Surface Ionization Technique Research Articles

A new technique for real-time measurements of potassium and sodium aerosols based on field-reversal surface ionization

A new method for real-time measurements of potassium and sodium containing aerosol particles is described and verified. The method is based on surface ionization technique and may be used to explore the alkali chemistry related to high temperature chemistry processes. The measurement device is a further development of the simple and cost-effective surface ionization detector previously used for online alkali measurements in combustion and gasification research. The discrimination between sodium and potassium is possible due to differences in their surface desorption kinetics and facilitated by rapidly reversing the field potential between the ion source and the nearby collector. The instrument is evaluated in a series of laboratory experiments using size-selected alkali salt particles containing KCl, NaCl, K2SO4, Na2SO4, KNO3 and NaNO3. The filament temperature was found to be a key influencing factor in order to optimize the strength and Na–K deviation of the observed ion current. The ability to simultaneously report absolute concentrations of Na and K makes the instrument attractive for solid fuel conversion of alkali-rich fuels such as low-grade biomass and to explore behavior deviations of Na and K in high temperature processes.

α -decay properties of Fr200,202

Background: The neutron-deficient lead region provides a range of nuclear phenomena, including isomerism at low energies. This phenomenon can be studied by α decay because the degree of hindrance of α decay provides information on the change in nuclear structure of connected states. Purpose: The aim of this work was to investigate the α-decay properties of $^{200,202}$FR and daughter products. Method: Neutron-deficient francium nuclei are produced at ISOLDE-CERN bombarding a UCx target with 1.4 GeV protons. Surface ionization and mass-separation techniques were employed to provide a pure radioactive ion beam at a radiation-detection setup. Results: Due to the very high statistics and the high beam purity, improved decay data for $^{202}$FR and its daughters were obtained. In particular, this data set allowed us to identify many fine-structure α lines with a relative reduced α-decay width up to five orders of magnitude lower as the strongest ground-to-ground state or isomeric-to-isomeric state α-decay transition. In addition, several half-life values were extracted with similar or better precision as compared with the literature. Conclusions: The observation of crossover transitions positioned the isomeric high-spin level of $^{198}$At at an excitation energy of 265(3) keV. Half-life values of 4.47(5) s and 1.28(10) s were extracted for the ground state and isomeric state of $^{198}$At and 52(3) ms for the ground-state decay of $^{200}$FR. Furthermore, α-decay schemes for Fr202 and its daughter $^{198}$At could be constructed.

Distance-of-Flight Mass Spectrometry: What, Why, and How?

Distance-of-flight mass spectrometry (DOFMS) separates ions of different mass-to-charge (m/z) by the distance they travel in a given time after acceleration. Like time-of-flight mass spectrometry (TOFMS), separation and mass assignment are based on ion velocity. However, DOFMS is not a variant of TOFMS; different methods of ion focusing and detection are used. In DOFMS, ions are driven orthogonally, at the detection time, onto an array of detectors parallel to the flight path. Through the independent detection of each m/z, DOFMS can provide both wider dynamic range and increased throughput for m/z of interest compared with conventional TOFMS. The iso-mass focusing and detection of ions is achieved by constant-momentum acceleration (CMA) and a linear-field ion mirror. Improved energy focus (including turn-around) is achieved in DOFMS, but the initial spatial dispersion of ions remains unchanged upon detection. Therefore, the point-source nature of surface ionization techniques could put them at an advantage for DOFMS. To date, three types of position-sensitive detectors have been used for DOFMS: a microchannel plate with a phosphorescent screen, a focal plane camera, and an IonCCD array; advances in detector technology will likely improve DOFMS figures-of-merit. In addition, the combination of CMA with TOF detection has provided improved resolution and duty factor over a narrow m/z range (compared with conventional, single-pass TOFMS). The unique characteristics of DOFMS can enable the intact collection of large biomolecules, clusters, and organisms. DOFMS might also play a key role in achieving the long-sought goal of simultaneous MS/MS. Graphical Abstract ᅟ.

