Mass-analyzed Ion Research Articles

Ｎａｎｏ‐ＥＳＩプローブの開発と高分解能測定法およびＭＩＫＥスペクトル法を用いた有機イオンの分解機構に関する研究

A new technique is described for accurate mass measurement by using multiple sprayers nano electrospray ionization mass spectrometry (nano-ESI/MS). A nano-scale high-performance liquid chromatography (nano-LC) was combined with a magnetic sector instrument. A metal-coated glass capillary was used for the introduction of the reference compound solution, and a metal-coated fused silica capillary was used to connect the nano-LC column to ionization chamber. By shifting the position of the each sprayers to the sampling orifice, the spectra were obtained for the sample compounds eluted from the column and the reference one. Several standard compounds were examined by using this technique and satisfactory accurate masses were obtained. It was not problems for the differences between the ionization efficiency of the sample and the reference compounds. Studies on the unimolecular metastable ion decomposition of several organic compounds are also described by using high-resolution mass spectrometry, MIKE (mass-analyzed ion kinetic energy) spectrometry and D-labeling technique. The m/z 45 ions generated from 2-methoxyethylamine (CH3OCH2CH2NH2) consist of two isobaric ions, methoxymethyl ion, CH3OCH2+, and C2H7N+. The m/z 69 ions generated from methyl trifluoroacetoacetate (CF3COCH2COOCH3) and 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (CF3COCH2COCF3) also consist of two isobaric ions, trifluoromethyl ion, CF3+, and protonated carbon suboxide, OCCH+CO.

Mechanisms and dynamics of the metastable decay in Ar2+.

A detailed experimental as well as theoretical investigation of the properties of the metastable dissociation Ar2+ --> Ar+ + Ar is presented. The mass-analyzed ion kinetic energy (MIKE) scan technique has been performed using a three sector field mass spectrometer. The possible mechanisms of the metastability of Ar2+ have been examined and the observed decay process is assigned to the II(1/2)(u)-->I(1/2)(g) bound to continuum radiative transition, in agreement with earlier work. The calculation of the theoretical shape of the kinetic energy release distribution of fragment ions allowed us to construct the theoretical MIKE peak and compare it with the raw experimental data. The accuracy of various sets of potential energy curves for Ar2+ is discussed, as well as the way of production of the metastable Ar2+[II(1/2)(u)] electronic state by electron impact. Excellent agreement between the experimental data and theoretical model has been observed.

The formation of thick buried oxide layers using ion implantation from water plasma

An implanter without an ion mass analyzer has been used to successfully fabricate silicon-on-insulator (SOI) materials by H 2O +, HO +, and O + ion implantation using water plasma. Based on the consideration that the masses of those three ions are very close, this fabrication makes it possible to form a single buried oxide (BOX) layer by choosing the appropriate implantation energy and dose. Cross-sectional transmission electron microscopy (XTEM) results indicated that the BOX thickness of the SOI materials fabricated using a water plasma approach is increased more than 50% over that of the conventional separation by implantation of oxygen (SIMOX) process. Secondary ion mass spectroscopy (SIMS) depth profile analysis on the as-implanted wafers showed that there are two hydrogen enrichment peaks around both sides of the projected range R p of oxygen, which correspond to the two interfaces of the BOX layer of the annealed samples. Additional designed experiments revealed that the heavily damaged region with hydrogen-induced defects appears to be the adsorption center for the outside oxygen to diffuse into the silicon during the high-temperature annealing process, and consequently, thicken the BOX layer of the SOI structure. The findings in the present work may provide a possible solution to reduce the cost of the conventional SIMOX–SOI wafers while maintaining a desirable BOX thickness.

