Reaction of analyte ions with neutral chemical ionization gas

Analytical Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA Ion-molecule reactions of neutral methane with analyte ions under normal methane chemical ionization conditions are discussed. Reactant ions can be generated by direct electron ionization (EI) fragmentation, chemical ionization (CI) fragmentation, or collision-induced dissociation (CID). Examples in which products of such reactions appear in mass spectra in both conventional CI sources in “beam” instruments and low pressure CI in a quadrupole ion trap are presented. Also shown is an example in which MS/MS product ions react with neutral methane used for CI in an ion trap. It is shown that it is relatively straightforward to recognize such reactions in a quadrupole ion trap and in certain cases to minimize or preclude them. Effects of various operating parameters have been investigated and are discussed.     

Solution chemistry and secondary ion emission from amine-glycerol solutions

Analytical Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA Secondary ion mass spectra were obtained from a series of C₄-C₁₀ n-alkylamines introduced via the gas phase onto glycerol. It was found that the amine-characteristic secondary ion intensity varied linearly with amine partial pressure. Henry's law constants and surface activity constants for each of the amines in glycerol solution were measured. A linear correlation was found between amine-characteristic secondary ion intensity and Henry's law concentrations. The concentrations calculated from Henry's law were too low to yield the intensities observed, indicating that secondary ion precursors were not free-base amine molecules but ions in solution. Explicit kinetic equations describing glycerol and amine protonation and deprotonation as a result of primary ion damage to the solutions are derived to rationalize the observed spectra.     

A wide-angle secondary ion probe for organic ion imaging

A secondary ion source has been developed for an organic ion microprobe capable of imaging samples up to 2 em in diameter. The source uses a focused 5 keY Cs⁺ ion beam which is rastered across the sample surface, and secondary ions from each point on the sample are collected and formed into a low energy beam to be analyzed by a quadrupole mass filter. Dynamic emittance matching is employed to deflect ions from off-axis points on the sample back onto the mass analyzer axis. Rastering and dynamic emittance matching are rapidly controlled by assembly language programs using an IBM/AT (80286) type computer. A low energy ion monitor was used to tune and evaluate the secondary ion source by providing a magnified cross-sectional image of the ion beam at the source exit aperture. A well-focused and centered secondary ion beam was obtained from each point on the sample, indicating that large-scale dynamic emittance matching with high collection efficiency is possible. Mass resolved images of grids and glycerol samples are shown to demonstrate the performance of the integrated secondary ion source mass analyzer and control system.     

Methyl guanine isomer distinction by hydrogen / deuterium exchange using a fourier transform mass spectrometer

Analytical Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA Differentiation of the seven isomers of methyl guanine has been accomplished by monitoring gas-phase hydrogen/deuterium (H/D) exchange reactions of the protonated molecular ions with deuterium oxide (D₂O) in a Fourier transform mass spectrometer. In each case a distinctive reaction rate for the first H/D exchange was observed, and exchanges of up to three deuterium atoms occurred with characteristic ion abundances that could be used to differentiate the isomers. O⁶-Methyl guanine, for example, showed only one slow H/D exchange with D₂O, whereas l-methyl guanine exchanged two hydrogen atoms at a significantly faster rate. On comparison of the possible resonance structures of each protonated isomer with the experimental information about the number and rate of H/D exchanges observed, a reaction mechanism involving a concerted proton abstraction-deuterium cation donation was proposed.     

Present and future positron-molecular scattering experiments

Progress to date (June, 1999) of the Oak Ridge positron scattering project is reviewed. Results from our positron time-of-flight mass spectrometer include ionization and fragmentation of some halomethanes, positronium formation below the threshold for double ionization of Ne and the heavier noble gases, and the production of HeH⁺ by positron impact on mixtures of He and H₂. New directions for future experimental work are discussed. These entail the construction and testing of a new spectrometer which measures both the masses and recoil energies of charged products, including secondary electrons. We hope to use an intense positron beam, such as the one at Lawrence Livermore National Laboratory or a similar beam, as the ionizing agent for the new spectrometer, which contains a pulsed supersonic molecular beam. With such an instrument, a range of new phenomena can be studied.     

