| SUMMARIES OF FY 1996 RESEARCH IN THE CHEMICAL SCIENCES |
Molecular Processes Program
| Investigator(s) | Fritz, J.S. | $139,000 | ||
|---|---|---|---|---|
| Phone | 515-294-5987 | |||
| kniss@ameslab.gov | ||||
The project objective is to devise practical, innovative methods for analytical separations and chemical analysis. Capillary electrophoresis (CE), and ion chromatography are used to separate and determine anions and metal cations in complex samples. A novel CE method enables neutral organic compounds of very similar chemical structure to be separated effectively without resorting to the use of micelles. New resins and techniques are developed for solid-phase extractions and for chromatographic separations. Resins of small particle size are incorporated into membranes to obtain rapid mass transfer. Chelating reagents and chemicals are prepared for isolation of selected metal ions prior to their measurement by atomic or mass spectroscopy. Low-cost resins are being developed for effective cleanup of toxic metal ions in wastes.
| Beginning of this section | Table of Contents | Investigator Index | Institution Index, | Topic Index |
Molecular Processes Program
| Investigator(s) | Houk, R.S. | $397,000 | ||
|---|---|---|---|---|
| Phone | 515-294-9462 | |||
| rshouk@iastate.edu | ||||
The basic principles and practical aspects of several important methodologies for ultratrace analysis are studied in this project. Plasma sources for atomic spectroscopy and mass spectrometry are emphasized, particularly mechanistic and analytical investigations of the inductively coupled plasma (ICP). New directions in ICP mass spectrometry include basic studies of the sample introduction and ion extraction processes, development of instrumental methods for removing interferences, and the use of ICP-MS in conjunction with chromatographic separations for measurement of elemental speciation. These ICP studies have resulted in state-of-the-art analytical methodologies that are utilized extensively elsewhere in DOE and in the outside analytical community. New studies in ion trapping and ion formation in electrospray mass spectrometry are also being initiated.
| Beginning of this section | Table of Contents | Investigator Index | Institution Index, | Topic Index |
Molecular Processes Program
| Investigator(s) | Porter, M.D. | $166,000 | ||
|---|---|---|---|---|
| Phone | 515-294-6433 | |||
| porter@ameslab.gov | ||||
This project explores novel approaches to the design, synthetic fabrication, and molecular level characterization of monomolecular and thin polymeric films at liquid-solid and gas-solid interfaces. Projects this year have entailed (1) fabricating chemically-gatable interfaces with size selective molecular recognition properties, (2) examining the nucleation and growth of spontaneously adsorbed monomolecular films formed from alkanethiols at gold and silver surfaces, and (3) probing solvent-monolayer interactions at such interfaces with in situ infrared reflection and Raman spectroscopies. The molecular recognition effort examines the incorporation of ionizable size-selective channels in long alkyl chain monolayers. The nucleation and growth studies are aimed at unraveling the origins of structural defects (e.g., grain boundaries) within such structures. The in situ investigations employ infrared reflection and Raman spectroscopies, optical ellipsometry, electrochemistry, and contact angle measurements. The overall objective is to develop relationships that form a basis for broader correlations between the composition and molecular arrangement (spatial orientation and packing density) of organic interfaces with macroscopic physical and chemical properties (e.g., lubrication, catalysis, adhesion, and chemical analysis).
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Process and Techniques Program
| Investigator(s) | Porter, M.D.; Angelici, R.J. | $175,000 | ||
|---|---|---|---|---|
| Phone | 515-294-6433 | |||
| mporter@porter1.ameslab.gov | ||||
Remediation of the large volumes of high level wastes (HLWs) in the DOE complex requires separating radioactive materials into high and low level waste streams. Remediation also dictates the minimization of HLW stream volumes to reduce long term storage costs. This program explores the reversible electrochemical transformation of selective chelates tethered to carbon packings as a novel method for concentrating highly radioactive constituents in HLWs. The aim is to exploit the unique capabilities of a new series of metal-ion selective crown ethers (CEs) that incorporate redox transformable moieties like catechol and hydroquinone within the CE cavity. Since the stability constants for metal ion binding are expected to decrease markedly by the oxidation of these types of transformable moieties, a new separation process can be envisioned in which a column can be switched between concentration and stripping modes by the respective reduction and oxidation of the immobilized chelate. This program is aimed at assessing the range and scope of this new separation concept.
