bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of Total Styrene in Styrene/Butadiene Block Copolymers by Process NMR and Chemometrics Modeling
Authors: Sardashti Maziar , Gislason Jason J. , Lai Xiaonian , Stewart Carol A. , O'Donnell Daniel J.
Published: October 2003

A new method involving the use of chemometric techniques was developed on a process nuclear magnetic resonance (NMR) spectrometer for measurement of total styrene in styrene/butadiene (Sty/BD) block copolymers. The method uses partial least-squares (PLS) regression to correlate the total styrene data produced by solutions H-1 NMR to the data produced by process NMR. The new method has comparable accuracy and precision to the solution NMR method, but it is much faster and easier to perform. It also has the additional capability of being selective for a specific process and/or polymer. The NMR method and chemometrics models are discussed, and results for validation of the models and prediction of the total styrene in unknown samples are presented.
29Si-NMR Studies of the Sol-Gel Hybrid Solution Containing Octadecyltriethoxysilane and Tetraethoxysilane Used to Fabricate a Stationary Phase for Open Tubular Capillary Electrochromatography
Authors: Rodríguez Shirley A. , Colón Luis A.
Published: October 2003

n-Octadecyltriethoxysilane (C18-TEOS) and tetraethoxysilane (TEOS) were used as the precursors to fabricate an organic-inorganic hybrid composite by sol-gel processing. The hydrolysis and initial condensation reactions of TEOS and C18-TEOS/TEOS mixtures were studied by 29Si-NMR spectroscopy. The rate of disappearance of the silane precursors and the evolution of the various silicon species during the reaction indicate that TEOS hydrolyzes and condenses faster than C18-TEOS. The rate of hydrolysis for C18-TEOS, however, increases when reacting in the C18-TEOS/TEOS hybrid mixture, indicating that the condensation reactions involving TEOS species drive the reaction of C18-TEOS. The formation of cross-condensed products leads to the composite with octadecyl groups incorporated into the final glass material. The maximum degree of condensation in the C18-TEOS/TEOS mixture was observed after 2 h of reaction. Fused-silica capillary columns were coated with the C18-TEOS/TEOS mixture while in its liquid-like stage. After drying, the columns were tested for open tubular capillary electrochromatography (OT-CEC). Coating of the columns was performed after the maximum degree of condensation was achieved, which has been shown to correlate with maximum chromatographic retention.
Use of a Laser Scanning Confocal Microscope to Obtain Concentration Profiles of a Diffusant in a Polymer Film
Authors: McFarland E. G. , Michielsen S. , Carr W. W.
Published: October 2003

The use of laser scanning confocal microscopy (LSCM) to view textile substrates is a relatively new field. It has been used to determine fiber shapes and concentrations of a fluorescent dye in a fiber. However, this technique is limited to very low concentrations of strongly absorbing species. A new technique based on LSCM is developed for obtaining concentration profiles at much higher concentrations where the effects of absorption of the incident light cannot be ignored. Sample preparation is particularly simple. Although this new approach is specific to planar films, it permits the study of dye diffusion in polymers at normal dye concentrations and with dyes that are not traditionally considered fluorescent dyes. The concentration profiles are used to obtain the diffusion coefficient of C.I. Disperse Blue 3 in nylon 6,6 film.
Mechanistic Aspects of the Oxygen Quenching of the Solid-Matrix Phosphorescence of Perdeuterated Phenanthrene on Partially Hydrophobic Paper
Authors: Hurtubise Robert J. , Ackerman Amanda H. , Smith Barry W.
Published: October 2003

The effects of oxygen over a wide concentration range on the solid-matrix phosphorescence (SMP) of perdeuterated phenanthrene (D10) adsorbed on partially hydrophobic paper (1PS) were investigated. The SMP lifetime results of D10 adsorbed on Whatman 1PS paper and Whatman No. 1 paper were considered, and the SMP intensities and SMP lifetimes of D10 on 1PS paper were compared. The SMP quenching model employed showed that diffusional quenching was not very extensive for D10 adsorbed on both types of paper. In addition, a large fraction of the D10 phosphor molecules did not undergo diffusional quenching in either paper. The changes in the SMP intensities for D10 adsorbed on 1PS paper were much greater than the corresponding SMP lifetime changes, which indicated that static quenching by oxygen was very effective for D10 on 1PS paper. Also, the SMP intensity data indicated that a relatively large fraction of the D10 molecules were not quenched statically. The quenching data were interpreted and compared with equations that permitted both linear and nonlinear models to be employed.
Room-Temperature Phosphorescence of 1-Bromonaphthalene upon Formation of Beta-Cyclodextrin Ternary Complexes with Alcohols and Surfactants: Optimization of Analytical Figures of Merit by Rigorous Equilibrium Studies
Authors: Escandar Graciela M. , de la Peña Arsenio Muñoz
Published: October 2003

