(* denotes corresponding author)

Abstracts

Focal Point Article

Fluorescence Fluctuation Spectroscopy: A Coming of Age Story

by *Alan Van Orden, Keir Fogarty, and Jaemyeong Jung, Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523  USA

Appl. Spectrosc., 58 [4] 122A-137A (2004).

Accelerated Paper

Infrared Complex Refractive Index Measurements and Simulated Reflection Mode Infrared Absorption Spectroscopy of Shock-Compressed Polymer Thin Films

by *D. S. Moore, S. D. McGrane, and D. J. Funk, Los Alamos National Laboratory, Los Alamos, New Mexico 87545  USA

Appl. Spectrosc., 58 [5] 491-498 (2004).

Thin film interference effects complicate the interpretation of reflection-mode infrared absorption spectra obtained in shock-compressed thin film materials and must be carefully accounted for in any analysis attempting to unravel shock-induced energy transfer or reactivity. We have calculated such effects for spectrally simple model systems and also, to the extent possible, for real systems such as polymethylmethacrylate (PMMA) and nitrocellulose (NC). We have utilized angle-dependent infrared (IR) reflectometry to obtain the ambient spectral complex index for PMMA and NC for use in the calculations and to interpret experiments. A number of counter-intuitive spectral effects are observed versus film thickness and during uniaxial shock compression: absorption band shifts, changes of shape, and changes in both absolute and relative peak intensities. The film thickness effects can be predicted by thin film interference alone, while additional assumptions are required to predict the effects due to shock compression. Since it is very difficult to obtain the complex index in the shock state, we made very simple assumptions regarding the change in vibrational spectra upon shock loading. We illustrate general thin film interference effects that could be expected and compare them to experimental results for the antisymmetric NO₂ stretch mode of NC.

Feature Article

Kramers–Kronig Relations and Sum Rules in Nonlinear Optical Spectroscopy

by *Kai-Erik Peiponen, Valerio Lucarini, Jarkko J. Saarinen, and Erik Vartiainen, Department of Physics, Univeristy of Joensuu, FIN-80100 Joensuu, Finland

Appl. Spectrosc., 58 [5] 499-509 (2004).

The full potential of the Kramers–Kronig relations and sum rules for nonlinear susceptibilities has unfortunately drawn relatively little attention in nonlinear optical spectra analysis. In this feature article a simple treatment of an anharmonic oscillator model in description of the nonlinear susceptibility of media and holomorphic properties of the nonlinear susceptibility were utilized. Using such concepts, conventional Kramers–Kronig, multiply-subtractive Kramers–Kronig, and generalized Kramers–Kronig dispersion relations can be derived. We demonstrate how in practice the variety of different Kramers–Kronig relations mentioned above, as well as various sum rules, can be applied in nonlinear optical spectra analysis. As an example we treat the third-harmonic wave generation spectrum from a polymer. 

Submitted Papers

Thermal Signature Characteristics of Vehicle/Terrain Interaction Disturbances: Implications for Battlefield Vehicle Classification

by *John W. Eastes, George L. Mason, and Alan E. Kusinger, U. S Army Engineer Research and Development Center, Topographic Engineering Center, 7701 Telegraph Rd, Alexandria , Virginia 22315-38604  USA

Appl. Spectrosc., 58 [5] 510-515 (2004).

Thermal emissivity spectra (8–14 μm) of track impressions/background were determined in conjunction with operation of six military vehicle types, T-72 and M1 Tanks, an M2 Bradley Fighting Vehicle, a 5-ton truck, a D7 tractor, and a High Mobility Multipurpose Wheeled Vehicle (HMMWV), over diverse soil surfaces to determine if vehicle type could be related to track thermal signatures. Results suggest soil compaction and fragmentation/pulverization are primary parameters affecting track signatures and that soil and vehicle/terrain-contact type determine which parameter dominates. Steel-tracked vehicles exert relatively low ground-contact pressure but tend to fragment/pulverize soil more so than do rubber-tired vehicles, which tend mainly to compact. In quartz-rich, lean clay soil tracked vehicles produced impressions with spectral contrast of the quartz reststrahlen features decreased from that of the background. At the same time, 5-ton truck tracks exhibited increased contrast on the same surface, suggesting that steel tracks fragmented soil while rubber tires mainly produced compaction. The structure of materials such as sand and moist clay-rich river sediment makes them less subject to further fragmentation/pulverization; thus, compaction was the main factor affecting signatures in these media, and both tracked and wheeled vehicles created impressions with increased spectral contrast on these surfaces. These results suggest that remotely sensed thermal signatures could differentiate tracked and wheeled vehicles on terrain in many areas of the world of strategic interest. Significant applications include distinguishing visually/spectrally identical lightweight decoys from actual threat vehicles.

