bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of Procaine and Tetracaine in Cocaine Samples by Variable-Angle Synchronous Fluorimetry
Authors: Nevado J. J. Berzas , Pulgarín J. A. Murillo , Escudero O. I. Reillo
Published: October 2003

Derivative variable-angle synchronous spectrometry has been developed to improve the selectivity of fluorescence measurements without loss of sensitivity. The first-derivative variable-angle synchronous scanning permits the rapid simultaneous determination of tetracaine and procaine in a mixture from a single spectrum. The analysis was performed in 90% ethanol medium and 8.10−3 M NaOH. These local anaesthetics can be determined in the presence of large amounts of cocaine. Talc (hydrous magnesium silicate) and kaolin (aluminum silicate hydroxide) are the most common compounds that can be present in cocaine samples, but they can be eliminated by filtration, because they are insoluble in ethanol. Possible interference by other local anaesthetics likely to be present along with the compounds to be determined has been investigated. A complete and exhaustive statistical analysis of the experimental data was realized to demonstrate the validity of the method. The detection limit according to Long and Winefordner was 2.6 μg L−1 for procaine and 1.20 μg L−1 for tetracaine, and the detection limit proposed by Clayton was 3.00 μg L−1 for procaine and 1.38 μg L−1 for tetracaine.
Analysis of the Effect of Crystal Size and Color Distribution on Fluorescence Measurements of Solid Sugar Using Chemometrics
Authors: Baunsgaard D. , Munck L. , Nørgaard L.
Published: October 2003

Fluorescence from sugar crystal samples has previously been used to obtain information about factory imprint and sugar quality. Solid-phase fluorescence has potential as a fast screening method, but the spectra are highly influenced by the measurement geometry and sugar crystal sample. The aim of the present study was to examine how the fluorescence measurements are related to the sugar crystals for a better understanding of both. Initially, five sugar samples of varied composition were sieved into five crystal size fractions. Fluorescence excitation-emission landscapes of the fractions were measured with solid transmission and reflection techniques and in solution. The transmission fluorescence was quenched at ultraviolet wavelengths, and light scatter highly influenced the reflection fluorescence. Principal component analysis (PCA) showed that large crystals favored the transmission fluorescence, whereas smaller crystals improved the reflection fluorescence measurements. The multi-way method PARAFAC (parallel factor analysis) was used to resolve spectra of individual components from the fluorescence landscapes. Transmission and solution components had similar spectral profiles at higher wavelengths, characterizing a colorant and a colorant intermediate. The resolved components of the reflection data were very influenced by scatter. Color predictions based on a few significant wavelength variables equaled the model results of full-spectrum models using partial least-squares regression (PLS). The variables corresponded to wavelength maxima of the resolved colorants and ultraviolet wavelengths characterizing colorant precursors.
Processing FT-IR Imaging Data for Morphology Visualization
Authors: Bhargava Rohit , Wang Shi-Qing , Koenig Jack L.
Published: October 2003

Fourier transform infrared (FT-IR) imaging yields large volumes of spatially specific spectral data in a short time. While chemical information about a specific sample area is a goal, complete morphological visualization similar to that obtained by optical microscopy is desirable. To obtain morphological images from this large data volume with the highest possible fidelity, specific techniques are required. However, in general, fast FT-IR imaging (3–5 min of collection time) leads to noisy morphological images due to hardware limitations. The data can be transformed by using transformations to eliminate noise. Image display techniques and filters can then be used to further refine, display, and carry out quantitative morphological analysis. This paper classifies various techniques and demonstrates their applicability to FT-IR absorbance image analysis.
Difficulties with Direct-Current/Arc Optical Emission Spectrometric Analysis of Molybdenum Powder for Chromium, Iron, and Nickel
Authors: Spitsberg Anna T. , Otis Janet S.
Published: October 2003

A new sample preparation procedure for the analysis of molybdenum powder by a direct-current/arc optical emission spectrometer for chromium, iron, and nickel is introduced. This procedure requires treatment of an oxidized molybdenum sample with nitric acid (HNO3) in order to ensure the homogeneity of the analyzed subsample. In this work, it has been shown that the Mo-Cr-Fe-Ni scales formed on the surface of the reduction tubes and boats during the hydrogen reduction process of molybdenum oxide are the main source of Cr-Fe-Ni contamination in the molybdenum powder. The formation mechanism of those scales is out of the scope of the present work. In this study, it was assumed that the chromium in Mo-Cr-Fe-Ni scales exists partly as a metal and partly as an oxide, which is why it is impossible to dissolve a contaminated sample of molybdenum powder completely in any commonly used mineral acid. The use of perchloric acid (HClO4) was not taken into consideration, since it has explosive and hazardous properties that make it difficult to use for routine sample preparation. For these reasons, the application of techniques that require a complete dissolution of the sample prior to analysis [atomic absorption (AA), inductively coupled plasma mass spectrometry (ICP-MS), or ICP atomic emission spectrometry (ICP-AES), for example] can lead to low chromium results. It has been shown that using a bigger subsample weight and an acid treatment procedure can dramatically improve the precision of chromium, iron, and nickel determination in the reduced molybdenum powder with the use of direct-current/arc optical emission spectrometry.
Raman Microimaging of Polymer Blends
Authors: Appel R. , Zerda T. W. , Waddell W. H.
Published: October 2003