Room-temperature phosphorimetry of ternary β-cyclodextrin complexes of the model compound 1-bromonaphthalene has been examined. The selected third partners were alcohols (cyclohexanol, cyclopentanol, and 1-pentanol) and surfactants (Triton X-100 and sodium dodecyl sulfate). A thorough analysis of all equilibria involved in the interaction between the components is performed and discussed. A computational procedure, not previously employed to study this type of complex systems, is used for the determination of the equilibrium constants and stoichiometries of the formed species. It is shown that a rigorous analysis of the equilibria is necessary for a proper optimization of analytical methods based on roomtemperature phosphorescence of ternary complexes. The best working conditions are inferred from the examination of three-dimensional and contour plots of the ternary complex concentration as a function of those of the reagents. The latter plots are constructed once the relative stabilities of all intervening species are known. On the basis of the calibration results, the relative advantages of employing the examined systems for determining the studied compound are presented.
High-Precision, Simultaneous Analysis of Pt, Pd, and Rh in Catalytic Converter Samples by Carius Tube Dissolution and Inductively Coupled Plasma Atomic Emission Spectroscopy with Charge-Injection Device Detection
Authors: Pennebaker Frank M. , Denton M. Bonner
Published: October 2003

A robust method of analysis that uses multichannel array detector technology is presented for high-precision, accurate measurement of Pt, Pd and Rh in catalytic converters. Catalytic converter samples, National Institute of Standards and Technology (NIST) reference standards, and a fresh converter sample are dissolved and analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Complete dissolution of sample sizes up to 2 g of NIST reference standards is achieved with the use of high-pressure, high-temperature carius tubes. Carius tube dissolution of a modern catalytic converter sample is found to be incomplete because of the presence of higher concentrations of Ce, Ni, and Zr. For this sample, the addition of FeCl3 increases the dissolving power of the carius tube for base metals and noble metals, particularly Rh. Although interference problems are encountered in samples bearing high concentrations of Fe, use of a high-resolution ICP-AES system alleviated these problems. Precise quantitation of Pt, Pd, and Rh is accomplished by using the method of standard additions, with high accuracy and a precision of 1–2% RSD (relative standard deviation). This analysis also confirmed the values determined by NIST by using isotope dilution inductively coupled plasma mass spectrometry (ICP-MS) for standard reference materials (SRMs) 2556 and 2557.
Self-Referencing Raman Probes for Quantitative Analysis
Authors: Zheng X. , Fu W. , Albin S. , Wise K. L. , Javey A. , Cooper J. B.
Published: October 2003

Diamond is evaluated as an internal reference for remote Raman spectroscopy using three different fiber-optic probe designs. The three probe designs include (1) a six-around-one fiber-optic probe with a flat diamond window; (2) a six-around-one fiber-optic probe with a quartz lens window with an embedded diamond particle, and (3) a filtered probe design with a flat diamond window. It is found that the second probe design provides a compact and inexpensive probe head which allows quantitative measurements of Raman-active analytes independent of changes in the incident laser power and independent of changes in the refractive index of the solution. In addition, the second probe design minimizes the glass Raman background from the fiber optics without the use of filters.
Curve Fitting and Linearity: Data Processing in Raman Spectroscopy
Authors: Vickers Thomas J. , Wambles Ronald E. , Mann Charles K.
Published: October 2003

A study has been made of the use of polynomial curve fitting for removal of nonlinear background and high-spatial-frequency noise components from Raman spectra. Two variations on polynomial curve fitting through a least-squares calculation are used. One, involving fitting data x values to corresponding y values, was used to approximate background functions, which are subtracted from the original data. For smoothing, a reference matrix of six vectors that contains a unity d.c. level, a ramp made up of x values, a quadratic made up of x2 values, etc., is fitted to a section of data. The reference vectors are scaled by the fit values and added to give the smoothed estimate of a spectral peak. It is demonstrated, with factor analysis as a test procedure, that the background removal procedure does remove nonlinearities that were present in the original data. The smoothing procedure rejects high-spatial-frequency noise without introducing detectable nonlinearities.
Surface-Enhanced Raman Scattering of Azobenzene-Containing Long-Chain Fatty Acids Adsorbed on Metal Colloids
Authors: Jung Young Mee , Tashiro Hideo , Ikeda Teruki , Ozaki Yukihiro
Published: October 2003

We have investigated the surface geometry of azobenzene-containing long-chain fatty acids ( nA mH; n = 8, 12, m = 3, 5) adsorbed on silver and gold colloids as well as the interaction between nA mH and the two kinds of metal colloidal surface by means of near-infrared and visible surface-enhanced Raman scattering (SERS). The 488.0 and 514.5 nm excited Raman spectra of nA mH adsorbed on silver colloid and the 1064 nm excited Fourier transform (FT)-Raman spectrum adsorbed on gold colloid show a marked SERS effect. The lowest concentration at which the SERS signals were observed was 10−10 and 10−8 M for the silver and gold colloids, respectively, in the present study. The 488.0 nm excited SERS spectrum of 12A3H adsorbed on silver colloid is very similar to a Raman spectrum of 12A3H in chloroform, while the 1064 nm excited SERS spectrum of 12A3H adsorbed on gold colloid is quite different; a number of new bands appear, and the relative intensity of bands changes markedly in the 1064 nm excited SERS spectrum. Probably, a chemical mechanism contributes significantly to the emergence of the SERS effect for 12A3H on gold colloid. Particularly striking in the SERS spectrum of 12A3H adsorbed on gold colloid is the observation that bands at 1586, 1166, and 834 cm−1 due to the phenyl ring modes show remarkable enhancement. It seems likely that the COO− group is adsorbed directly on the silver colloid surface, while one of the phenyl groups is adsorbed directly on the gold colloid surface. The effect of the particle size on the SERS intensity has been explored for 12A3H on gold colloid. It was found from the frequency of the -N=N- stretching band that 12A3H assumes a cis conformation on the gold colloid with the smaller particle size.
Infrared Detection of the Nerve Agent Sarin (Isopropyl Methylphosphonofluoridate) in Water Using Magnesium Oxide for Preconcentration
Authors: Ewing K. J. , Lerner B.
Published: October 2003