Fourier Transform Infrared–Attenuated Total Reflectance Nitrate Determination of Soil Pastes Using Principle Component Regression, Partial Least Squares, and Cross-Correlation

by *Raphael Linker, Amit Kenny, Avi Shaviv, Liviu Singher, and Itzhak Shmulevich, Faculty of Civil and Environmental Engineering, Lowdermilk Division of Agricultural Engineering, Technion - Israel Institute of Technology, Haifa, Israel, 32000

Appl. Spectrosc., 58 [5] 516-520 (2004).

This paper investigates the use of Fourier transform infrared (FT-IR) attenuated total reflectance (ATR) spectroscopy as a fast and simple way for direct determination of nitrate concentration in soil pastes, which would assist precision fertilizer placement and reduce nitrate pollution. Eight types of soils are investigated, with nitrate concentrations ranging from 0 to 1000 ppm-N. The spectral region around the nitrate band (1300–1550 cm^–1) is analyzed by (1) principal component regression (PCR), (2) partial least squares (PLS), and (3) cross-correlation with reference libraries that include spectra of pure ions and/or soils. The main obstacle to accurate nitrate measurement appears to be an interfering band present in calcareous soils. This band, which may be due to carbonate, is located around 1450 cm^–1 and overlaps with the nitrate band centered around 1370 cm^–1. For non-calcareous soils, and in particular for light sandy agricultural soils, PLS and cross-correlation with a reference library containing only spectra of ions in water give similar results (about 8 ppm-N on dry soil basis), while PCR leads to slightly poorer results. When calcareous soils are included in the analysis, the predictions errors are about twice as large. In this case, the best results are obtained using PLS, followed by PCR, while cross-correlation with reference libraries leads to poorer results.

Infrared Spectroscopy of OD Vibrators in Minerals at Natural Dilution: Hydroxyl Groups in Talc and Kaolinite, and Structural Water in Beryl and Emerald

by *Philippe de Donato, Alain Cheilletz, Odile Barres, and and Jacques Yvon, Ecole Nationale Supérieure de Géologie ENSG – INPL, Laboratoire Environnement et Minéralurgie - UMR 7569 du CNRS, 15, avenue du Charmois, BP 40, 54501 Vandoeuvre lès Nancy - France

Appl. Spectrosc., 58 [5] 521-527 (2004).

An infrared (IR) study of natural deuteration is conducted on minerals containing hydroxyl groups (talc and kaolinite) and channel-water-bearing minerals (beryl and emerald). In talc, the OD valence vibration is located at 2710 cm^–1, corresponding to OD groups surrounded by 3 Mg atoms. In kaolinite, the OD valence vibrations are located at 2671 cm^–1 (inner OD group), 2712, 2706, and 2700 cm^–1 (three inner-surface OD groups). In beryl and emerald, natural deuteration of channel water is observed for the first time by infrared microspectroscopy. In beryl from Minas Gerais (Brazil), the OD profiles are characterized by four bands at 2735, 2686, 2672, and 2641 cm^–1. In emeralds from Colombia and Brazil, the OD profiles are characterized by five or four bands, respectively, at 2816, 2737, 2685, 2673, and 2641 cm^–1 (Colombia) and 2730, 2684, 2672, and 2640 cm^–1 (Brazil). The band at 2816 cm^–1 can be assigned to –OD or OD^–, and bands at 2686–2684, 2673–2672, and 2641–2640 cm^–1 can be assigned to type-I and type-II HOD molecules. The band at 2737–2730 cm^–1 is partially disturbed by combination bands of the mineral. Such OD profiles are different from those obtained by artificial deuteration at higher OD dilution.