Raman microimaging was used to estimate the effect of the silica filler on phase separation in binary polymer blends composed of brominated poly(isobutylene-co-para-methylstyrene) (BIMS) and cis-1-4–polybutadiene (BR). The domain sizes, relative concentration of polymer components within domains, and distribution of particulate silica filler and zinc stearate curative were characterized for blends of different compositions and history of aging treatments. The presence of increased concentrations of precipitated silica results in better polymer morphology since domain sizes are reduced. Increased temperature treatment also decreases domain sizes up to about 150 °C, but treatment at 200 °C appears to induce separation of the elastomer components. Silica is usually found near the centers of the BIMS domains. There is little difference in silica distribution before and after curing.
Surface-Enhanced Resonance Raman Scattering and Near-Infrared Fourier Transform Raman Scattering as in Situ Probes of Ink Jet Dyes Printed on Paper
Authors: Rodger C. , Dent G. , Watkinson J. , Smith W. E.
Published: October 2003

The characterization of ink jet dyes and inks printed onto paper surfaces is of importance for the development of ink jet ink formulations and for use in forensic science. Raman spectroscopy is an effective and informative probe for this purpose if problems associated with fluorescence are overcome. A comparison is made here between two effective techniques, surface-enhanced resonance Raman scattering (SERRS) and near-infrared Fourier transform Raman scattering (NIR-FTR). SERRS provides a good method for obtaining in situ measurements using a visible laser system. It is fast (1–10 s accumulations) and requires very low laser powers (<1 mW). However, it requires the addition of a small dot of silver colloid to the paper surface in order to produce the enhancement. NIR-FTR is noninvasive and simpler to use. However, much higher laser powers are required (>200 mW), and the spectral accumulation time is significantly longer. Both methods overcome fluorescence effectively in most samples studied; however, each is more effective than the other with selected inks and paper substrates. SERRS involves resonant enhancement of the chromophore of the dye in contact with the silver surface, and consequently it is the dye chromophore which is uniquely identified. With NIR-FTR, signals from the paper and the filler are also observed. Comparable spectral patterns with clear, explicable differences are obtained from each method, indicating in particular that SERRS spectra can be interpreted without recourse to specific surface selection rules. The combination of the two techniques provides some information on the electronic as well as the vibrational properties of the dyes in situ.
Construction of Novel Nanosecond Temperature Jump Apparatuses Applicable to Raman Measurements and Direct Observation of Transient Temperature
Authors: Yamamoto Kohji , Mizutani Yasuhisa , Kitagawa Teizo
Published: October 2003

Two types of nanosecond temperature jump (T-jump) apparatuses applicable to time-resolved Raman measurements were constructed. T-jump was achieved by direct heating of water using near-infrared (NIR) pulses at 1.89 μm in one type and at 1.56 μm in the other. The two NIR pulses were generated through stimulated Raman scattering (SRS) of H2 or D2 excited by the fundamental line of a Q-switched Nd:YAG laser, in which a single-pass configuration with H2 was sufficient for 1.89 μm pulses but a seeding-amplification configuration with D2 was necessary for 1.56 μm pulses. The seeding-amplification configuration yielded significant improvements in conversion efficiency, pulse-to-pulse stability, and beam quality. These apparatuses were applied to transient Raman measurements of MoO42– solution, and transient temperatures of the heated volume were determined from ratios of anti-Stokes to Stokes Raman intensities. Temporal behaviors of the temperature of the heated volume upon illumination of nanosecond heat pulses at 1.89 or 1.56 μm were explored, and its applicability to studies on the primary process of thermal reactions was examined. It became clear that the continuation time of raised temperature is determined only by the replacement of the sample in the case of a thick cell and by both thermal transfer and sample replacement in the case of a thin cell, while thermal diffusion is not effective for either cell.
Quantitative Phosphate Analysis in Industrial Raw Phosphoric Acid Based on Evaluation of Bandshifts in FT-Raman Spectroscopy
Authors: Abderrazak H. , Dachraoui M. , Cañada M. J. Ayora , Lendl B.
Published: October 2003

We present a new approach for quantitative chemical analysis by Raman spectroscopy with the example of phosphate analysis in highly concentrated industrial raw phosphoric acid. The proposed method is based on the direct measurement of the Raman shift of the vs(P-OH) band of phosphoric acid, which suffers a blue shift upon increasing concentration. Correlation of the exact band position rather than band intensity with the concentration of the analyte eliminated the need to reference the measured Raman signal to an internal or external standard, which is usually needed to account for changes in laser power or optical throughput. A calibration curve ranging from 100 to 1400 gL−1 phosphoric acid was established (coefficient of variation of the method, Vxo: 0.99%; analysis time: 7 min per sample). The applicability of the developed method to industrial samples was proven by an interference study including sulfate, magnesium, aluminum, and iron(III) as well as by comparing the results to those of gravimetry. The observed peak shift due to changes in phosphate concentration was investigated by two-dimensional (2D) correlation analysis, which provided valuable insight in the inter- and intramolecular interactions in highly concentrated phosphoric acid.
Enhancement of Aluminum, Titanium, and Iron in Glass Using Pre-Ablation Spark Dual-Pulse LIBS
Authors: Stratis Dimitra N. , Eland Kristine L. , Angel S. Michael
Published: October 2003