Detection of the nerve agent Sarin is investigated by using diffuse reflectance infrared spectroscopy with magnesium oxide (MgO) as a preconcentrating medium. Magnesium hydroxide, produced from magnesium oxide and water, initially hydrolyzes the Sarin to isopropyl methylphosphonic acid (IMPA). The IMPA then reacts with magnesium hydroxide (a slightly soluble product of the addition of MgO to water) to form an insoluble salt. Gas chromatography mass spectrometry (GC-MS) analysis of the Sarin/water solution indicates hydrolysis of the Sarin after 5 min of addition of the Nantek MgO and within 15 min after addition of the Aldrich MgO. Capillary electrophoresis analysis of the same Sarin/water solution shows that approximately 30% of the IMPA produced by the Nantek MgO hydrolysis of Sarin is not detected in solution, while most of the IMPA produced by the Aldrich MgO is detected. The diffuse reflectance infrared (IR) spectrum of the IMPA/MgO sample clearly indicates the presence of IMPA for both the Nantek MgO and Aldrich MgO samples. Well-resolved bands for methylphosphonic acid (MPA) are also evident for the Nantek MgO/Sarin sample, while less resolved, weaker bands due to MPA are seen for the Aldrich MgO/Sarin sample. These data suggest that a significant percentage of the Sarin is hydrolyzed to MPA by using the Nantek MgO. A detection limit of 98 ppb (Aldrich MgO) and 170 ppb (Nantek MgO) Sarin in water is calculated on the basis of the band heights and signal-to-noise ratio.
Pyrolysis of Kapton® in Air: An in situ DRIFT Study
Authors: Ortelli E. E. , Geiger F. , Lippert T. , Wokaun A.
Published: October 2003

Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was used to study the pyrolysis of polyimide (Kapton®). The samples were prepared in a KBr matrix, which did not show pronounced interferences, such as increased emissivity, during the measurements. The pyrolysis of Kapton® reveals pronounced differences from laser-induced (UV) decomposition. The polyimide system decomposes thermally in distinct steps, i.e., first the imide ring, without elimination of the carbonyl groups, followed by the aromatic system and then the carbonyl groups. Several intermediates, such as nitriles and alkynes, are identified. The quantitative analysis of the spectra suggests that Kapton® decomposes in two steps, i.e., as a growing particle with shrinking core followed by a shrinking particle. The growing particle with shrinking core is the nonreacted polymer as core and a polyamic structure as the growing part, while the shrinking particle is the complete pyrolysis of the polymer. The activation energies for these two steps were determined. The reaction rate appears to be diffusion controlled at low temperatures and surface reaction controlled at higher temperatures.
Mid-Infrared Fiber-Optics Reflectance Spectroscopy: A Noninvasive Technique for Remote Analysis of Painted Layers. Part I: Technical Setup
Authors: Fabbri Martha , Picollo Marcello , Porcinai Simone , Bacci Mauro
Published: October 2003

Mid-infrared chalcogenide fiber optics coupled with Fourier transform infrared (FT-IR) benches has made it possible to perform noninvasive reflectance measurements of layers of paint. The technique has potential applications for noninvasive analysis of works of art. These measurements can present large distortions in the spectrum, both in band shape and absorption frequency, which may depend on the band strength, on the concentration of the sample, or on the optical layout of the measuring system. Therefore, it is difficult to compare reflectance spectra with those collected in the transmission mode and, consequently, with the available databases. The work deals with an overall survey of the limits and problems involved in the utilization of this analytical technique, an estimate of the reproducibility of the measurements, and the development of a correct measurement procedure.
Mid-Infrared Fiber-Optics Reflectance Spectroscopy: A Noninvasive Technique for Remote Analysis of Painted Layers. Part II: Statistical Analysis of Spectra
Authors: Fabbri Martha , Picollo Marcello , Porcinai Simone , Bacci Mauro
Published: October 2003

Mid-infrared fiber-optics reflectance spectroscopy supported by classification procedures based on the Mahalanobis distance in the principal component space was applied to investigate laboratory samples simulating actual paintings. The spectral data obtained were analyzed by means of principal component analysis (PCA). The application of PCA to first-derivative spectra resulted as a robust method of processing spectral data and made it possible to distinguish the binding medium and/or the pigment/dye, and to classify test samples by means of the Mahalanobis distance discrimination method.
Retrieving CO Concentrations from FT-IR Spectra with Nonmodeled Interferences and Fluctuating Baselines Using PCR Model Parameters
Authors: Bak Jimmy
Published: October 2003