Formation of C 6H nSi + ( n = 5–8) from phenylsilane: an experimental and theoretical study

The metastable ion decomposition (MID) spectra of C 6H n Si + ( n = 6–8) generated by electron ionization of phenylsilane were obtained using mass-analyzed ion kinetic energy spectrometry (MIKES). H and H 2 losses were the main channels in the MID of C 6H 8Si + ( 1). The dominant product ion in the MIDs of C 6H 7Si + ( 2) and C 6H 6Si + ( 3) was C 6H 5Si + ( 4) formed by H 2 and H losses, respectively. Density functional theory calculations were performed to investigate isomerizations and dissociations of 1– 3 at the B3LYP/6-311++G(d,p) level. RRKM model calculations were performed to understand their dissociation kinetics. These theoretical results predict that the consecutive dissociation 1 → 3 (+ H 2) → 4 + H dominates at low energies, while 1 → 2 (+ H ) → 4 + H 2 at high energies. It has been found that several isomers of 1– 3 including ion–molecule complexes, C 6H 6·SiH x + ( x = 0–2), play important roles in the dissociation of 1. Reaction mechanisms are proposed for the formation of several isomers of 1– 4 from the phenylsilane molecular ion.

Electron ionization mass spectrometry as a tool for the investigation of the ortho effect in fragmentation of some Schiff bases derived from amphetamine analogs

The electron ionization-induced fragmentation patterns of three forensically relevant Schiff bases, originating from the condensation between 2-, 3- and 4-methoxyamphetamine and the corresponding ketones, were studied. The proposed fragmentation routes and ion structures are supported by high-resolution data and B/E linked-scan and mass-analyzed ion kinetic energy spectra. The rationalization of the ortho effect, which is responsible for the formation of the [M-OCH3] fragment in the case of the imine bearing ortho-substituted methoxy group, is given.

The anomalous shape of the cross section for the formation of SF3+ fragment ions produced by electron impact on SF6 revisited.

The partial ionization cross section for the formation of SF(3) (+) fragment ions following electron impact on SF(6) is known to have a pronounced structure in the cross section curve slightly above 40 eV. We used the mass-analyzed ion kinetic energy (MIKE) scan technique to demonstrate the presence of a channel contributing to the SF(3) (+) partial ionization cross section that we attribute to the Coulomb explosion of doubly charged metastable SF(4) (2+) ions into two singly charged ions SF(3) (+) and F(+), with a threshold energy of about 45.5 eV. Thus the observed unusual shape of the SF(3) (+) partial ionization cross section is the result of two contributions, (i) the direct formation of SF(3) (+) fragment ions via dissociative ionization of SF(6) with a threshold energy of 22 eV and (ii) the Coulomb explosion of metastable SF(4) (2+) ions with a threshold energy of about 45.5 eV. A detailed analysis of the MIKE spectrum reveals an average kinetic energy release of about 5 eV in the Coulomb explosion of the SF(4) (2+) ions with evidence of a second channel corresponding to an average kinetic energy release of about 1.1 eV.

Collisional Activation of Peptide Ions in FT‐ICR Mass Spectrometry

AbstractFor Abstract see ChemInform Abstract in Full Text.

Isomerization and dissociation of the acetonitrile molecular cation

The unimolecular dissociation of the acetonitrile molecular cation (CH 3CN +) has been investigated using mass-analyzed ion kinetic energy spectrometry. Kinetic energy release distribution was obtained for the H loss. Density functional theory calculations have been performed to investigate isomerization and dissociation of CH 3CN +. The potential energy surface (PES) for the H loss has been constructed from the calculations at the UB3LYP/6-311++G(3df,3pd) level. The RRKM model calculations based on the obtained PES predict that CH 3CN + interconverts to CH 2CNH + and CH 2NCH + followed by dissociation to a cyclic C 2H 2N + via a cyclic C 2H 3N + intermediate near the threshold. The present and previous experimental data for the dissociations of C 2H 3N + isomers are interpreted with the theoretical results.