| Beginning of this section | Table of Contents | Investigator Index | Institution Index, | Topic Index |
Molecular Processes Program
| Investigator(s) | Yeung, E.S. | $324,000 | ||
|---|---|---|---|---|
| Phone | 515-294-8062 | |||
| yeung@ameslab.gov | ||||
With the development of new energy technologies, materials problems, environmental pollution, and health effects present challenges to the analytical chemist. We are developing several laser-based analytical techniques to gain unique insight into elemental, organic, and gaseous pollutants associated with energy utilization, to study chemical changes of ultrasmall samples, and to probe variations in the surface composition of materials. We emphasize (1) studies of the fundamental processes in atom sources such as laser-generated plumes; (2) liquid chromatographic and capillary electrophoretic determination of organic, inorganic, and biochemical species using more sensitive or more selective detectors; (3) laser-based detection of large molecules deposited or adsorbed on surfaces of materials; and (4) real-time spectroscopic probes of chemical reactions down to the single-molecule limit.
| Beginning of this section | Table of Contents | Investigator Index | Institution Index, | Topic Index |
Chemistry Division
| Investigator(s) | Horwitz, E.P.; Barrans, R.E.; Chiarizia, R.;Dietz, M.L. | $1,039,000 | ||
|---|---|---|---|---|
| Phone | 630-252-3653 | |||
| jan_nolan@qmgate.anl.gov | ||||
The objectives of this program are (A) to develop new and improved reagents that may be applied to help solve major problems in environmental remediation and waste management and (B) to elucidate the basic chemistry involved in utilizing these new reagents. The major subdivisions of the program are (1) the study of basic interactions between the extractant and diluent with the goal of achieving major alterations in extractant behavior, particularly with regard to both enhancing extraction efficiency and improving the physical properties of the system; (2) the study of isomer effects on molecular recognition by macrocyclic polyethers with the goal of understanding how conformational changes in the macrocyclic ring affect metal complex stability and macrocycle selectivity; (3) the design, synthesis, and characterization of new classes of multifunctional extractants that show extraordinary selectivities for selected metal ions; and (4) the design, synthesis, and characterization of a new class of aqueous-soluble molecules that will serve as selective guests for chelated metal ions and subsequently form a precipitate. All four objectives are directed towards application in nuclear technology, such as actinide separations, waste processing, by-product recovery from nuclear wastes, and hydrometallurgical processing.
| Beginning of this section | Table of Contents | Investigator Index | Institution Index, | Topic Index |
Department of Applied Science
| Investigator(s) | Adzic, R. | $382,000 | ||
|---|---|---|---|---|
| Phone | 516-344-4522 | |||
| adzic@solids.phy.bnl.gov | ||||
The objective of this program is to enhance the understanding of the relationship between the structure of an electrode surface and its function in an electrochemical process. A unique feature of this work is the emphasis on in situ determination of the structure of an electrode surface with atomic resolution during the course of an electrochemical reaction, i.e., the identification of atomic geometry of the reaction sites, as well as the identification of adsorbates, intermediates and products, with molecular specificity. Besides insights into fundamental surface electrochemistry and electrocatalysis, the results will have potential applicability in electrochemical energy conversion, electroorganic synthesis and sensors. X-ray scattering (utilizing the National Synchrotron Light Source) scanning tunnelling microscopy, (nonenhanced) Raman scattering and Fourier transform infrared spectroscopy will be the primary in situ probes. Specific studies will focus on determination of structures of metal atom, anion and molecular adsorbates in the absence and in the presence of several important electrocatalytic reactions and exploring of laws of ordering of the adsorbates on surfaces. These results will help to establish the correlations between the surface structure and its electrocatalytic activity and provide a basis for prediction of surface electrocatalytic properties.