It is demonstrated that good predictions of gas concentrations based on measured spectra can be made even if these spectra contain totally overlapping spectral features from nonidentified and nonmodeled interfering compounds and fluctuating baselines. The prediction program (CONTOUR) is based solely on principal component regression (PCR) model parameters. CONTOUR consists of two smaller algorithms. The first of these is used to calculate pure component spectra based on the PCR model parameters at different concentrations. In the second algorithm, the calculated pure component spectra are subtracted one by one from the contaminated spectrum, and the length of the spectral contour within specified wavenumbers is then calculated. When the length of the contour is at a minimum, a condition is reached where the pure component part of the measured spectrum is absent and only the background signal remains. The assumptions are that the background and analytical signals must be additive and that no accidental match between these signals takes place. The best results are obtained with the use of spectra with a high selectivity. The use of the program is demonstrated by applying simple single-factor PCR models based on pure gaseous 1 and 4 cm−1 CO Fourier transform infrared (FT-IR) spectra (50–400 ppm) measured at ambient temperatures. The program is validated with measured CO spectra containing interferents such as N2O, CO2, and added Hitran-simulated H2O, CO2, and COS spectra, representing strong features in the CO spectral region.
Applications of ICP-OES with a New Argon-Filled CCD Spectrometer Using Spectral Lines in the Vacuum Ultraviolet Spectral Range
Authors: Wieberneit Nataly , Heitland Peter
Published: October 2003

It is shown that the use of analytical lines in the spectral range between 125 and 195 nm opens new analytical possibilities for inductively coupled plasma optical emission spectrometry (ICP-OES). Prominent emission lines in the vacuum ultraviolet (VUV) spectral region were used for different analytical applications with a new ICP optical emission spectrometer with charge-coupled device detectors (CCDs). These applications include the determination of Cl and S in organic samples (oil and gasoline), the determination of Al, Br, I, and P in high-saline 200 g/L NaCl solutions, and the determination of Pb, Sn, and In in highly pure 99.9% (m/m) Pd and Pt. The superiority of the VUV emission lines of Al 167, Br 148, Cl 134, Cl 135, Ga 141, I 161, In 158, P 177, Pb 168, Sn 140, and Sn 147 nm in these applications with respect to power of detection and freedom from spectral interferences is shown. The limits of detection (LODs) are tabulated for a series of further elements with prominent spectral lines in the 125–195 nm range using pneumatic nebulization of aqueous solutions for sample introduction. These results are compared with those for lines above 195 nm. In some cases VUV lines are superior to commonly used lines; for example, calculated LODs for Al(II) 167.080 nm, In(II) 158.637 nm, and Ga(II) 141.444 nm are 0.07, 0.2, and 0.8 μg/L, respectively, compared to 1.1, 7.1, and 5.9 μg/L for Al(I) 396.152, In(I) 230.606, and Ga I 417.204 nm, respectively. In other cases LODs in the μg/L range are possible only with VUV lines, such as for Cl(I) 134.724 or Br(I) 154.065 nm.
Flow-Injection Inductively Coupled Plasma Mass Spectrometer Incorporated with an Ultrasonic Nebulizer-Membrane Dryer: Application to Trace Lead Detection in Aqueous Solution and Seawater
Authors: Ke Su-Hui , Huang Li-Shing , Huang Jer-Shing , Lin King-Chuen
Published: October 2003

Flow-injection (FI) incorporated with inductively coupled plasma mass spectrometry (ICP-MS) was used to determine lead in aqueous solutions and seawater. Lead was retained in the form of Pb-DDPA complex in a sorbent microcolumn packed with C18-bonded silica, and then carried to an ultrasonic nebulizer with methanol as eluent. The ultrasonic nebulizer removed about 66% of methanol solvent vapors from entering the detector. A multi-tube Nafion® membrane dryer, installed along the passage prior to the ICP torch, further removed 50% of methanol. Reducing the amount of methanol solvent significantly improved the signal-to-background ratio of the detector. Accordingly, when the sample was loaded for 15 and 60 s, respectively, Pb detection limits were determined to be 0.162 and 0.028 ng/L, one to two orders of magnitude lower than those reported. The enrichment factors were also measured to be 7 and 28, with the sampling frequencies of 31 and 21 h−1, respectively. The method was applied for the determination of Pb in a reference seawater. The obtained result was 0.013 ± 0.001 ng/mL, consistent with the certified value of 0.013 ± 0.005 ng/mL.
Prediction of Multiple Matrix Interferences in Inductively Coupled Plasma Mass Spectrometry
Authors: Tromp John W. , Cole Amanda , Ying Hai , Salin Eric D.
Published: October 2003

Matrix effects for pairs of interferents (Al, Na, K, Ba, and Cs) were investigated and compared to predictions of the amount of interference determined by single interferent experiments in order to test a model called the total interference level (TIL), which assumes that the effects of different interferents add linearly. The TIL model is part of an Autonomous Instrument and is designed to indicate when a simple default calibration, such as external calibration or internal standardization, is inadequate for the desired accuracy of analysis. The performance of the TIL model was examined in terms of a daily calibration basis, which should be more accurate, and an occasional calibration basis, which is more convenient, considering simple external standardization and internal standardization as the techniques to be tested for desired accuracy. The results are encouraging for multiple interferences and show that the TIL model can serve a useful function in predicting calibration errors, even given the presence of instrument drift on ICP-MS.
Real-Time Interactive Self-Modeling Mixture Analysis
Authors: Chen Guoxiang , De B. Harrington Peter
Published: October 2003