In this paper, we report the first enhanced emission for elements in a nonmetal or nonconducting matrix, glass, with the use of a pre-ablation spark. The glass samples used in this work are prototypes of samples used to immobilize inorganic waste at the Savannah River Site Vitrification Facility. We have found that using a pre-ablation spark results in larger signal enhancements, 11- to 20-fold for titanium, aluminum, and iron in glass compared to the metal under the same experimental conditions. We also demonstrate that this method is more sensitive than single-pulse LIBS experiments for the direct solid sampling of vitrified waste glass.
Evaluation of Mirage Effect Spectrometry for Optical Absorption Depth Profiling of Photodegradation in Thin Poly(Vinylchloride) Films
Authors: Power J. F. , Nepotchatykh O. V. , Fu S.-W.
Published: October 2003

Mirage effect (photothermal deflection) spectrometry was examined as a tool for the quantitative depth profiling of the optical absorption coefficient in thin films of poly(vinylchloride) (PVC) photolyzed under ultraviolet (UV) light. Profiles of the photoproduct of dehydrochlorination reactions were induced by controlled UV photolysis in test films on the scale of 10–100 μm, with total absorbance in the range 0.3–0.5 a.u. at 465 nm. Photolyzed test samples were prepared as laminate assemblies containing 10–25 individual layers fused together under pressure, according to a methodology we previously developed. These assemblies were mechanically separated into individual layers after photolysis and spectrophotometrically analyzed. Photothermal depth reconstructions of the optical absorption coefficient were made in these assemblies via inverse problem theory applied to the experimental photothermal deflection response, with the destructive layer-by-layer spectrophotometric analysis performed in parallel as a reference measurement. Optical absorption coefficient profiles recovered by the mirage effect were in agreement with the reference spectrophotometric data to within a root-mean-square error of better than 15% of full scale, with a nearly quantitative recovery of the peak absorption, depth, and initial slope of the film's absorption profile.
Analysis of Sulfuric Acid Aerosols by Laser-Induced Breakdown Spectroscopy and Laser-Induced Photofragmentation
Authors: Núñez Montserrat Hidalgo , Cavalli Paolo , Petrucci Giuseppe , Omenetto Nicoló
Published: October 2003

Laser-induced breakdown spectroscopy and laser photofragmentation spectroscopy are investigated as potential approaches to the detection and quantification of the sulfuric acid aerosols resulting from the oxidation of dimethylsulfide in air. The former, direct technique, where aerosols are introduced in the plasma formed by focusing the fundamental frequency of a Nd:YAG laser in air, and atomic sulfur emission is measured in the region 180 nm, gives a limit of detection of 165 ppbv for a 15 min integration time, which is inadequate for our purposes. The second, indirect approach, based on the photofragmentation, with 193 nm photons, of the compound resulting from interaction between sodium chloride and sulfuric acid aerosols, gives a detection limit of 46.5 ppbv in 10 s measuring time. With this method, a complete “titration curve” for sulfuric acid aerosols can be obtained in “quasi” real-time.
Surface-Enhanced Raman of Dopamine and Neurotransmitters Using Sol-Gel Substrates and Polymer-Coated Fiber-Optic Probes
Authors: Volkan Mürvet , Stokes David L. , Vo-Dinh Tuan
Published: October 2003

Surface-enhanced Raman spectroscopy (SERS) is used to detect catecholamines—viz., dopamine, norepinephrine, epinine, and isoproterenol—using a new substrate prepared with sol-gel technology. Catecholamines are complexed at the surface by iron(III) ions, which were introduced during the reduction of the silver ions embedded inside the sol-gel matrix. With the use of a He-Ne laser at a power of only 12 mW, it is possible to measure dopamine in the micromolar concentration range. A single-fiber SERS probe system was also introduced that has great potential for sampling in microenvironment applications such as in vivo measurements of dopamine. In this microprobe design both excitation and SERS signals are transmitted through the same fiber simultaneously. The tips of tapered fibers were coated with a polyvinyl alcohol polymer doped with metallic silver particles. The potential of the SERS method and microprobes for medical diagnostics is discussed.
Development of a Raman Detector for Capillary Electrophoresis
Authors: Ruddick Andrew , Batchelder David N. , Bartle Keith D. , Gilby Anthony C. , Pitt G. David
Published: October 2003

Efficient detector optics incorporating a hyperhemispherical element have been developed to facilitate the coupling of capillary electrophoresis or microchromatography with Raman spectroscopy. The design has a high tolerance for alignment and focusing errors. A simple model has been developed to predict the behavior of the system as capillary diameter is varied. This approach was found to provide good qualitative agreement with experiment. Limits of detection in capillary electrophoresis experiments without preconcentration were found to be ∼ 5 mM for nitrate and perchlorate ions. Direct detection of several carbohydrates was also demonstrated; with the use of sample stacking, limits of detection were in the millimolar range. The analytes were distinguishable by their Raman spectra.
Study of the Use of Molecular Spectroscopy for the Authentication of Extra Virgin Olive Oils. Part I: Fourier Transform Raman Spectroscopy
Authors: Davies Antony N. , McIntyre Peter , Morgan ED
Published: October 2003

