bluuebunny/crossref_metadata_2025 huggingface dataset:
Detection of Bacillus Globigii Spores Using a Fourier Transform Infrared–Attenuated Total Reflection Method
Authors: Li He , Tripp Carl P.
Published: October 2009

The use of an alumina-coated ZnSe internal reflection element (IRE) to detect spores by attenuated total reflection infrared spectroscopy (FTIR-ATR) was investigated. Two methods for coating the IRE with alumina are described. It is shown that the adsorption proceeds through an interaction of the carboxylate groups on Bacillus globigii (BG) and positively charged sites on the alumina. The amount adsorbed is highly dependent on solution pH and passes through a maximum value near pH 5, which is dictated by the charge density on the spores and the charge density on the alumina surface. Furthermore, it is shown that lateral–lateral repulsion between the spores limits the maximum adsorbed amount, giving rise to a detection limit of 107 spores per cm2 of the IRE.
Determination of Omega-6 and Omega-3 Fatty Acids in Pork Adipose Tissue with Nondestructive Raman and Fourier Transform Infrared Spectroscopy
Authors: Olsen Elisabeth Fjærvoll , Rukke Elling-Olav , Egelandsdal Bjørg , Isaksson Tomas
Published: October 2009

In order to predict omega-6 and omega-3 fatty acids in the diet of humans, seventy-three pork back fat adipose tissue samples were measured with Raman spectroscopy directly on adipose tissue and on melted fat. Melted fat samples were, in addition, measured with Fourier transform infrared (FT-IR) spectroscopy. Gas chromatography analyses were conducted as the reference analysis. Partial least squares regression (PLSR) was used to calibrate and validate all models predicting omega-3 and omega-6 fatty acids contents from spectra. Omega-6 fatty acids in melted fat measured with FT-IR was predicted with a correlation coefficient ( R) of 0.93 and a root mean square error of cross-validation (RMSECV) of 1.61% of the total amount of fatty acids. Raman spectra measured on melted fat gave a prediction of omega-6 fatty acids with R = 0.97, and RMSECV = 0.99% of total amount of fatty acids. Omega-6 fatty acids were predicted with R = 0.94, and RMSECV = 1.50% of the total amount of fatty acids using Raman spectra recorded on adipose tissue. For omega-3 fatty acids, the highest R = 0.91, and lowest RMSECV = 0.23% of the total amount of fatty acids were obtained from Raman spectra acquired on melted fat. FT-IR and Raman spectroscopy may be used as rapid, nondestructive methods to determine omega-6 and omega-3 fatty acids in melted fat. Raman spectroscopy can also be used directly on adipose tissue.
Accurate and Precise Wavelength Calibration for Wide Bandwidth Array Spectrometers
Authors: Martinsen Paul , Jordan Bob , McGlone Andrew , Gaastra Paul , Laurie Tom
Published: October 2009

Calibrating the wavelength scale of an array spectrometer typically involves measurements of lines at well-known wavelengths from a calibration lamp such as a mercury–argon source. This process is relatively straightforward when the lines are well separated, relative to the bandwidth of the spectrometer. When the spectrometer's bandwidth is large, compared with the distance between calibration wavelengths, it becomes increasingly difficult to accurately locate lines in the calibration spectrum. Even calibrations for instruments with a modest bandwidth of 12 nm can be difficult. Here we present results from a simple approach to improve the accuracy of wavelength calibration for an instrument with a large bandwidth (12 nm, center-to-center pixel spacing 3.3 nm). A monochromator has been used to filter the source so that each calibration line can be measured separately. For ten spectrometers, we were able to achieve accuracy better than 0.12 nm, or 0.09 nm on average; this is less than 3% of the pixel spacing. We anticipate this approach will be useful for improving the accuracy of measurements on array spectrometers and particularly in transferring multivariate calibrations between instruments.
Simulated Radiance Profiles for Automating the Interpretation of Airborne Passive Multi-Spectral Infrared Images
Authors: Sulub Yusuf , Small Gary W.
Published: October 2009

Methodology is developed for simulating the radiance profiles acquired from airborne passive multispectral infrared imaging measurements of ground sources of volatile organic compounds (VOCs). The simulation model allows the superposition of pure-component laboratory spectra of VOCs onto spectral backgrounds that simulate those acquired during field measurements conducted with a downward-looking infrared line scanner mounted on an aircraft flying at an altitude of 2000–3000 ft (approximately 600–900 m). Wavelength selectivity in the line scanner is accomplished through the use of a multichannel Hg:Cd:Te detector with up to 16 integrated optical filters. These filters allow the detection of absorption and emission signatures of VOCs superimposed on the upwelling infrared background radiance within the instrumental field of view (FOV). By combining simulated radiance profiles containing analyte signatures with field-collected background signatures, supervised pattern recognition methods can be employed to train automated classifiers for use in detecting the signatures of VOCs during field measurements. The targeted application for this methodology is the use of the imaging system to detect releases of VOCs during emergency response scenarios. In the work described here, the simulation model is combined with piecewise linear discriminant analysis to build automated classifiers for detecting ethanol and methanol. Field data collected during controlled releases of ethanol, as well as during a methanol release from an industrial facility, are used to evaluate the methodology.
Chemical Imaging with Variable Angles of Incidence Using a Diamond Attenuated Total Reflection Accessory
Authors: Chan K. L. Andrew , Tay Feng H. , Poulter Graham , Kazarian Sergei G.
Published: October 2009