A modified algorithm of SIMPLe-to-use Interactive Self-modeling Mixture Analysis (SIMPLISMA) has been developed to build models in real time from ion mobility spectrometry (IMS) data. A real-time LabVIEW virtual instrument (VI) has been developed to continuously acquire data and simultaneously extract spectra and concentration profiles. The concentration profiles indicate changes of the individual component concentrations in the instrument response with respect to sample acquisition time, and the spectra indicate the characteristic peaks of the components with respect to the ion mobility. This display allows subtle changes in the instrument's response and the complete measurement history to be visualized while the spectra are acquired. Modifications concerning pure variable selection and determination of the number of component have been made to the SIMPLISMA algorithm for real-time processing. The VI determined the component number automatically. The time constraints of the real-time algorithm were compared to SIMPLISMA and standard data acquisition.
Principal Component Global Analysis of Fluorescence and Absorption Spectra of 2-(2'-Hydroxyphenyl)Benzimidazole
Authors: Al-Soufi W. , Novo M. , Mosquera M.
Published: October 2003

Principal component analysis (PCA) of a series of absorption and emission spectra of 2-(2'-hydroxyphenyl)benzimidazole (HBI) in aqueous solutions in the pH range from 1.11 to 12.3 and 3.85 to 9.62, respectively, reveals the presence of three contributing components both in the ground and in the excited state. The combination of PCA with global analysis (PCGA) confirms the previously proposed reaction mechanism and allows the determination of p Ka values, pure component spectra, and concentration profiles of the ground- and excited-state species in spite of their strong spectral overlap. PCGA is proved to be a powerful complement to standard nonlinear least-squares analysis of physicochemical systems.
Step-Scan FT-IR Time-Resolved Spectroscopy in the Solid State
Authors: Smith Gregory D. , Hutson M. Shane , Lu Yu , Tierney Mark T. , Grinstaff Mark W. , Palmer Richard A.
Published: October 2003

The use of KBr pellets as an interference-free matrix for performing time-resolved infrared (TR-IR) measurements on samples in their crystalline state is described and demonstrated. Step-scan Fourier transform infrared time-resolved spectroscopy (S2FT-IR TRS) is used to measure the infrared (IR) absorption difference (Δ A, excited state minus ground state) spectra of the long-lived charge-transfer excited states of polypyridine Ru(II) and Pt(II) complexes pressed into KBr pellets. A comparison of the difference spectra measured for the metal-to-ligand charge-transfer (3MLCT) state of the Ru(II) complex in a KBr pellet vs. acetonitrile (ACN) solution is used to validate the technique. The Pt(II) complex could not be analyzed in solution because of its extremely poor solubility. Thus, these results illustrate one of the significant advantages of performing TR-IR measurements on solid KBr sample pellets.
New Cryogenic Apparatus for FT-IR Spectroscopic Studies
Authors: Kang Ning , Xu Yizhuang , Ferraro J. R. , Li Weihong , Weng Shifu , Xu Duanfu , Wu Jinguang , Soloway R. D. , Xu Guangxian
Published: October 2003

Cryogenic Fourier transform infrared (FT-IR) spectroscopy, being an effective technique in improving the spectral resolution and signal-to-noise ratio, is utilized in our group. However, we have found the traditional cryogenic apparatus inconvenient in the following aspects: (1) The system does not work very well in preventing moisture/frost from condensing on the salt windows or samples. (2) The indirect way of cooling using a metal cold finger limits the efficiency of the system. We have designed a new cryogenic apparatus. The apparatus is composed of a cooling stage and a measuring stage. In the cooling stage, the sample is directly immersed in liquid nitrogen. In the measuring stage, the sample is lifted just above the surface of liquid nitrogen, and the FT-IR spectrum is recorded. The dry cold nitrogen gas evaporated from liquid nitrogen forms a protective layer surrounding the sample and prevents moisture from condensing on the sample. Thus, neither vacuum nor salt windows are needed in cryogenic spectroscopic experiments using this method. The experimental results show that our method is effective in cryogenic FT-IR spectroscopic studies.
Calibration Transfer between PDA-Based NIR Spectrometers in the NIR Assessment of Melon Soluble Solids Content
Authors: Greensill C. V. , Wolfs P. J. , Spiegelman C. H. , Walsh K. B.
Published: October 2003

In near-infrared (NIR) spectroscopy, the transfer of predictive models between Fourier transform near-infrared (FT-NIR) and scanning–grating-based instruments has been accomplished on relatively dry samples (< 10% water) using various chemometric techniques—for example, slope and bias correction (SBC), direct standardization (DS), piecewise direct standardization (PDS), orthogonal signal correction (OSC), finite impulse transform (FIR) and wavelet transform (WT), and application of neural networks. In this study, seven well-known techniques [SBC, DS, PDS, double-window PDS (DWPDS), OSC, FIR, and WT], a photometric response correction and wavelength interpolative method, and a model updating method were assessed in terms of root mean square error of prediction (RMSEP) (using Fearn's significance testing) for calibration transfer (standardization) between pairs of spectrometers from a group of four spectrometers for noninvasive prediction of soluble solid content (SSC) of melon fruit. The spectrometers were diffraction grating-based instruments incorporating photodiode array photodetectors (MMS1, Carl Zeiss, Jena, Germany), used with a standard optical geometry of sample, light source, and spectrometer. A modified WT method performed significantly better than all other standardization methods and on a par with model updating.
On-Line Estimation of Molecular Orientation in Polypropylene Fibers Using Polarized Raman Spectroscopy
Authors: Paradkar Rajesh P. , Sakhalkar Subodh S. , He Xiaojun , Ellison Michael S.
Published: October 2003