| Beginning of this section | Table of Contents | Investigator Index | Institution Index, | Topic Index |
Department of Applied Science
| Investigator(s) | Tang, I.N.; Fung, K.H. | $243,000 | ||
|---|---|---|---|---|
| Phone | 516-344-4517 | |||
| tang1@bnl.gov | ||||
Aerosol particles are present abundantly and ubiquitously in nature and in environments associated with many energy-conversion systems, industrial processes, and health-related areas as well. These microparticles need to be characterized by their physical state and chemical composition, thus requiring the exploration of physical and chemical principles which can lead to entirely new methods of analysis specific to microparticles. This program focuses specifically on a basic understanding and novel applications of laser based spectroscopic methods for in situ characterization of suspended microparticles. Because of the nondestructive and species specific nature of Raman scattering, a unique single particle - Raman spectroscopy technique is currently being developed for physical and chemical characterization of microparticles. Progress has been made in establishing the detection limits for various Raman processes on microparticles. Sensitivity enhancement by resonance Raman scattering is being investigated. In addition, the single-particle levitation technique, in conjunction with spectroscopic tools to probe the physical and chemical state of molecular and ionic species in microparticles, is ideally suited for obtaining insight into the nature of ion association and solute phase transformation at high concentrations otherwise unattainable in bulk solutions. Thus, new amorphous metastable states that exist only in hygroscopic microparticles, but not in the bulk phase, have been identified. This research will not only continue to discover and elucidate heretofore unknown properties unique to microparticles, but also will provide the science and technology basis for advanced analytical techniques.
| Beginning of this section | Table of Contents | Investigator Index | Institution Index, | Topic Index |
| Investigator(s) | Delmore, J.E.; Appelhans, A.D.;Dahl, D.A. | $306,000 | ||
|---|---|---|---|---|
| Phone | 208-526-2820 | |||
| jed2@inel.gov | ||||
The elucidation of mechanisms for the formation of gas phase ions from high temperature inorganic condensed state matrices is the main thrust of this program. There are two main approaches for producing these ion emitters; embedding the desired pre-synthesized species in a suitable matrix, and production of the desired species via a chemical reaction as the ions are emitted. Several instruments have been devised to assist in these studies. Tube ion sources have been developed in which large samples of these ion emitting matrices can be pressed into refractory metal tubes and heated to ion emission temperature. These sources can be exchanged between an ion/neutral mass spectrometer, a conventional magnetic sector mass spectrometer and an ion source imaging instrument. The ion/neutral mass spectrometer was completed this past year, and allows the ions and neutrals subliming from the emitters to be measured in sequence. Preliminary data from this instrument demonstrates that important insights into ion emission mechanisms can be gained from this approach. Gases can also be diffused through the material in the tube so that high temperature gas/solid reactions can be studied in the mass spectrometers. Imaging of emitters have demonstrated that ion emission is exclusively from the surface of the bulk of the emitter, and that cracks in the emitter allow greatly enhanced emission. Understanding the role of cracks in the transport of ions has allowed new design concepts to be developed to increase ion intensity from these emitters. This work indicates that these emitters are micro chemical factories which either produce the species needed for ion emission, or preserve the pre-synthesized species. This understanding has led to new techniques for the custom design of emitters. A new line of study will test the theory that ions can be stored on surfaces and then pulsed out, using a repulsive electric field to hold the ions on the surface, and then an attractive field to cause them to desorb. A time-of-flight mass spectrometer has been modified to conduct these studies. In order to model the interactions of ions in electrostatic and magnetic fields, ion optic models have been developed. SIMION 6.0 was developed on this program and released this past year.