First successful ionization of Lr (Z = 103) by a surface-ionization technique

We have developed a surface ionization ion-source as part of the JAEA-ISOL (Isotope Separator On-Line) setup, which is coupled to a He/CdI2 gas-jet transport system to determine the first ionization potential of the heaviest actinide lawrencium (Lr, Z = 103). The new ion-source is an improved version of the previous source that provided good ionization efficiencies for lanthanides. An additional filament was newly installed to give better control over its operation. We report, here, on the development of the new gas-jet coupled surface ion-source and on the first successful ionization and mass separation of 27-s (256)Lr produced in the (249)Cf + (11)B reaction.

A REVIEW RECENT DEVELOPMENTS IN SAMPLE IONIZATION INTERFACES USED IN MASS SPECTROMETRY

The challenges of how to best ionize the enormous diversity of organic compounds that are of interest to the scientific community have led to advances in mass spectrometry interface design. Developments for both surface and flow ionization techniques, including ambient ionization and high throughput methods, are presented. In addition, representative applications suited for each source are described.

Utility of spatially-resolved atmospheric pressure surface sampling and ionization techniques as alternatives to mass spectrometric imaging (MSI) in drug metabolism

Tissue distribution studies of drug molecules play an essential role in the pharmaceutical industry and are commonly undertaken using quantitative whole body autoradiography (QWBA) methods.The growing need for complementary methods to address some scientific gaps around radiography methods has led to increased use of mass spectrometric imaging (MSI) technology over the last 5 to 10 years. More recently, the development of novel mass spectrometric techniques for ambient surface sampling has redefined what can be regarded as “fit-for-purpose” for MSI in a drug metabolism and disposition arena.Together with a review of these novel alternatives, this paper details the use of two liquid microjunction (LMJ)-based mass spectrometric surface sampling technologies. These approaches are used to provide qualitative determination of parent drug in rat liver tissue slices using liquid extraction surface analysis (LESA) and to assess the performance of a LMJ surface sampling probe (LMJ-SSP) interface for quantitative assessment of parent drug in brain, liver and muscle tissue slices.An assessment of the utility of these spatially-resolved sampling methods is given, showing interdependence between mass spectrometric and QWBA methods, in particular there emerges a reason to question typical MSI workflows for drug metabolism; suggesting the expedient use of profile or region analysis may be more appropriate, rather than generating time-intensive molecular images of the entire tissue section.

On-line alkali analysis of individual aerosol particles in urban air

On-line measurements of individual alkali-containing submicron particles in ambient air have been performed at two urban sites in Göteborg, on the west coast of Sweden. Results obtained with a recently developed particle beam mass spectrometer are presented. This instrument combines an optimized particle inlet with mass spectrometric techniques and detection of particle-bound alkali metal is based on surface ionization technique. The concentrations of Na and K in submicron particles were followed over periods of a few weeks. Mass concentrations of alkali in ambient air varied in the range 0.02–100 ng m −3 during the measurement periods depending on air mass history, wind direction, season, and contributions from local sources. The number of alkali-containing particles varied between 0.1 and 100 cm −3. Most detected individual particles contained a relatively small amount of Na, and few particles had sufficient Na content to be identified as pure sea-salt particles. The detected aerosol was concluded to be dominated by emissions from combustion of biomass and fossil fuels, with a significant contribution from sea-salt particles only during intrusion of marine air. This conclusion was supported by backward air mass trajectories and calculated K/Na weight ratios that generally agreed well with earlier measurements in urban environments.

Online Measurements of Individual Alkali-Containing Particles Formed in Biomass and Coal Combustion: Demonstration of an Instrument Based on Surface Ionization Technique

Online measurements of individual alkali-containing submicrometer particles in a circulating fluidized bed (CFB) combustion facility are presented. A recently developed particle beam mass spectrometer based on surface ionization technique is demonstrated and its performance during a field campaign in a 12 MW CFB reactor operating under atmospheric conditions is discussed. The boiler was fired with a biomass fuel consisting of a mixture of wood chips and pellets. During part of the campaign K2CO3, HCl, and SO2 were also added to the fuel to investigate their influence on alkali-related processes. Size-selected particles with diameters of 50−300 nm in general had high potassium content, while sodium, rubidium, and cesium were present as minor constituents. Particles formed by recondensation of compounds evaporated during the combustion process could be distinguished from fly ash particles on the basis of their potassium and sodium contents. The number of alkali-containing particles increased when the K, Cl, and S fluxes into the boiler increased, and the trend was confirmed by independent measurements of the total particle concentrations in the flue gas. The concentration of potassium bound to submicrometer particles was found to be in the range 0.8−13 mg/m3 under the studied operating conditions. When the facility was instead fired with bituminous coal as a fuel, the relative concentration of sodium compared with potassium was higher, and a larger fraction of the alkali compounds were found in fly ash particles. The particle beam mass spectrometer is concluded to accurately provide online information on particle-bound alkali concentrations under the conditions typically prevailing at a commercial-size boiler, and the possibilities for future research and technical development are discussed.