Electrically driven oscillations of a mercury-droplet electrode

The resonance frequencies of 13 polygonal vibrations plus 11 axisymmetric vibrations have been observed for a 4.0-mg sessile mercury droplet submerged in 0.10 N KCl solution. When an input voltage with suitable dc and ac components was applied between the mercury droplet and a Ag/AgCl counter electrode, the mercury droplet could be observed under a microscope to oscillate. The mechanism that drives this droplet into oscillation differs from past electrokinetic mechanisms. Basically, the oscillating input voltage causes periodic changes in the interfacial surface tension which, at specific input frequencies, induce resonant vibrations within the droplet by interacting with its expanding and contracting surface area. Because there are two cycles of surface-area variation and two cycles of surface-tension variation per cycle of droplet oscillation, the most effective driving frequency (but not the only driving frequency) is twice the frequency of the droplet oscillation. This work was performed at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee.     

<Superscript>3</Superscript>H and <Superscript>90</Superscript>Sr in urine radiobioassay intercomparison results from the intercomparison studies program at Oak Ridge National Laboratory: statistical analysis of laboratory performance

The Intercomparison Studies Program (ISP) at the Oak Ridge National Laboratory (ORNL, Oak Ridge, TN USA) provides natural-matrix human urine quality-assurance/quality-control (QA/QC) samples to radiobioassay analysis laboratories. Samples are provided to these laboratories as “single-blind” or “double-blind” unknowns, spiked with radioactive-solution standards at “low” levels (e.g., 0.7–7 Bq g⁻¹ for ³H and 0.7–7 Bq kg⁻¹ for ⁹⁰Sr). Participants use the results as a tool for self-evaluation and a measure of performance. In this paper, sample preparation and the results of testing during the years 2001–2005 for ³H and ⁹⁰Sr are presented and discussed.     

The influence of ion beam sputtering on the composition of the near-surface region of silicon carbide layers

The concentrations and the lattice structure of silicon carbide layers and single crystals are influenced by ion beam sputtering. The influence of ion beam sputtering and primary ion energy on preferential sputtering is investigated by Auger measurements and T-DYN simulations. In dependence on primary ion energy C is enriched. Preferential sputtering increases with decreasing ion energy. Sputtering has a strong influence on the Auger peak shapes of SiC. Except for low ion energy and glancing incidence the peak shapes are independent of the primary ion energy. T-DYN simulations help to explain and understand the near-surface processes during sputtering of SiC. For ion energy dependence of preferential sputtering there is a good agreement of the T-DYN simulation and the Auger measurement. Received: 10 October 1998 / Revised: 26 March 1999 / Accepted: 2 April 1999     

Mass spectral studies of cycloheptatrienes. II—The monochlorocycloheptatrienes

The mass spectra of isomeric chlorocycloheptatrienes have been studied at high and low electron beam energies. Ion kinetic energy spectrometry was utilized to examine the major decomposition pathways. The extreme similarity found in the spectral characteristics of these compounds provides information about the structure of the decomposing molecular ion.     

Neutron field produced by a KAMAN A-711 sealed tube generator

Utilization of a sealed tube neutron generator requires the knowledge of the lateral flux density distribution and the mean energy of primary neutrons near to the target. The ion composition of the incident beam is related to the operating conditions of a generator. These parameters have been determined for a KAMAN A-711 sealed tube machine by the foil activation method using different energy and fluence monitor reactions. An analytical expression is also given for the calculation of the relative flux density for a typical geometry.     

Investigation of UV matrix-assisted laser desorption fourier transform mass spectrometry for peptides

Analytical Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA Ultraviolet matrix-assisted laser desorption can be used to enhance formation of [M + H]⁺, [M + Na]⁺, and [M + K)⁺ ions from small peptides for Fourier transform mass spectrometry (FTMS). In accord with laser desorption (LD) time-of-flight experiments, matrices such as nicotinic acid and 2-pyrazinecarboxylic acid exhibit strong enhancement effects (i.e., formation of abundant protonated and cationized molecules for the analyte with virtually no fragment ions) for 266 nm LD/FTMS, whereas pyrazinedicarboxylic acid provides no matrix enhancement at this wavelength. Both sinapinic acid and coumarin-120 provide strong matrix enhancement effects for the 355-nm LD of peptides. For the small peptides examined in this study, no significant differences in the abundance of fragment ions were observed between the 266- and 355-nm wavelengths. Matrix-assisted LD/FTMS is useful for the generation and characterization of ions corresponding to protonated and cationized molecules from virtually all biological compounds with molecular weights up to 2000. The lack of observation of biological ions with m/ z > 2500 may be related to inefficient trapping of these laser-desorbed ions or instrumental detection limitations of FTMS and is under further investigation.     

