bluuebunny/crossref_metadata_2025 huggingface dataset:
Body-Site Variation of Skin Autofluorescence
Authors: Davies Mark A. , Hogan Michael P.
Published: October 2003

The body-site variation of skin autofluorescence was monitored in vivo in order to characterize individual contributions to the overall signal. Body sites having a range of chronic solar exposure were selected. The site-to-site spectral data sets were acquired from thirteen subjects. Incident light of 325-nm wavelength was used to excite fluorescence, observed between 360 nm and 570 nm. Principal factor analysis coupled with alternating least-squares optimization of within-subject body-site dependence revealed that two factors accounted for all of the body-site spectral variability. The factors were virtually the same for all subjects. The spectra were interpreted in terms of collagen cross-links and NADH. The body-site variation of component scores (relative concentrations) exhibited a consistent pattern between subjects. The factor assigned to collagen had highest scores at protected body sites; in contrast, NADH had highest scores at more exposed sites.
Single and Double Infrared Transitions in Rapid-Vapor-Deposited Parahydrogen Solids: Application to Sample Thickness Determination and Quantitative Infrared Absorption Spectroscopy
Authors: Tam Simon , Fajardo Mario E.
Published: October 2003

We present a convenient method for determining the thickness of a cryogenic parahydrogen (pH2) solid from its infrared (IR) absorption spectrum. Millimeters-thick pH2 solids of exceptional optical clarity can be produced by the rapid vapor deposition method [M.E. Fajardo and S. Tam, J. Chem. Phys. 108, 4237 (1998)]. Doping of these pH2 solids is readily accomplished by co-deposition of the desired impurities, making them excellent hosts for high-resolution matrix isolation spectroscopy. The intensities of the IR “double” transitions Q1(0) + S0(0) and S1(0) + S0(0) of the pH2 host are insensitive to the matrix microstructure and to the presence of dopants, so these absorptions are especially well suited for thickness determinations. We calibrate the integrated absorption intensities of these two bands against the sample thicknesses determined from transmission interference fringes appearing in the same experimental spectra; we report: α˜[Q1(0) + S0(0)] = 4.84(±0.18) × 10−14 cm3/s, and α˜[S1(0) S0(0)] = 0.35(±0.02) × 10−14 cm3/s (95% confidence). We also discuss several other advantages of rapid-vapor-deposited pH2 solids as hosts for quantitative IR absorption spectroscopy of dopant species.
Temperature Corrections for Ion Mobility Spectrometry
Authors: Tabrizchi Mahmoud
Published: October 2003

The displacements of 30 peaks of eight chemicals over a wide range of temperatures, from 30 to 250 °C, with 20 °C increments, were studied. Experimental results show that the separations remain fairly constant and ion mobility spectra can be corrected by shifting all drift times by Δ td (Δ T/T)[ a + b(Δ T/T)] where T is the absolute temperature and a and b are constants which depend on pressure and the instrumental parameters. Also, by using the reactant ion peak as an internal standard, a factor of k = ( t – tR)/ tR, has been defined, where t is the drift time, tR is the reactant ion drift time, and k is called the adjusted drift time. This factor is independent of instrumental parameters and increases linearly with temperature as: k = α( T1/2 − 11.88). It can be normalized to a standard temperature of 298 K to give k298 = 5.3827 kT/( T1/2 − 11.88). The k298 values were determined for the 30 peaks over a temperature range of 30–250 °C. These values show less sensitivity to temperature than their corresponding reduced mobilities. By transforming the entire drift time to the reduced adjusted drift time, k298, the peak shifts were corrected for all spectra recorded at temperatures (30–250 °C) such that the spectra superimposed.
Confocal Raman Depth Profiling of Surface-Modified Polymer Films: Effects of Sample Refractive Index
Authors: Reinecke Helmut , Spells Stephen J. , Sacristán Javier , Yarwood Jack , Mijangos Carmen
Published: October 2003

A solution-cast poly(vinyl chloride) (PVC) film of thickness 81 μm was modified with aminothiophenol using surface-selective reaction conditions. After the identification of suitable Raman bands characteristic of the modifier (1596 cm−1) and the polymer (1425 cm−1), confocal Raman measurements demonstrated a depth variation of the modifier peak intensity which was consistent with a highly surface-selective reaction. Data also showed features clearly attributable to refractive index effects, principally the lack of symmetry in the modifier depth profile obtained from the raw data and an underestimated film thickness. The film was cross sectioned under liquid nitrogen to allow conventional lateral Raman measurements across its thickness. The depth profile obtained directly in this way was in good agreement with confocal data after normalization using the polymer peak intensity and an expansion of the thickness scale to the value obtained independently with a micrometer. The nondestructive confocal method has clear advantages in analyzing small samples or where spatial mapping is also required. To simulate the effect of sample refractive index, the directly measured cross-sectional depth profile was used to calculate the confocal depth profile, using the method of analysis developed by Everall.1,2 The general features of the profile were reproduced, assuming a “fill factor” for the 100× microscope objective of 0.63. However, a broadening of features was apparent in the simulated profile. This suggests that direct conventional Raman measurements of a sectioned film may provide a more sensible approach for the detection of interfaces in polymer films.
Electrospray-Ionization Time-of-Flight Mass Spectrometry: pH-Dependence of Phosphomolybdate Species
Authors: Easterly C. Elliott , Hercules David M. , Houalla Marwan
Published: October 2003

