An ion trap-ion mobility-time of flight mass spectrometer with three ion sources for ion/ion reactions

This instrument combines the capabilities of ion/ion reactions with ion mobility (IM) and time-of-flight (TOF) measurements for conformation studies and top-down analysis of large biomolecules. Ubiquitin ions from either of two electrospray ionization (ESI) sources are stored in a three dimensional (3D) ion trap (IT) and reacted with negative ions from atmospheric sampling glow discharge ionization (ASGDI). The proton transfer reaction products are then separated by IM and analyzed via a TOF mass analyzer. In this way, ubiquitin +7 ions are converted to lower charge states down to +1; the ions in lower charge states tend to be in compact conformations with cross sections down to ～880 Ų. The duration and magnitude of the ion ejection pulse on the IT exit and the entrance voltage on the IM drift tube can affect the measured distribution of conformers for ubiquitin +7 and +6. Alternatively, protein ions are fragmented by collision-induced dissociation (CID) in the IT, followed by ion/ion reactions to reduce the charge states of the CID product ions, thus simplifying assignment of charge states and fragments using the mobility-resolved tandem mass spectrum. Instrument characteristics and the use of a new ion trap controller and software modifications to control the entire instrument are described.     

Simulated ion trajectory and induced signal in ion cyclotron resonance ion traps

We present a numerical method for computation of electrostatic (trapping) and time-varying (excitation) electric fields and the resulting ion trajectory and detected time-domain-induced voltage signal in a rectangular (or cubic) ion cyclotron resonance (ICR) ion trap. The electric potential is calculated by use of the superposition principle and relaxation method with a large number of grid points (e.g., 100 × 100 × 100 for a cubic trap). Complex ICR experiments and spectra may now be simulated with high accuracy. Ion trajectories may be obtained for any combination of trapping and excitation modes, including quadrupolar or cubic trapping in static or dynamic mode; and dipolar, quadrupolar, or parametric excitation with single-frequency, frequency-sweep (chirp), or stored waveform inverse Fourier transform waveforms. The resulting ion trajectory may be represented either as its three dimensional spatial path or as two-dimensional plots of x-, y-, or z-position, velocity, or kinetic energy versus time in the absence or presence of excitation. Induced current is calculated by use of the reciprocity principle, and simulated ICR mass spectra are generated by Fourier transform of the corresponding time-domain voltage signal.     

Mutual storage mode ion/ion reactions in a hybrid linear ion trap

Ion/ion proton transfer reactions involving mutual storage of both ion polarities in a linear ion trap (LIT) that comprises part of a hybrid triple quadrupole/linear ion trap mass spectrometer have been effected. Mutual ion storage in the x- and y-dimensions arises from the normal operation of the oscillating quadrupole field of the quadrupole array, while storage in the z-dimension is enabled by applying unbalanced radio-frequency amplitudes to opposing sets of rods of the array. Efficient trapping (>90%) is achieved for thermalized ions over periods of several seconds. Reactions were demonstrated for multiply charged protein/peptide cations formed by electrospray with anions derived from glow discharge ionization of perfluoro(methyldecalin) (PMD) introduced from the side of the LIT rod array. Doubly and singly charged protein ions are readily formed via ion/ion reactions. The parameters that affect ion/ion reactions are discussed, including the degree of RF unbalance on the LIT rods, vacuum pressure, nature of the buffer gas, reaction time, anion abundance, and the low mass cutoff for ion/ion reaction. The present system has a demonstrated upper mass-to-charge ratio limit of at least 33,000. The system also has high flexibility with respect to defining MS(n) experiments involving both collision-induced dissociation (CID) and ion/ion reactions. Experiments are demonstrated involving beam-type CID in the pressurized collision quadrupole (Q2) followed by ion/ion reactions involving the product ions in the LIT. Ion parking experiments are also demonstrated using the mutual storage ion/ion reaction mode in the LIT, with a parking efficiency over 60%.     

Transmission mode ion/ion proton transfer reactions in a linear ion trap

A new method is described for effecting ion/ion proton transfer reactions that involves storage of analyte ions while oppositely charged ions are transmitted through the stored ion population. In this approach, the products are captured and stored in the linear ion trap for subsequent mass analysis. Charge reduction of multiply charged protein ions is used as an example to illustrate the analytical usefulness of this method. In another variation of the transmission mode ion/ion reaction approach, two charge inversion experiments, implemented by passing analyte ions through a population of multiply charged reagent ions in a LIT, are also demonstrated. A pulsed dual ion source approach coupled with a hybrid triple quadrupole/linear ion trap instrument was used to demonstrate these two methods. The results for ion/ion reactions implemented using these so-called "transmission mode" experiments were comparable to those acquired using the more conventional mutual storage mode, both in terms of efficiency and information content of the spectra. An advantage of transmission mode experiments compared with mutual storage mode experiments is that they do not require any specialized measures to be taken to enable the simultaneous storage of oppositely charged ions.     