| Beginning of this section | Table of Contents | Investigator Index | Institution Index, | Topic Index |
Energy and Environment Division
| Investigator(s) | Russo, R.E. | $208,000 | ||
|---|---|---|---|---|
| Phone | 510-486-4258 | |||
| rerusso@lbl.gov | ||||
The interaction of a high-powered pulsed laser beam with solid materials offers widespread importance to many areas within the DOE and U.S. industries, including environmental analysis, non-proliferation, materials, electronics, and medical. Importantly, the laser material interaction (LMI) is a powerful technology for chemical separations and analysis. A pulsed, high-powered laser beam ablates constituent elements from any sample material into the vapor phase, which can be analyzed by classical spectroscopic techniques. However, the explosive laser material interaction is not fundamentally defined for general application. Critical issues to resolve are the fundamental mechanisms underlying the interaction, mass ablation rate behavior, and stoichiometric ablation. This Basic Energy Sciences supported research endeavors to elucidate fundamental mechanisms of the laser-material interaction and to develop laser sampling capabilities for DOE needs in chemical separations and analysis. The research emphasizes the study of repetitive-pulsed laser material interactions at atmospheric pressure. Atomic emission spectroscopic (AES) data from an inductively coupled plasma (ICP) demonstrate changes in the laser material interaction as a function of laser and material properties. ICP-AES is one of the only technologies for studying LMI at atmospheric pressure. Piezoelectric sensors are used to study the propagation of acoustic waves induced in the material by the pulsed irradiation. Probe-beam deflection is employed to determine the onset of material removal and the formation of a laser initiated surface plasma. Fundamental mechanisms describing the laser material interaction are developed by drawing correlations between these acoustic, deflection, and atomic emission data. Improved capabilities for direct solid sample chemical analysis are reported to the DOE and scientific community through technical publications and conference meetings.
| Beginning of this section | Table of Contents | Investigator Index | Institution Index, | Topic Index |
Chemical Technology Division
| Investigator(s) | Byers, C.H.; DePaoli, D.W.; Tsouris, C.; Zhang, X. | $339,000 | ||
|---|---|---|---|---|
| Phone | 423-574-4653 | |||
| kdb@ornl.gov | ||||
This program is comprised of several fundamental studies that explore the use of electromagnetic fields to enhance the efficiency of multiphase separations processes. Experimental, theoretical, and computational methods are employed to investigate the effect of electromagnetic fields on transport processes in liquid-liquid, gas-liquid, and solid-liquid systems. This work will provide information necessary to devise novel means to dramatically improve transport rates in these systems, and thus will have widespread benefit for separations processes such as solvent extraction and distillation as well as applications in environmental and biotechnology areas. There are three areas of current focus: (1) interface deformation and breakup, including analyses of electrostatic spraying of droplets and bubbles, drop formation, pendant drop oscillations, stretching liquid bridges, and drop impact; (2) electrocoalescence, including electrostatic and hydrodynamic interactions between charged, deformable drops; and (3) magnetic separations, including a fundamental analysis of high-gradient magnetic flocculation and filtration.
| Beginning of this section | Table of Contents | Investigator Index | Institution Index, | Topic Index |
Chemical Technology Division
| Investigator(s) | Cochran, H.D. | $356,000 | ||
|---|---|---|---|---|
| Phone | 423-574-6821 | |||
| hdc@ornl.gov | ||||
The striking properties of solutions in supercritical solvents can be understood in terms of the underlying fluid microstructure and molecular interactions. Fundamental understanding of these properties is the aim of theoretical and experimental studies. Such solutions are important in novel separations technologies such as supercritical extraction and supercritical chromatography and in other technologies as well. Understanding of supercritical solutions of simple fluids has been gained through our past theoretical studies, molecular simulations, and neutron scattering experiments of solutions of noble gas mixtures. This understanding is being extended to more complex fluids of practical importance to industry-for example, solutions in supercritical water and solutions of polymers with supercritical solvents-using molecular simulation techniques. We have also performed neutron scattering and x-ray scattering studies of polymers and of reverse micelles containing polymers in supercritical CO2. With our new molecular simulation codes for calculations on massively parallel supercomputers we have begun studies of ion speciation in supercritical water; other codes have been developed for studying polymer systems. Complementary applied research is performed to support U.S. industry in areas such as supercritical water oxidation of hazardous wastes, polymerization in supercritical CO2, and extraction of fatty acids in bioprocessing.