Electrospray ionization (ESI) time-of-flight mass spectrometry has been used to investigate the pH-dependence of phosphomolybdates in solution from pH = 1.7 to 10.2. Mass spectra are reported for the first time for H2Na2P2Mo5O232–, PMo9O313–, PMo10O343–, and PMo11O373–. The pH dependence of phosphomolybdate species as measured by electrospray is compared with measurements reported for combined potentiometry—31P NMR. The pH ranges of most species are similar (±1 pH unit) when measured by these two methods, although some differences are observed. Protonation and solvation of phosphomolybdate species measured by ESI differ from those observed by 31P NMR. However, the core phosphomolybdate species are measured correctly by ESI.
Analysis of Ferromanganese and Ferromanganese Slag by Means of Inductively Coupled Plasma Optical Emission Spectrometry
Authors: Potgieter Izak M.
Published: October 2003

A new inductively coupled plasma optical emission spectrometry (ICP-OES) procedure has been developed for the simultaneous determination of major and minor elements in ferromanganese and ferromanganese slag as well as feed materials (fine ferromanganese and ferromanganese dust) for a ferromanganese smelter. The samples are dissolved by fusion with a mixture of sodium peroxide and sodium carbonate, followed by leaching of the melt with hydrochloric acid. In this way all elements are brought quantitatively into solution. The calibration solutions were prepared similarly from appropriate certified reference materials, and the calibration graphs were verified by means of ferromanganese and manganese ore certified reference materials.
Picosecond Time-Resolved Raman Spectroscopy of Solids: Capabilities and Limitations for Fluorescence Rejection and the Influence of Diffuse Reflectance
Authors: Everall Neil , Hahn Thomas , Matousek Pavel , Parker Anthony W. , Towrie Michael
Published: October 2003

It has been known for many years that it should be possible to discriminate between Raman and fluorescence phenomena on the basis of their differing temporal responses. However, it is only relatively recently that optical technology has advanced sufficiently to achieve the necessary combination of high repetition rate and picosecond laser pulses, coupled with “gateable” multichannel detectors with matched repetition rates and short on-times. Both electronic and optical gating technologies have been shown to significantly improve the Raman spectra of highly fluorescent solutions. However, the performance of such systems with solid materials has not been reported in detail. To partially redress this imbalance, this article describes the ps-time-resolved Raman spectroscopy of solid films and powders. Excellent temporal resolution and fluorescence rejection was obtained with homogeneous films, but with powders, multiple scattering has the potential to significantly blur the time resolution. For example, after incidence of a 1-ps pulse on a powdered sample of trans-stilbene, the Rayleigh signal was spread over 100 ps in time and the Raman signal persisted for more than 300 ps. Simple models are presented that predict these temporal responses on the assumption that photons randomly “diffuse” through the powder, scattering at particle boundaries and sometimes reemerging to be detected at a later time. These dynamics imply that fluorescence rejection with bulk powders might be less effective than with homogeneous solids as the broadened Raman signal would be incompletely captured within the short detector “on” period. The fluorescence would be rejected, but so would the Raman signal (to some extent), giving a poor signal-to-noise ratio. This long-term signal persistence could also complicate the interpretation of pump-probe spectroscopy studies. However, further work is needed to assess the practical implications of these findings.
Fiber-Optic Quantum Counter Probe for Incident Excitation Energy Correction in Fluorescence Measurements
Authors: Hart Sean J. , Jones Patrick J.
Published: October 2003

Excitation-power correction of fluorescence spectra is essential for meaningful interpretation of analytical data. In particular, fluorescence measurements obtained using optical fibers require special consideration due to the possibility of variations in the light intensity delivered to the sample or the incident excitation energy. A quantum counting fiber-optic probe has been developed to simultaneously and independently collect fluorescence spectra of both analytes and a quantum counter. The probe consists of excitation and emission fibers angled to maximize distal cone overlap and a third fiber positioned at a greater angle to allow excitation of rhodamine B, which is affixed to its distal end with a polymer. The fluorescence of the quantum counter affixed to the fiber was linear with incident 266 nm excitation energy over the measured range 1.2 × 1014 photons per exposure to 1.2 × 1015 photons per exposure at 266 nm. The corrected fluorescence signals were immune to adverse condition experiments such as laser power reduction and launch fiber–laser beam misalignment, while the uncorrected signals suffered greatly. The concentration calibration generated using the fiberoptic quantum counter method showed an improvement in the correlation coefficient, r2 = 0.950, compared with the calibration generated using uncorrected data, r2 = 0.906. Different types of adverse conditions were tested including power attenuation, power increase, and fiber launch misalignment; the prediction errors were between −87% and 366% for the uncorrected data compared with prediction errors between −9% and 15% when using the fiber-optic quantum counter method.
Identification of Synthetic Resins Used in Works of Art by Fourier Transform Infrared Spectroscopy
Authors: Doménech-Carbó M. T. , Doménech-Carbó A. , Gimeno-Adelantado J. V. , Bosch-Reig F.
Published: October 2003