A new development in Fourier transform infrared (FT-IR) imaging using a diamond attenuated total reflection (ATR) imaging accessory in a novel manner that allows the angle of incidence to be varied in order to obtain images from subsurface layers of different thickness is introduced. Chemical images of samples from the same area but with different depths of penetration are obtained by changing the angle of incidence as well as using different spectral bands at different wavenumbers. Changes in the angle of incidence with this accessory were made possible by taking advantage of the relatively large numerical aperture employed by the original imaging optics. This arrangement allowed us to introduce an additional movable aperture in the optical design to restrict the angle of incidence to certain values. Two samples have been studied, one for the calibration of the angle of incidence while the other demonstrates the capability of obtaining three-dimensional (3D) information using this approach. Advantages of this new approach include the relatively high spatial resolution (it can spatially resolve features as small as 12 μm without a microscope) and no change in the imaging area and sampling area during manipulation of the angle of incidence.
Effects of in-Office and at-Home Bleaching on Human Enamel and Dentin: An in vitro Application of Fourier Transform Infrared Study
Authors: Severcan Feride , Gokduman Kurtulus , Dogan Ayca , Bolay Sukran , Gokalp Saadet
Published: October 2009

In-office and at-home bleaching techniques are widely used methods for the whitening of teeth. However, the safety of these techniques has not been clarified yet. The aim of the current study is to investigate the in-office- and at-home-bleaching-induced structural and quantitative changes in human enamel and dentin at the molecular level, under in vitro conditions. The Fourier transform mid-infrared (mid-FT-IR) spectroscopic technique was used to monitor bleaching-induced structural changes. Band frequency and intensity values of major absorptions such as amide A, amide I, phosphate (PO4), and carbonate (CO3−2) bands, for treatment groups and control, were measured and compared. The results revealed that both procedures have negligible effects on dentin constituents. In office-bleached enamel, in addition to demineralization, a decrease in protein and polysaccharide concentrations, mineral-to-protein ratio, and the strength of hydrogen bonds around NH groups, as well as a change in protein secondary structure were observed. The protein structure changed from β-sheet to random coil, which is an indication of protein denaturation. However, no significant variations were observed for at-home bleached enamel. The control, at-home, and in-office bleached enamel samples were differentiated with a high accuracy using cluster analysis based on FT-IR data. This study revealed that office bleaching caused deleterious alterations in the composition and structure of enamel that significantly affected the crystallinity and mineralization of the tissue. Therefore, at-home bleaching seems to be much safer than in-office bleaching in terms of molecular variations.
Tip-Enhanced Raman Spectroscopy and Imaging: An Apical Illumination Geometry
Authors: Schultz Zachary D. , Stranick Stephan J. , Levin Ira W.
Published: October 2009

Results are presented illustrating the use of tip-enhanced Raman spectroscopy (TERS) and imaging in a top-illumination geometry. A radially polarized beam is used to generate an electric field component in the direction of beam propagation, normal to the surface, resulting in a 5× increased enhancement compared to a linearly polarized beam. This multiplicative enhancement facilitates a discrimination of the near-field signal from the far-field Raman background. The top illumination configuration facilitates the application of TERS for investigating molecules on a variety of surfaces, such as Au, glass, and Si. The near-field Raman spectra of Si(100), rhodamine B, brilliant cresyl blue, and single wall carbon nanotubes are presented. Sufficient enhancement is obtained to permit a sub-diffraction-limited resolution Raman imaging of the surface distribution of large bundles of carbon nanotubes of various diameters.
Sensitivity of Raman Spectra to Chemical Functional Groups
Authors: Judge Kevin , Brown Chris W. , Hamel Lutz
Published: October 2009

Spectral features in Raman spectra of organic molecules can be attributed to certain functional groups. A library of 1222 Raman spectra was used to train an artificial neural network (ANN) for predicting the presence of 13 functional groups. Sensitivity analysis was applied to the ANN models to determine a sensitivity factor or feature spectrum for each functional group. The feature spectra could then be used to predict the presence of specific groups based on Bayes' theorem. Once a model is constructed for each functional group, it can be applied directly to measured spectra of structurally unknown molecules and provide real-time predictions. Prediction accuracies of greater than 90% were obtained for aromatic, alkene, aldehyde, ketone, ester, nitro, and nitrile linkages. Accuracies for alcohols and amines were in the 80% range.
Pressure Broadening of H2O Absorption Lines in the 1.3 μm Region Measured by Continuous Wave-Cavity Ring-Down Spectroscopy: Application in the Trace Detection of Water Vapor in N2, SiH4, CF4, and PH3
Authors: Fiadzomor Phyllis A. Y. , Baker Derek M. , Keen Anthony M. , Grant Robert B. , Orr-Ewing Andrew J.
Published: October 2009