A secondary ion microprobe ion trap mass spectrometer

An ion trap mass analyzer has been attached to an organic secondary ion microprobe. A pressure differential >100 can be maintained between the ion trap and microprobe. The well-focused secondary ion beam can transit a small (2 mm) diameter tube, but gas flow from ion trap to microprobe is impeded. This pressure differential allows the microprobe to retain imaging capability. Ion trap and microprobe data systems are integrated by taking advantage of the highly reproducible periodicity of the ion trap operating in resonant ejection mode and asynchronous signal and data acquisition afforded by commercially available interface cards. Secondary ion mass spectra and images obtained indicate an approximately 10-fold improvement in sensitivity, although preliminary evidence indicates low (<1%) trapping efficiency. Image data acquisition using the ion trap for mass analysis requires at least 10 times as much time compared to using a quadrupole mass filter because the mass-selected instability mode is used for mass analysis, i.e., mass resolution in the ion trap is not continuous as it is in the quadrupole.     

Product ion spectral simplification using time-delayed fragment ion capture with tandem linear ion traps

A new technique to generate product ion spectra as the internal energy of a collisionally activated precursor ion evolves is described. The precursor ion is activated by acceleration into a mass-selective linear ion trap under conditions whereby some of the fragment ions formed are unstable within the trap. After a time delay the stability parameters of the ion trap are changed to allow capture of fragments that that were previously unstable. The result is a product ion spectrum that originates from precursor ions with a modified internal energy distribution. It is possible to follow the evolution of the precursor internal energy distribution for many milliseconds after admittance of the precursor ions into the linear ion trap. Time-delayed fragmentation product ion spectra typically display reduced sequential fragmentation products leading to spectra that are more easily interpreted. Several important experimental parameters important to time-delayed fragmentation have been identified and are discussed. The technique has applications for both small precursor ions and multiply charged peptides.     

Corner ion,edge-center ion,and face-center ion Madelung expressions for sodium chloride

Building on work of Tyagi (Progr Theor Phys 114(3):517–521, 2005), we present expressions for calculating the corner ion, edge-center ion, and face-center ion Madelung constants for bulk sodium chloride crystals.     

Nonamethylosmocenylcarbenium ion

Conclusions Nonamethylosmocenylcarbenium ion salts were synthesized. The stabilization of the C₅Me₅MC₅Me₄CH₂ ⁺ cations increased in the series Fe < Ru < Os, which was probably due to intensification of the direct interaction of the metal atom with the carbenium center in this series.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No.7, pp. 1620–1622, July, 1987.     

Three-body ion—ion recombination in mercury-halide lasers

The role of ion—ion recombination in the formation of excited states in mercury-halide lasers is outlined. A generalization of Natanson's treatment to unequal-mass constituents and general mean free paths is proposed. Rates as high as (2.6–1.5) × 10^?6 cm³ s^?1 are hence determined for the recombination of Hg⁺ with F^?, Cl^?, Br^? and I^? respectively, in Ar at (1.7–3.5) atm and 300 K. Somewhat higher rates (3.4?1.9) × 10^?6 cm³ s^?1 at slightly lower densities are obtained for the corresponding cases involving Ar⁺.     

Nitrate ion association with Sm3+ ion

A solvent extraction method withTBP as an extractant was used for the determination of the stability constantsK ₁ ^o for the SmNO ₃ ²⁺ complex, for different least approach distanceså of ions. It was established thatå=6.5 Å for SmNO ₃ ²⁺ .

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Zur Assoziation von Nitrat-Ion mit Sm³⁺

Zusammenfassung Die StabilitätskonstantenK ₁ ^o für den SmNO ₃ ²⁺ -Komplex bei verschiedenen Mindestannäherungsdistanzenå der Ionen wurden mittels einer Lösungsmittelextraktionsmethode mitTBP ermittelt. Der beste Wert fürå war 6.5 Å.