Differentiation between the synthetic polymers used in former restorations of works of art and the original materials used by the artist is of great interest; such differentiation is needed to establish an adequate process of restoration for the work of art. A specific method of sample preparation based on a filtration and deposition-evaporation sequence is proposed, which permits the separation and preconcentration of the synthetic polymer that is being analyzed and avoids problems arising from the simultaneous interpretation of IR spectra obtained from complex mixtures of organic and inorganic compounds present in small artistic samples. In addition to the identification of characteristic IR absorption bands, quantitative diagnostic criteria based on two-dimensional diagrams of relative intensity of selected peaks have been developed. Standards of acrylic, alkyd, cellulose nitrate, epoxy, ketone, poly(vinyl acetate), polyurethane, silicone synthetic polymers and semi-synthetic wax used as binding media, adhesives, and coatings have been prepared by this proposed experimental procedure, and IR spectra have been obtained. Finally, several samples from paintings and artistic objects dating from the 16th to the 20th century have been analyzed, and synthetic and semi-synthetic organic materials have been successfully identified by comparison with the standards using the proposed method of analysis.
Fourier Transform Infrared Studies of pH- and Temperature-Dependent Conformational Changes of Solid Poly(Methacrylic Acid)
Authors: Dong J. , Tsubahara N. , Fujimoto Y. , Ozaki Y. , Nakashima K.
Published: October 2003

Fourier transform infrared (FT-IR) spectral measurements have been undertaken to investigate the conformational changes of poly(methacrylic acid) (PMA) cast from salt-free aqueous solutions. pH values, which markedly affect the overall conformation of the polymer, i.e., contracted coil at low pH (<4) and expanded coil at higher pH (>6), have a significant influence on the hydrogen bonding structure of the COOH side group. The COOH groups with different hydrogen bonding strengths and associated forms are ionized successively in the pH range of 3∼8, in accord with the development of conformational states. Ionization of the bonded COOH in the interior can be regarded as the onset of the overall conformational change (pH ∼ 5). The temperature-variable FT-IR spectra facilitate discrimination of the local conformational changes that are also brought about by pH changes. The interaction between the methyl groups is weakened by both the local conformational changes and the overall expansion of the chain, whereas the interaction between the COO− anions occurs significantly only during the transition. The present study shows how the hydrogen bonding force as a key player stabilizes the coiled conformation of PMA by using different forms of COOH groups. The importance of hydrophobic interaction between methyl groups in the conformational transition in the aqueous solutions is also elucidated, as continuing from the solid to solution state, the addition of the hydrophobic interaction gives rise to a sharper transition of the chain state.
On-Line Mid-Infrared Spectroscopic Data and Chemometrics for the Monitoring of an Enzymatic Hydrolysis
Authors: Ruckebusch Cyril , Sombret Bernard , Froidevaux Rénato , Huvenne Jean-Pierre
Published: October 2003

Multivariate models have been designed in order to be implemented at pilot plant scale. They allow the prediction of the degree of the enzymatic hydrolysis of bovine hemoglobin from on-line mid-infrared (MIR) attenuated total reflection (ATR) measurements. The procedure is very safe and practical, but the spectral information is unfortunately difficult to use. First, remote MIR optical fiber measurements induce a significant energy loss. Secondly, the spectra of proteins in aqueous solutions generally consist of broad and overlapping signals. Principal component analysis (PCA) of the full data set reveals some variations between the different batches as well as definite deviations from the ideal linear situation. This suggests the use of artificial neural networks (ANNs), which have the useful qualities of generalization ability and robustness. Preprocessing of the spectral data (including PCA and wavelet transforms) have been tested. In addition, the reliability of the calibration is ensured by the interpretation of the spectroscopic information. This permits the construction of very parsimonious models and contributes to greater confidence in the analytical tool built for process monitoring. Finally, the estimations of the prediction error are demonstrated to be acceptable. With an unknown proteolysis batch, this error is found to be lower than 0.4 for the degree of hydrolysis covering the range 0 to 8.7.
Global Phase Angle Description of Generalized Two-Dimensional Correlation Spectroscopy: 1. Theory and its Simulation for Practical Use
Authors: Morita Shin-Ichi , Ozaki Yukihiro , Noda Isao
Published: October 2003

The concept of a global phase map derived from generalized two-dimensional synchronous and asynchronous correlation spectra is introduced to extract the purely correlational information by intentionally canceling amplitude information. For the practical usage of a global 2D phase map, a filtering method based on the standard deviation spectrum obtained from the time series intensity profiles is proposed to remove the effect of small amplitude noise. A simulation created with the use of three synthesized bands with exponential decay has clearly detected the only difference in the characteristic rate constant of the decay process in the global 2D phase map, although the three bands have different initial values of the peak intensity amplitudes.
Small Fourier Transform Spectroscope Using an Integrated Prism-Scanning Interferometer
Authors: Kiyokura Takanori , Ito Takahiro , Sawada Renshi
Published: October 2003