Determination of the authenticity of extra virgin olive oils has become more important in recent years following some infamous adulteration and contamination scandals. There is significant economic advantage to be gained by falsely marketing lower quality oils as top-quality products or by adulterating the end product with cheaper alternative oil. The analysis of olive oils is complicated by their complex nature. The conventional analytical techniques involve complicated analyses of individual components in the oil in order to determine their authenticity; however, molecular spectroscopy combined with modern chemometric techniques offers a rapid analytical solution to this complex problem. This paper describes the initial results from the experimental application of Fourier transform Raman spectroscopy in this area.
Time-Resolved Multispectral Imaging Spectrometer
Authors: Khait Oleg , Smirnov Sergev , Tran Chieu D.
Published: October 2003

A new multispectral imaging spectrometer with millisecond resolution has been developed. This instrument is based on the use of an acousto-optic tunable filter (AOTF) for spectral tuning and a simple progressive scan camera capable of snapshot operation for recording. The fast multispectral imaging can be performed in two configurations: recording images as a function of time or as a function of wavelength. In the first configuration, multiple images are recorded, grabbed, and stored per one wavelength. Upon completion, the AOTF is scanned to a new recording wavelength and a new set of images are recorded. It was found that, in this configuration, the imaging spectrometer is capable of recording, grabbing, and storing up to 33 images per s (i.e., 30 ms per image). Because an external signal is used to start the event and the recording of images, and the period between the start of the event and the recording and grabbing of images can be appropriately adjusted by a delay line, the time resolution of the spectrometer is not limited to 30 ms but rather can be adjusted to a shorter or longer time scale. In the second configuration, the recording wavelength is rapidly scanned (by the AOTF) and only one image is rapidly recorded, grabbed, and stored for each wavelength. Because additional time is needed to scan the AOTF, the maximum number of images that can be grabbed in this case is 16 frames per s. Preliminary applications of the imaging spectrometer include measurements of photo-induced changes in temperature-sensitive cholesteric liquid crystals as a function of time and wavelength. It was found that irradiating with a near-infrared (NIR) diode laser of 805 nm led to changes in the liquid crystal. The changes were found to vary with time and wavelength, namely, at about 360 ms after the NIR laser pulse the liquid crystal underwent changes in the visible region around 570 nm. The changes shifted toward longer wavelength concomitantly with time; i.e., maximum change at about 600 ms shifted to 718 nm.
Effect of Focal Plane Array Cold Shield Aperture Size on Fourier Transform Infrared Micro-Imaging Spectrometer Performance
Authors: Bhargava Rohit , Fernandez Daniel C. , Schaeberle Michael D. , Levin Ira W.
Published: October 2003

Micro-imaging spectrometers incorporating focal plane array (FPA) detection require careful demarcation of cold shield aperture size for both optimal performance and prevention of errors. This study examines the effects of changing the diameter of the cold shield aperture on the intensity and spatial homogeneity of the incident radiation. A uniform polystyrene film was repeatedly imaged by using cold shields of varying aperture sizes. It is shown that a smaller than optimal aperture size leads to image edge clipping, resulting in an inefficient use of the array, lower overall signal, spectral distortions, and higher noise characteristics. Use of an aperture size larger than required causes a decrease in the effective dynamic range of measurements, resulting in higher noise levels. The advantages and necessity of optimizing imaging spectrometer performance by employing a cold shield with an appropriately sized aperture are discussed.
Determination of the Stray Light Levels in a Dispersive Near-Infrared Spectrometer with Trichloromethane
Authors: Busch Kenneth W. , Soyemi Olusola O. , Rabbe Dennis , Busch Marianna A.
Published: October 2003

The stray light level in a dispersive near-infrared (NIR) spectrometer was determined at 1152, 1410, 1692, and 1861 nm with the sharp absorption bands of trichloromethane. The stray light level in the dispersive spectrometer was found to be a function of wavelength and was greatest at the lower and upper extremes of the free spectral range of the instrument. Stray light measurements with and without a blocking filter showed that the majority of the stray light in the instrument was due to the overlap of higher diffraction orders produced by the diffraction grating. A theoretical model to predict the stray light in the instrument was developed. When compared with the model, the measured stray light levels were found to be consistent with those expected if the primary source of stray light was due to the overlap of higher diffraction orders in the monochromator of the spectrometer. Measurements of absorbance as a function of pathlength were made with the four absorption bands of trichloromethane (1152, 1410, 1692, and 1861 nm). After correction for the results for stray light, the linear regression data for the absorbance vs. pathlength plots were determined and reported. The measured slopes should be useful in checking the photometric accuracy of NIR spectrometers over the wavelength range from 1100 to 1900 nm.
Infrared Spectroscopy of Lipoproteins: A Comparative Study of Normal and Diabetic Plasma Lipoproteins
Authors: Lopez Gema , Martinez Rebeca , Gallego Jesús , Tarancon Maria-Jesus , Carmona Pedro , Fraile Maria Victoria
Published: October 2003