Polarized Raman spectra obtained at different points along the spin line during pilot-scale melt spinning of polypropylene fibers are presented for the first time. Measurements of the 841/809 cm−1 band intensity ratio for these fibers with varying draw are made and shown to correlate with birefringence. The effect of sample throughput and take-up velocity on real-time polarized Raman spectra of these fibers is also discussed. On the basis of the results obtained it is confirmed that the ratio of the 841/809 cm−1 band intensities can be used to estimate the molecular orientation in polypropylene fibers.
Raman Spectroscopy and DSC Determination of Conversion in DDS-Cured Epoxy Resin: Application to Epoxy-Copolyethersulfone Blends
Authors: Van Overbeke E. , Devaux J. , Legras R. , Carter J. T. , McGrail P. T. , Carlier V.
Published: October 2003

Methods have been developed to determine by Raman spectroscopy the epoxide conversion in a 4,4'-diaminodiphenylsulfone (DDS)-cured epoxy resin as well as in blends of this resin with copolyethersulfone thermoplastic. The proposed spectral treatments consisted of a peak ratio method and of multivariate analysis. The Raman data were first successfully calibrated on the basis of neat resin samples with the use of the values of epoxide conversions provided by differential scanning calorimetry (DSC) measurements. The use of DSC as a reference technique is discussed. In order to be applied to blends of the same epoxy resin and reactive copolyethersulfone, the calibrations were based on spectral data that would not be influenced by the presence of this thermoplastic. The blend samples were homogeneous at the scale of the Raman laser focusing. The epoxide conversions deduced from the Raman and the DSC results were compared for these blends. Limitations associated with both techniques are discussed.
Effect of Temperature on the Conformation of Extended α-Keratin
Authors: Lyman Donald J. , Murray-Wijelath Jacqueline , Feughelman Max
Published: October 2003

Attenuated total reflection Fourier transform infrared (ATR/FT-IR) spectra of wet horse hair α-keratin indicate that the conformation of extended α-keratin is affected by the water temperature. Extension of the wet horse hair in 21 °C water gives rise to parallel β-sheet structures, thus suggesting that the original α-helical structure is also parallel. In contrast, extension of the wet horse hair α-keratin in 95 °C water gives rise to anti-parallel β-sheet structures (consistent with reported literature where X-ray diffraction was used), suggesting that disulfide interchange and/or increased chain mobility at elevated temperatures plays a role in altering the secondary structure.
Evaluation of Chemical Protective Clothing by FT-IR/ATR Spectroscopy
Authors: O'Callaghan Kristina , Fredericks Peter M. , Bromwich David
Published: October 2003

An attenuated total reflectance (ATR) permeation cell has been used to evaluate the permeation of polymer samples from chemical protective clothing (CPC), mainly gloves, by several chemical types including a solvent, a commercial pesticide mix, and a volatile solid. Good contact between sample and ATR crystal was ensured by the use of low gas pressure. The passage of the chemicals through the CPC sample could be readily followed by analysis of sets of Fourier transform infrared (FT-IR) spectra measured during permeation experiments. Diffusion coefficients could only be estimated. The ATR method is compared with the traditional two-compartment cell used for evaluation of CPC, and its advantages and disadvantages are discussed.
Characterization of Edible Coatings and Microorganisms on Food Surfaces Using Fourier Transform Infrared Photoacoustic Spectroscopy
Authors: Yang Hong , Irudayaraj Joseph , Sakhamuri Sivakesava
Published: October 2003

Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS) was used to study edible coatings and microorganisms on fruit surfaces (apple and honeydew melon). In the experiment, pregelatinized starch and whey protein concentrate were used to prepare edible coatings, while Saccharomyces cerevisiae, Lactobacillus casei, Escherchia coli, and Staphylococcus aureus were used for microbial study. The spectra obtained from the edible coatings on the apple surface indicate that the FT-IR/PAS technique can effectively distinguish the coating surface and the food substrate by examination of magnitude, phase angle, and generalized two-dimensional (G2D) correlation spectra. Results reported show the first application of FT-IR/PAS to directly differentiate a fruit surface (apple and honeydew melon) with/without microorganisms without elaborate sample preparation. The results demonstrate the potential of FT-IR/PAS to characterize the presence of microorganisms on fruit surfaces.
Estimates of Optical Parameters Based on Mixing Rules Extending over a Wide Range of Wavelengths
Authors: Lambrakos S. G. , Moore P. G. , Loschialpo P. , Smith D.
Published: October 2003

We examine a procedure for constructing estimates of optical parameters for composite materials, whose associated reflectivity function consists of multiscale features relative to wavelength, via mixing rules that extend over a wide range of wavelengths. The parameters associated with these mixing rules define a system representation of the optical properties of a composite material. In our procedure, these parameters are optimized with respect to the measured reflectivity of the composite material and existing optical data for materials similar to those making up the composite system. Estimates of optical parameters that extend over a wide range of wavelengths can provide for well-conditioned inversion, via parameter optimization, of reflectivity measurements characterized by multiscale features relative to wavelength.
Dual-Beam Near-Infrared Hadamard Spectrophotometer
Authors: da Silva Henrique Eduardo Bezerra , Pasquini Celio
Published: October 2003

