3D-Atom-probe study of oxygen-adsorption on stepped platinum surfaces

Oxygen adsorbed on Pt (011), (012) and (113) has been studied by means of field desorption in a three-dimensional atom-probe. The formal procedure of these experiments is quite similar to thermal desorption. Comprehensive investigations with the thermal desorption technique report on a highly stable atomic oxygen phase on Pt, which has been attributed to a subsurface oxygen layer or platinum oxide. In atom-probe depth profiling experiments oxygen was measured only in the topmost layer. Oxygen and platinum have been detected almost as single atomic ions, Pt-oxygen complexes have not been observed in the time-of-flight mass spectra. The 2D plots of the impact positions of the desorbed ions as well as field ion micrographs show most of the oxygen adsorbed in highly co-ordinated sites on the (012) and (113) planes.     

Fragmentation of polyatomic molecules by grazing incidence surface-induced dissociation (GI-SID).

The grazing incidence surface-induced dissociation (GI-SID) of n-hexadecylpyridinium and verapamil ions generated by fission fragment desorption was studied. These molecules show the effect of enhanced surface-induced dissociation at grazing incidence as it was observed in former experiments with metal organic ions. A liquid film of perfluorinated polyether is used as collision surface. Small hydrocarbon fragment ions predominate in the GI-SID spectra. Pyridine ions appear as specific fragment ions in the GI-SID spectrum of n-hexadecylpyridinium. The GI-SID conversion efficiency varies in the range 40-70%. The experimental results are discussed within the scope of a quantum mechanical model which is based on the accumulation of internal molecular energy by resonant excitation of collective vibrational states and energy transfer to a trap bond due to dipole-dipole interactions. In this context the GI-SID spectra of n-hexadecylpyridinium and verapamil ions are compared with the fragmentation occurring in regular (252)Cf plasma desorption mass spectrometry.     

Fragmentation of oligosaccharide ions with 157 nm vacuum ultraviolet light

The 157 nm photofragmentation of native and derivatized oligosaccharides was studied in a linear ion trap and in a home-built matrix-assisted laser desorption/ionization (MALDI) tandem time-of-flight (TOF/TOF) mass spectrometer, and the results were compared with collision-induced dissociation (CID) experiments. Photodissociation produces product ions corresponding to high-energy fragmentation pathways; for cation-derivatized oligosaccharides, it yields strong cross-ring fragment ions and provides better sequence coverage than low- and high-energy CID experiments. On the other hand, for native oligosaccharides, CID yielded somewhat better sequence coverage than photodissociation. The ion trap enables CID hybrid MS3 experiments on the high-energy fragment ions obtained from photodissociation.     

Peptide photodissociation at 157 nm in a linear ion trap mass spectrometer

The photodissociation by 157 nm light of singly- and doubly-charged peptide ions containing C- or N-terminal arginine residues was studied in a linear ion trap mass spectrometer. Singly-charged peptides yielded primarily x- and a-type ions, depending on the location of the arginine residue, along with some related side-chain fragments. These results are consistent with our previous work using a tandem time-of-flight (TOF) instrument with a vacuum matrix-assisted laser desorption/ionization (MALDI) source. Thus, the different internal energies of precursor ions in the two experiments seem to have little effect on their photofragmentation. For doubly-charged peptides, the dominant fragments observed in both photodissociation and collisionally induced dissociation (CID) experiments are b- and y-type ions. Preliminary experiments demonstrating fragmentation of multiply-charged ubiquitin ions by 157 nm photodissociation are also presented.     

Determination of neptunium using high resolution sequential ICP-AES

In view to separate La(III), Pr(III) and U(VI) ions, from aqueous solutions, batch experiments are carried out for the sorption and desorption of these ions onto and from a novel functionalized resin. The sorption capacities varied from 1.06 to 47.30 mg/g and increased in the following order La(III), Pr(III) and U(VI), while yields desorption ranged from 73.0 to 94.3% and increased in the following order Pr(III), La(III) and U(VI). Considering the largest difference in sorption capacity and desorption yield of these three elements, at different operates conditions, this material can be potential candidate for the separation of U(VI), Pr(III) and La(III) ions from nuclear and other industrial wastewater.     

Kinetics of fission products accumulation on structural materials

The aim of the present work was to reveal the kinetics of the accumulation of some possible contaminant on the surfaces of structural materials (zirconium alloys and 08H18N10T stainless steel) in the primary circuit of Paks NPP. The kinetics of adsorption and desorption of iodide, caesium and cerium ions were investigated by quartz crystal microbalance (QCM) installed into a flow cell. The results on thin layers were confirmed by immersing experiments, using radiotracer technique and ??-spectrometry to detect the traced ions on the surfaces. Experiments were carried out in electrolyte solution which was similar to the cooling water. All measurements were carried out at room temperature. Both adsorption and desorption were found to be fast, taking only several seconds; time constants were also evaluated.     

