De Groote Ph. , Rouxhet P. G. , Devaux J. , Godard P.
Published: October 2003

The molecular associations of N-( n-hexyl)hexanamide (PA-12MC) and N-( n-butyl)benzenesulfonamide (BBSA), taken as model compounds for polydodecamide (PA-12) and benzenesulfonamide plasticizers, respectively, were examined by Fourier transform infrared spectroscopy. In solution, the amide is distributed between a self-associated form, involving intermolecular hydrogen bonding, and isolated species. Dissociation is favored in an electron donor solvent due to hydrogen bonding between the amide and the solvent. Comparatively, BBSA has much less tendency to dissociate. Molecular modeling suggests that BBSA dimer associations exist in the condensed state thanks to intermolecular hydrogen bonds, while gas-phase infrared spectroscopy supports a stabilizing intramolecular interaction between the sulfonamide proton and the sulfonyl lone pairs for isolated molecules. Mixtures of the amide model compound with BBSA show the creation of a strong S-N-H … O=C hydrogen bond between the sulfonamide proton and the amide's carbonyl lone pairs. The amide N-H groups liberated from the former amide-amide interaction find themselves involved in a weaker C-N-H … O=S hydrogen bond (“free N-H”) with the plasticizer's sulfonyl lone pairs, the concentration of these bonds being maximum at mid-composition. For polyamide/BSAs mixtures, the accessibility of the amide and sulfonamide groups can restrict these associations. Mixtures of AAPA, an aliphatic amorphous polyamide, with a plasticizer bearing a branched alkyl chain, generate a low free N-H concentration and cause phase separation to occur, which confirms the steric sensibility of their interaction. A bifunctional benzenesulfonamide plasticizer appears to be less efficient than BBSA and leads to an increased dispersion in hydrogen bond distribution, both of which could be ascribed to the bulk of this molecule. Incorporation of BBSA in semicrystalline PA-12 leads to a behavior identical to that of AAPA/BBSA mixtures.
Time-Resolved Step-Scan Fourier Transform Infrared and Visible Absorption Difference Spectroscopy for the Study of Photosystem I
Authors: Hastings Gary
Published: October 2003

Step-scan Fourier transform infrared and visible absorption difference spectroscopy, with nanosecond to millisecond time resolution, has been applied to the study of photosystem I particles from photosynthetic oxygen-evolving organisms. In particular, time-resolved infrared (1800–1200 cm−1) and visible (680–850 nm) difference spectra associated with flash induced oxidation of the primary electron donor in photosystem I particles from Synechocystis sp. 6803 and Acarychloris marina are presented. These spectra are compared directly to static, photoaccumulated Fourier transform infrared and visible difference spectra from both species. The detailed bonding interactions of P740, the primary donor in photosystem I particles from Acarychloris marina, are very similar to that found for P700, the primary donor in photosystem I particles from Synechocystis sp. 6803. P740 consists of at least two chlorophyll molecules, both of which are probably chlorophyll-d. Combined time-resolved step-scan Fourier transform infrared and visible absorption difference spectroscopy is shown to be a powerful tool for the study of single molecular bond dynamics in proteins as large as 0.4 mega-Daltons.
Comparative Evaluation of Vibrational Circular Dichroism and Optical Rotation for Determination of Enantiomeric Purity
Authors: Zhao Chunxia , Polavarapu Prasad L.
Published: October 2003

Vibrational circular dichroism (VCD) is used to determine enantiomeric purity (EP) of three sample groups, and the results are compared with those obtained from optical rotation. In most typical cases EP determination from optical rotation is more accurate than that from VCD. However, in cases where either optical rotation is very small or different chiral samples are present as a mixture, EP determination from VCD provides definite advantages with reasonable accuracy.
Comparison of SPME/Transmission IR and SPME/ATR-IR Spectroscopic Methods in Detection of Chloroanilines in Aqueous Solutions
Authors: Yang Jyisy , Tsai Fang-Pei
Published: October 2003