A Surface Ionization Instrument for On-Line Measurements of Alkali Metal Components in Combustion: Instrument Description and Applications

An instrument for on-line measurements of alkali components in hot flue gas streams is presented. The instrument is based on surface ionization technique and is equipped with a hot sampling line used to extract flue gas for continuous alkali measurements at pressures up to 30 bar. The instrument, its support system and the calibration procedure is described. Field campaigns with the instrument have been performed at fluidized-bed combustion facilities operating under pressurized and atmospheric conditions and using several fuels, including coal, biomass, and demolition waste. The instrument performance has been satisfactory both during pressurized circulating fluidized-bed coal combustion with alkali concentrations downstream of a hot gas filter in the ppb range, and in particle-laden conditions with alkali levels up to about 10 ppm. The measured alkali concentration corresponds to the concentration of alkali components present as vapors and fine-mode particles. In systems with high levels of fluidized-be...

The effects of fuel washing techniques on alkali release from biomass

The influence of different washing techniques on the alkali release during pyrolysis of biomass is studied. After washing and drying, samples of wheat straw, wood waste and cellulose are subjected to a constant heating rate in a N 2 atmosphere, and the release rate of alkali compounds from the sample is measured continuously by a surface ionization technique. Alkali is released from the untreated biomass in two temperature intervals: (1) in connection with the pyrolysis process taking place at 200–500°C, and (2) from the material remaining after pyrolysis at temperatures above 600°C. Separate vacuum pyrolysis experiments show that the alkali release is dominated by potassium-containing compounds, with minor contributions from sodium-containing compounds. The effect of water washing of the biomass is compared with a more thorough acid leaching technique. In the temperature range 200–500°C, washing with water reduces the alkali emission from wood waste and wheat straw by 5–30%, while acid leaching is more effective and reduces the emission by around 70%. Above 600°C where the vaporization of alkali compounds from untreated wheat straws increases sharply, the washing procedures are sufficient for a reduction in the measured alkali release by more than 90%. Experiments with pure cellulose (ash content 0.07%) indicate that the washing methods are ineffective in removing alkali bound to the organic structure of the biomass. The results support the conclusion from earlier studies that relatively simple washing techniques can improve the combustion properties of biomass fuels with a high ash content. For fuels with a lower ash content like woody biomass, the concentration of alkali bound to the organic structure limits the effect of the washing techniques.

Alkali Metal Emission from Filter Ash and Fluidized Bed Material from PFB Gasification of Biomass

The alkali metal emission from materials collected in a PFB biomass gasification pilot plant has been characterized. Samples of SiC filter ash and fluidized bed particles from different operating conditions were subjected to a constant heating rate up to 1000 degrees C in a nitrogen atmosphere, and the alkali metal emission was monitored continuously by a surface ionization technique. For all samples, two characteristic emission intervals are identified. In the range 100-500 degrees C, a small fraction of the alkali metal content is emitted. Above 600 degrees C, the alkali metal release increases sharply and the rise is close to exponential up to 900 degrees C. For fluidized bed particles, the alkali metal emission is significantly lower for agglomerates compared to material used during 1 day, which is attributed to the formation of less volatile compounds. For the filter ash samples, the alkali metal emission is enhanced in samples collected after longer filter cleaning intervals, indicating that the formation of a filter deposit improves the alkali capture efficiency. (Less)