Water-Related Matrix Isolation Phenomena During NO₂ Photolysis in Argon Matrix

by *David L. Cocke, Jewel A. G. Gomes, John L. Gossage, Kuyen Li, Che-Jen Lin, and Satish Tandel, Department of Chemical Engineering, Lamar University, Beaumont, Texas 77710  USA

Appl. Spectrosc., 58 [5] 528-534 (2004).

Photolysis (350–450 nm) of NO₂ molecules trapped in argon matrices at 10 K has been studied using Fourier transform infrared (FT-IR) spectroscopy to examine the mobility of the photolysis products, O(³P) and NO, and their subsequent reactions. The formation of N₂O₅ and N₂O₃ from reactions of these mobile species with immobilized NO₂ and N₂O₄ is confirmed. Water molecules from the background gases in the vacuum have been found to be isolated in the argon matrix during deposition of diluted NO₂ in Ar. The entrapped water molecules along with some of their NO₂ adducts have been characterized. Exposure of the matrix to photons to photolyze NO₂ resulted in not only internal matrix reactions but also an enhanced deposition of ice over the surface of the argon matrix. This is caused by photodesorption of water molecules from the walls of the matrix isolation chamber and their subsequent condensation on the matrix surface. This ice overlayer has been found to give a very significant dangling OH band and a substantial librational band in the FT-IR spectra, indicating substantial surface area and internal porosity, respectively. The potential of using photodesorbed water to establish high surface area ice interfaces with dangling OH groups for heterogeneous photoreaction studies is discussed. 

Fourier Transform Infrared Studies on Deblocking and Crosslinking Mechanisms of Some Fluorine Containing Monocomponent Polyurethanes

by *S. Radice, S. Turri, and M. Scicchitano, Solvay Solexis , R&D Center, Viale Lombardia 20, 20021-Bollate (MI) – Italy

Appl. Spectrosc., 58 [5] 535-542 (2004).

The thermal reactivity of a set of different blocked perfluoropolyether (PFPE) containing polyisocyanates and one monocomponent polyurethane containing a PFPE diol was investigated by Fourier transform infrared (FT-IR) spectroscopy. With the former series of products the deblocking kinetics at 90 °C and 120 °C were investigated with time-dependent spectral data, showing the highest thermal deblocking activity for 3,5 dimethylpyrazole blocking agent. The crosslinking reaction of the PFPE diol with ketoxime blocked isocyanurate at 150 °C was monitored by infrared (IR) spectroscopy and two-dimensional (2D) correlation analysis; the results suggested a prevailing direct condensation mechanism and the formation of urea by-products in the later stages of reaction. Both synchronous and asynchronous spectra were considered and discussed, pointing out the time relation of the chemical functions during the crosslinking experiment.

Quantitative Analysis of the in Situ Fourier Transform Infrared Absorption and Emission Spectrum of Gas Phase SiO(Δν = 1 and 2) Produced in Si-N-O Fiber Growth

by *P. A. Martin, R. Daum, A. Beil, U. Vogt, A. Vital, W. Graehlert, M. Leparoux, and V. Hopfe, Department of Chemical Engineering,University of Manchester Institute of Science and Technology (UMIST),PO Box 88, Manchester M60 1QD, United Kingdom

Appl. Spectrosc., 58 [5] 543-551 (2004).

The in situ Fourier transform infrared (FT-IR) spectrum of gas-phase SiO produced in silicon oxynitride fiber growth has been quantitatively analyzed. Both absorption and emission FT-IR spectra at a spectral resolution of 0.5 cm^–1 were produced from the reaction zone at 1450 °C. The fundamental and hot bands were observed with vibrational levels up to v = 7. For the purposes of quantitative analysis the individual vibration–rotation integrated line strengths for the three main isotopes, ²⁸SiO, ²⁹SiO, and ³⁰SiO, were calculated based on ab initio quantum chemical calculations of the electric dipole moment function and the transition moment. Vibrational anharmonicity and Hermann–Wallis correction factors were also incorporated. From the line strengths at specific temperatures and the known Dunham coefficients, the absorbance spectrum was simulated with best fits giving the averaged SiO concentration in the 400 mm reaction zone of 1.0 × 10¹⁷ molecules/cm³. Such quantitative measurements demonstrate the power of in situ infrared (IR) spectroscopy combined with quantum chemical calculations. The rapid determination of synthetic calibration datasets for chemometric analysis can thus lead to correlation of gas-phase species concentrations with fiber growth properties and subsequently to real-time process control.