A dual-beam Hadamard multiplexed spectrophotometer is described. The instrument is intended to work in the near-infrared region of the electromagnetic spectrum (900–1800 nm) and is based on the use of a linear Hadamard mask containing 255 multiplexing elements. Simple symmetric Czerny–Turner optics were employed based on 10 cm diameter, 20 cm focus spherical mirrors and a plane grating containing 295 grooves mm−1. The dual-path system employs the multiplexed beam exiting from the mask, which can then be split by using either an integrating sphere, a bifurcated optical bundle, or a beamsplitter. Two cooled PbS or InAs detectors were employed to collect the 255 multiplexed intensities in about 8 s. Signal was obtained by linear displacement of the mask, which was controlled by software written in VisualBasic 4.0. Spectral data were demultiplexed with a program written in the same language. The instrument can successfully correct for the drift of the light source intensity. The wavelength precision is 0.4 nm, while the average standard deviation for absorbance measurements taken from 900 to 1800 nm is 1.5 × 10−3 absorbance units, a value that is about three times lower than that obtained for the single-beam multiplexed approach. The instrument has been applied to the determination of water in fuel ethanol with the use of partial least-squares modeling. The absolute standard error of prediction was 0.07% (w/w).
Determination of F, Cl, and Br in Solid Organic Compounds by Laser-Induced Plasma Spectroscopy
Authors: Tran Michael , Sun Qing , Smith Benjamin W. , Winefordner James D.
Published: October 2003

The feasibility of using laser-induced plasma spectroscopy (LIPS) as a rapid and simple method to analyze fluorine, chlorine, and bromine in solid organic compounds was investigated. A Nd:YAG laser at 1064 nm with pulse energy of 100 mJ was used to produce the plasma. This method presents many advantages for the determination of halogens in organic compounds, including very simple sample preparation and near-real-time analysis. Solid organic compounds were measured in air and helium atmospheres. Carbon in organic compounds was chosen as the internal standard for the measurement of F, Cl, and Br. Linear responses for these elements were obtained for both atmospheres. However, the sensitivity was much higher and the background noise was much lower in the helium atmosphere.
Raman Spectroscopic Studies of Methane—Ethane Mixtures as a Function of Pressure
Authors: Hansen S. Brunsgaard , Berg R. W. , Stenby E. H.
Published: October 2003

Raman spectra of methane and methane–ethane mixtures (100, 85, and 49 mole % CH4) have been obtained as a function of pressure in the pressure range 0.1 to 15.3 MPaA (MPa absolute). For these mixtures methane v1 (symmetric C–H stretching) band positions are given as a function of pressure; for pure methane they are in agreement with previous results. The new data on the methane v1 band position of ethane-containing mixtures clearly depend on the kind of molecules surrounding the vibrating methane molecule. The v1 band position decreases with increasing pressure; the stronger the dependency, the higher the content of ethane. The ethane v1 band position in the two mixtures showed the same kind of dependency. A qualitative explanation for this behavior is attempted, relating it to changes in van der Waals-type interactions on pressure.
Optimization of Raman Spectroscopy for Speciation of Organics in Water
Authors: Collette Timothy W. , Williams Ted L. , D'Angelo Joseph C.
Published: October 2003

We describe herein a method for determining constants for simultaneously occurring, site-specific “microequilibria” (as with tautomers) for organics in water. The method is based in part on modeling temperature-variant Raman spectra according to the van't Hoff equation. Spectra are measured with a charge-coupled device (CCD)-based, dispersive Raman spectrometer. The success of the method depends on accurate quantification of small spectral changes that are monotonic with temperature due to changes in relative concentration of equilibrium components. The method assumes that we can neglect intensity and frequency fluctuations in spectra collected over a period of days that are not due to chemical compositional changes (e.g., frequency shifts due to ambient instrument temperature fluctuations). Also, the method assumes that we can neglect the temperature dependence of the Raman spectrum of an individual conformer. We have investigated these assumptions and found that we can typically reduce frequency and intensity fluctuations to tolerable levels by normalizing all spectra on the basis of the atmospheric N2 stretching band at 2331 cm−1, which is observed in all of our spectra. Further, we have found that we can typically neglect the temperature dependence of Raman spectra if areas of depolarized bands are used in the modeling.
Performance Comparisons of Conventional and Line-Focused Surface Raman Spectrometers
Authors: Ramsey Jeremy , Ranganathan Srikanth , McCreery Richard L. , Zhao Jun
Published: October 2003