This paper describes an integrated prism-scanning interferometer that consists of a sliding triangular prism with two mirror surfaces attached to a fixed triangular prism beamsplitter. This design eliminates the effect of ambient air and simplifies the alignment. It also halves the stage moving distance because the optical path difference is doubled as a result of both mirrors moving while the sliding prism is scanning. The volume of the interferometer is 2 cm3. We tested the basic operation. The resolution of 0.14 nm and the accuracy of 0.012 nm are obtained at the wavelength of 1525 nm. This interferometer is a significant step towards the realization of a field-use spectrometer based on Fourier transform spectroscopy.
Development and Commercial Evaluation of Laser-Induced Breakdown Spectroscopy Chemical Analysis Technology in the Coal Power Generation Industry
Authors: Chadwick Bruce L. , Body Doug
Published: October 2003

An instrumentation variation on laser-induced breakdown spectroscopy (LIBS) has been developed and applied in the operations of power generating companies utilizing low-ash lignite as the fuel source. The instrument design allows simultaneous determination of all detectable elements using a multiple spectrograph and a synchronized, multiple charge-coupled device (CCD) spectral acquisition system. The application of internal ratio analysis has enabled the development of a stable system that can be operated routinely for over a month without recalibration. Detection limits vary depending on the element but are typically on the order of 0.01% by weight for heterogeneous materials such as the moist lignite used in these power stations. Independent testing of the instrument has shown good correlation between the routine LIBS analysis and the analysis of the coal via acid extraction techniques for key ash-forming elements. Testing over a one month period shows excellent correlation between the two methods for elements such as Al ( R = 0.96) and Na ( R = 0.92). The principle limitation is not the accuracy of the LIBS method but rather the inherent errors in sampling heterogeneous materials such as lignite. Because the LIBS analysis takes less than 30 seconds it has clear advantages over traditional methods used in elemental analysis for these materials.
Performance of Fiber-Optic Raman Probes for Analysis of Gas Mixtures in Enclosures
Authors: Berg John M. , Rau Karen C. , Veirs D. Kirk , Worl Laura A. , McFarlan James T. , Hill Dallas D.
Published: October 2003

The feasibility of using fiber-optic Raman probes to identify and quantify gases in enclosures is investigated by measuring and comparing detection thresholds using several probe and enclosure designs. Unfiltered, non-imaging, fiber-optic probes are shown to achieve lower detection thresholds than a filtered, imaging, fiberoptic probe, provided that light scattering within the sample enclosure is minimized and provided that a window is not used between the probe and the analyte gas. Achievable thresholds for hydrogen, oxygen, nitrogen, carbon monoxide, and methane in gas mixtures are demonstrated to be below 1 kPa with ten seconds signal acquisition and 0.1 kPa with twenty minutes signal acquisition with the use of 0.4 W of 532-nm excitation. Ambient carbon dioxide in air (.03 kPa) is shown to be detectable in a twenty minute acquisition, and ambient water vapor is well above the detection threshold. Background signals generated within the optical fibers remain the principal factors limiting detection thresholds. Factors affecting the magnitudes of these signals reaching the detector are investigated and discussed. A flat piece of light-absorbing colored glass tilted to direct reflected light away from the fiber-optic probe performs well as a beam stop to reduce background signal in a simple, cylindrical sample enclosure.
Determination of Chlorinity in Aqueous Fluids Using Raman Spectroscopy of the Stretching Band of Water at Room Temperature: Application to Fluid Inclusions
Authors: Dubessy Jean , Lhomme Thérèse , Boiron Marie-Christine , Rull Fernando
Published: October 2003

A new analytical method, based on the Raman spectroscopy of the ν(OH) stretching vibration of water, has been developed for the determination of the concentration of chloride in aqueous solutions with the goal of reconstructing the bulk ion content of fluid inclusions that are relics of paleo-fluid circulation in rocks. The method involves calibrating the area of one band of the spectrum difference between pure water and solutions of appropriate composition with respect to the chloride concentration. Calibration curves were constructed for the major geological chemical salts LiCl, NaCl, KCl, CaCl2, and MgCl2, and NaCl–CaCl2 systems. The application to fluid inclusions has been confirmed using synthetic fluid inclusions. For cubic minerals such as fluorite, the calibration curve for the NaCl system correctly estimates the chlorinity. For birefringent minerals, such as quartz, the Raman spectrum of the aqueous solution depends on the orientation of the host crystal. The crystal must be oriented in such a way that one axis of the ellipse of the indicatrix projects parallel to the spectrometer slit. This method complements micro-thermometric data and allows the determination of chlorinity when ice-melting temperature cannot be used.
Quantitative Analysis of Crude Oils by Fluorescence Lifetime and Steady State Measurements Using 380-nm Excitation
Authors: Ryder Alan G.
Published: October 2003