Photoacoustic Distributed Feedback Laser Spectroscopy on Hydrogen Fluoride

by *M. Wolff, H. Groninga, and H. Harde, Universitaet der Bundeswehr Hamburg, Lasertechnik und Werkstoffkunde, Holstenhofweg 85, 22043 Hamburg, Germany

Appl. Spectrosc., 58 [5] 552-554 (2004).

We have developed a photoacoustic spectrometer based on a distributed feedback (DFB) diode laser. The single-mode emission of the laser can be tuned continuously over 700 GHz enabling the precise determination of absorption line parameters. Our experiments were performed on the rotational lines P2 and P3 of the vibrational transition 2–0 (overtone) of hydrogen fluoride (HF) at 1304.534 nm and 1312.591 nm (vacuum), respectively. The pressure broadening coefficient due to elastic collisions with N₂ molecules is found to be 5.92 ± 0.04 GHz/atm (296 K) and 5.38 ± 0.04 GHz/atm, respectively. The Doppler linewidths turn out to be 630 ± 40 MHz and 670 ± 40 MHz (296 K), respectively. The pressure-induced line shifts of the absorption lines for N₂ are 540 ± 40 MHz/atm and 580 ± 40 MHz/atm, respectively.

Vibrational Spectra and Surface-Enhanced Vibrational Spectra of 1-Nitropyrene

by E. A. Carrasco-Flores, R. E. Clavijo, M. M. Campos-Vallette, and *R. F. Aroca, University of Windsor, School of Physical Sciences, Materials and Surface Science Group, Windsor, Ontario N9B 3P4, Canada

Appl. Spectrosc., 58 [5] 555-561 (2004).

The present report on the vibrational spectra of 1-nitropyrene (1-NP) describes the infrared and Raman spectra; their interpretation is aided by local density functional theory (DFT) calculations at the B3LYP/6-311G(d,p) level of theory and by the surface-enhanced vibrational spectra (SEVS) with the final objective of trace organic analytical applications. The surface-enhanced Raman scattering (SERS) on silver island films and mixed silver/gold island films was investigated with several laser lines in the visible region. Surface-enhanced infrared absorption (SEIRA) was attempted on silver and gold island films. The interface of the organic 1-NP with smooth metal surfaces of silver and copper was also probed using reflection–absorption infrared (RAIRS) spectra that, in conjunction with the transmission spectra, allow one to extract the molecular orientation in vacuum evaporated thin solid films. Chemical adsorption of 1-NP on silver and further photochemical decomposition of the 1-NP-metal adsorbates was detected with all visible laser lines. Resonance Raman scattering (RRS) using UV-laser excitation at 325 nm was also recorded.

Adsorption of a Cholesteric Liquid Crystal Polyester on Silver Nanoparticles Studied by Surface-Enhanced Raman Scattering and Micro Raman Spectroscopy

by M. Pérez-Méndez, R. Marsal-Berenguel, and *S. Sánchez-Cortés, Instituto de Estructura de la Materia, CSIC, Serrano, 121. 28006-Madrid, Spain

Appl. Spectrosc., 58 [5] 562-569 (2004).

A Raman study of the adsorption of thermotropic cholesteric liquid crystal polyester PTOBDME ([C₃₄H₃₆O₈]_n) on Ag surfaces is presented in this work. The affinity and adsorption mechanism of this polymer was tested on Ag metal colloids and on Ag films obtained by direct immobilization of the colloidal nanoparticles. We have first studied the structure of PTOBDME suspended in several solvents in order to identify the Raman bands used as structural markers. The adsorption of the polymer leads to a deep conformational change involving both the main chain, and the aliphatic side chain. The interaction of polymers like PTOBDME with metals could be interesting in the formation of functionalized surfaces, providing them with specific physicohemical properties with possible applications in recognition phenomena, which can be easily characterized by Raman spectroscopy.

Part I: Surface-Enhanced Raman Spectroscopy Investigation of Amino Acids and Their Homodipeptides Adsorbed on Colloidal Silver

 by Edyta Podstawka, Yukihiro Ozaki, and *Leonard M. Proniewicz, Faculty of Chemistry, Chemical Physics Division, Jagiellonian University, 3 Ingardena Street, 30-060 Krakow, Poland

Appl. Spectrosc., 58 [5] 570-580 (2004).