Four Raman spectrometer configurations were compared for obtaining spectra of surface monolayers, including a new design that employed a line rather than point focus. Each spectrometer used a 514.5 nm laser and charge-coupled device (CCD) detector, but they differed in collection efficiency and sampling optics. Previously defined figures of merit for Raman signal and signal-to-noise ratio (SNR) were determined for each spectrometer, to aid quantitative comparison. The figure of merit for SNR, FSNR, is demonstrated to be useful for comparisons because it permits prediction of SNR for a given spectrometer, sample, and measurement conditions. A rigorous definition of FSNR is based on power density and takes into account the laser damage threshold of the sample. A simpler but less rigorous definition is based on laser power at the sample rather than power density and may be more useful to users who rarely determine the laser spot size. A new spectrometer design employing line focusing and collection is presented, with f/2 optics and a 6 mm slit image at the CCD. A proprietary aberration correction prevents slit image curvature common to most spectrographs with low f/#, and permits full height binning of the CCD. The line-focused spectrometer yielded an SNR and FSNR which are comparable to those for a point focus using the same collection optics and slightly lower than those for the most efficient spectrograph examined. However, the line focus permitted much lower power densities to be employed, or yielded much larger signal for the same power density at a point focus. In quantitative terms, the new line-focused design yielded an SNR which is 67 times that of the best point-focused system, for the same sample, measurement time, and laser power density.
Dispersion Relations and Phase Retrieval in Infrared Reflection Spectra Analysis
Authors: Brun Jean-Francois , De Sousa Meneses Domingos , Rousseau Benoit , Echegut Patrick
Published: October 2003

A variant of the maximum entropy method (MEM), recently developed by Vartiainen et al., is proposed for infrared reflectivity spectra analysis. The procedure uses a new interpolation algorithm to estimate the so-called error phase that is the key step of the model. As shown by several examples, this approach is a good alternative to the well known Kramers–Kronig phase retrieval relation for the determination of the dielectric function and proved to be particularly efficient in dealing with conductor materials.
Infrared Spectroscopy as Applied to Glycinin Film and Gel Formation Kinetics
Authors: Robert P. , Mangavel C. , Renard D.
Published: October 2003

Secondary structural changes of glycinin during film and gel formation were studied by infrared spectroscopy. Two complementary data treatments—i.e., principal component analysis and two-dimensional correlation spectroscopy—were applied to the infrared spectra in order to determine the time evolution of conformational changes. Kinetic curves, assessed by taking scores of the first principal components into account, revealed more pronounced changes in the case of film formation. The development of aggregates in film and gel, through intermolecular β-sheets, was identified by an increase of the absorbance band at around 1620 cm−1. Two-dimensional infrared correlation spectroscopy made it possible to observe a decrease in both α-helices and disordered structures prior to the appearance of aggregates. Changes in intramolecular β-sheets took place in a second step. The more drastic changes observed in the case of film formation were believed to result from dehydration and aggregation coupled phenomena.
In situ Infrared Technique for Studying Adsorption onto Particulate Silica Surfaces from Aqueous Solutions
Authors: Ninness Brian J. , Bousfield Doug W. , Tripp Carl P.
Published: October 2003

An in situ infrared technique is described which allows the detection of adsorbed surface species on metal oxide particles in an aqueous environment. The technique involves first formulating a “coating” comprised of high-surface-area silica particles and a polymeric binder in a suitable solvent. The resulting coating is applied to the surface of an internal reflection element and mounted in a flow-through attenuated total reflection (ATR) apparatus. The technique is demonstrated with a ZnSe element coated with fumed silica particles in a polyethylene (PE) matrix. Access of the silica surface in the matrix to adsorbates was evaluated by comparing the gas-phase reaction of silanes on silica/PE-coated CsI windows in transmission with silica/PE-coated ZnSe in an ATR evacuable cell. It is shown that the PE weakly perturbs about 25% of the surface hydroxyl groups, and that all surface groups are available for reaction with silanes. The silica/PE is indefinitely stable in an aqueous environment and has advantages of at least 2 orders higher sensitivity and a wider spectral range over studies using oxidized silicon wafers. The usefulness of this technique for studying adsorption on metal oxide surfaces is demonstrated with the reaction of succinic anhydride on an aminosilanized silica surface. This reaction sequence is a common method used to prepare glass surfaces in the attachment of probe oligonucliotides for microarray biochip technology.
Intrinsic Fluorescence of Carboxylate-Terminated Polyamido Amine Dendrimers
Authors: Larson Charlotte L. , Tucker Sheryl A.
Published: October 2003

The “intrinsic” fluorescence of carboxylate-terminated polyamido amine (PAMAM-CT) dendrimers is studied by two fluorescence techniques—excitation-emission matrices (EEMs) and lifetimes. The EEMs show similar spectral profiles for all dendrimer generations (a broad peak with an excitation and emission maximum of 380 and 440 nm, respectively) and an overall increase in relative fluorescence emission with increasing generation. Three distinct, fairly discrete lifetimes are also recovered. The shortest lifetime (0.2–0.4 ns) is a background signal from the solvent. The two longer lifetimes (1.3–2.5 and 4.2–7.1 ns) are attributed to the dendrimer. There is a general shift to longer lifetimes in τ2 and τ3, with increasing generation (G n). Both lifetimes nearly double in magnitude, going from G2.5 to G7.5, which is indicative of a specific fluorescent component being in a more protected or constrained microenvironment. These results imply that the dendrimer becomes densely packed with increasing generation. The weak, but detectable, fluorescence is most likely due to an n → π transition from the amido groups throughout the dendritic structure. Even though the exact nature of PAMAM-CT fluorescence is not fully understood, it is clear that this property shows the unique aspects of the architecture of these dendrimers and can be utilized in their characterization.