Fluorescence emission and lifetime spectroscopy using 380-nm excitation have been successfully applied to the determination of API gravity and aromatic concentration of crude petroleum oils. Twelve crude oils from the North Sea with American Petroleum Institute (API) gravities of between 20 and 50 were analyzed; emission spectra were obtained with a standard fluorometer and the lifetime data with a pulsed ultraviolet light-emitting diode (UV-LED) coupled to a fluorescence lifetime system assembled in-house. A strong correlation between API gravity and the ratio of the fluorescence intensities recorded at 650 nm and 450 nm yielded a partial least-squares (PLS) regression model with an accurcy of ±4.6 °API; using the fluorescence intensity ratio at 650 nm and 550 nm gave an accuracy of ±5.8 °API. The average fluorescence lifetimes (τ̄) of the oils ranged from 1.9 to 18.6 ns, with τ̄ first increasing and then decreasing as the emission wavelength increased. These effects are due to the interplay between energy transfer and the quenching processes, which are governed by oil composition. A strong linear correlation was found between the ratio of the fluorescence lifetime measured at 650 nm and 550 nm and the aromatic concentration. A PLS regression model using this ratio had an accuracy of ±4% for aromatic concentration. Combining the fluorescence intensity with the lifetime measurements at 550 nm and 650 nm provides a rapid, quantitative, non-contact, nondestructive method of oil characterization.
Quantitative Analysis of Various Citrus Oils by ATR/FT-IR and NIR-FT Raman Spectroscopy
Authors: Schulz H. , Schrader B. , Quilitzsch R. , Steuer B.
Published: October 2003

The essential oils of various commercial citrus species were studied by ATR/FT-IR as well as NIR-FT Raman spectroscopy. Some of the most relevant monoterpene components occurring in the oil, such as limonene and γ-terpinene, show characteristic key bands in the IR and Raman spectra, which are useful for making a quantitative distinction between different oil types. Applying principal component analysis (PCA) to the spectral data, the individual citrus products are located, in most cases, as separated clusters in a 3-dimensional factor space. Cross-validation statistics showed that a partial least-square (PLS) algorithm was able to produce high quality predictions of the relative oil composition as well as general quality parameters. Both complementary spectroscopic techniques described in this study have the potential to replace existing analytical procedures because they are capable of faster quality control measurements and they allow on-line analyses during distillation or extraction processes to be performed.
Application of Partial Least-Squares Quantitative Analysis of Infrared Spectroscopic Data to Low-Vulnerability Ammunition Propellant Powders
Authors: Ouellet N. , Brochu S. , Lussier L.-S.
Published: October 2003

Reported herein is an application of partial least-squares (PLS) quantitative analysis to Fourier transform infrared spectra of a low-vulnerability ammunition (LOVA) propellant powder. The propellant components analyzed included a highly-energetic material, 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), an energetic binder, nitrocellulose, a non-energetic binder, cellulose acetate butyrate, and a plasticizer agent, acetyl triethyl citrate. The propellant system consisted of one major (RDX, 76% nominally by weight) and four minor components. Consequently, separate calibrations were developed to cover the two different concentration ranges. Samples were analyzed with the use of a simple KBr transmission cell over the 1800–1500 cm−1 region. The optimized PLS calibration models created were found to provide estimations within 1% error for both validation and real propellant samples without any separation or purification step. The mathematical model built by such an algorithm could serve to develop a quality control method to monitor the composition of gun powders.
Characterization of Colorectal Adenocarcinoma Sections by Spatially Resolved FT-IR Microspectroscopy
Authors: Lasch Peter , Haensch Wolfgang , Lewis E. Neil , Kidder Linda H. , Naumann Dieter
Published: October 2003

A combination of Fourier transform infrared (FT-IR) spectroscopy and microscopy, FT-IR microspectroscopy, has been used to characterize sections of human colorectal adenocarcinoma. In this report, a database of 2601 high quality FT-IR point spectra from 26 patient samples and seven different histological structures was recorded and analyzed. The computer-based analysis of the IR spectra was carried out in four steps: (1) an initial test for spectral quality, (2) data pre-processing, (3) data reduction and feature selection, and (4) classification of the tissue spectra by multivariate pattern recognition techniques such as hierarchical clustering and artificial neural network analysis. Furthermore, an example of how spectral databases can be utilized to reassemble false color images of tissue samples is presented. The overall classification accuracy attained by optimized artificial neural networks reached 95%, highlighting the great potential of FT-IR microspectroscopy as a potentially valuable, reagent-free technique for the characterization of tissue specimens. However, technical improvements and the compilation of validated spectral databases are essential prerequisites to make the infrared technique applicable to routine and experimental clinical analysis.
Triglycerides and Glycerol Concentration Determinations Using Plasma FT-IR Spectra
Authors: Petibois Cyril , Cazorla Georges , Déléris Gérard
Published: October 2003

FT-IR spectrometry was used for plasma triglyceride and glycerol concentration measurements, based on their most characteristic IR absorbances within the 1200–800 cm−1 interval. Plasma samples from 68 sportsmen were taken at rest and after an endurance exercise that induced important lipolysis. After subtraction of glucose and lactate absorbances from exercise plasma FT-IR spectra, triglyceride concentration was accurately determined using the spectral window centered at 1106 cm−1 (0.86 ± 0.19 vs. 0.84 ± 0.17 mMol/L; r = 0.97, P < 0.01; SEP = 0.14 mMol/L). Total glycerol concentration (sum of glycerol and glyceryl residue concentrations) was determined using the spectral window centered at 926 cm−1, which was found common to triglycerides and glycerol (0.306 ± 0.057 vs. 0.326 ± 0.051 mMol/L; r = 0.98, P < 0.01; SEP = 0.02 mMol/L). Glycerol concentration could be determined using the spectral window centered at 852 cm−1 (0.216 ± 0.039 vs. 0.231 ± 0.048 mMol/L; r = 0.95, P < 0.01; SEP = 0.03 mMol/L). However, weak glycerol concentration could be only indirectly determined by subtracting glyceryl residue concentration from total glycerol concentration that had been determined using the spectral window centered at 926 cm−1 (0.191 ± 0.061 vs. 0.176 ± 0.051 mMol/L; r = 0.90, P < 0.05; SEP = 0.02 mMol/L). Indeed, FT-IR spectrometry appears to be an accurate method for multiple biomolecular concentration determination on plasma samples.
Orientation and Relaxation in Thick Poly(ethylene Terephthalate) Films by Transmission Infrared Linear Dichroism
Authors: Pellerin Christian , Rousseau Marie-Eve , Prud'Homme Robert E. , Pézolet Michel
Published: October 2003