Infrared spectroscopy has been applied to study the composition and secondary structures of very low-density (VLDL), low-density (LDL), and high-density (HDL) plasma lipoproteins from diabetic and nondiabetic control rats. Both nondiabetic and diabetic lipoproteins generate spectra characterized by distinct amide I band spectral profiles, which were fitted to a sum of component bands diagnostic for types of protein secondary structure. From the spectra of both diabetic and healthy rat groups we find the following results: (1) although the esterified lipid/apoprotein ratio is conserved in both groups of HDL, LDL, and VLDL lipoproteins, healthy LDL particles seem to be richer in phospholipids than diabetic LDL; (2) this different lipid composition is accompanied by a lower β-sheet proportion in diabetic LDL lipoproteins; (3) The percentage area corresponding to tyrosine residue is higher in healthy HDL and LDL lipoproteins compared with the diabetic ones. The reverse occurs for VLDL lipoproteins, which indicates either an apoprotein composition change or an apoprotein transfer from HDL and LDL to VLDL particles during the diabetic process. All the above changes in lipid and apoprotein composition as well as protein conformational changes during diabetes disease can result in a decreased binding of apoproteins to the cellular LDL receptor.
FT-IR Spectroscopy of Organic Matter in Tropical Soils: Changes Induced through Deforestation
Authors: Haberhauer G. , Feigl B. , Gerzabek M. H. , Cerri C.
Published: October 2003

This article describes a series of transmission Fourier transform infrared (FT-IR) spectroscopy measurements of soil layers, especially organic soil layers, originating from a tropical forest and from a pasture, which was developed after deforestation of the tropical soil in 1987. Spectral information obtained from forest and pasture soil layers from central Rondônia, Brazil, was analyzed and compared. A variety of bands characteristic of molecular structures and functional groups have been identified for these complex samples. Cluster analysis revealed that such land use change affects the spectroscopic behavior of the organic soil layers. A significantly closer relationship between the pasture soil layers in comparison to the forest soil layers was obtained. This result indicates a higher homogeneity of the intoduced litter from pasture vegetation compared to forest. The application of regression models enabled the estimation of soil parameters, such as organic carbon and nitrogen; the identification and differentiation of organic forest soil horizons; and the determination of the decomposition status of soil organic matter in distinct layers. On the basis of the data presented in this study, it may be concluded that FT-IR spectroscopy is a powerful tool for the investigation of decomposition dynamics and litter quality in tropical soils.
Analysis of Prostatic Stent Encrustation and of Entrapped Urinary Stone Using FT-IR and FT-Raman Spectroscopy
Authors: Kontoyannis C. G. , Bouropoulos N. , Dauaher H. H. , Bouropoulos C. , Vagenas N. V.
Published: October 2003

Fourier transform infrared spectroscopy (FT-IR) and Fourier transform Raman spectroscopy (FT-RS) were used in order to characterize the encrusted deposits formed on a metallic thermosensitive prostatic stent. A 4 mm urinary stone entrapped within the lumen was also analyzed. Six different substances, a very rare occurrence, were detected, yielding complex spectra. Struvite (STR), hydroxyapatite (HAP), calcium oxalate monohydrate (COM), potassium urate (PU), and ammonium urate (AU) were the main components of concretion formed on the metal surface. STR and PU were detected on the 0.2 mm external surface of the stone, while the 3.8 mm core was found to be uric acid (UA). The broad and overlapping FT-IR bands of STR and COM made their identification difficult, while the detection of HAP was hindered by the presence of numerous urates bands, which, on the other hand, were used for the discrimination among UA, AU, and PU. Raman spectroscopy proved to be more sensitive to urate presence than did FT-IR, while the identification of STR, COM, and HAP was easier for FT-RS but more difficult with respect to AU and UA since all their bands, but three, coincide. A combination of the two techniques was necessary for the qualitative analysis of the encrustation and the stone.
FT Surface-Enhanced Raman Evidence of the Oxidative Condensation Reactions of Caffeic Acid in Solution and on Silver Surface
Authors: Sánchéz-Cortés S. , García-Ramos J. V.
Published: October 2003

Fourier transform (FT)-Raman spectroscopy and FT surface-enhanced Raman spectroscopy (FT-SERS) are applied for the first time to study the chemical oxidative changes undergone by caffeic acid (CA) in solution and when adsorbed on silver colloids. UV-visible spectroscopy was also applied to follow the polymerization of CA. Normal Raman techniques have only a limited application in the characterization of CA oxidation products owing to the high fluorescence background emitted by them. Nevertheless, the use of silver colloids may both quench the fluorescence signal and catalyze the CA oxidation, with the additional advantage of analyzing very small concentrations of the CA derivatives formed in situ on the surface. The influence of the solvent (water or ethanol) in the oxidation of the stock solution, the pH, and the storage time on the SERS spectra was investigated and analyzed on the basis of the oxidation and polymerization mechanisms proposed by several authors in the literature. The results found for CA were compared with those for other chemically related molecules as catechol and isoferulic acid in order to assign the vibrational spectra obtained at the different conditions employed to carry out the study of CA oxidation. The results found in this study demonstrate that the polymerization mechanism followed by CA depends on the conditions of CA storage and those at which the SERS spectra are recorded. The conclusions derived from this work can be very useful in the understanding of the chemical processes undergone by CA, which lead to possible changes in the nutritional value of the foods where this molecule appears. The advantage of this technique in relation to those employed so far in similar investigations is the ability to carry out in situ time-resolved measurements, thus allowing assignments of the different mechanisms of CA oxidation under the different experimental conditions employed.
Molecular Self-Assembling of Butan-1-ol, Butan-2-ol, and 2-Methylpropan-2-ol in Carbon Tetrachloride Solutions as Observed by Near-Infrared Spectroscopic Measurements
Authors: Iwahashi Makio , Suzuki Masayuki , Katayama Norihisa , Matsuzawa Hideyo , Czarnecki Mirosław A. , Ozaki Yukihiro , Wakisaka Akihiro
Published: October 2003