Surface-enhanced Raman scattering spectra (SERS) were measured for various amino acids: L-methionine (Met), L-cysteine (Cys), L-glycine (Gly), L-leucine (Leu), L-phenylalanine (Phe), and L-proline (Pro) and their homodipeptides (Met-Met, Cys-Cys, Gly-Gly, Leu-Leu, Phe-Phe, and Pro-Pro) in silver colloidal solutions. The geometry and orientation of the amino acids or dipeptides on the silver surface, and their specific interaction with the surface, were deducted by detailed spectral analysis of the SERS spectra. This analysis has allowed us to propose the particular surface geometry of amino acids or dipeptides and also implied that C–C bonds were almost parallel to the surface, as evidenced by the absence of marker bands in the skeletal C–C stretching region of the spectra. Additionally, using “time-dependent” SERS measurements we solved an existing controversy regarding the binding specificity of Gly-Gly on the silver surface.

Part II: Surface-Enhanced Raman Spectroscopy Investigation of Methionine Containing Heterodipeptides Adsorbed on Colloidal Silver

by Edyta Podstawka, Yukihiro Ozaki, and *Leonard M. Proniewicz, Faculty of Chemistry, Chemical Physics Division, Jagiellonian University, 3 Ingardena Street, 30-060 Krakow, Poland

Appl. Spectrosc., 58 [5] 581-590 (2004).

Surface-enhanced Raman scattering (SERS) spectra of methionine (Met) containing dipeptides: Met-X and X-Met, where X is: L-glycine (Gly), L-leucine (Leu), L-proline (Pro), and L-phenylalanine (Phe) are reported. Using pre-aggregated Ag colloid we obtained high-quality SERS spectra of these compounds spontaneously adsorbed on colloidal silver. Additionally, we measured Raman spectra (RS) of these heterodipeptides in a solid state as well as in acidic and basic solutions. The RS and SERS spectra of Met-X and X-Met presented in this work appear to be different. One of the most prominent and common features in the SERS spectra of all these dipeptides is a band in the 660–690 cm^–1 range that is due to the C–S stretching, ν(CS), vibration of Met. This suggests that all the abovementioned compounds adsorb on the silver surface through a thioether atom. On the other hand, the SERS spectra of X-Met show clearly that not only the S atom but also the carboxylate group interact with the colloid surface as manifested by the enhancement of bands in the 920–930 and 1380–1396 cm^–1 regions. These bands are ascribed to the ν(C–COO^–) and ν_sym(COO^–) vibrations, respectively. Additionally, a SERS spectrum of Phe-Met indicates that the interaction of the thioether atom, amine group, and aromatic side chain with the silver surface is favorable and may dictate the orientation and conformation of adsorbed peptide.

Photon Migration in Raman Spectroscopy

by *Neil Everall, Thomas Hahn, Pavel Matousek, Anthony W. Parker, and Michael Towrie, ICI PLC, Wilton Research Centre, Wilton, Redcar, TS10 4RF, United Kingdom

Appl. Spectrosc., 58 [5] 591-597 (2004).

Monte Carlo simulation has been applied to study time-resolved Raman and Tyndall photon migration in opaque samples under isotropic and forward scattering conditions. For isotropic scattering, Raman and Tyndall intensities are predicted to decay according to t^(1–n) and t^–n, respectively, where the value of n depends on the ratio of the optical collection aperture to the mean scattering length. The simulation correctly reproduced the analytical results of n = 3/2 and n = 5/2 for a point source in infinite and semi-infinite media, respectively. In addition the model can be used to relate the time at which a Raman photon exits the sample to the mean depth at which it was generated. This could provide a useful tool for depth profiling the chemical composition of turbid systems, and hence be a useful addition to the established array of photon-migration techniques. The model was applied to analyze experimentally observed Raman and Tyndall decay profiles from powdered trans-stilbene. The transport mean free path (l_t) was calculated to be ~400 μm, which was significantly larger than the particle sizes present in the sample (~10–100 μm). This implies that the particles were highly forward scattering, as would be expected for this size range. When highly anisotropic scattering was introduced into the model a much more reasonable scattering length (l_s ~ 40 μm) was obtained. Finally, a simple analytical model was developed that gives the correct relationship between the Raman and Tyndall decay exponents for isotropic scattering. To the best of our knowledge this work represents the first detailed study of Raman photon migration under time-resolved conditions.