高速有機化合物分子の表面電離質量スペクトル： モノテルペン類

This paper describes an experimental study on the influence of kinetic energy of fast monoterpene molecules on the surface ionization efficiency and on the mass spectral patterns, using rhenium oxide (ReO2) surface. Molecular kinetic energy, given to the molecules through the acceleration in the seeded supersonic molecular beam, ranged from 1 to 10 eV. Hyperthermal surface ionization mass spectra (HSIMS) were taken for various incident kinetic energies and surface temperatures. The observed mass spectra were interpreted in a purely empirical way, by means of evidence from the previous investigations, and they were compared with conventional EI techniques and with the thermal energy surface ionization technique (SIOMS; Surface Ionization Organic Mass Spectrometry). Ionization efficiency (β) was also studied.Under hyperthermal surface ionization (HSI) conditions, many kinds of fragment ions, including quite abundant odd electron ions (OE+·) are observed. HSIMS patterns of monoterpenes are different among 6-isomers, contrary to those of SIOMS and EIMS, where very similar patterns for isomers are observed. HSIMS patterns are strongly dependent on the molecular kinetic energies. The surface temperature does not affect much the spectral patterns, but it controls the total amount of ion formation. We conclude from these mass spectral findings, HSI-mechanism contains an impulsive process of ion formation, followed by the fragmentation process as a results of the internal energies acquired through the collision processes.

Surface Ionization Study of the Hypervalent Li2F Molecule

The surface ionization method offers the possibility of measuring ionization energies of atoms, inorganic and organic molecules and clusters. In this study we report the results of the surface ionization of Li2F molecules on a rhenium surface. This work is an attempt to investigate the applicability of the surface ionization technique for the measurment of the ionization energies of hypervalent molelcules at high temperature. There are currently no reliable experimental data for the ionization energy of the Li2F molecule. This molecule has been chosen because previous theoretical calculations have shown that Li2F is a hypervalent (hyperlithiated) molecule with a low ionization energy. The ionization energy was determined to be 5.42±0.04 eV.

Electron spin resonance studies of the methane radical cations (12,13CH+4, 12,13CDH+3, 12CD2H+2, 12CD3H+, 12CD+4) in solid neon matrices between 2.5 and 11 K: Analysis of tunneling

The radical cation of methane isolated in neon matrices exhibits highly unusual electron spin resonance (ESR) spectral features between 2.5 and 11 K. The anomaly has been clarified by invoking large amplitude tunneling motions of the hydrogens among several symmetrically equivalent Jahn–Teller distorted structures. The effect of the tunneling motions upon the ESR spectrum was investigated by an analysis scheme based upon permutation–inversion group theory. All the deuterium substituted cations, i.e., CDH+3, CD2H+2, CD3H+, and CD+4 were also studied. The hyperfine coupling constant of 13C was obtained from the study of 13CDH+3 and 13CH+4. Several independent generation methods were employed during the course of these methane cation studies, including photoionization, electron bombardment, x-irradiation, and a pulsed laser surface ionization technique.

The thermal dissociation process of metal carbonyls on the heated Re surface: Fe(CO)5 and Mn2(CO)10

Thermal dissociation processes of Fe(CO) 5 and Mn 2 (CO) 10 were investigated under conditions where gaseous molecules impinge on an incandescent rhenium surface, using the surface ionization (SI) technique in conjunction with mass spectrometric detection. In the case of Fe(CO) 5 this process is dominated by thermal dissociation of the compound in a sequential manner, releasing carbonyl ligands, followed by ionization of the dissociated species. In the case of Mn 2 (CO) 10 , a metal—ligand cleavage reaction occurs in competition with the metal—metal cleavage process and produces bare metal atoms and dimetallic species.

Alkali emission accompanying fracture of sodium silicate glasses

Measurements of atomic Na emission accompanying the fracture of sodium trisilicate glass and a soda lime glass in vacuum were made by quadrupole mass spectroscopy and surface ionization techniques. Peak Na° emission intensities occur some 3–6 ms after the fracture event and decay over tens of milliseconds. This behavior is attributed to the diffusion of Na+ ions into a layer of damaged material at the surface where the ions are subsequently neutralized and thermally emitted as Na°. Charge carriers generated during fracture and subsequently trapped at defect sites apparently play important roles in charge compensating Na+ diffusion and in neutralizing Na+. During the first 300 ms following fracture, we also observe intense, short lived (400 μs) bursts in Na° emission which may be associated with catastrophic relaxation of residual stresses. The kinetics of Na emission suggest that the relaxation of newly formed glass surfaces involves rather complex surface physical and chemical processes.