The self-associations of butan-1-ol, butan-2-ol, and 2-methylpropan-2-ol ( tert-butanol) in the pure liquid state and in carbon tetrachloride solutions have been studied mainly through near-infrared spectroscopic observation at various temperatures. A new analysis assuming a successive association process for the alcohol molecules was applied to the sharp band around 1410 nm (the first-overtone band of the OH stretching vibration mode attributed to free OH monomer and partly to OH polymer); it became clear that the mean association number for each alcohol increases with increasing concentration and decreases with increasing temperature. Comparisons of the association numbers at various constant temperatures for the three kinds of alcohols show that the association abilities are on the order butan-1-ol > butan-2-ol > 2-methylpropan-2-ol.
Studies of the Spectral Dependence of Photoionization Spectrometry Measurements of NO in Air
Authors: Elwood S. A. , Simeonsson J. B.
Published: October 2003

The relative merits of five laser excitation schemes have been evaluated for photoionization spectrometry (PIS) measurements of NO in air. All five schemes utilize wavelengths near 215 nm, which correspond to excitation of rovibronic transitions in the A 2Σ+–X 2πi (1,0) bands of NO. Photoionization of the excited NO molecules is accomplished by using wavelengths ranging from 215 to 1064 nm. Excitation spectra of the five PIS schemes reveal a significant enhancement when 355 nm radiation is used for photoionization. The enhancement is hypothesized to be related to a resonance or near-resonance ionization process for selected lines in the A 2Σ+–X 2π1/2 band [specifically the R11 + Q21 ( J″ = 8.5–12.5) lines and the P21 + Q11 ( J” 9.5–10.5) lines] and the A 2Σ+–X 2π3/2 band [specifically the R12 + Q22 ( J” 8.5–12.5) lines and the P22 + Q12 ( J” = 9.5–10.5) lines] of NO. Comparison measurements using all five schemes demonstrate that the highest sensitivity and highest signal-to-noise ratios are observed by using the 215 nm + 355 nm scheme, for which a limit of detection of 80 parts per trillion by volume for NO in air has been achieved.
Use of Multivariate Analysis to Determine Temperature from Low-Resolution Infrared Spectra of Carbon Dioxide
Authors: Szczepanski Michael P. , Fountain Augustus W.
Published: October 2003

The remote optical monitoring of gaseous contaminants is important for both military and industrial applications. An important parameter for quantifying chemical species and for predicting plume dynamics is the temperature. While in some industrial monitoring situations it may be practical to independently measure the temperature of stack emissions, for compliance monitoring and military chemical reconnaissance a remote optical means of estimating gas plume temperature is required. It was noticed that the band shape of low-resolution spectra of carbon dioxide in equilibrium with an exhaust plume was very sensitive to temperature. Spectra of carbon dioxide were acquired under controlled laboratory conditions in 5° increments from 20 to 200 °C. Various multivariate models were used to predict the temperature. It was found that partial least-squares (PLS) was unable to effectively model the simultaneous changes in amplitude and bandwidth with temperature. However, principal component regression (PCR) was found to be well correlated with temperature and allowed cross-validated prediction within 4% error.
IR Chemical Sensor for Detection of Aromatic Compounds in Aqueous Solutions Using Alkylated Polystyrene-Coated ATR Waveguides
Authors: Yang Jyisy , Huang Yuh-Shenq
Published: October 2003

The combination of solid-phase micro-extraction (SPME) with infrared (IR) attenuated total reflection (ATR) spectroscopic methods provides a fast and convenient way to detect organic compounds in aqueous solutions. In an effort to overcome the limitation of commercially available polymers, polystyrene (PS) was derivatized with different alkyl groups chain lengths to increase the performance of SPME-IR/ATR in detection of various aromatic compounds in aqueous solutions. The alkylated PS provides higher extraction efficiency and speed of diffusion in analysis of aromatic compounds than the commonly used polymers in SPME-IR/ATR methods. The increase of extraction efficiency is mainly caused by the π–π interaction between the phenyl rings of PS and the aromatic compounds. Meanwhile, the high rate of diffusion in the SPME phase is due to the lower crystallinity after alkylation. Results from analysis of different polarity aromatic compounds indicated that alkylated PS provides both a higher partition coefficient and a faster diffusion rate for the examined aromatic compounds. Better extraction performance of longer chain length PS was observed for low-polarity aromatic compounds. For higher polarity aromatic compounds, the increased chain length reduces the extraction efficiency in detection of this type of compound. This observation may reveal that the π–π interaction is more important in attraction of medium to polar aromatic compounds.
Thermal Cure Study of a Low-k Methyl Silsesquioxane for Intermetal Dielectric Application by FT-IR Spectroscopy
Authors: Wang C. Y. , Shen Z. X. , Zheng J. Z.
Published: October 2003

