The analytical solution for the optimum voltage on regularizing electrodes of the open dynamically harmonized cell.

The Fourier transform ion cyclotron resonance method holds the lead in mass accuracy and resolving power among all other mass spectrometry methods. The dynamically harmonized cell is largely responsible for the supremacy. This cell has an ideal hyperbolic trapping potential after averaging over fast cyclotron motion. Recently we have introduced an open modification of the cell (especially useful with ultrahigh magnetic fields) and have found the analytical solution for the averaged potential inside it. The voltage on specific "regularizing" electrodes determines how close a potential is to the hyperbolic one. In this article, we find the optimal voltage on these "regularizing" electrodes analytically. This will assist with both further analysis and tuning of the trap after manufacturing.

Generalization of an Open Dynamically Harmonized Cell for Ultrahigh FT ICR Resolution.

FT ICR mass spectrometry is the leader in resolving power among all mass spectrometry methods. Introduction of the dynamically harmonized measuring cell─a closed-cylindrical cell with specifically shaped electrodes─helps to reach the resolving power of more than 107 with a magnetic field of about 7 T. From the theory of FT ICR mass spectrometry it follows that the resolving power of this type of instrument depends linearly on the magnetic field under various conditions. However, the results obtained on this type of mass spectrometer with the maximum magnetic field achievable today did not show a proportional increase in resolving power. In one of our previous papers, we assumed that the reason for this was insufficient vacuum inside the cell, since vacuum quality should be at least proportional to the magnetic field, since the mean free run time decreases proportionally to the magnetic field growth. We have presented an open modification of the dynamically harmonized cell that can help improve the cell pumping conditions. However, the electric potential distribution inside this new cell is slightly different from the ideal (harmonic) one, obtained inside the closed version of the cell, and the resolving power may have been limited by this difference.

Evaluation of major historical ICR cell designs using electric field simulations.

In Fourier-transform ion cyclotron resonance mass spectrometry, ions are detected by measuring image current induced in the detecting electrodes by trapped ions rotating in a magnetic field at their cyclotron frequencies. The ion trap used for this purpose is called the Penning trap. It can have various configurations of electrodes that are used to create a trapping electric field, to excite cyclotron motion, and to detect the induced signal. The evolution of this type of mass spectrometry is mainly driven by progress in the technology of superconducting magnets and in the constantly improved design of the ion cyclotron resonance (ICR) measuring cell. In this review, we focus on ICR cell designs. We consider that the driving forces of this evolution are the desire to increase resolution, mass accuracy and dynamic range, as well as to adapt new methods for creating and trapping ions.

How to Increase Further the Resolving Power of the Ultrahigh Magnetic Field FT ICR Instruments? The New Concept of the FT ICR Cell-the Open Dynamically Harmonized Cell as a Part of the Vacuum System Wall.

FT ICR mass spectrometry continues to be the leader in the resolving power among all mass spectrometry methods. With the introduction of the dynamically harmonized FT ICR cell, it has become possible to achieve the resolving power of more than 10 million at m/q = 1000 with moderate magnetic fields of about 7 T. A further increase in the mass resolving power is desirable mainly for two reasons: with this we are increasing the number of resolved components in analyses of complex mixtures (like oil and natural organic matter (NOM)) and increasing the number of the mass of molecules for which a fine structure can be resolved. In recent years, some attempts have been made to further increase the mass resolving power by increasing the magnetic field and using the multielectrode detection method. An increase in the magnetic field to 21 T did not show a proportional increase in the mass resolving power. Likely, the reason for this is an insufficiently high vacuum to satisfy the requirement of an increase in the mean free path of ions with the increasing magnetic field power. We offer a new design for the FT ICR cell and the whole mass spectrometer, in which an open, dynamically harmonized FT ICR cell is integrated into a vacuum system with the outer surfaces of the cell electrodes at atmospheric pressure. In this design, the trap electrodes are the walls of the vacuum system and have the minimized active surfaces by combining the vacuum system surface and the cell surface into one. In this design, the pumping process is accelerated, and the factor of insufficient vacuum in FT ICR mass spectrometers with an ultrahigh magnetic field is eliminated.

Analytical Solution for the Electric Field Inside Dynamically Harmonized FT-ICR Cell.

Dynamically harmonized FT-ICR cell has a saddle-like hyperbolic field distribution inside when averaged over a cyclotron trajectory around the axis of the cell. Such a field distribution makes the motion along the magnetic field independent of the motion in the x,y-plane, as well as the cyclotron motion independent of the magnetron motion and prevents any disintegration of excited coherent ion clouds, which is ruining the resolution in the other types of FT-ICR cells providing by this ideal phasing of single-m/z ion clouds in the entire volume of the cell. FT-ICR instruments with such a cell show resolutions of more than ten million at m/z 1000 at relatively small magnetic fields like 7 Tesla in quadrupole detection mode, what is not reachable by any other type of modern mass spectrometers. We have found that for such ion traps, it is possible to find the analytical solution in the working volume of the trap without any averaging. The potential distribution for the almost whole volume of such a cell can be presented in the form ϕ(x, y, z) = αz2 + f2D(x, y), where f2D(x, y) is the solution of 2D Poisson equation, which could be found by the method of conformal transformation. This solution is applicable in the practical case and can serve as a base for an analytical theory of signal detection using such cells and as a standard for solutions obtained by numerical simulations of the cell field.