Characterization of the Structures of Size-Selected TiO₂ Nanoparticles Using X-ray Absorption Spectroscopy

by Hyun Chul Choi, Hyo-Jin Ahn, Young Mee Jung, Min Kyu Lee, Hyun Joon Shin, *Seung Bin Kim, and Yung-Eun Sung, Department of Chemistry, Pohang University of Science and Technology (POSTECH), San 31, Hyojadong, Namgu, Pohang 790-784, Republic of Korea

Appl. Spectrosc., 58 [5] 598-602 (2004).

To investigate the relationship between the size and structure of TiO₂ nanoparticles, three size-selected samples of TiO₂ nanoparticles were prepared via a hydrolysis method that uses Ti[OCH(CH₃)₂]₄ as the starting material. The structures of the nanoparticles were characterized using powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray absorption spectroscopy (XAS). Analysis of the XRD patterns and of the TEM images showed that the samples were dispersed, with an average particle size of ~30 nm (sample A), ~12 nm (sample B), and ~7 nm (sample C). Their X-ray absorption spectra indicate that samples A and B have an anatase structure, whereas sample C has a structure very similar to that of the TiO₂ II phase, which generally arises only under high-pressure conditions. This difference can be attributed to size-induced radial pressure within the smaller nanoparticles, which plays an important role in the phase of TiO₂ nanoparticles in sample C.

Comparison of Methods for Rapid Evaluation of Lifetimes of Exponential Decays

by Christopher Moore, Sing Po Chan, *J. N. Demas, and *B. A. DeGraff, Chemistry Department, University of Virginia, Charlottesville, Virginia 22904 ( J.N.D.) and Chemistry Department, James Madison University, Harrisonburg, Virginia 22807  USA (B.A.D.)

Appl. Spectrosc., 58 [5] 603-607 (2004).

Thin film interference effects complicate the interpretation of reflection-mode infrared absorption spectra obtained in shock-compressed thin film materials and must be carefully accounted for in any analysis attempting to unravel shock-induced energy transfer or reactivity. We have calculated such effects for spectrally simple model systems and also, to the extent possible, for real systems such as polymethylmethacrylate (PMMA) and nitrocellulose (NC). We have utilized angle-dependent infrared (IR) reflectometry to obtain the ambient spectral complex index for PMMA and NC for use in the calculations and to interpret experiments. A number of counter-intuitive spectral effects are observed versus film thickness and during uniaxial shock compression: absorption band shifts, changes of shape, and changes in both absolute and relative peak intensities. The film thickness effects can be predicted by thin film interference alone, while additional assumptions are required to predict the effects due to shock compression. Since it is very difficult to obtain the complex index in the shock state, we made very simple assumptions regarding the change in vibrational spectra upon shock loading. We illustrate general thin film interference effects that could be expected and compare them to experimental results for the antisymmetric NO₂ stretch mode of NC.

Further Investigations on a Poly(vinyl alcohol)–Polyelectrolyte Chemically Selective Optical Film

by Jean R. Paddock, Imants Zudans, William R. Heineman, and *Carl J. Seliskar, Department of Chemistry, University of Cincinnati, P.O. Box 210172, Cincinnati, Ohio 45221-0172 USA

Appl. Spectrosc., 58 [5] 608-612 (2004).

The ionomer poly(vinylbenzyltrimethylammonium chloride) has been blended with cross-linked poly(vinyl alcohol) to form optically clear composites that can be covalently linked as thin films to oxide surfaces. Films are characterized using spectroscopic ellipsometry with refractive index (n) and extinction coefficient (k) data presented for wavelengths 300 to 1100 nm. A refractive index of 1.54 and average thickness of 709 nm are typical of an air dry film prepared by spin-coating. Dynamic in situ ellipsometry results for films exposed to 0.1 M KNO₃ and 1.0 mM K₄Fe(CN)₆^–3 are presented. Upon initial exposure to 0.1 M KNO₃, an air dry film expands by about 160% and stabilizes in size and refractive index at about 18 hours. Ion exchange of film cationic groups with ferricyanide is marked by slight film contraction, presumably due to electrostatic cross-linking by the multivalent anion. These films are useful in the spectroelectrochemical sensor with our newly developed fluorescence detection mode, as demonstrated by results of the reversible incorporation of the fluorescent anion fluorescein.