Study of in-situ surface cleaning for Si and SiGe epitaxy on Si with a novel ion beam vapor/assisted deposition technique

Ion beam vapor deposition is a new technique to grow Si and SiGe layers on Si substrates at low temperatures. The in situ surface cleaning prior to the deposition is a crucial step in the epitaxial growth of Si and SiGe films and is achieved by Ar ion bombardment with substrates kept at ambient temperature. A high temperature annealing (800 °C) is needed to repair the damage caused by this bombardment. We studied the effects of ion beam energy and the substrate temperature during the in situ cleaning on the quality of the grown films. An ion beam energy of 150–200eV is found to be sufficient to clean the surface for epitaxial growth. While the films deposited on properly cleaned surfaces are epitaxially grown, the inadequately cleaned surface leads to the formation of polycrystalline layers especially at low substrate temperatures.     

Vibrations of microscopic mercury droplets on glass

Personnel at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee, and at the University of Tennessee, Knoxville, have measured two types of oscillations for individual, microscopic mercury droplets within a sealed glass cell under partial vacuum. Droplet dimensions were determined by measuring the displacement of a microscope stage as the edges of either the base or the maximum diameter of a pendant droplet were sighted at high magnification. Resonance frequencies were measured by varying the input frequency until droplet oscillation was observed under a microscope. One type of vibration was identified as a special type of polygonal vibration in which the droplet is bound to a solid surface. Another type is an axisymmetric vibration of a bound droplet for which an eigenvalue notation has previously been derived. For 12 microscopic mercury droplets, each less than 9 nl in volume, the agreement between measured and calculated frequencies was within ±4.5%, but ±1% was common. This excellent agreement is consistent with assumptions that the surface tension corresponded to that of pure mercury, that these microscopic droplets were spherical sections, and that these droplets had fixed contact lines. Alternative analytical applications of resonance-frequency measurements on bound droplets are also described.     

Fluence measurements applied to 5–20 MeV/amu ion beam dosimetry by simultaneous use of a total-absorption calorimeter and a Faraday cup

A Faraday cup was fabricated for measuring the beam current of a few tens MeV/amu ion beams of the TIARA AVF cyclotron. It has been applied as a beam monitor for studying the characteristics of film dosimeters that are well-established for high doses of ⁶⁰Co γ-rays and 1 to 10 MeV electrons. A total absorption calorimeter designed to measure energy fluence has also been tested for estimating the uncertainty in fluence measurement of 5–20 MeV/amu ion beams, by simultaneous use of the calorimeter and the Faraday cup in a broad uniform fluence field. The estimated fluence was evaluated on the basis of nominal particle energy values derived from the cyclotron acceleration parameters. The average ratio of the measured fluence values to the estimated values is 1.024, and the average precision is within ±2% at a 68% confidence level, for most of the ion beams with a range of kinetic energy per nucleon, 5–20 MeV/amu, at an integrated charge above 5 nC/cm².     

Ion kinetic energy spectroscopy

Preliminary results indicate the value of ion kinetic energy (1KE) spectra in adding a new dimension to structural information obtained by mass spectrometry. These spectra are especially useful in the distinction of some isomer pairs. Energy spectra provide a summary of gaseous ion chemistry occurring as metastable transitions in the first-field free-drift region of the double-focusing (Mattauch-Herzog geometry) mass spectrometer and are produced by scanning the electrostatic sector voltage while recording the ions transmitted by the sector with the beam monitor electrometer.     