A continuous wave cavity ring-down (cw-CRD) spectrometer has been developed for the measurement of trace levels of water vapor by absorption spectroscopy at wavelengths in the vicinity of 1358 nm and 1392 nm. The speed of data acquisition and selectivity make cavity ring-down spectroscopy potentially more useful than current techniques for measurement of trace water in process gases and vacuum environments used for semiconductor manufacture where water vapor contamination has a detrimental effect on the final product. The pressure broadening coefficients (γ) for bath gases N2, air, and Ar and semiconductor process gases SiH4, PH3, and CF4 were determined for a range of absorption lines in the 2 v1 and v1 + v3 bands of H2O. For the transitions investigated, the concentration of water vapor in the sample gas varied from 1.7 × 1012 to 2.9 × 1015 molecule cm−3 in N2 at a total pressure of <10 mbar and was mixed with the bath gas of increasing pressure up to ∼200 mbar. The values of γ quantify the reduction in peak absorption cross-sections with bath gas pressure and, thus, their effects on the detection limit of water vapor. For a CRD spectrometer with a ring-down time of τ = 12.0 μs measured with a precision of 0.6%, detection limits for the measurement of water vapor in 1 atm N2 and of CF4 were estimated to be 18 and 14 ppbv, respectively. Competing absorption by SiH4 and PH3 in the 1.3 μm wavelength region results in respective detection limits for water vapor of 98 and 319 ppbv (relative to 1 atm) in 0.2 atm SiH4 and 0.37 atm PH3.
A Mid-Infrared Flow-Through Sensor for Label-Free Monitoring of Enzyme Inhibition
Authors: Armenta S. , Tomischko W. , Lendl B.
Published: October 2009

Label-free monitoring of acetylcholinesterase (AChE) activity was achieved with a mid-infrared flow-through sensor. The flow-through sensor comprised agarose beads, carrying covalently immobilized AChE, which were placed in a temperature-controlled (37 °C) CaF2 flow cell with an optical path of 60 μm. The sensor was incorporated into a computer-controlled sequential injection (SI) system for automated liquid handling. Different mixtures of enzyme substrate acetylcholine (ACh) and inhibitor (tacrine) were prepared and fed into the flow-through sensor. The flow was stopped as soon as the prepared mixtures reached the sensor. Enzymatic hydrolysis of ACh by AChE was directly monitored as it took place in the flow-through sensor. The inhibition effect of tacrine was calculated from the reaction-induced spectral changes, revealing an important decrease in the activity of AChE, approaching zero when the inhibitor concentration is high enough. The developed mid-infrared flow-through sensor is flexible and can be used to study the inhibitor activity of different target molecules as well as different enzymes.
Correction of Ultraviolet-Induced Fluorescence Spectra for the Examination of Polychromy
Authors: Verri Giovanni , Clementi Catia , Comelli Daniela , Cather Sharon , Piqué Francesca
Published: October 2009

Ultraviolet-induced fluorescence spectroscopy is a commonly used technique for the characterization and identification of painting materials, such as organic binders and colorants. Its interpretation is strictly connected to both the experimental setup and an understanding of the physical and chemical interactions among materials in paint layers, which are commonly composed of a fluorescent organic binder and a pigment. When irradiated with ultraviolet radiation, the light emitted by fluorophores present in the organic binder undergoes several types of interactions, in particular scattering and absorption by neighboring pigmented particles and auto-absorption. As a result of scattering and absorption phenomena, the emission spectrum is deformed according to the physical properties of the surrounding pigmented particles. This can lead to shifts of the emission maxima and/or to the formation of apparent new emission bands. The extent of the modifications to the emission spectra, caused by auto-absorption and selective absorption phenomena, may lead to the erroneous characterization or identification of the fluorescent materials. As a consequence, the interpretation of the emission signal can be greatly compromised. A correction based on the Kubelka–Munk theory is proposed to evaluate the extent of the spectral distortion and is assessed on modern replicas of wall paintings of known composition. Although the model cannot be applied to all cases, qualitative distinctions between real and apparent emissions are achieved.
Changes in the Absorption and Scattering Properties in the Near-Infrared Region during the Growth of Bacillus Subtilis in Liquid Culture
Authors: Dzhongova Elitsa , Harwood Colin R. , Thennadil Suresh N.
Published: October 2009

Multiple scattering of light by cells poses a significant challenge in the development of near-infrared-based methodologies to reliably extract chemical and physical information contained in the spectra collected during the bacterial growth cycle. The extent of information that can be obtained from NIR spectra could, in principle, be vastly improved if the scattering and absorption effects can be effectively separated. This study focuses on the methodology for extracting the bulk optical properties over the course of the bacterial growth cycle and investigates the nature and extent of changes in the optical properties with time. By inverting the radiative transfer equation (RTE) using three measurements, total diffuse reflectance, total diffuse transmittance, and collimated transmittance, the bulk absorption coefficient (μa), the bulk scattering coefficient (μs), and the anisotropy factor ( g) are extracted and their changes during the course of the growth cycle are investigated. In this study, a simple bacterial growth system consisting of Bacillus subtilis growing in an aqueous solution (minimum medium) was investigated. The changes in the optical properties of this system during bacterial growth, stationary, and decline phases were investigated by inverting the measurements using the adding-doubling method to solve the RTE in the wavelength region of 950–1850 nm. This study shows that during growth in liquid culture, the absorption and scattering property changes can be consistently extracted from measurements under multiple light scattering conditions. The estimation of the anisotropy factor was not reliable beyond 1200 nm at low bacterial cell counts, but reliability increased with increasing biomass concentration. At all stages in the growth cycle, the anisotropy factor could not be reliably extracted in the first overtone region. However, this does not appear to adversely affect the estimation of the absorption and scattering coefficients.
Bandpass Effects in Time-Resolved Diffuse Spectroscopy
Authors: Farina A. , Bassi A. , Pifferi A. , Taroni P. , Comelli D. , Spinelli L. , Cubeddu R.
Published: October 2009