Compact surface plasma sources for heavy negative ion production

Features of a compact surface plasma source designed for heavy negative ion beam production are considered. Discharges in crossed E×B fields with hollow cathodes were used for efficient plasma generation. Production of heavy negative ion beams by plasma interaction with the surface of spherical focusing emitters made of different materials, such as copper and lanthanum hexaboride, with cesium catalysis are presented. The dynamics of emitter activation is discussed. dc ion beams with current up 0.9 mA have been extracted from the compact surface plasma sources with a 12-mm-diam LaB6 emitter and a emission aperture of 3 mm diam. Minimizing plasma and gas thickness between emitter and emission aperture is essential for minimizing negative ion destruction and maximizing high intensity beam production. A small mass analyzer and secondary ion mass spectroscopy were used to quantify boron ion yield. Presence of atomic and molecular boron negative ions is confirmed. The estimated emittance of the 0.5 mA heavy negative ion beam is ε=13 π mm mrad(MeV)1/2.

New design for a time-of-flight mass spectrometer with a liquid beam laser desorption ion source for the analysis of biomolecules

We describe a novel liquid beam mass spectrometer, based on a recently discovered nanosecond laser desorption phenomenon, [W. Kleinekofort, J. Avdiev, and B. Brutschy, Int. J. Mass Ion. Processes 152, 135 (1996)] which allows the liquid-to-vacuum transfer, and subsequent mass analysis of pre-existing ions and ionic associates from liquid microjets of aqueous solutions. The goal of our novel technical approach is to establish a system with good mass resolution that implements improvements on critical components that make the system more reliable and easier to operate. For laser desorption pulsed dye-laser difference frequency mixing is used that provides tunable infrared light near the absorption maximum of liquid water around 3 μm. Different types of liquid beam glass nozzles (convergent capillary and aperture plate nozzles) are investigated and characterized. Starting from theoretical considerations of hydrodynamic drag forces on micrometer size droplets in supersonic rarefied gas flows we succeeded in capturing efficiently the liquid beam in a liquid beam recycling trap operating at the vapor pressure of liquid water. For improving the pollution resistance, the liquid jet high vacuum ion source region is spatially separated from the reflectron time-of-flight mass spectrometer (TOF–MS) working behind a gate valve in an ultrahigh vacuum environment. A simple (simulation optimized) ion optics is employed for the ion transfer from the source to the high vacuum region. This new feature is also mostly responsible for the improved mass resolution. With the present tandem-TOF–MS setup a resolution of m/Δm≈1800 for the low and m/Δm≈700 in the high mass region has been obtained for several biomolecules of different mass and complexity (amino acids, insulin, and cytochrome c).

Plasma Diagnostics in Pulsed Plasma Doping (P<tex>$^2$</tex>LAD) System

As semiconductor devices continue to shrink in size, demands for the formation of ultra-shallow junctions (USJ) are increasing. Pulsed plasma doping (P/sup 2/LAD) has emerged as a scaleable and cost effective solution to dopant delivery, since it is capable of high dose rates at ultra-low energies (0.02-20 kV). In P/sup 2/LAD, a pulsed plasma is generated adjacent to the silicon wafer using pulsed biases. Typical pulse widths range between 5 and 50 /spl mu/s, and pulse repetition rates are between 100 and 10000 Hz. Time-resolved Langmuir probe measurements showed that cold plasma is present during the afterglow period, which may play an important role in process control. Probe measurements also showed the presence of primary electron and electron beams during the initial pulse-on stage in both Ar and BF/sub 3/ plasmas. Ion mass and energy analysis indicated that BF/sub 2//sup +/ is the dominant ion species in the BF/sub 3/ plasmas, with BF/sup +/ as the second-most abundant ion species.

Kinetic energy release of protonated methanol clusters using the low-temperature fast-atom bombardment: experiment and theory combined.

Low-temperature fast-atom bombardment was found to be an excellent method for generating large protonated methanol clusters, (CH(3)OH)(n)H(+) (n = 2 to 15). Metastable dissociations of these clusters, involving elimination of one methanol molecule, were studied using mass-analyzed ion kinetic energy spectra (MIKES). From metastable peak profiles kinetic energy release (KER) distributions were obtained, even for clusters as large as (CH(3)OH)(15)H(+). The results were analyzed by a simple thermal model, by the finite heat bath theory (FHBT) and by the RRKM-based MassKinetics algorithm. The KER distribution was shown to correspond to a three-dimensional translational energy distribution, implying statistical energy partitioning in the transition state. The mean KER values and transition state temperatures were found to increase with cluster size, reaching 25 meV and approximately 210 K for large clusters (n = 10).