Infrared spectroscopy is a powerful tool for the study of the orientation in amorphous and semi-crystalline polymers, but it is generally limited to thin samples. In this study, we have used transmission infrared linear dichroism to study the orientation of thick poly(ethylene terephthalate) (PET) films. To overcome the saturation problem of the intense bands of PET, overtones and combination bands in the high-frequency region of the mid-infrared spectrum were used. Using polarization-modulation infrared linear dichroism (PM-IRLD), it was possible to follow in real-time the relaxation of orientation of uniaxially oriented PET films up to 500 μm thick. It was observed that between 30 and 500 μm, the thickness of the films has no effect on the orientation relaxation dynamics. It should, therefore, be possible to use thick films, which are much easier to prepare than thin films, for future infrared studies of the deformation of PET. A very good correlation was also observed for the relaxation curves obtained using high- and low-frequency bands related to gauche and trans conformers in thin and thick films. An example of the application of these high-frequency bands to obtain orientation and structural information is also given in the case of a commercial PET bottle showing a biaxial orientation.
Thickness-Dependent Optical Effects in Infrared Reflection-Absorption Spectra of a Fairly Thick Polymer Layer
Authors: Gunde Marta KlanjšEk , Orel Zorica Crnjak
Published: October 2003

Thickness-dependent intensities and positions of absorption lines in infrared reflection-absorption spectra of thin films on reflective substrates at near-normal incidence are investigated. Two types of absorption bands in a polymer, the weak and the strong, were examined. Their optical properties were determined by the dielectric response function. The optical path of the beam was described by the coherent sum of all successively reflected beams. The thickness-dependent properties of absorption bands were examined in three typical thickness regions. At small thickness, the peak intensity oscillates around the mean value defined by the simple internal absorptance of the beam crossing the double layer. For medium thickness, the peak position swings around the original frequency and its intensity oscillations move above the simple internal absorptance. In layers within the high-thickness region, optical distortions cause large changes in line shape due to approaching the bulk reflectance. A simple analytical interpretation is possible only within the low-thickness region. The width of these thickness regions depends on the absorptivity of the considered band; for strong bands they are considerably narrower than for weak bands. The theoretically predicted effects compare well with those measured in RAS spectra of variously thick silicon resin layers on aluminium substrates.
Nanosecond Time-Resolved Step-Scan FT-IR Spectroscopy in Conventional and Supercritical Fluids Using a Four-Window Infrared Cell
Authors: Sun Xue Z. , Nikiforov Sergei M. , Yang Jixin , Colley Christopher S. , George Michael W.
Published: October 2003

Fast time-resolved step-scan FT-IR (s2–FT-IR) has been used to study excited states and reaction intermediates in conventional and supercritical solvents. We have developed a four-port IR cell for s2–FT-IR measurements. The generation of W(CO)5(Xe), following photolysis of W(CO)6 in supercritical Xe, has been used to optimize our s2–FT-IR measurements in supercritical fluids using the four-port IR cell. We have compared a number of different approaches for obtaining transient time-resolved IR (TR-IR) data. The IR diode-laser-based and s2–FT-IR approaches for TR-IR have been compared directly. The kinetic decay of the CpMo(CO)3 (Cp = η5–C5H5) radical in supercritical CO2 has been determined using both TR-IR approaches, and we find no significant difference in signal-to-noise between these techniques for most of our TR-IR kinetic measurements. We have attempted to compare s2–FT-IR to the scanning dispersive TR-IR method by obtaining the infrared spectrum of the triplet excited state of 4-phenylbenzophenone, which has been published previously. The importance of obtaining high spectral resolution s2–FT-IR spectra for reactions in condensed phases is investigated. The IR spectrum of the CpFe(CO)2 radical in n-heptane shows that important information regarding the structure of the radical can only be obtained by performing time-resolved s2–FT-IR experiments at high spectral resolution.
Quantitation of Mixtures of Diprotic Organic Acids by FT-IR Flow Titrations and Multivariate Curve Resolution
Authors: Diewok Josef , De Juan Anna , Tauler Romà , Lendl Bernhard
Published: October 2003