This paper discusses the spectral distortions occurring when time-resolved spectroscopy of diffusive media is performed illuminating with a wide bandpass. It is shown that the spectral region within the bandpass that exhibits the lowest absorption will dominate the resulting time-resolved curve, leading to significant underestimations of absorption as well as distortions in the spectral shape (including shifts in peak positions). Due to the nonlinear behavior of absorption, this effect becomes even more pronounced when including longer and longer photon path lengths. First, a theoretical treatment of the problem is given, and then the distortion is described by time-resolved reflectance simulations and experimental measurements of lipid and water samples. A spectrally constrained data analysis is proposed that takes into account the spectrum of the light injected into the sample, used to overcome the distortion and improve the accuracy of the estimation of chromophore concentrations from absorption spectra. Measurements on a lipid sample show a reduction of the error from 30% to 6%.
Characterization of Carbon Dioxide Mobile Phase Density Profiles in Packed Capillary Columns by Raman Microscopy
Authors: Baker L. Robert , Orton Andrew W. , Goates Steven R. , Horn Brent A.
Published: October 2009

Efforts to understand and optimize separations employing compressible mobile phases have been limited by a lack of understanding of the mobile phase density gradient. Mobile phase compressibility leads to gradients in linear velocity and solute retention and affects separation speed and efficiency, especially in packed columns. Gas chromatography (GC), supercritical fluid chromatography (SFC), and solvating gas chromatography (SGC) each rely on compressible mobile phases. This work describes the on-column density measurement of carbon dioxide, a common carrier fluid for SFC and SGC, in packed capillary columns using Raman microspectroscopy of the position of the Fermi doublet. Correlation of the spectrum with density was calibrated over a pressure range of 15 to 290 atm at 125 and 150 °C, which then allowed for determination of the density gradient of fluid flowing through a packed capillary column. The results of this work will be used to model the flow behavior of compressible fluids to understand the effects of mobile phase compressibility on separation speed and efficiency.
Spectroscopic Imaging for Detection and Discrimination of Different E. Coli Strains
Authors: Gilbert Michael K. , Frick Caleb , Wodowski Andrew , Vogt Frank
Published: October 2009

Food contaminations with E. coli bacteria are a major concern for public health. Current techniques for detection are based on sample extractions, time-consuming sample preparations, and labor intensive analyses. Because some strains can be toxic at a level of tens of bacteria and some are not harmful at all, a method of colony localization and strain classification must be developed. In this study we present first results that are based on Fourier transform infrared (FT-IR) spectroscopy and FT-IR imaging. Due to the chemical similarity of different E. coli strains, the acquired spectra show a strong resemblance. It is demonstrated here that based on a correlation analysis samples of the same strain are classified as such and that different strains can be discriminated. The next step is to move from single-spot analyses towards spectroscopic imaging—a technique that facilitates detection of localized bacteria colonies. However, the sheer amount of data acquired in short periods of time prevents many chemical imaging techniques from being feasible for online sensing or for screening extended areas. To improve the time resolution, a data compression approach based on three-dimensional wavelet compression has been applied. It is shown that even with slight compression computation times can be cut down by over an order of magnitude while preserving enough information for localization and classification.
Quantification of Trace Metalloids and Metals in Airborne Particles Applying Dynamic Reaction Cell Inductively Coupled Plasma Mass Spectrometry
Authors: Lamaison L. , Alleman L. Y. , Robache A. , Galloo J.-C.
Published: October 2009

Determination of trace contents of metals and metalloids, monitored in airborne particles for their adverse health and environmental impact or to discriminate pollutant particulate emission sources, requires very sensitive analytical methods. Dynamic reaction cell inductively coupled plasma mass spectrometry (DRC-ICP-MS) has been applied to measure ultra-trace elements found in PM10 atmospheric particles in order to determine simultaneously, rapid and accurate concentrations for well known highly interfered isotopes (75As, 59Co, 52Cr, 53Cr, 58Ni, 60Ni, 78Se, 45Sc, and 51V). The challenge resides in the extremely low content of these elements encountered in PM10 particles, while thorough mineralization procedures in complex matrices are necessary to deal with refractory minerals. The potentially interfering polyatomic ions combining Ar, Cl, F, O, N, and C isotopes were significantly reduced by using NH3 as the reaction gas in the DRC, optimizing the reaction cell band pass and tuning of the gas flow rate. Standard Reference Material (NIST 1648) as well as real atmospheric samples were analyzed under the best defined conditions to validate and exemplify our methodology. The method detection limits are 450 ng/L for As, 13 ng/L for Co, 1210 ng/L for Cr, 780 ng/L for Ni, 47 ng/L for Se, 22 ng/L for Sc, and 26 ng/L for V. Based on real atmospheric sample measurements, DRC-ICP-MS associated with NH3 is confirmed as a cost effective technique to produce accurate results during routine working procedures for all these elements except Se.
Infrared Surface Analysis Using a Newly Developed Thin-Sample Preparation System
Authors: Nagai Naoto , Nishiyama Itsuo , Kishima Yoshio , Iida Katsuhiko , Mori Koichi
Published: October 2009