In this paper, Fourier transform infrared (FT-IR) spectroscopy is used to study the thermal properties of methyl silsesquioxane (MSQ), an important low-dielectric-constant organic spin-on glass for semiconductor device fabrication. The compositional and structural changes of MSQ with temperature are investigated in detail. The cross-linking process, where the three-dimensional networked structure is formed, is found to start at room temperature, and is almost complete at the typical baking temperature of 250 °C. Further cross-linking occurs during the curing process at 425 °C, and small short-chain clusters can also be driven away at this temperature by sublimation. In this study, we have assigned all the MSQ IR peaks and we have used the long-chain O–Si–O IR peak to calculate the “degree of cross-linking” quantitatively.
Depth Profiles in Coated Paper: Experimental and Simulated FT-IR Photoacoustic Difference Magnitude Spectra
Authors: Wahls M. W. C. , Kenttä E. , Leyte J. C.
Published: October 2003

Experimental photoacoustic (PA) magnitude spectra of a coated paper and the uncoated basepaper are presented. The normalized and scaled PA magnitude spectra are used to calculate difference magnitude spectra. It was decided to scale all PA magnitude spectra to (low) equal intensity at the approximately optically thin spectral range before subtraction. Then no infrared (IR) bands of identical band shape and height (as needed for common difference spectroscopy) in either PA magnitude spectrum are needed. Contributions of the two individual layers to the IR-PA magnitude spectrum of the coated paper are separated in the difference spectrum by their sign. An increasing relative contribution of the coating layer with an increasing phase modulation frequency is found. On decreasing the thermal length to a value near the coating thickness, the difference spectra increasingly show positive coating bands and negative bulk signals. The extension of the Rosencwaig–Gersho theory to a double-layered system introduced by N. C. Fernelius [J. Opt. Soc. Am. 70, 480 (1980) and J. Appl. Phys. 50, 650 (1980)] applied to synthetic spectra confirms the experimental observation. It is found that photoacoustic difference spectroscopy may provide quantitative depth-resolved spectral information due to the presented scaling procedure, and photoacoustic difference magnitude spectra of any polymeric laminate may therefore be calculated.
Raman Spectroscopy Study of Molten MxAlF3+x —M'xAlF3+x Systems (M, M' = Li, Na, K)
Authors: Robert E. , Gilbert B.
Published: October 2003

Raman spectra of (M, M')F–AlF3 (M, M' =Li, Na, K) molten salts have been obtained at 1293 K. The intensity ratios between the bands that are characteristic of the different complexes are strongly affected by the ratio M/M', especially when one of the alkaline cations is Li+. Its presence together with another cation seems to produce an increase in the acidity of the melt. The result of the deconvolution of the spectra compares well with vapor pressure data from the literature, showing the same kind of deviation. A qualitative explanation is proposed, but a quantitative modeling has not been possible up to now, because there is a lack of thermodynamic data that would allow a comparison with the spectroscopic results.
Raman Spectroscopy of Nontronites
Authors: Frost Ray L. , Kloprogge J. Theo
Published: October 2003

Smectites including the iron-bearing smectites have proved difficult to measure using the techniques of Raman spectroscopy. The use of Fourier transform (FT)-Raman spectrometers using indium-gallium-arsenide detectors has enabled the spectra of a selection of high iron-bearing smectites and nontronites to be measured. Low-intensity hydroxyl stretching Raman bands were found at 3436 and 3355 cm−1 and are attributed to the Fe–FeOH unit. Low-frequency bands were observed at around 201, 163, 128, and 90 cm−1. The 90 cm−1 band is ascribed to the stretching vibration of the hydrated cation. Bands observed at around 780 and 880 cm−1 are ascribed to the hydroxyl deformation modes of the Fe–FeOH and Fe–AlOH.
Interval Partial Least-Squares Regression (iPLS): A Comparative Chemometric Study with an Example from Near-Infrared Spectroscopy
Authors: Nørgaard L. , Saudland A. , Wagner J. , Nielsen J. P. , Munck L. , Engelsen S. B.
Published: October 2003

A new graphically oriented local modeling procedure called interval partial least-squares ( iPLS) is presented for use on spectral data. The iPLS method is compared to full-spectrum partial least-squares and the variable selection methods principal variables (PV), forward stepwise selection (FSS), and recursively weighted regression (RWR). The methods are tested on a near-infrared (NIR) spectral data set recorded on 60 beer samples correlated to original extract concentration. The error of the full-spectrum correlation model between NIR and original extract concentration was reduced by a factor of 4 with the use of iPLS ( r = 0.998, and root mean square error of prediction equal to 0.17% plato), and the graphic output contributed to the interpretation of the chemical system under observation. The other methods tested gave a comparable reduction in the prediction error but suffered from the interpretation advantage of the graphic interface. The intervals chosen by iPLS cover both the variables found by FSS and all possible combinations as well as the variables found by PV and RWR, and iPLS is still able to utilize the first-order advantage.
Transformation of the Near-Infrared Bands of Cellulose Surface Hydroxyls under the Influence of Adsorbed Water Molecules
Authors: Švedas Vitas
Published: October 2003