Desorption due to charge exchange in low-energy collisions of organofluorine ions at solid surfaces

Collisions of organofluorine ions at a metal surface result in efficient emission of adsorbate species as gas-phase ions. The experiments are done at 120° scattering angle in a hybrid (BQ) mass spectrometer; the primary ions, mass-selected by a magnetic sector (B), are allowed to collide with a target at a selected kinetic energy in the tens of eV range and the emitted ions are mass-analyzed using a quadrupole mass filter (Q). It is proposed that the impinging ions undergo neutralization accompanied by desorption of hydrocarbon ions and that the amount of internal energy deposited in the desorbed ions is strongly dependent on the collision energy and affects their degree of fragmentation. Competing processes include reflection and fragmentation of the colliding particle, along with such ion/adsorbate reactions as hydrogen atom abstraction by the fluorinated ion. Small even-electron ions, such as [CHF₂]⁺ and [C₂H₂F]⁺ are more effective in promoting chemical sputtering of the surface adsorbate as compared to larger ions (e.g. [C₃F₅]⁺) and odd-electron ions (e.g. [C₂F₄]⁺˙ and [C₂HF₂]⁺˙). At low energies some odd-electron fluorinated ions undergo collision without any secondary ions being emitted from the surface. In these cases the parent ions are apparently neutralized, but without sufficient energy transfer to cause hydrocarbon ion desorption. Non-fluorinated organic ions yield fragment ions and ion/surface reaction products under the condition of these experiments, but do not cause significant desorption of hydrocarbon ions.     

On-line electrochemically controlled solid-phase extraction interfaced to electrospray and inductively coupled plasma mass spectrometry

Electrochemically controlled solid-phase extractions of anions were interfaced on-line to electrospray mass spectrometry (ESI-MS) and inductively coupled plasma mass spectrometry (ICP-MS), using polypyrrole coated electrodes and a thin-layer electrochemical (EC) flow cell. The results indicate that electrochemically controlled solid-phase extraction (EC-SPE) can be used as a versatile potential controlled sample preparation technique for a range of anions and that the properties of the polypyrrole coatings can be modified by altering the electrodeposition conditions. In the present study, the influence of interfering anions (i.e., fluoride and sulfate), and the anion used during the electropolymerisation, on the bromide extraction recovery was investigated for EC-SPE interfaced to ICP-MS. The results of these experiments show that the interference due to the presence of similar concentrations of sulfate can be reduced when using a polypyrrole coating electropolymerised in the presence of bromide ions. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements were also used to study the morphology of the coatings, as well as the variations in the film thickness within the coatings. The effect of different desorption techniques on the bromide preconcentration factor in the ICP-MS on-line flow system was also examined. Stopped-flow desorption was found to give rise to significantly increased preconcentration factors in comparison with desorptions in flowing solutions. While the desorption efficiency depends on the type of desorption electrolyte (the electrolyte in which the desorption takes place), due to the competing influx of cations, the influence of the pH on the switching charge of the polypyrrole coating was found to be small, at constant ionic strength. To study the applicability of the EC-SPE technique with respect to real samples, investigations were also made with tap water samples spiked with different bromide concentrations. The results of these experiments, which were carried out using a modified thin-layer EC flow cell allowing in situ polymerisation of polypyrrole yielding a polymer plug covering the cross section of the channel, demonstrate that 3 microM concentrations of bromide could be detected in the tap water sample. This demonstrates that the extraction technique allows extractions of low concentrations of ions in the presence of significantly higher concentrations of other similar ions. The fact that the extraction and desorption steps are electrochemically controlled makes EC-SPE particularly well suited for inclusion in miniaturised lab-on-a-chip systems.     

Fragmentation of multiply-charged intact protein ions using MALDI TOF-TOF mass spectrometry

Top down proteomics in a TOF-TOF instrument was further explored by examining the fragmentation of multiply charged precursors ions generated by matrix-assisted laser desorption ionization. Evaluation of sample preparation conditions allowed selection of solvent/matrix conditions and sample deposition methods to produce sufficiently abundant doubly and triply charged precursor ions for subsequent CID experiments. As previously reported, preferential cleavage was observed at sites C-terminal to acidic residues and N-terminal to proline residues for all ions examined. An increase in nonpreferential fragmentation as well as additional low mass product ions was observed in the spectra from multiply charged precursor ions providing increased sequence coverage. This enhanced fragmentation from multiply charged precursor ions became increasingly important with increasing protein molecular weight and facilitates protein identification using database searching algorithms. The useable mass range for MALDI TOF-TOF analysis of intact proteins has been expanded to 18.2 kDa using this approach.     

