Ion motion in a Fourier transform ion cyclotron resonance wire ion guide cell

Ion dynamics in a trapped ion mobility spectrometer

In the present paper, theoretical simulations and experimental observations are used to describe the ion dynamics in a trapped ion mobility spectrometer. In particular, the ion motion, ion transmission and mobility separation are discussed as a function of the bath gas velocity, radial confinement, analysis time and speed. Mobility analysis and calibration procedure are reported for the case of sphere-like molecules for positive and negative ion modes. Results showed that a maximal mobility resolution can be achieved by optimizing the gas velocity, radial confinement (RF amplitude) and ramp speed (voltage range and ramp time). The mobility resolution scales with the electric field and gas velocity and R = 100-250 can be routinely obtained at room temperature.

The spontaneous loss of coherence catastrophe in Fourier transform ion cyclotron resonance mass spectrometry

The spontaneous loss of coherence catastrophe (SLCC) is a frequently observed, yet poorly studied, space-charge related effect in Fourier-transform ion cyclotron resonance mass spectrometry (FTICR-MS). This manuscript presents an application of the filter diagonalization method (FDM) in the analysis of this phenomenon. The temporal frequency behavior reproduced by frequency shift analysis using the FDM shows the complex nature of the SLCC, which can be explained by a combination of factors occurring concurrently, governed by electrostatics and ion packet trajectories inside the ICR cell.

Orbitrap mass spectrometry: instrumentation, ion motion and applications

Since its introduction, the orbitrap has proven to be a robust mass analyzer that can routinely deliver high resolving power and mass accuracy. Unlike conventional ion traps such as the Paul and Penning traps, the orbitrap uses only electrostatic fields to confine and to analyze injected ion populations. In addition, its relatively low cost, simple design and high space-charge capacity make it suitable for tackling complex scientific problems in which high performance is required. This review begins with a brief account of the set of inventions that led to the orbitrap, followed by a qualitative description of ion capture, ion motion in the trap and modes of detection. Various orbitrap instruments, including the commercially available linear ion trap-orbitrap hybrid mass spectrometers, are also discussed with emphasis on the different methods used to inject ions into the trap. Figures of merit such as resolving power, mass accuracy, dynamic range and sensitivity of each type of instrument are compared. In addition, experimental techniques that allow mass-selective manipulation of the motion of confined ions and their potential application in tandem mass spectrometry in the orbitrap are described. Finally, some specific applications are reviewed to illustrate the performance and versatility of the orbitrap mass spectrometers.

The 'hybrid cell': a new compensated infinity cell for larger radius ion excitation in Fourier transform ion cyclotron resonance mass spectrometry

A new 'hybrid' ion cyclotron resonance (ICR) trap is proposed and analyzed by computer simulations. The trap is basically a hybrid of a segmented end cap (Infinity) and capacitively coupled cylindrical cell, with additional electrodes placed at the center of each end cap. The new trap produces an on-axis electric field z-profile similar to that of the Infinity cell or capacitively coupled open cylindrical cell during ion excitation. Simion simulations demonstrate that, during detection, appropriate changes of the potentials applied to the two new sets of electrodes produce a radial electric field z-profile that more closely approaches that for an ideal axial three-dimensional quadrupolar potential at high post-excitation ICR orbital radius, for improved signal-to-noise ratio and resolving power, and minimal m/z-discrimination.

Reduction of axial kinetic energy induced perturbations on observed cyclotron frequency

With Fourier transform ion cyclotron resonance (FTICR) mass spectrometry one determines the mass-to-charge ratio of an ion by measuring its cyclotron frequency. However, the need to confine ions to the trapping region of the ion cyclotron resonance (ICR) cell with electric fields induces deviations from the unperturbed cyclotron frequency. Additional perturbations to the observed cyclotron frequency are often attributed to changes in space charge conditions. This study presents a detailed investigation of the observed ion cyclotron frequency as a function of ion z-axis kinetic energy. In a perfect three-dimensional quadrupolar field, cyclotron frequency is independent of position within the trap. However, in most ICR cell designs, this ideality is approximated only near the trap center and deviations arise from this ideal quadrupolar field as the ion moves both radially and axially from the center of the trap. To allow differentiation between deviations in observed cyclotron frequency caused from changes in space charge conditions or differences in oscillation amplitude, ions with identical molecular weights but different axial kinetic energy, and thus amplitude of z-axis motion, were simultaneously trapped within the ICR cell. This allows one to attribute deviations in observed cyclotron frequency to differences in the average force from the radial electric field experienced by ions of different axial amplitude. Experimentally derived magnetron frequency is compared with the magnetron frequency calculated using SIMION 7.0 for ions of different axial amplitude. Electron promoted ion coherence, or EPIC, is used to reduce the differences in radial electric fields at different axial positions. Thus with the application of EPIC, the differences in observed cyclotron frequencies are minimized for ions of different axial oscillation amplitudes.

Computer simulations of a new three rods ion optic (TRIPOLE) with high focusing and mass filtering capabilities

A novel three rod (tripole) ion optic to which three AC voltages with symmetrically delayed phase shifts were applied to each electrode. We studied its ion guiding, focusing, and mass filtering capabilities by SIMION ver. 7.0 computer simulations. An electric field mathematical model was developed to calculate the pseudopotential of the tripole radial AC force. The tripole showed stable ion guiding for wide ranges of AC amplitude; better collisional focusing than hexapole and octapole and similar focusing as quadrupole (rod pole). Also, the ion optic clearly showed interesting mass filtering potential when the phase shift was asymmetrically delayed. The symmetric shape of the pseudopotential field explained the tripole ion guiding and focusing capabilities. For mass filtering, the pseudopotential was asymmetric and its effect was balanced with DC voltage to separate the ions, depending in their masses. The resolution was much lower than quadrupole but useful when rough filtering was required.

Coaxial multi-electrode cell ('O-trap') for high-sensitivity detection at a multiple frequency in Fourier transform ion cyclotron resonance mass spectrometry: main design and modeling results

Separation of the functions of ion excitation and detection between different cell compartments allows for implementation of excitation and detection techniques unattainable in a single compartment of the conventional ion cyclotron resonance (ICR) cell. In particular, multi-electrode detection at a multiple of the main cyclotron frequency can be utilized without the loss of sensitivity and other negative effects. The new O-trap designed exclusively for ion detection adds an additional, internal coaxial cylinder around which ions with excited cyclotron orbits rotate. Comparison of simulated performance characteristics of the new O-trap with those of the same-size conventional cylindrical cell shows that the O-trap can provide higher sensitivity and ion capacity. Multiplexing of the O-traps can further increase the analysis speed. Future efforts will be aimed at building and testing experimentally the coaxial O-trap, including optimization of the method of ion transfer between the compartments of the cell.