| Beginning of this section | Table of Contents | Investigator Index | Institution Index, | Topic Index |
Chemical Technology Division
| Investigator(s) | Toth, L.M.; Dai, S | $343,000 | ||
|---|---|---|---|---|
| Phone | 423-574-5021 | |||
| lmt@ornl.gov | ||||
This project is one of only a few remaining fundamental research efforts that are concerned with the physical-chemical characteristics of the actinides and fission products as related to separations schemes. Although the efforts are generally focused on spectroscopic and photochemical approaches, other techniques such as neutron/X-ray small angle scattering have been employed as a means of identifying more macroscopic properties of these systems (e.g., the sizes and geometries of colloidal species). The fundamental concerns are aimed at defining the chemistry of (1) molten salt systems containing actinides or fission products (which have some potential for separations or waste isolation development); (2) these elements trapped and photolyzed in the controlled environment of a solid matrix (which could encourage novel separations under these conditions); and (3) hydrolytic polymers (namely, the factors controlling their formation, reactivity, and ultimate size, which ultimately influences separations involving these species). The common thread in this effort is speciation, seeking to relate the macroscopically observed chemical properties, eg., changes in thermodynamic properties, to variations in the molecular species found in the systems. Recent impact of these fundamental studies is found in several EM programs including the Molten Salt Reactor Experiment Remediation project.
| Beginning of this section | Table of Contents | Investigator Index | Institution Index, | Topic Index |
Chemical and Analytical Sciences Division
| Investigator(s) | Goeringer, D.E.; Buchanan, M.V.; Hurst, G.B.; McLuckey, S.A. | $150,000 | ||
|---|---|---|---|---|
| Phone | 423-574-3469 | |||
| goeringerde@ornl.gov | ||||
The objective of this work is to conduct research and development on laser photoionization (PI) in combination with tandem mass spectrometry for real-time detection and measurement of oxygenated compounds in automotive exhaust. Current analytical protocols for analysis of some classes of vehicle emissions, including oxygenated compounds, require collection of exhaust samples and off-line analysis in an analytical laboratory. We propose to use single-photon ionization with coherent vacuum ultraviolet (118 nm, 10.5 eV) light in combination with ion trap tandem mass spectrometry to obtain the improvements in speed, sensitivity, and specificity needed for real-time analysis of complex automobile emissions. Because ionization potentials (IP's) for many oxygenated and other organics are below 10.5 eV, PI should, with a few exceptions, be universal for these exhaust components. Furthermore, several potential interferences (H2O, CO2, SO2, and N2O) have IP's well above 10.5 eV, and thus will not be ionized. Because some exhaust components have identical molecular weights, isomer discrimination through tandem mass spectrometry (MS/MS) will also be explored. The increased specificity of compound identification via MS/MS relies both on the mass of the parent ion formed by PI and the mass(es) of the product ion(s) formed from unimolecular decomposition under MS/MS conditions. The quadrupole ion trap mass spectrometer, which is intrinsically suited for use with pulsed ionization methods such as laser PI, is capable of executing ion manipulation operations for MS/MS and MSn experiments on the time scale (tens-hundreds of msec) necessary for real-time emissions monitoring.
| Beginning of this section | Table of Contents | Investigator Index | Institution Index, | Topic Index |
Chemical and Analytical Sciences Division
| Investigator(s) | Hulett, L.D., Jr. | $243,000 | ||
|---|---|---|---|---|
| Phone | 423-574-8955 | |||
| hulettldjr@ornl.gov | ||||
In recent years the availability of monoenergetic beams of positrons has given rise to a spectacular increase in the utility of positron spectroscopy and has demanded a better understanding of the fundamental interactions of positrons with atoms and molecules. It is believed that the formation of positronium compounds occurs in a large number of cases, and thus an effort to explicitly identify these intermediates has begun. Evidence for the formation of positronium hydroxide (PsOH) has been seen. Positrons displace protons, which are detected by time-of-flight mass spectrometry. The heat of formation of the PsOH lowers the threshold energy required by the positrons by about 0.6 eV. There is even stronger evidence of the formation of positronium chloride (PsCl), for which the heat of formation has been calculated to be about -2 eV. In the ionization of CH3Cl a break was seen in the ion current-vs-positron energy plot, which was about this magnitude. The resolution and peak-to-background ratio of the time-of-flight mass spectrometer have been improved sufficiently to allow measurements of the sub-positronium ionization cross sections for helium and the other inert gases. Secondary electron emission from organic compounds undergoing sub-positronium interactions will be studied. Collaborators in the above work include Fisk University, Maquette University, the University of Texas, Arlington, Arhus University, Denmark, University College London, and two Japanese scientists, from the Electrotechnical Institute and the National Institute for Chemistry and Materials.