Reproducibility and extent of fragmentation of laser-desorbed ions : Relation to mechanism of desorption

The reproducibility of decomposition patterns of laser desorbed propyltriphenyl-phosphonium ions and (M + Na)⁺ ions of sucrose is evaluated. These compounds were chosen because they desorb by two different mechanisms commonly ascribed to “thermal” desorption. The phosphonium ions desorb directly whereas sucrose requires cationization with an alkali metal ion. Samples were either pipetted or electrosprayed onto both “smooth” and “rough” copper probe tips. The precision of two ratios of ion abundances are slightly worse for laser desorption of the phosphonium ions than for ions produced by electron ionization of toluene and 2,5-dibromotoluene. Little improvement was obtained by turning to electrospray as a means of depositing the sample. Worse precision was found for ion abundance ratios obtained from the laser desorption of (M + Na)⁺ of sucrose which hadbeen pipetted onto the probe. The precision was improved by using the electrospray deposition method. Fragmentation of the phosphonium ions was greater if desorption was from a “rough” probe tip whereas less decomposition of the (M + Na)⁺ of sucrose occurred with desorption from a “rough” tip. The trends in precision and extent of fragmentation are rationalized in terms of mechanisms of ion desorption. Chemical ionization of laser-desorbed neutral species was found to be impossible under the experimental conditions used.     

Polarization dependent fragmentation of ions produced by laser desorption from nanopost arrays

Tailored silicon nanopost arrays (NAPA) enable controlled and resonant ion production in laser desorption ionization experiments and have been termed nanophotonic ion sources (Walker et al., J. Phys. Chem. C, 2010, 114, 4835-4840). As the post dimensions are comparable to or smaller than the laser wavelength, near-field effects and localized electromagnetic fields are present in their vicinity. In this contribution, we explore the desorption and ionization mechanism by studying how surface derivatization affects ion yields and fragmentation. We demonstrate that by increasing the laser fluence on derivatized NAPA with less polar surfaces that have decreased interaction energy between the structured silicon substrate and the adsorbate, the spectrum changes from exhibiting primarily molecular ions to showing a growing variety and abundance of fragments. The polarization angle of the laser beam had been shown to dramatically affect the ion yields of adsorbates. For the first time, we report that by rotating the plane of polarization of the desorption laser, the internal energy of the adsorbate can also be modulated resulting in polarization dependent fragmentation. This polarization effect also resulted in selective fragmentation of vitamin B(12). To explore the internal energy of NAPA generated ions, the effect of the post aspect ratios on the laser desorption thresholds and on the internal energy of a preformed ion was studied. Elevated surface temperatures and enhanced near fields in the vicinity of high aspect ratio posts are thought to contribute to desorption and ionization from NAPA. Comparison of the fluence dependence of the internal energies of ions produced from nanoporous silicon and NAPA substrates indicates that surface restructuring or transient melting by the desorption laser is a prerequisite for the former but not for the latter.     

Efficient multicyclic sorption and desorption of lead ions on facilely prepared poly(m-phenylenediamine) particles with extremely strong chemoresistance

Nitric acid, hydrochloric acid and EDTA were carefully chosen as desorbent to systematically evaluate the adsorption/desorption performance of the Pb(2+)-adsorbing fine microparticles of poly(m-phenylenediamine). The sorption/desorption efficiency was maximized by optimizing desorption condition including the desorbent concentration, contact time, and desorption mode. The variation of the solution pH with Pb(2+) desorption was recorded to speculate the desorption mechanism. The practical reusability of the microparticles was elaborated through the sorption-desorption cycle experiments in an optimum condition. It was found that the desorption was very rapid with an equilibrium time of several minutes. A strong dependence of the desorbability on the species and concentration of the desorbents was observed. When 20 mM EDTA was chosen as the desorbent, the highest desorptivity was up to 94.2% that was much higher than those using nitric and hydrochloric acids. A successive sorption-desorption study employing nitric acid indicated that the microparticles could be simply regenerated and reutilized for more than 5 cycles together with Pb(2+) re-adsorption efficiency of about 50% and accumulative Pb(2+) adsorption capacity of up to 720.4 mg L(-1). Facilely prepared, extremely chemoresistant and cost-effective PmPD microparticles would be potentially used for multicyclic sorption of lead ions from aqueous solution.     