An analysis of mass spectrometric study of negative ions extracted from negative corona discharge in air

In this paper we report the detection and mass analysis of negative ions formed in a negative corona discharge using both dry and ‘wet’ air at pressures between 5 and 27kPa. The yield of individual ions is strongly affected by trace concentrations of ozone, nitrogen oxides and water vapour. In dry air the dominant ion is CO3−. In presence of water this is converted very efficiently to cluster ions containing one and more water molecules. If ozone and nitrogen oxides are added, or are produced in discharge in sufficient concentrations, NO3− ions and NO3− hydrated clusters are formed. Ozone concentrations greater than 25ppm are sufficient to completely suppress the appearance of O2− ions and its clusters both in dry and wet air. Such observations allow a comprehensive review of the physical and chemical processes within the discharge.

Mass spectral fragmentation of 2a,4-disubstituted 2,2a,3,4-tetrahydro-2-phenoxy-1H-azeto[2,1-d][1,5]benzothiazepin-1-ones under electron impact ionization conditions.

The mass spectrometric fragmentation of 2a,4-disubstituted 2,2a,3,4-tetrahydro-2-phenoxy-1H-azeto[2,1-d][1,5]benzothiazepin-1-ones has been investigated using the aid of mass-analyzed ion kinetic energy spectrometry. All compounds tend to eliminate a phenoxy, phenol, and phenoxyketene, respectively, from molecular ions. [M(+)-PhO] ions could also form [M(+)-PhOH] ions, which could further lose alkenes. [M(+)-PhOCH=C=O] ions could further yield 2-arylbenzothiazole ions and other fragment ions.

Mn implanted GaAs by low energy ion beam deposition

High dose Mn was implanted into semi-insulating GaAs substrate to fabricate embedded ferromagnetic Mn–Ga binary particles by mass-analyzed dual ion beam deposit system at room temperature. The properties of as-implanted and annealed samples were measured with X-ray diffraction, high-resolution X-ray diffraction to characterize the structural changes. New phase formed after high temperature annealing. Sample surface image was observed with atomic force microscopy. All the samples showed ferromagnetic behavior at room temperature. There were some differences between the hysteresis loops of as-implanted and annealed samples as well as the cluster size of the latter was much larger than that of the former through the surface morphology.

Liquid chromatography coupled to negative electrospray/ion trap mass spectrometry for the identification of isomeric glutathione conjugates of catechol estrogens

Conjugation to glutathione (GSH) represents an important detoxification pathway for preventing DNA damage due to oxidation products of catechol estrogens. In order to identify isomeric GSH conjugates of catechol estrogens, liquid chromatography coupled to electrospray/ion trap mass spectrometry was used. For this purpose, both positive and negative ion modes were applied, generating protonated and deprotonated species, respectively. Energy-resolved fragmentation of each isomeric quasi-molecular ion was achieved in two regions of the mass spectrometer: (i) the mass analyzer (ion trap mass spectrometer) and (ii) the interface region of the electrospray ionization source. The resonance excitation of [M+H] + protonated ions carried out into the ion trap did not show any isomeric differentiation. Although ion source fragmentation of these same species allowed identification of each isomer, this method requires a good chromatographic separation, making it inefficient for the analysis of low sample amounts from in vitro or in vivo sources. Conversely, using resonance excitation of deprotonated ions, isomer distinction could be achieved. Thus, this technique should yield the best data for the direct characterization of isomers of catechol estrogen–GSH conjugates from biological samples.