| Beginning of this section | Table of Contents | Investigator Index | Institution Index, | Topic Index |
Chemical and Analytical Sciences Division
| Investigator(s) | Moyer, B.A.; Sachleben, R.A.; Bonneson, P.V.; Bryan, J.C. | $911,000 | ||
|---|---|---|---|---|
| Phone | 423-574-6718 | |||
| moyerba@ornl.gov | ||||
Research in this program concerns the synthesis, structure, and thermodynamics of crown compounds and related selective extractants for the solvent extraction and ion exchange of metal ions from aqueous solution. The major fundamental issue currently being investigated is the relationship between extractant structure and both the efficiency and selectivity of extraction for alkali metal cations and their counteranions. This issue is being addressed in the context of the often-extraordinary influence of the solvent environment. Principles of chemical recognition form the basis for probing the influence of complementarity, exclusivity, preorganization, strain, inductive effects, and steric factors on host-guest interactions. With input from molecular-mechanics calculations, synthetic efforts target large- and small-ring crown compounds having systematically varying structural features. NMR methods and X-ray crystallography provide detailed structural information on extractants and their complexes. Extraction efficiency and selectivity are evaluated by distribution studies, using ion chromatography, ICP spectrometry, and radiotracer methods. Potentiometry, calorimetry, and FTIR and UV/vis spectroscopies provide additional information. Interpretation of the extraction results is aided by advanced equilibrium analysis using our unique program SXLSQI to develop accurate speciation models. Overall, results potentially benefit applied USDOE programs (e.g., Office of Environmental Management) and industries concerned with separations.
| Beginning of this section | Table of Contents | Investigator Index | Institution Index, | Topic Index |
Chemical and Analytical Sciences Division
| Investigator(s) | Ramsey, J.M.; Barnes, M.D.; Shaw, R.W.; Whitten, W.B.; Young, J.P. | $514,000 | ||
|---|---|---|---|---|
| Phone | 423-574-5662 | |||
| ramseyjm@ornl.gov | ||||
The objective of this program is to utilize fundamental developments in optics, lasers, chemistry, and physics to enable the development of new laser-based techniques to improve the sensitivity and/or specificity of chemical measurements. These techniques are applicable to a broad range of chemical measurement problems in fields encompassing environmental monitoring, process control, materials analysis, and biotechnology. Areas of research include ultrasensitive fluorescence detection, nonlinear optical processes, and resonance ionization mass spectrometry. We are addressing fundamental principles that must be understood to advance the area of single molecule detection. Microdroplet sampling is utilized to achieve picoliter to femtoliter probe volumes for the detection of single fluorescent molecules. These small probe volumes and the absence of diffusional losses has allowed detection of single chromophore molecules at high sensitivity (S/N 8950). Further understanding of cavity quantum electrodynamic effects and increased spontaneous emission rates for chromophores in microdroplets promises to enhance the sensitivity of these experiments. Surface nonlinear optical probes will be used to study surface chemistry within the top monolayer of thin films during growth in chemical vapor deposition reactors. These probes are expected to assist understanding of materials growth mechanisms. Multiphoton ionization experiments coupled with mass spectrometry are being investigated for isotopic analysis of elements and to further understand molecular energetics of trapped ions. A custom laser system is being constructed to advance the objectives of this program.