We developed a new sampling system, the Nano Catcher, for measuring the surface chemical structure of polymers or industrial products and we evaluated the performance of the system. The system can directly pick up surface species whose depth is on the order of ∼100 nm and can easily provide a sample for a Fourier transform infrared (FT-IR) system without the necessity of passing it over to a measurement plate. The FT-IR reflection data obtained from the Nano Catcher were compared with those obtained using the attenuated total reflection (ATR) method and sampling by hand. Chemical structural analysis of a depth region from a few tens of nanometers to a few hundred nanometers can be directly performed using this system. Such depths are beyond the scope of conventional X-ray photoelectron spectroscopy (XPS) and ATR methods. We can expect the use of the Nano Catcher system to lead to a great improvement in the detection of signals of surface species in these depth regions.
Modeling of Temperature-Induced Near-Infrared and Low-Field Time-Domain Nuclear Magnetic Resonance Spectral Variation: Chemometric Prediction of Limonene and Water Content in Spray-Dried Delivery Systems
Authors: Letíci Andrade , Farhat Imad A. , Aeberhardt Kasia , Bro Rasmus , Engelsen Søren Balling
Published: October 2009

The influence of temperature on near-infrared (NIR) and nuclear magnetic resonance (NMR) spectroscopy complicates the industrial applications of both spectroscopic methods. The focus of this study is to analyze and model the effect of temperature variation on NIR spectra and NMR relaxation data. Different multivariate methods were tested for constructing robust prediction models based on NIR and NMR data acquired at various temperatures. Data were acquired on model spray-dried limonene systems at five temperatures in the range from 20 °C to 60 °C and partial least squares (PLS) regression models were computed for limonene and water predictions. The predictive ability of the models computed on the NIR spectra (acquired at various temperatures) improved significantly when data were preprocessed using extended inverted signal correction (EISC). The average PLS regression prediction error was reduced to 0.2%, corresponding to 1.9% and 3.4% of the full range of limonene and water reference values, respectively. The removal of variation induced by temperature prior to calibration, by direct orthogonalization (DO), slightly enhanced the predictive ability of the models based on NMR data. Bilinear PLS models, with implicit inclusion of the temperature, enabled limonene and water predictions by NMR with an error of 0.3% (corresponding to 2.8% and 7.0% of the full range of limonene and water). For NMR, and in contrast to the NIR results, modeling the data using multi-way N-PLS improved the models' performance. N-PLS models, in which temperature was included as an extra variable, enabled more accurate prediction, especially for limonene (prediction error was reduced to 0.2%). Overall, this study proved that it is possible to develop models for limonene and water content prediction based on NIR and NMR data, independent of the measurement temperature.
Optical Interference Effects in the Design of Substrates for Surface-Enhanced Raman Spectroscopy
Authors: Shoute Lian C. T. , Bergren Adam Johan , Mahmoud Amr M. , Harris Ken D. , McCreery Richard L.
Published: October 2009

This paper presents results showing that the design of substrates used for surface-enhanced Raman spectroscopy (SERS) can impact the apparent enhancement factors (EFs) obtained due to optical interference effects that are distinct from SERS, providing additional enhancement of the Raman intensity. Thus, a combination of SERS and a substrate designed to maximize interference-based enhancement is demonstrated to give additional Raman intensity above that observed for SERS alone. The system explored is 4-nitroazobenzene (NAB) and biphenyl (BP) chemisorbed on a nanostructured silver film obtained by vacuum deposition of Ag on thermally oxidized silicon wafers. The enhancing silver layer is partially transparent, enabling a standing wave to form as a result of the combination of the incident light and light reflected from the underlying Si substrate (i.e., light that passes through the Ag and the intervening dielectric layer of SiOx). The Raman intensity is measured as a function of the thickness of the thermal oxide layer in the range from ∼150 to ∼400 nm, and despite a lack of morphological variation in the silver films, there is a strong dependence of the Raman intensity on the oxide thickness. The Raman signal for the optimal SiOx interlayer thickness is 38 times higher than the intensity obtained when the Ag particles are deposited directly onto Si (with native oxide). To account for the trends observed in the Raman intensity versus thickness data, calculations of the relative mean square electric field (MSEF) at the surface of the SiOx are carried out. These calculations are also used to further optimize the experimental setup.
Cotton Fiber Quality Characterization with Light Scattering and Fourier Transform Infrared Techniques
Authors: Thomasson J. A. , Manickavasagam S. , Mengüç M. P.
Published: October 2009

Fiber quality measurement is critical to assessing the value of a bale of cotton for various textile purposes. An instrument that could measure numerous cotton quality properties by optical means could be made simpler and faster than current fiber quality measurement instruments, and it might be more amenable to on-line measurement at processing facilities. To that end, a laser system was used to investigate cotton fiber samples with respect to electromagnetic scattering at various wavelengths, polarization angles, and scattering angles. A Fourier transform infrared (FT-IR) instrument was also used to investigate the transmission of electromagnetic energy at various mid-infrared wavelengths. Cotton samples were selected to represent a wide range of micronaire values. Varying the wavelength of the laser at a fixed polarization resulted in little variation in scattered light among the cotton samples. However, varying the polarization at a fixed wavelength produced notable variation, indicating that polarization might be used to differentiate among cotton samples with respect to certain fiber properties. The FT-IR data in the 12 to 22 μm range produced relatively large differences in the amount of scattered light among all samples, and FT-IR data at certain combinations of fixed wavelengths were highly linearly related to certain measures of cotton quality including micronaire.
Preliminary Investigations into Macroscopic Attenuated Total Reflection—Fourier Transform Infrared Imaging of Intact Spherical Domains: Spatial Resolution and Image Distortion
Authors: Everall Neil J. , Priestnall Ian M. , Clarke Fiona , Jayes Linda , Poulter Graham , Coombs David , George Michael W.
Published: October 2009