The combination of FT-IR flow titrations and second-order calibration methods is assessed for the first time as a potential method for quantifying mixtures of organic acids. FT-IR spectral information is richer and more specific than that provided by other spectrometric techniques. Also, the flow titration of the sample allows the use of second-order data analysis methods, such as multivariate curve resolution, which can quantify multianalyte systems using pure analyte standards in the presence of unknown interferents. Problems linked to FT-IR flow titrations, such as the impossibility of using buffer substances and the presence of major baseline contributions in the measurements due to changes in the water structureless absorption, have been overcome through the design of an adapted experimental setup and the use of second derivative spectra. Malic and/or tartaric acid are the model substances chosen to be quantified in the presence or absence of interferents. Both substances are diprotic acids with similar p Ka values and, therefore, similar pH-dependent evolution. Samples with one or both acids with their related standards in the presence or absence of an inert interferent (sugar) are successfully resolved and quantified for a wide range of [analyte]: [interferent] ratios with no need for pH control in the process. These results suggest this methodology as an optimal and robust alternative for routine analysis.
Automated On-Line Noninvasive Optical Glucose Monitoring in a Cell Culture System
Authors: Jung Byungjo , Lee Seungjun , Yang In Hong , Good Theresa , Coté Gerard L.
Published: October 2003

Current techniques for monitoring glucose concentration during cell culture are invasively performed using an off-line measurement system. Even though in situ or ex situ analyte sensors have been tried for on-line measurement, they suffer from difficulties including the inability to keep them sterile, their limited lifetime, and their lack of stability. In this research an alternative optical noninvasive on-line monitoring system based on near-infrared absorbance spectroscopy was developed to measure glucose concentration of cell culture media in a rotary cell culture system. The system included an automatic sampling component controlled by a LabVIEW program and a high-throughput fiber coupling component connected to a Fourier transform near-infrared spectrometer. The effectiveness of the system was investigated via noninvasive on-line measurement of glucose absorbance spectra in the cell culture media during T-cell culture. Glucose absorbance spectra were collected in the spectral range of 2.0 to 2.5 μm. Partial least-squares regression was employed to build a successful multivariate calibration model. The standard error of prediction and mean percent error for glucose were 7.7 mg/dL and 1.0%, respectively. The successful results represent an important step in the development of a noninvasive, closed-loop, system for monitoring analytes in cell culture.
Correction of Matrix Effect in Multielemental Quantitative Analysis by X-Ray Fluorescence Spectroscopy Using the Linear Behavior in the Analytical Range of the Substitution-Dilution Method
Authors: Bosch-Reig F. , Gimeno-Adelantado J. V. , Sánchez-Ramos S. , Yusá-Marco D. J. , Bosch-Mossi F. , Doménech-Carbó A.
Published: October 2003

This paper is an analytical study of the possibility of applying the linear range of the substitution-dilution method to correct the matrix effect in quantitative analysis by X-ray fluorescence (XRF) spectroscopy. The analytical range is obtained from a series of samples prepared in the form of glass discs by substituting the unknown sample with a standard sample (substitution factor, h) including a diluent-melt. In general, the substitution-dilution method is hyperbolic in character and therefore the diluent is required to ensure linear behavior between If vs. h in the experimental range. The linear range is located between the concentrations of standard and unknown for each element analyzed. This linear model makes it possible to correct the matrix effect in quantitative analysis by XRF using a single multi-elemental standard for different types of samples with a complex matrix, such as geologicals and cements. The results found for Si, Ti, Al, Fe, Mn, Ca, K, and P in soil and sediment samples and Si, Fe, Al, Ca, and K in cements (white and gray) are statistically satisfactory. Thus, the mean relative standard deviation calculated for all analytes in each sample was: ±4.0% and ±5.0% in soils; ±5.0% in sediments; and ±6.0% or ±3.0% in cements, white and gray, respectively.
Design and Performance of a Planar Array Infrared Spectrograph That Operates in the 3400 to 2000 cm−1 Region
Authors: Elmore Douglas L. , Tsao Mei-Wei , Frisk Simon , Chase D. Bruce , Rabolt John F.
Published: October 2003

A prototype, no-moving-parts, plane array infrared spectrograph (PA-IR) capable of routine spectral acquisition in the 3400 to 2000 cm−1 region has been constructed. The instrument includes a continuous source, Czerney–Turner type monochromator system and an infrared camera that incorporates a 320 × 256 pixel InSb focal plane array detector cooled with liquid nitrogen. PA-IR spectra (∼3400 to 2550 cm−1) of polystyrene (PS) and poly(ethylene naphthalate) (PEN) films have been obtained at a resolution of ∼8 cm−1 with excellent signal-to-noise ratios (SNR). Peak-to-peak noise levels of ∼1 × 10−3 absorbance units are observed for single acquisition spectra with 1.5 ms integration times and 17 ms total acquisition times. Integration times as low as 10 μs are possible (with good SNR); however, data acquisition is limited by the frame rate (60 frames/s) of the software acquisition package currently used. In this work, an apertured image of the source is displayed over ∼20 rows of the array and the expected square root improvement in SNR is observed when multiple rows and/or frames are averaged. We have also shown that a square root improvement in SNR continues to occur with further signal averaging, providing noise levels as low as 1.5 × 10−5 absorbance units. Several additional advantages and options associated with the PA-IR method are discussed, including time-resolved spectroscopy, real-time monitoring, and spectroscopic mapping.
Characterization of Erucamide Profiles in Multilayer Linear Low-Density Polyethylene and Propylene-Ethylene Copolymer Films Using Synchrotron-Based FT-IR Microspectroscopy
Authors: Sankhe Shilpa Y. , Hirt Douglas E.
Published: October 2003