Structural and optical study of GaMnAs/GaAs

GaMnAs/GaAs was obtained with mass-analyzed low energy dual ion beam depostion technique with Mn ion energy of 1000 eV and a dose of 1.5 × 1018 Mn+/cm2 at the substrate temperature of 400°C and was annealed at 840°C. X-ray diffraction spectra showed that Ga5.2Mn, Ga5Mn8, α-Mn and Mn3Ga were obtained in the as-grown sample. After annealing Mn3Ga and α-Mn disappeared, Ga5Mn8 tended to disappear, Ga5.2Mn crystallized better and new phase of Mn2As was generated. The photoluminescence spectra of the as-grown sample showed that the 1.5042 eV GaAs exciton peak, 1.4875 eV peak involving a carbon acceptor and a broad band near 1.35 eV. After annealing at 840°C, the 1.5042 eV peak and 1.4875 eV shifted to 1.5065 and 1.4894 eV, respectively, and the photoluminescence intensity of the 1.35 eV band increased greatly.

Unimolecular Reactions of Diethyl Malonate Cation in Gas-phase

Unimolecular reactions of diethyl malonate cation (CH3CH2OC(=O)CH2C(=O)OCH2CH3+· ; 1+·, Mw : 160) induced by electron ionization, have been investigated by use of mass-analyzed ion kinetic energy (MIKE) spectrometry and D-labeling in conjunction with thermochemistry. In the metastable time window, the molecular ions 1+· lead not only to the formation of the major fragment ions m/z 133 ([M-C2H3]+) through a McLafferty + 1 rearrangement, but also to two minor fragment ions m/z 132 ([M-C2H4]+·) through a McLafferty rearrangement (or [M-CO]+·) and m/z 88 ([M-C3H4O2]+·). These dissociations are rationalized by the idea of ion-neutral complex. The m/z 88 ions are generated via at least two different routes. The m/z 133 ([M-C2H3]+) ions decompose into the ions at m/z 115, 106, and 105 by the losses of H2O, C2H3, and C2H4, respectively. A large part of the first fragment ions would be in the keto form and it decomposes into the m/z 71 and 43 ions by the losses of CO2 and C3H4O2 (or C2O3), and a small part would be in the enol form and decomposes into the m/z 87 ions by the loss of C2H4, not CO. The m/z 43 ions are isobaric, C2H3O+ and C3H7+.

FexSi grown with mass-analyzed low-energy dual ion beam deposition

Heavily iron-implanted silicon was prepared by mass-analyzed low-energy dual ion beam deposition technique. Auger electron spectroscopy depth profiles indicate that iron ions are shallowly implanted into the single-crystal silicon substrate and formed 35nm thick FexSi films. X-ray diffraction measurements show that as-implanted sample is amorphous and the structure of crystal is partially restored after as-implanted sample was annealed at 400°C. There are no new phases formed. Carrier concentration depth profile of annealed sample was measured by Electrochemical C–V method and indicated that FexSi film shows n-type conductivity while silicon substrate is p-type. The p–n junction is formed between FexSi film and silicon substrate showing rectifying effect.

Peptide sequencing using a patchwork approach and surface-induced dissociation in sector-TOF and dual quadrupole mass spectrometers

Surface-induced ion activation in combination with a database search strategy based on the Patchwork concept is applied to the determination of peptide sequences. Surface-induced dissociation (SID) is performed in a tandem quadrupole mass spectrometer and in a hybrid sector/time-of-flight mass spectrometer in order to evaluate the importance of accurate mass analysis of the SID fragment ions for peptide identification. The modified Patchwork approach is based on piecing together the peptide blocks in a bidirectional way, simultaneously using low-mass fragments originating from the C-terminus and N-terminus of the molecule, and relying on the measurement of the peptide's molecular weight with moderate mass accuracy. The results from this analysis are used as search filters in MASCOT's (http://www.matrixscience.com) Sequence Query search engine, with the simultaneous addition of the full MS/MS peak list. SID is performed with collision targets coated with pure and mixed composition self-assembled monolayers produced by fluorocarbon and hydrocarbon alkanethiolate solutions of varying chemical composition. The resulting MS/MS spectra produced on pure and mixed hydrocarbon SAMs are submitted to the modified version of Patchwork sequencing. It is found that hydrocarbon surfaces improve the relative abundance of larger fragments. Under the moderate mass accuracy conditions (±0.3 u) offered by our linear-TOF-SID instrument, it is found that increasing the abundance of larger fragments dramatically improves the sequencing scores.