This paper describes preliminary investigations into the spatial resolution of macro attenuated total reflection (ATR) Fourier transform infrared (FT-IR) imaging and the distortions that arise when imaging intact, convex domains, using spheres as an extreme example. The competing effects of shallow evanescent wave penetration and blurring due to finite spatial resolution meant that spheres within the range 20–140 μm all appeared to be approximately the same size (∼30–35 μm) when imaged with a numerical aperture (NA) of ∼0.2. A very simple model was developed that predicted this extreme insensitivity to particle size. On the basis of these studies, it is anticipated that ATR imaging at this NA will be insensitive to the size of intact highly convex objects. A higher numerical aperture device should give a better estimate of the size of small spheres, owing to superior spatial resolution, but large spheres should still appear undersized due to the shallow sampling depth. An estimate of the point spread function (PSF) was required in order to develop and apply the model. The PSF was measured by imaging a sharp interface; assuming an Airy profile, the PSF width (distance from central maximum to first minimum) was estimated to be ∼20 and 30 μm for IR bands at 1600 and 1000 cm−1, respectively. This work has two significant limitations. First, underestimation of domain size only arises when imaging intact convex objects; if surfaces are prepared that randomly and representatively section through domains, the images can be analyzed to calculate parameters such as domain size, area, and volume. Second, the model ignores reflection and refraction and assumes weak absorption; hence, the predicted intensity profiles are not expected to be accurate; they merely give a rough estimate of the apparent sphere size. Much further work is required to place the field of quantitative ATR-FT-IR imaging on a sound basis.
The Use of Ultraviolet Resonance Raman Spectroscopy in the Analysis of Ionizing-Radiation-Induced Damage in DNA
Authors: Shaw C. P. , Jirasek A.
Published: October 2009

Ultraviolet resonance Raman spectroscopy (UVRRS) was used to determine damage done in both calf-thymus DNA (CT-DNA) and a short stranded DNA oligomer (SS-DNA) due to ionizing radiation from a medical 60Co radiation therapy unit used in the treatment of cancer. Spectra were acquired at incident UV wavelengths of 248, 257, and 264 nm in order to utilize the differences in UVRR cross-sections of the bases with wavelength. Through the analysis of difference spectra between irradiated and unirradiated DNA at each of the incident UV wavelengths, damage to CT- and SS-DNA was observed and identified. Significant radiation-induced increases in the difference spectra of the CT-DNA indicated disruption of the stable, stacked structure of its bases, as well as the disruption of Watson–Crick hydrogen bonds between the base pairs. Base unstacking was not as evident in the SS-DNA, while radiation-induced spectral decreases suggest disruption of the structure of the nucleotides. As demonstrated, UVRRS has the ability to highlight contributions from specific moieties with the use of varying incident UV wavelengths, thus enhancing the already information-rich content of the Raman spectra.
Laser-Induced Breakdown Spectroscopy for In-Cylinder Equivalence Ratio Measurements in Laser-Ignited Natural Gas Engines
Authors: Joshi Sachin , Olsen Daniel B. , Dumitrescu Cosmin , Puzinauskas Paulius V. , Yalin Azer P.
Published: October 2009

In this contribution we present the first demonstration of simultaneous use of laser sparks for engine ignition and laser-induced breakdown spectroscopy (LIBS) measurements of in-cylinder equivalence ratios. A 1064 nm neodynium yttrium aluminum garnet (Nd:YAG) laser beam is used with an optical spark plug to ignite a single cylinder natural gas engine. The optical emission from the combustion initiating laser spark is collected through the optical spark plug and cycle-by-cycle spectra are analyzed for Hα (656 nm), O (777 nm), and N (742 nm, 744 nm, and 746 nm) neutral atomic lines. The line area ratios of Hα/O777, Hα/N746, and Hα/Ntot (where Ntot is the sum of areas of the aforementioned N lines) are correlated with equivalence ratios measured by a wide band universal exhaust gas oxygen (UEGO) sensor. Experiments are performed for input laser energy levels of 21 mJ and 26 mJ, compression ratios of 9 and 11, and equivalence ratios between 0.6 and 0.95. The results show a linear correlation ( R2 > 0.99) of line intensity ratio with equivalence ratio, thereby suggesting an engine diagnostic method for cylinder resolved equivalence ratio measurements.
High-Throughput Spectroscopic Imaging Applied to Permeation through the Skin
Authors: Andanson Jean-Michel , Chan K. L. Andrew , Kazarian Sergei G.
Published: October 2009