| Beginning of this section | Table of Contents | Investigator Index | Institution Index, | Topic Index |
Chemical and Analytical Sciences Division
| Investigator(s) | Smith, D.H.; Barshick, C.M.; Duckworth, D.C.; Riciputi, L.R. | $330,000 | ||
|---|---|---|---|---|
| Phone | 423-574-2449 | |||
| smithdh@ornl.gov | ||||
The goal of this research is to advance the state-of-the-art in inorganic mass spectrometry. Areas of interest include glow discharge, isotope ratio, secondary ion, and inductively coupled plasma mass spectrometries. Areas of concentration in glow discharge mass spectrometry include development of a rf glow discharge cell for analysis of non-conducting materials and interfacing of a glow discharge to an ion trap. The ion trap holds great promise for both applied and fundamental studies. Metal ion chemistry and collision-induced dissociation are being explored, and the trap's properties provide several ways to address molecular interferences, thus enhancing capabilities for quantification. Fundamental studies using our sector mass spectrometer have been undertaken to elucidate the formation of rare species such as metal argides in a glow discharge; both rare and reactive gases are being used. The goal is to gain a better understanding of plasma chemistry through, for example, the closing of various thermodynamic cycles. An ICP sector mass spectrometer equipped with seven collectors is being evaluated for measurement of isotope ratios. In secondary ion mass spectrometry, our primary effort is directed toward understanding the relationship between the chemical composition of the sample and variations in instrumental bias in the measurement of isotope ratios. A linear relationship with respect to chemical composition between two end members (e.g., FeO and MgO) was established; this work is currently being extended to more complex systems. The relative merits of high resolution and extreme energy filtering when applied to the S isotope ratios were evaluated, with extreme energy filtering being the more accurate. Speciation of toxic metals in soils using gas chromatography-mass spectrometry has recently been undertaken; the goal is to quantify both inorganic and organic forms of the element in a single sample.
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Chemical and Analytical Sciences Division
| Investigator(s) | Todd, P.J.; McMahon, J.M.; Short, R.T. | $427,000 | ||
|---|---|---|---|---|
| Phone | 615-574-6824 | |||
| toddpj@ornl.gov | ||||
This research concerns advancing the applicability of secondary ion mass spectrometry (SIMS) by identifying the fundamental causes of barriers to applicability, characterizing these barriers, and then finding a suitable method to overcome the barrier. For example, primary ion damage limits the utility of SIMS for mapping the distributions of organic compounds. We found that the effects of chemical damage could be mitigated by using a beam of cluster ions in conjunction with a primary Cs+ beam to ablate the surface. Currently, we are modifying this approach by using a focused beam of cluster ions to perform ionization and ablation simultaneously; this will permit direct imaging by cluster ion impact, and should permit analysis of higher molecular weight molecules. As another example, we are developing methods for imaging and isotope ratio measurement of targeted elements from geologic samples. Here, the historic barriers have included limited precision and reproducibility. These barriers arise from the peculiarities of the mass spectrometer. To overcome them, we are using a mass spectrometer that permits simultaneous detection of isotopic ions and alternate measurement of an isotopic standard with measurements from the sample.
| Beginning of this section | Table of Contents | Investigator Index | Institution Index, | Topic Index |
Chemical and Analytical Sciences Division
| Investigator(s) | VanBerkel, G.J.; Goeringer, D.E.;McLuckey, S.A.;Ramsey, R.A. | $390,000 | ||
|---|---|---|---|---|
| Phone | 423-574-1922 | |||
| vanberkelgj@ornl.gov | ||||
The goal of this research program is to enhance organic mass spectrometry as an analytical tool via improved understanding of the underlying chemical and physical processes involved. A broad range of chemical reactions and physical processes can occur within the context of an organic mass spectrometry experiment due to the extremely wide range of reaction conditions that can be established. Unimolecular, bimolecular, and termolecular reactions (gas-phase processes) can occur as well as the wide variety of processes associated with ionization (gas-phase and solution processes). Ionization by glow discharge, laser irradiation, and electrospray are of primary interest in this program. The current research effort is focused on three main areas of investigation: electrostatic spray ionization, gas-phase reactions of polyatomic multiply-charged ions, and quadrupole ion trap mass spectrometry. The work with electrostatic spray systems, such as the electrospray (ES) and electrohydrodynamic (EH) ion sources, focuses on understanding the fundamental operation of these condensed-phase ion sources so as to widen their applicability and overall analytical utility. In particular, chemical, electrochemical, and optical techniques are used to correlate the solution chemistry of analytes with the gas-phase ions produced by these ion sources. These same techniques are also used to create ionic species for gas-phase study. Elucidating the effects of the coulombic field of multiply-charged ions on their gas-phase structure, stability, and reactivity is the focus of the ion chemistry studies. The use of ion-molecule and, more recently, ion-ion reactions is central to this work. Understanding the fundamental physical and chemical effects of operational parameters on gas-phase ions is a major theme in the quadrupole ion trap work. One major effort in this regard is the ongoing refinement of a detailed theoretical model for the collision-induced dissociation process (CID) as it occurs within the ion trap. Enhanced analytical utility of ion trap CID (i.e., tandem mass spectrometry) for structural determinations is one expected outcome from this advanced theory. This theory also shows that the ion trap might be used as a fundamental research mass spectrometer to garner such basic physical and chemical information as critical dissociation energies.