     

Field-modulated selective ion storage in a quadrupole ion trap

A new method of selective ion storage in a quadrupole ion trap is described. Broadband waveforms were applied to the endcaps of an ion trap to eject unwanted ions by resonance excitation, which enhanced the storage of selected target ions. A unique trapping field amplitude modulation technique allowed the use of waveforms with fewer frequency components. The requirements and methods of calculations for frequency-optimized wave-forms are discussed. Advantages of this method include the reduction of target ion loss that results from collision-activated dissociation. In other applications, equivalent performance, relative to methods that use nonmodulated trapping fields combined with waveforms that have a higher frequency density, was shown.     

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.     

Coulometric titration of thallous ion with electrogenerated ferricyanide ion

Thallous ion can be coulometrically titrated to thallic oxide in strongly alkaline medium by means of ferricyanide ion generated by anodic oxidation of ferrocyanide ion at a platinum anode. The equivalence point may be detected either potentiometrically or amperometrically. With 8 to 20 mg of thallous ion in 125 ml the accuracy and precision are within ± 0.2%.     

Asymmetric rectilinear ion trap with unidirectional ion ejection capability

In this paper, the shapes of the electrodes are modified based on a rectilinear ion trap to achieve unidirectional ejection of ions. The designed asymmetric rectilinear ion trap (ARIT) analyzer adds convex and concave circular structures with a height of 0.5 mm on the two X‐electrodes, so that the electric field center of the ion trap is inclined to the concave side. The electric field lines of the convex side are compressed to the concave side. Both simulations and experimental results show that ions are more likely to emit from the slit on the concave side plate when performing ion resonance ejection. The mass spectrum signal intensity can reach more than twice that of the original rectilinear trap when using only one detector. Calculations of the electric field components in the trap show that the even‐order higher field proportion in the ion trap has not been significantly affected. Combined with the experimental test results, the study further confirmed that the developed ARIT has no significant loss in mass resolution, tandem mass spectrometry capability, and quantitative analysis capability. The proposed asymmetric structure modification scheme can achieve single‐side ejection without significantly affecting other performances of the analyzer, which provides a new idea for the structural optimization of the subsequent ion trap analyzers.     

Molecular ion fluorescence excitation spectrum from an ion beam

The laser-induced excitation spectrum for the 0.0 band of the A²II → X²X⁺ transition of CO⁺ has been observed from an ion beam. Analysis of electron-bombardment excitation fluorescence in the same ion beam indicates radiative lifetime for the A²IIν′ = 0 state of CO⁺ of 7.4 ± 1.0 μs.     

A pulsed triple ionization source for sequential ion/ion reactions in an electrodynamic ion trap

A pulsed triple ionization source, using a common atmosphere/vacuum interface and ion path, has been developed to generate different types of ions for sequential ion/ion reaction experiments in a linear ion trap-based tandem mass spectrometer. The triple ionization source typically consists of a nano-electrospray emitter for analyte formation and two other emitters, an electrospray emitter and an atmospheric pressure chemical ionization emitter or a second nano-electrospray emitter for formation of the two different reagent ions. The three emitters are positioned in a parallel fashion close to the sampling orifice of the tandem mass spectrometer. The potentials applied to each emitter are sequentially pulsed so that desired ions are generated separately in time and space. Sequential ion/ion reactions take place after analyte ions of interest and different set of reagent ions are sequentially injected into a linear ion trap, where axial trapping is effected by applying an auxiliary radio frequency voltage to the end lenses. The pulsed triple ionization source allows independent optimization of each emitter and can be readily coupled to any atmospheric pressure ionization interface with no need for instrument modifications, provided the potentials required to transmit the ion polarity of interest can be synchronized with the emitter potentials. Several sequential ion/ion reactions examples are demonstrated to illustrate the analytical usefulness of the triple ionization source in the study of gas-phase ion/ion chemistry.     

A linear ion trap mass spectrometer with versatile control and data acquisition for ion/ion reactions

A linear ion trap (LIT) with electrospray ionization (ESI) for top-down protein analysis has been constructed. An independent atmospheric sampling glow discharge ionization (ASGDI) source produces reagent ions for ion/ion reactions. The device is also meant to enable a wide variety of ion/ion reaction studies. To reduce the instrument's complexity and make it available for wide dissemination, only a few simple electronics components were custom built. The instrument functions as both a reaction vessel for gas-phase ion/ion reactions and a mass spectrometer using mass-selective axial ejection. Initial results demonstrate trapping efficiency of 70% to 90% and the ability to perform proton transfer reactions on intact protein ions, including dual polarity storage reactions, transmission mode reactions, and ion parking.