Infrared (IR) spectroscopy has been successfully applied to study the permeation of substances through human skin in a high-throughput manner. The sample of skin was placed on the measuring surface of an attenuated total reflection (ATR) crystal and was divided into several areas. These areas were separated using a specially designed grid created on the surface of the skin and each area was subjected to a different combination of permeant and enhancer. ATR Fourier transform infrared (FT-IR) imaging was applied to measure the permeation of 12 liquid samples through a piece of skin smaller than 5 cm2. This work demonstrated that, using the ATR-FT-IR imaging method, it is possible to measure and directly compare the transdermal processes of several permeants under identical conditions.
Chemical Fingerprinting of Ready-Mixed House Paints of Relevance to Artistic Production in the First Half of the Twentieth Century. Part I: Inorganic and Organic Pigments
Authors: Gautier Gwénaëlle , Bezur Anikó , Muir Kimberley , Casadio Francesca , Fiedler Inge
Published: October 2009

This study reports the multi-analytical investigation of ready-mixed house paints used by artists such as Pablo Picasso (1881–1973) in the first half of the twentieth century. The pigment composition of paint swatches on four historic paint sample cards from the Art Institute of Chicago reference collection was characterized by thorough screening using Fourier transform infrared (FT-IR) and X-ray fluorescence (XRF) spectroscopies, followed by Raman spectroscopy when necessary. Spectroscopic investigations highlighted the dominance of zinc-based whites, the consistent choice of particular pigments or their mixtures, as well as the avoidance of others to achieve the various hues on the sample cards. Notable findings included the documentation of strong spectroscopic signatures of metal soaps. Given the similarities in composition of early twentieth century artists' and house paints, the results indicate that the identification of house paints in works by Pablo Picasso and others must be based on a combination of parameters rather than the detection of a single chemical marker. Results have been applied to the case study of Picasso's 1935 sculpture Figure (AIC 1988.428), which incorporates direct evidence of the use of house paint by the artist.
Spectroscopic Investigations of Bourdichon Miniatures: Masterpieces of Light and Color
Authors: Burgio Lucia , Clark Robin J. H. , Hark Richard R. , Rumsey Mike S. , Zannini Carlotta
Published: October 2009

Metallic bismuth, pyrite (FeS2), and specular hematite (Fe2O3) were found to have been used extensively on two miniatures taken from the Book of Hours of Louis XII by Jean Bourdichon, painter at the Royal Court of France between the end of the 15th and the beginning of the 16th centuries. These unusual materials were identified, together with thirteen other more traditional pigments and dyes, by Raman microscopy and X-ray fluorescence. Pyrite was found in many areas, suggesting that it may have been deliberately added as a pigment. The luminary quality of both miniatures was enhanced by the extensive use of shell gold throughout, but other less common materials such as specular hematite and mosaic gold were also utilized. Metallic bismuth was used, alone or in admixture with other pigments, to create a soft gray color. Its identification as a paint material was complemented by the study of the optical and visual properties of standard samples of metallic bismuth and several bismuth compounds. Evidence for the use of a bismuth pencil was also found.
Surface-Enhanced Raman Scattering of Rat Tissues
Authors: Aydin Ömer , Kahraman Mehmet , Kiliç Ertuğrul , Çulha Mustafa
Published: October 2009

Surface-enhanced Raman scattering (SERS) is proven to be a powerful tool for investigation of biological structures. In this study, tissues obtained from different rat organs are examined using SERS. The tissue samples are crushed with a pestle after sudden freezing in liquid nitrogen and mixed with a concentrated colloidal silver nanoparticle suspension. The reproducibility of SERS spectra acquired from several tissue samples from different organs is demonstrated. The collected spectra are comparatively evaluated based on the physiological function of the organ from which the tissue is obtained. The spectra from the tissues show significant differences and indicate that they can be used for tissue characterization and differentiation. The identification of the origins of the bands on the spectra is also attempted. This study suggests that SERS can be used to monitor the changes at the molecular level during metabolic changes in an organ or tissue as a result of a disease or another cause.
Rapid Classification of Simulated Street Drug Mixtures Using Raman Spectroscopy and Principal Component Analysis
Authors: Noonan Kathryn Y. , Tonge Lindsey A. , Fenton Owen S. , Damiano David B. , Frederick Kimberley A.
Published: October 2009

The ability to accurately and noninvasively analyze illicit drugs is important for criminal investigations and prosecution. Current methods involve significant sample pretreatment and most are destructive. The goal of this work is to develop a method based on Raman spectroscopy to classify simulated street drug mixtures composed of one drug component and up to three cutting agents including those routinely found in confiscated illicit street drug mixtures. Spectra were collected on both a homebuilt instrument using a HeNe laser and on a handheld commercial instrument with a 785 nm light source. Mixtures were prepared with drug concentrations ranging from 10 to 100 percent. Optimal preprocessing for the data set included truncating, Savitzky–Golay smoothing, normalization, differentiating, and mean centering. Using principal component analysis (PCA), it was possible to resolve the spectral differences between benzocaine, lidocaine, isoxsuprine, and norephedrine and correctly classify them 100 percent of the time.
Arsenic Speciation in Biological Samples Using XAS and Mixed Oxidation State Calibration Standards of Inorganic Arsenic
Authors: Parsons J. G. , Lopez M. L. , Castillo-Michel H. , Peralta-Videa J. R. , Gardea-Torresdey J. L.
Published: October 2009