An ion source for low energy ion scattering spectrometry

The alkali ions have been of interest in low energy ion scattering experiments because of their low neutralization probabilities. A method to produce alkali ions has been developed based on the surface ionization technique. A modified surface ionization source uses a sawtooth type sample filament to maintain the slow evaporation of the alkali samples doped on it, and a flat ribbon ionization filament in parallel to it to ionize the alkali vapour. Different alkali compounds have been tried, and high ion currents in the μ A range with the life span of more than 20 h have been obtained using the beta-eucryptite compounds. The intensity of the ion beam can be maintained at a constant value when the operation of the ion source reaches the steady state in less than 30 min. Most ions were singly charged atomic ions with energy spread in the order of 1 eV.

Selective surface ionization of quaternary salts on a platinum filament

AbstractSurface ionization of quaternary ammonium and pyridinium salts evaporated onto a platinum filament has been investigated. The experiments reveal a high selectivity for the formation of intact cations from these salts with virtually no fragmentation up to about 1000 K, and a low level of fragmentation up to about 1300 K, while even at higher temperatures the ionization of volatile non‐ionic compounds such as trialkyl amines is largely suppressed. The fragmentation of quaternary cations at higher temperatures is attributed in part to decomposition reactions in a two‐dimensional ion trap on the surface formed by the image force of the ions. For some compounds and mixtures, evidence is presented of the exchange of alkyl groups for cations as a thermal reaction prior to volatilization of the salts. The surface ionization technique appears promising for selective detection of quaternary salts from complex mixtures.

A study of the carbon adlayer on iridium

A study of the phase composition, structure and properties of the carbon adlayer on iridium by Auger electron and thermal desorption spectroscopy and the surface ionization and CsCl dissociation techniques has been continued. It has been confirmed that the central valence-saturated part of the graphite islands is elevated by ≳ 4 A ̊ above the metal surface, the valence-active edges of the islands being bonded to it chemically. The chemisorbed carbon gas has been shown to occupy all of the iridium surface both beyond the graphite islands and under the raised islands. It is present also under the graphite monolayer. The critical degree of coverage θ c in the chemisorbed carbon gas at equilibrium with the graphite islands on the metal surface (representing an analog of the saturated vapor pressure in a liquid-vapor system) has been determined for the first time. This fundamental characteristic of the phase transition in the carbon adlayer on iridium can be described by the expression θ c = 2 × 10 5 exp(−2.3 eV/ kT). The obtained high resolution ( ΔE/E ⋍ 0.1%) differential Auger spectra of carbon from the graphite islands and chemisorbed gas are shown to be essentially different. It is shown that the temperature-controlled process of graphite island dissolution and carbon gas condensation can be visualized by monitoring the shape of the carbon Auger peak.

The nature of the adsorption bond between graphite islands and iridium surface

Abstract To reveal the nature of adsorption bonds between two-dimensional graphite islands and iridium (111) and (100) faces, a study has been made of the adsorption of potassium and cesium atoms on the surface of these systems, using thermal desorption and Auger electron spectroscopy, as well as surface ionization and thermionic emission techniques. The graphite islands are shown to be weakly bound to the iridium substrate by Van der Waals forces. The unsaturated valence bonds at the periphery of the graphite islands are “lowered down” on to the metal. The recess between the graphite layer and the metal is filled by adsorbing particles through defects in the graphite layer. The atoms can penetrate into the recess in two ways: at T > 1000 K directly from the flux incident on the surface, and at T 1900 K liberates the potassium and cesium atoms from under the graphite islands. Our study suggests that the reason for the “raised” position of the islands lies in the valence bonds of the graphite layer being saturated, the valence bonds of the metal and its crystallographic orientation being less significant. Therefore one may expect the graphite layer to be raised also above other metals as well. The filling by cesium of the recess between the graphite layer and iridium and of the adsorption phase on the graphite surface, does not change the general “graphitic” shape of the carbon Auger peak. This cesium results, however, in a pronounced splitting of the negative spike on the carbon peak (which provides information on its location relative to the graphite layer) indicating the appearance in the valence band of graphite near the Fermi level of two narrow (∼ 2−3 eV) regions with an enhanced density of states originating from the presence of the alkali metal.