The diffusion of erucamide in single layer polymer films has been monitored previously using FT-IR microspectroscopy [ Appl. Spectrosc., 53, 11 (1999)]. This research extends that work to multilayer films. In particular, erucamide migration is characterized in press-laminated bilayer and coextruded trilayer linear low-density polyethylene (LLDPE) films and also coextruded bilayer films of LLDPE and a propylene-ethylene copolymer (PEC). Results in bilayers and trilayers demonstrate that the erucamide prefers to migrate to a film surface rather than into an adjacent layer, even in the presence of steep concentration gradients at layer–layer boundaries. The same behavior was observed for bilayers of LLDPE and PEC where it was anticipated that erucamide may diffuse into the less dense PEC layer. Attenuated total reflectance FT-IR was also used to confirm that little or no erucamide diffused through an additive-deficient layer to reach a film–air interface in a bilayer structure. However, results clearly showed erucamide migration from a core layer through additive-deficient skin layers to reach the surfaces of a trilayer film.
Vibrational Overtone Spectroscopy of Ethylene Glycol Diacrylate and Ethylene Glycol Dimethacrylate, Monomer and Polymer
Authors: Gerasimov T. G. , Snavely D. L.
Published: October 2003

The vibrational overtone spectra of ethylene glycol diacrylate (EGDA) and ethylene glycol dimethacrylate (EGDMA) monomers and corresponding polymers were recorded in the spectral range 4500–15 000 cm−1. This spectral range encompasses the first through the fourth CH stretch vibrational overtone transitions. The CH stretch spectral features were assigned by a comparison of the number and type of different CH oscillators in the two compounds and a comparison to the spectra of acrylic acid and ethylene glycol diisobutyrate. Peaks corresponding to transitions for the vinyl, methylenic, and methyl types of the CH stretch were identified. The anharmonicities and mechanical frequencies for each progression in each monomer and polymer sample are reported. From the integrated areas of the vinyl and methyl/methylenic peaks for the first, second, third, and fourth vibrational overtone transitions of EGDMA, the degree of polymerization was calculated. These results were compared to the degree of polymerization determined from IR spectroscopy.
Headspace FT-IR Analysis of Rapeseed Oil Oxidation
Authors: Ahro Mikko , Hakala Mari , Kauppinen Jyrki , Kallio Heikki
Published: October 2003

Volatile compounds formed by oxidation of rapeseed oil at 60 °C in open beakers were studied as a function of time over 289 h. A direct inlet gas-phase FT-IR method was introduced and compounds indicating lipid oxidation were detected and quantified. The development of 1,3,5-trimethylbenzene, 2,4-hexadienal, 2-methyl-1,3-butadiene, 2-methyltetrahydrofuran, acetic acid, methyl cyclopentane, methyl hexanoate, n-butanal, n-hexanal, n-octanal, n-propanal, and trans, trans-2,4-heptadienal was followed. The results showed that gas-phase FT-IR is a potential method of fast analysis for monitoring oil quality. Headspace-gas chromatography-mass spectrometry (HS-GC-MS) was used for compound identification.
Regularized Linear Discriminant Analysis of Wavelet Compressed Ion Mobility Spectra
Authors: Mehay Aaron W. , Cai Chunsheng , De B. Harrington Peter
Published: October 2003

Wavelet compression (WC) coupled to a regularized version of linear discriminant analysis (LDA) was evaluated as an effective classifier for identification of benzene, toluene, ethyl benzene, and the xylene isomers (BTEX) from their positive ion mobility spectra. A novel LDA classifier was devised that uses pseudoinverses of the within-group covariance matrices. The pseudoinverse allows LDA to be applied directly to underdetermined data. Wavelet compression improved the classification by removing noise from the spectra. Spectra compressed with the daublet 22 filter yielded better prediction than data compressed by principal components. Ion mobility spectrometry (IMS) affords rapid and sensitive measurements that may be used for process monitoring. This study demonstrates that classification by LDA directly on the wavelet-compressed (WTLDA) positive ion spectra can be used for identification of BTEX compounds. The accompanying benefits include fast model building, removal of noise, and improved classification. Benzene, toluene, ethyl benzene, and o-, m-, and p-xylene at high and low concentrations were used to construct the classification models. Spectra from intermediate concentrations were used for evaluation. Optimization of prediction favored shorter wavelet filters than those obtained from filters optimized for reconstruction.
Spectral Editing of Carbon Thirteen Hexopyranose Ring Nuclei by One-Dimensional NMR Extended Distortionless Enhancement by Polarization Transfer Experiments
Authors: Pouységu L. , De Jéso B. , Lartigue J. C. , Pétraud M. , Ratier M.
Published: October 2003

This paper reports application of the one-dimensional 13C NMR “extended” distortionless enhancement by polarization transfer (DEPT) editing method to the determination of hexopyranose ring 13C nuclei. Relative spatial arrangements of the vicinal protons in the local environment of a skeletal carbon atom are determined from the signs of intensity modulation profiles and connected with their specific positions in the ring. In combination with a computer simulation program, the “extended” DEPT sequence allows the straightforward and unambiguous assignment of the hexopyranose ring carbon atoms.