两种有机物改性膨润土对Cu2+和Zn2+的吸附-解吸研究

选用天然有机物料(猪粪降解液)和有机化学试剂[十六烷基三甲基溴化胺(HDTMA)]对钠基膨润土进行表面改性,比较了膨润土对两类有机物的吸附特性,以及两种有机物改性膨润土对Cu2+、Zn2+吸附-解吸性能的差异。结果表明,膨润土对HDTMA和猪粪降解液是优惠吸附,且前者最大吸附量为382.4mg/g,是后者的4.19倍。HDTMA改性膨润土对Cu2+、Zn2+的最大吸附量均大于猪粪降解液改性膨润土,前者分别为后者的1.12倍(Cu2+)和1.09倍(Zn2+),且两种吸附剂对Cu2+的最大吸附量和吸附速率均大于Zn2+。Zn2+在两种改性膨润土上的解吸率均高于Cu2+,且Cu2+、Zn2+在猪粪改性膨润土上的解吸率均要高于在HDTMA改性膨润土的。两种有机物改性的钠基膨润土对重金属离子具有良好的吸附性能,可以用于含重金属废水的处理和重金属污染土壤的钝化修复,而猪粪降解液改性膨润土是环境友好的重金属钝化剂。     

Structural characterization of poly(N-alkyl-4-vinylpyridinium) triflates using pyrolysis/tandem mass spectrometry

Desorption chemical ionization (DCI) and desorption electron ionization (DEI) of homo- and co-polymers of N-alkyl-4-vinylpyridinium triflates having ethyl, n-hexyl and n-dodecyl groups as N-alkyl substituents, produce mass spectra that display oligomeric ions. These positively charged ions are singly-charged and result from cleavage of the polymer into neutral oligomers and the loss of a single triflate anion per oligomer. Analogous negatively charged ions, in which each neutral oligomer carries an extra triflate anion, are observed in the desorption chemical ionization mass spectra. Each oligomer within the available mass range is represented in the mass spectra. The formation of cluster ions in which a single, multiply-charged cation is associated with a number of singly-charged anions, as observed for these ammonium polysalts, is unusual. Five major and three minor series of positively charged ions are observed in DCI and DEI methods of ionization. Ions in the different series correspond either to cleavage at different bonds between the constituent monomers or to hydrogen transfer in different directions. Unique and structurally diagnostic fragmentation processes are observed in tandem mass spectrometry (MS/MS) experiments performed using collision activated dissociation of mass-selected oligomeric ions.     

The nature of collision-induced dissociation processes of doubly protonated peptides: comparative study for the future use of matrix-assisted laser desorption/ionization on a hybrid quadrupole time-of-flight mass spectrometer in proteomics.

Comparative MS/MS studies of singly and doubly charged electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) precursor peptide ions are described. The spectra from these experiments have been evaluated with particular emphasis on the data quality for subsequent data processing and protein/amino acid sequence identification. It is shown that, once peptide ions are formed by ESI or MALDI, their charge state, as well as the collision energy, is the main parameter determining the quality of collision-induced dissociation (CID) MS/MS fragmentation spectra of a given peptide. CID-MS/MS spectra of singly charged peptides obtained on a hybrid quadrupole orthogonal time-of-flight mass spectrometer resemble very closely spectra obtained by matrix-assisted laser desorption/ionization post-source decay time-of-flight mass spectrometry (MALDI-PSD-TOFMS). On the other hand, comparison of CID-MS/MS spectra of either singly or doubly charged ion species shows no dependence on whether ions have been formed by ESI or MALDI. This observation confirms that, at the time of precursor ion selection, further mass analysis is effectively decoupled from the desorption/ionization event. Since MALDI ions are predominantly formed as singly charged species and ESI ions as doubly charged, the associated difference in the spectral quality of MS/MS spectra as described here imposes direct consequences on data processing, database searching using ion fragmentation data, and de novo sequencing when ionization techniques are changed.     

Mass spectrometric studies of benzoxazine resorcarenes

Eleven differently substituted 3,4-dihydro-2H-1,3-benzoxazine resorcarenes were studied by electrospray ionisation (ESI) and matrix-assisted laser desorption/ionisation (MALDI) mass spectrometry, using Fourier transform ion cyclotron resonance (FT-ICR) and time-of-flight (TOF) mass spectrometers, respectively. Under ESI conditions it was possible to transfer the intact resorcarenes from solution to the gas phase, yielding [M + H](+) and [M + 2H](+) ions as the main ions observed. Energy increase of the ions induced ready decomposition through successive eliminations of four CH(2)NR groups. Ion-molecule reactions showed that the ionising proton was situated somewhere inside the molecule and could not be reached with neutral reagent gases. In the host-guest complexation experiments, the benzoxazine resorcarenes studied turned out to be poor hosts for alkali metal and ammonium ions. In MALDI experiments, 2,5-dihydroxybenzoic acid proved to be the best matrix for these compounds. However, the intensity of the [M + H](+) ions was low for all compounds, and extensive fragmentation with consecutive elimination of CH(2)NR groups was observed.     