Time-Resolved Fluorescence Spectroscopic Study of Crude Petroleum Oils:  Influence of Chemical Composition

by Alan G. Ryder, National Centre for Biomedical Engineering Science, National University of Ireland - Galway, Galway, Ireland

Appl. Spectrosc., 58 [5] 613-623 (2004).

The fluorescence of crude petroleum oils is sensitive to changes in chemical composition and many different fluorescence methods have been used to characterize crude oils. The use of fluorescence lifetimes to quantitatively characterize oil composition has practical advantages over steady-state measurements, but there have been comparatively few studies in which the lifetime behavior is correlated with gross chemical compositional data. In this study, the fluorescence lifetimes for a series of 23 crude petroleum oils with American Petroleum Institute (API) gravities of between 10 and 50 were measured at several emission wavelengths (450–785 nm) using a 380 nm light emitting diode (LED) excitation source. It was found that the intensity average fluorescence lifetime () at any emission wavelength does not correlate well with either API gravity or aromatic concentration. However, it was found that  is strongly negatively correlated with both the polar and sulfur concentrations and positively correlated with the corrected alkane concentration. This indicates that the fluorescence behaviour of crude petroleum oils is governed primarily by the concentration of quenching species. All the strong lifetime-concentration correlations are nonlinear and show a high degree of scatter, especially for medium to light oils with API gravities of between 25 and 40. The degree of scatter is greatest for oils where the concentrations (wt %) of the polar fraction is ~10 ± 4%, the asphaltene component is ~1 ± 0.5%, and sulfur is 0.5 ± 0.4%. This large degree of scatter precludes the use of average fluorescence lifetime data obtained with 380 nm excitation for the accurate prediction of the common chemical compositional parameters of crude petroleum oils.

Influence of Wavelength Shifted Calibration Spectra on Multivariate Calibration Models

by Frank Vogt and Karl Booksh, Arizona State University, Department of Chemistry and Biochemistry, Mail stop 1604, Tempe, Arizona 85287  USA

Appl. Spectrosc., 58 [5] 624-635 (2004).

Multivariate calibration models are sensitive to wavelength shifts in calibration spectra as such disturbances are linearly independent from unshifted spectra and increase the calibration model’s dimension. However, if wavelength shifts included in the calibration model are random, the predictability of the model is not improved. On the contrary, overfitting is introduced, thereby increasing the prediction error. Because calibration spectra are defined to be error free and are the only available data at that point, there is no analytical way to find out that the calibration model is erroneous. This study gives a mathematical explanation of how the model’s dimension is increased by wavelength shifts and that the additional basis vectors, principal components for instance, possess derivative-shaped features. It is also demonstrated by means of an example that the reverse is not necessarily true. Hence, derivative-shaped features found in principal components are no indication of wavelength-shifted calibration spectra. A method is presented for analyzing calibration spectra for such shifts. The algorithm takes advantage of the fact that artificial shift compensations of true shifts increase the similarity, i.e., correlation, of shifted spectra with respect to the remaining, unshifted spectra. Synthetic and experimental data are used to demonstrate and assess the performance of the algorithm. It is shown that wavelength shifts in calibration spectra can be detected and corrected if a small number of spectra are disturbed. Significant improvements of the prediction errors of chemometric calibration models can be achieved by means of this shift-correction algorithm.

Notes

Application of Deep Blue Diode Laser to Resonance Raman Spectroscopy of Hemoproteins

by Kenji Oda, Shigeki Kuroiwa, and *Takashi Ogura, Department of Life Science, Graduate School of Arts and Sciences, The University of Tokyo, Komaba 3-8-1, Meguro-ku, Tokyo 153-8902, Japan and Department of Life Science, Graduate School of Science, Himeji Institute of Technology, Koto 3-2-1, Kamigori-cho, Ako-gun, Hyogo 678-1297, Japan

Appl. Spectrosc., 58 [5] 636-638 (2004).

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