Infrared (IR) optical sensors provide fast and nondestructive methods for the detection of organic compounds in aqueous solutions. Among the existing IR methods, attenuated total reflection (ATR) combined with the solid-phase micro-extraction (SPME) principle is the most frequently used method in the detection of organic compounds in aqueous solutions. In an effort to simplify this method for aqueous solution analysis, the SPME/transmission absorption infrared (TA-IR) method was developed in this work, and its performance was compared with that of the ATR-IR method. Results indicated that the SPME/TA-IR method provided better linearity (0 to 200 ppm concentration range) and sensitivity than the SPME/ATR-IR method in detection of chloroanilines. The lower linearity in the SPME/ATR-IR method was most likely caused by the change in the refractive index of the SPME phase after the absorption of different amounts of analytes. Because of the high-energy throughput in the SPME/TA-IR method, which largely reduced the noise level in the spectra, this method can provide slightly lower detection limits than the SPME/ATR-IR method. Another advantage of this new method is that the influence on IR signals by the SPME phase thickness phase can be partially compensated.
FT-IR Microscopic Base Imaging System: Applications for Chemical Analysis of Zn and Ni Atmospheric Corrosion
Authors: Lefez B. , Jouen S. , Kasperek J. , Hannoyer B.
Published: October 2003

The possible use of an FT-IR imaging system for surface studies of atmospheric corrosion products on zinc and nickel samples has been explored. Samples have been exposed in an urban site located at Rouen in France. Corrosion products, detected by means of energy-dispersive spectrometry/X-ray diffraction (EDS/XRD) and FT-IR spectroscopy, are mainly Zn4CO3(OH)6·H2O, ZnSO3·nH2O, Zn4SO4(OH)6·nH2O, and NiSO4·xH2O. IR microspectroscopy and mapping techniques allow the observation of the heterogeneous distribution of chemical species on sample surfaces. While the zinc corroded surface seems uniform, inhomogeneity in the development of carbonate and hydroxysulfate compounds in layers is observed. The imaging chemical analysis enables the assignment of the 1550 cm−1 absorption band of the corrosion product to zinc hydroxycarbonate. The corrosion mechanism observed on nickel is pitting corrosion. Pit size, chemical mapping, and 3-D visualization determined from SEM/EDS and FT-IR maps are very similar.
Geographical Origin Classification of Petroleum Crudes from Near-Infrared Spectra of Bitumens
Authors: Blanco M. , Maspoch S. , Villarroya I. , Peralta X. , González J. M. , Torres J.
Published: October 2003

Petroleum crudes of different geographical origin exhibit differences in chemical composition that arise from formation and ripening processes in the crude. Such differences are transmitted to the fractions obtained in the processing of petroleum. The use of unsupervised classification/sorting methods such as principal component analysis (PCA) or cluster analysis to near-infrared (NIR) spectra for bitumens obtained from petroleum crudes of diverse origin has revealed that composition differences among bitumens are clearly reflected in the spectra, which allows them to be distinguished in terms of origin. Accordingly, in this work we developed classification methods based on soft independent modeling of class analogy (SIMCA) and artificial neural networks (ANNs). While the latter were found to accurately predict the origin of the crudes, SIMCA methodology failed in this respect.
PARAFAC for Spectral Curve Resolution: A Case Study Using Total Luminescence in Human Dental Tartar
Authors: Reis Marlon M. , Biloti Débora N. , Ferreira Márcia M. C. , Pessine Francisco B. T. , Teixeira Gustavo M.
Published: October 2003

Chromophore identification in biological samples often requires the physical separation of the compounds, which can be difficult. Although there are several advantages to hyphenated spectroscopic techniques for identification of substances, complex mixtures of chromophores presenting overlapped spectra cannot be identified directly through this method. This work presents an application of chemometrics to compound identification in biological samples by a spectroscopic hyphenated technique using a curve resolution method. The PARAllel FACtor analysis model (PARAFAC), which has no rotational indeterminacy, was used for curve resolution of excitation-emission spectra of human dental tartars. PARAFAC was applied under constraints (i.e., unimodality and non-negativity) and evaluated with a validation procedure. The resolved profiles are porphyrinic-like spectra presenting excitation band maxima at 407, 416, and 431 nm in the Soret band region (390–440 nm) of these substances.
Reflectance and Probe Window Contamination: Study of Pulping Solutions
Authors: Mäkinen Martti O. A. , Peiponen Kai-Erik , Räty Jukka , Hyvåuinen Ville
Published: October 2003

The reflectance from industrial pulping solutions was investigated with the use of a reflectometer. It was observed that the reflectance is time-dependent on the contamination of the probe window. The optical constants of the pulping solutions were calculated by using Fresnel's theory and the concept of critical angle. A simple mathematical model, based on the random contamination of the probe window, was observed to yield satisfactory agreement between the measurement and theory of reflectance. It is proposed that optical constants of pulping solutions can be estimated despite the contaminated layer on the prism face.