The speciation of elements without pre-edge features preformed with X-ray absorption near edge structure (XANES) can lead to problems when the energy difference between two species is small. The speciation of arsenic (As) in plant samples was investigated using the mixtures As2S3/As2O5, As2S3/As2O3, or As2O3/As2O5. The data showed that the energy separation (eV) between As2O5 and As2S3 was 5.8, between As2O3 and As2O5 was 3.6, and between As2S3 and As2O3 was 2.1. From the intensity of the white-line feature and the concentration of As species, calibration curves showing a limit of detection of approximately 10% were generated. In addition, an error of ±10% was determined for the linear combination–XANES (LC-XANES) fitting technique. The difference between the LC-XANES fittings and calculations from the calibration curves was <10%. The data also showed that the speciation of As in a sample can be determined using EXAFS (extended X-ray absorption fine structure). Finally, it was also shown that both EXAFS and XANES of the sample should be examined to determine the true speciation of an element. Even though there is a difference of 2 eV between As(III) bound to O and As(III) bound to S, in the EXAFS region the As(III)–S and As(III)–O ligands are clearly visible. However, distinction between the As(III)–O and As(V)–O ligands in the EXAFS spectra was not clearly visible in this study.
Study on the Crystalline Structure Transition of Syndiotactic Polystyrene Film during Heat Treatment by Two-Dimensional Infrared Correlation Spectroscopy
Authors: Li Weizhen , Wu Peiyi
Published: October 2009

The crystal structure transition of syndiotactic polystyrene film from the helical conformation to the more stable planar zigzag conformation during a heating process was studied using Fourier transform infrared (FT-IR) spectroscopy in combination with two-dimensional (2D) correlation analysis and perturbation-correlation moving-window 2D analysis. The sequence of different conformations during the transition was investigated by analyzing two-dimensional FT-IR correlation spectra in the spectral ranges of 800–700 cm− and 600–500 cm−1. It was observed that the conformation of δ helical changes prior to γ helical, and the γ helical phase is faster than the α' planar zigzag phase. By utilizing the 2D asynchronous correlation spectra, the 744 cm−1 band, which is usually incorporated in the broad 750 cm−1 band, can now be uniquely attributed as the α' zigzag configuration for the first time. Furthermore, by employing thermal perturbation, the shorter helical segments consisting of m = 7–12 and m = 12–20 monomeric units were disturbed in a shorter time than the longer helical segments m = 20–30 during the heating process.
Quantitative Classification of Two-Dimensional Correlation Spectra
Authors: Chen Jianbo , Zhou Qun , Noda Isao , Sun Suqin
Published: October 2009

Two-dimensional (2D) correlation spectroscopy, which takes advantage of the apparent enhancement of spectral resolution, is known to be useful in qualitative discrimination of seemingly similar samples. The possibility of quantitative classification of 2D correlation spectra is even more desirable. Two useful parameters, namely Euclidian distance and correlation coefficient between 2D correlation spectra, are introduced for this purpose. Dry and sweet red wine samples are used to demonstrate the utility of these parameters. The distances between the 2D infrared (IR) spectra of sweet and dry red wines are roughly proportional to the differences of sugar contents in them. The result shows that the two parameters are useful measures for the quantitative evaluation of the similarity among the samples and their corresponding 2D correlation spectra.
Quantitative Surface-Enhanced Raman Spectroscopy Based Analysis of MicroRNA Mixtures
Authors: Driskell Jeremy D. , Primera-Pedrozo Oliva M. , Dluhy Richard A. , Zhao Yiping , Tripp Ralph A.
Published: October 2009

We have developed a rapid, sensitive, and quantitative method for identification of microRNA (miRNA) sequences in multicomponent mixtures using surface-enhanced Raman spectroscopy (SERS). The method uses Ag nanorod array substrates prepared by oblique angle vapor deposition as the SERS platform. We show that Ag nanorod-based SERS spectra are uniquely characteristic for each miRNA sequence studied, and that the spectral reproducibility is sufficient for quantitative analysis of miRNA profiles in multicomponent mixtures using partial least squares (PLS) regression analysis. This method was applied to individual sample mixtures consisting of two, three, and five miRNAs. Separate PLS models were generated for the two-, three-, and five-component mixtures from >150 calibration spectra covering a concentration range of 6 to 150 μM for each miRNA. The PLS models were externally validated with independent test samples resulting in root mean square errors of prediction (RMSEP) of 7.4, <7.4, and <10 μM for the two-, three-, and five-component models, respectively. These results demonstrate the applicability of SERS for quantitative detection and profiling of miRNAs and suggest that SERS may prove to be a novel, label-free method for identification of disease biomarkers.
Recovering Independent Components from Shifted Data Using Fast Independent Component Analysis and Swarm Intelligence
Authors: Rascon Caleb , Lennox Barry , Marjanovic Ognjen
Published: October 2009

Frequency displacement, or spectral shift, is commonly observed in industrial spectral measurements. It can be caused by many factors such as sensor de-calibration or by external influences, which include changes in temperature. The presence of frequency displacement in spectral measurements can cause difficulties when statistical techniques, such as independent component analysis (ICA), are used to analyze it. Using simulated spectral measurements, this paper initially highlights the effect that frequency displacement has on ICA. A post-processing technique, employing particle swarm optimization (PSO), is then proposed that enables ICA to become robust to frequency displacement in spectral measurements. The capabilities of the proposed approach are illustrated using several simulated examples and using tablet data from a pharmaceutical application.