Adsorption behavior of Pb(II) on montmorillonite

The present work investigated the adsorption and desorption behaviors of Pb(II) on montmorillonite. The adsorption experiments were carried out using batch process. The results show that the adsorption is dependent on the pH value of the medium, and the uptake of Pb(II) increases with the pH increasing in the pH range of 2.0–10.0. The adsorption kinetics is in better agreement with pseudo-second order kinetics, and the adsorption data is a good fit with Langmuir isotherm. The presence of EDTA may result in a decrease of the amount of Pb(II) adsorbed. The presence of electrolyte and EDTA may enhance the desorption of Pb(II) ions adsorbed. The adsorption mechanism of Pb(II) on montmorillonite may be explained in two aspects: the chemical binding between Pb(II) ions and surface hydroxyl groups; and the electrostatic binding between Pb(II) ions and the permanent negatively charged sites of montmorillonite.     

Grazing incidence surface-induced dissociation of protonated peptides generated by matrix-assisted laser desorption/ionization

The grazing incidence surface-induced dissociation (GI-SID) of various protonated peptides with typical kinetic energies of 350 eV was investigated. Peptide ions were generated by matrix-assisted laser desorption/ionization (MALDI) using delayed extraction. The collision target surfaces used were aluminum and a liquid film of perfluorinated hydrocarbons. All peptides studied in these experiments showed enhanced fragment ion yields at grazing incidence (GI-SID effect) as observed in our former experiments with other precursor ion types. In general the GI-SID spectra exhibit N-terminal a(1)-type fragment ions, immonium ions and side-chain fragment ions in the low mass-to-charge region. Fragment ion series of the peptide backbone were not observed, which are typical and abundant in the spectra of established fragmentation techniques like collision-induced dissociation, MALDI post-source decay or surface-induced dissociation at steeper angles. The potential of the GI-SID process to yield useful information for primary structure determination of peptides is indicated by the observed differences in the GI-SID spectra of the isomeric dipeptides LR and IR.     

Cd2+和Ni2+在粉煤灰上的吸附特性

考察了粉煤灰对Cd2+和Ni2+的单组分吸附和双组分吸附性能。结果表明,粉煤灰可有效吸附水溶液中的Cd2+和Ni2+,去除率随pH升高而增加。吸附约60min后趋于平衡。粉煤灰对Ni2+的吸附容量高于Cd2+。单组分吸附平衡符合Freundlich模型和Redlich Peterson (R P)模型。双组分吸附时,Ni2+和Cd2+之间存在明显的竞争吸附效应;随干扰离子浓度升高,竞争吸附效应增强。不同模型拟合结果表明,双组分吸附平衡符合Freundlich竞争吸附模型。脱附实验表明,Cd2+比Ni2+易于脱附;0.1mol/L HCl、0.1mol/L HNO3 和0.05mol/L H2SO4的脱附效果接近,对Cd2+脱附率>60%,对Ni2+脱附率>35%。     

Sequence information of peptides and proteins with in-source decay in matrix assisted laser desorption/ionization-time of flight-mass spectrometry

In-source decay coupled with matrix assisted laser desorption/ionization-mass spectrometry, which is a mass spectrometric degradation method for the sequencing of peptides and proteins, has been applied to several different polypeptides and proteins. The influence of the nature of the constituent amino acids on positively charged product ions is described. Relatively small molecular mass peptides produced c-, b-, and/or a-series ions usable for C-terminal sequencing as well as y- and/or z-series ions usable for N-terminal sequencing. The formation of the C-terminal sequencing ions (c, b and a) and the N-terminal sequencing ions (y and z) was strongly dependent on the location(s) of basic arginine and lysine residues. The presence of the arginine and/or lysine residues at the N-terminal region was one-sided in the formation of c-, b-, and/or a-series ions, while the presence of those at the C-terminal region was favorable for the formation of y- and z-series ions. In-source decay experiments of intact proteins, apomyoglobin and two viral coat proteins, led to large amounts of c-series ions and small amounts of y-series ions, which reflected internal sequences.