Near-infrared absorption spectra of sulfite cellulose with a varied adsorbed water content were studied. Analysis of the spectra has been made on the basis of previously published relations and results of the cellulose surface hydroxyls' interaction with absorbed water. Spectra of the OH overtone region of 1.3–1.65 μm were deconvoluted to components of cellulose volume and surface hydroxyls as well as to those of absorbed water. Besides the 1.53–1.55 μm component of “bound” water, the 1.42–1.44 μm component of “free” water starts to grow as the surface coverage exceeds 1.5. Comparison of the peak positions of these water components with those of liquid water suggests that bound water is constituted of hydrogen-bonded molecules. The 1.42–1.44 μm component of free water implies nonhydrogen-bonded and partially hydrogen-bonded molecules. The whole 1.363 μm band and a part of the 1.424 μm band of surface hydroxyls turn into the 1.52–1.53 and 1.57–1.59 μm peaks, respectively, after attachment of H2O molecules. The red shift of the surface bands by approximately 780 cm−1 caused by the adsorbate is consistent with a shift of the fundamental OH band of silica gel. The possible chemical, morphological, and physical causes of the two 1.363 and 1.424 m surface hydroxyl bands are discussed.
Statistical Error Calibration in UV-Visible Spectrophotometry
Authors: Tellinghuisen Joel
Published: October 2003

A procedure for spectrophotometric statistical error calibration is described, in which estimates of the variance (σ A2) in the absorbance A are derived as a function of A and the wavelength λ, directly from recorded spectra. Spectra are obtained over the desired wavelength range for a number of neutral-density filters, and are then least-squares fitted piecemeal to low-order polynomials. The variances from these fits constitute the estimates of the instrumental variance σ A2 for the λ and A of the respective fitted segments. These values are in turn expressed as functions of λ and A, by means of a small number of parameters. In the present case a representation in terms of A and I0, the “effective” source intensity, is even more compact, requiring only five parameters to cover the 200–850 nm region for absorbances up to and exceeding 2. For the instrument studied here, the high- A precision is limited by digitization error, the error being independent of λ and I0.
Determination of Wavelength Accuracy in the Near-Infrared Spectral Region Based on NIST's Infrared Transmission Wavelength Standard SRM 1921
Authors: Lowry Stephen R. , Hyatt Jim , McCarthy William J.
Published: October 2003

A major concern with the use of near-infrared (NIR) spectroscopy in many QA/QC laboratories is the need for a simple reliable method of verifying the wavelength accuracy of the instrument. This requirement is particularly important in near-infrared spectroscopy because of the heavy reliance on sophisticated statistical vector analysis techniques to extract the desired information from the spectra. These techniques require precise alignment of the data points between the vectors corresponding to the standard and sample spectra. The National Institute of Standards and Technology (NIST) offers a Standard Reference Material (SRM 1921) for the verification and calibration of mid-infrared spectrometers in the transmittance mode. This standard consists of a 38 μm-thick film of polystyrene plastic. While SRM 1921 works well as a mid-infrared standard, a thicker sample is required for use as a routine standard in the near-infrared spectral region. The general acceptance and proven reliability of polystyrene as a standard reference material make it a very good candidate for a cost-effective NIR standard that could be offered as an internal reference for every instrument. In this paper we discuss a number of the parameters in a Fourier transform (FT)-NIR instrument that can affect wavelength accuracy. We also report a number of experiments designed to determine the effects of resolution, sample position, and optics on the wavelength accuracy of the system. In almost all cases the spectral reproducibility was better than one wavenumber of the values extrapolated from the NIST reference material. This finding suggests that a thicker sample of polystyrene plastic that has been validated with the SRM 1921 standard would make a cost-effective reference material for verifying wavelength accuracy in a medium-resolution FT-NIR spectrometer.
ATR/FT-IR and Raman Microscopic Investigation of Diffusion and Distribution of Silane Coupling Agents in PVC Films
Authors: Eaton Peter , Holmes Paul , Yarwood Jack
Published: October 2003

We have combined attenuated total reflectance/Fourier transform infrared (ART/FT-IR) and Raman microscopy to examine the diffusion rates and redistribution profiles of three different silane adhesion coupling agents into plasticized and unplasticized PVC. Below the glass transition temperature ( Tg) of the polymer, little or no diffusion occurs, and above the Tg (for pure PVC at about 70 °C) the three silanes behave differently, reflecting their different propensities to hydrolysis and subsequent condensation. For plasticized PVC, the fitted diffusion coefficients (obtained via the dual mode model) increase rapidly with increasing (adipate) plasticizer content and decreasing Tg. Correlation of this behavior is with chain “mobility” and not with silane size nor shape. The infrared data for unplasticized PVC laminates were confirmed by using Raman microscopy. Redistribution within the polymer film is shown to be induced by heating to 70 °C. However, the Raman data give a more accurate picture of the silane distribution throughout the film. Although no direct adhesion mechanistic information has been obtained, it has been shown that there are detailed differences in silane diffusion behavior which must be associated with reactivity differences, both within the polymer and at the Si/SiO2/SiOH interface.