Evaluation of measurements of 238Pu, 239Pu and 240Pu in urine at the microbecquerel level using thermal ionization mass spectrometry and alpha-spectrometry at Los Alamos National Laboratory: Results of a two year comparison test (LA-UR-06-8055)

The Intercomparison Studies Program (ISP) at the Oak Ridge National Laboratory (ORNL, Oak Ridge, TN, USA) provides natural-matrix urine quality-assurance/quality-control (QA/QC) samples to radiobioassay analysis laboratories. In 2003, a single laboratory (Los Alamos National Laboratory LANL, Los Alamos NM USA) requested a change in the test-samples provided previously by the ISP. The change was requested to evaluate measurement performance for analyses conducted using thermal-ionization mass spectrometry (TIMS). Radionuclides included ²³⁹Pu at two activity levels (75–150 μBq^·sample⁻¹ and 1200–1600 μBq^·sample⁻¹) and ²³⁸Pu (3700–7400 μBq^·sample⁻¹). In addition, ²⁴⁰Pu was added to the samples so that the ^239+240Pu specific activity was 3700–7400 μBq^·sample⁻¹. In this paper, the results of testing during the period May, 2003 through September, 2005 are presented and discussed.     

Electron beam potential depression as an ion trap in Fourier transform ion cyclotron resonance mass spectrometry

Trapping of ions in the electron beam of a FTICR mass spectrometer is investigated and a simple model describing the confinement process is presented. Detection of resistive-wall destabilization of the magnetron motion of ions in the trapped-ion cell is used to determine conditions for ion trapping within and escape from the electron beam. The model predicts a potential well that is dependent on electron beam current, energy, and dimension in defining its capacity for low energy ions. Plots of ion retention time versus ion number are consistent with a model in which ions are initially trapped in the electron beam but with increasing ion formation will eventually overcome the potential depression in the electron beam and escape into magnetron orbits. Based upon this model, expressions are derived for ion retention time which are then fit to the experimental data. The model is used to estimate ion number, initial magnetron radius and ion cloud shape and density. One example in which electron trapping is important in the FTICR experiment is in the efficient transfer of ions between dual trapped-ion cells. Ion transfer within the potential depression of the electron beam environment is shown to be virtually 100% efficient over a 10 ms interval whereas all ions are lost to collisions with the conductance limit after 2 ms when transferring without the confining aid of the electron beam. Several analytical applications of electron traps in the ICR cell are now being investigated.     

低能离子与生物有机小分子相互作用机制的初步研究

利用低能离子束(N^+,Ar^+离子)辐照固态羧酸钠(甲酸钠)、(乙酸钠)、(苯甲酸钠)和固态嘧啶碱基两类样品,经电子顺磁共振谱(EPR)、富里叶红外光谱(FT-IR)的检测,结果发现,三种低能离子辐照后的甲酸钠样品中产生了[COO]^.^-自由基和亚甲基(CH2),氮离子辐照乙酸钠和苯甲酸钠样品后,形成了新的化学基团氰基(CN);同时,结合茚三酮反应,证明了辐照后的羧酸钠和碱基样品中还含有新的基团氨基(NH2),给出了氨基的产生量与注入离子的剂量的相关曲线。     

Neutron activation analysis of LWR ion exchange mixed-bed resins for129I

Iodine-129 was determined by neutron activation analysis (NAA) in mixed-bed ion exchange resins from four light water reactors (LWR), including two pressurized water reactors (PWR) and two boiling water reactors (BWR). Published procedures for NAA of¹²⁹I in LWR resins were modified and adapted to the particular requirements of the Oak Ridge National Laboratory (ORNL) High Flux Isotope Reactor (HFIR) irradiation system. Observed¹²⁹I concentrations, ranging from 1E-09 to 4E-07 Ci/g, were about 1000 times lower than the beta-gamma detection limits currently reported.     

A Fourier transform time-of-flight mass spectrometer. A SIMION calculation approach

A new kind of approach to time-of-flight type spectrometers is presented on the basis of SIMION calculations. The detector studied is a short cylindrical tube capacitor closed with parallel plates at both ends. The main principle of operation is to force ions of equal energy to circulate in the volume between the two tubes on a path of equal radius and measure their flight times pro revolution which corresponds to the frequency of oscillation. By performing spectral analysis on the received signal through transformation from the time domain to frequency space the different masses can be detected.To study the expected performance of the FT-TOF detector, calculations of ion trajectories have been made by varying the dimensions and electric potentials of the electrodes. The effect of the beam position, variations in the angle of entrance and ion energy to the trajectories was calculated to monitor the resolution that is achievable.