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Chemical Sciences Department
| Investigator(s) | Yonker, C.R.; Fulton, J.L. | $418,000 | ||
|---|---|---|---|---|
| Phone | 509-372-4748 | |||
| cr_yonker@pnl.gov | ||||
The objective of this program is to describe the molecular interactions underlying separations in supercritical fluids. The scope of these studies spans the range from simple bi-molecular solute/solvent interactions to more complex multi-molecular clustering, ion-pair formation, chelation, and micellization phenomena. Molecular level studies in supercritical fluids will provide an improved understanding of both fluids and condensed-phase interactions by bridging the gap between the gaseous and liquid states. This program focuses on the fundamental chemistry that controls solute/solvent intermolecular interactions and the behavior of complex molecular assemblies in supercritical fluids through experimental and theoretical investigations. The experimental effort entails the use and expansion of various spectroscopic techniques such as FTIR, Raman, NMR, XAFS, and small angle X-ray scattering for supercritical fluids. The parallel theoretical effort involves molecular dynamics simulations describing the fundamental behavior of fluid solvents. Continued studies seek to characterize angstrom- to micron-sized molecular assemblies in supercritical fluids, e.g., alcohol aggregates, chelates, hydrated ions, and reverse micelles. Newly initiated investigations involve the study of the photophysics of organometallic ligand substitution reactions using high-pressure NMR in addition to investigations of ion solvation in supercritical water and the solvation structure of metal chelates in supercritical carbon dioxide using XAFS spectroscopy. It is anticipated that this program will provide the basis for new and improved analytical separations and for larger scale separations and reactions needed in environmental remediation.
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Materials and Chemical Sciences Department
| Investigator(s) | Bushaw, B.A.; Alexander, M.L. | $310,000 | ||
|---|---|---|---|---|
| Phone | 509-375-2209 | |||
| ba_bushaw@pnl.gov | ||||
Prior studies of trace constituent analysis with simple and double-pulse laser ablation, followed by optical emission detection, have observed highly variable analysis results, with compositions varying by 40% or more from given bulk compositions. The highly non-linear dependence of the ablation process on laser pulse energy and matrix composition and morphology, as well as self-absorption by emitting species, electronic densities, and uncertainties in absolute transition strengths have been identified as major contributors to these deviations. Current studies are using high-resolution, time-resolved absorption measurements to determine the concentrations and physical environment of atomic species within laser ablation plumes. Under vacuum conditions, two distinct components of the atomic absorption are observed. The first component is short lived with a duration of approximately 1 µs. The absoption line is red shifted by up to 10 GHz consistent with both pressure induced shifts and Stark shifting at high electron densities. Also, the absorption linewidth is broad and highly time dependent. Analysis of linewidth as a function of time indicate the presence of a significant density of neutral atoms with effective temperatures in excess of 10,000K. This short-lived component is attributed to the expansion of the initially formed laser ablation plasma. A second, longer-lived (up to several hundred µs) component is observed at unshifted wavelength and with time dependent Doppler widths corresponding to temperatures of 500-1500K. This component is attributed to thermal evaporation from the ablation site after the initial ablation-plasma etching process is completed. This thermal evolution is expected to produce high fractionation of the bulk constituents. Similar studies have also been performed in the presence of a low pressure (<1 torr) cover gas and three distinct time components are observed. The new component, at intermediate times of 3-10 µs, is tentatively assigned to shock-wave formation at the boundary of the plasma expansion, however, a bimodal Doppler distribution, as would be expected for two shock fronts at opposite sides of the expansion, has not yet been observed. Continuing studies will examine the dependence of the slow and fast components as a function of ablation laser wavelength, pulse duration and energy, and substrate material in order to quantify the conditions which yield plume compositions that are most representative of the bulk composition.
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