Multi electrode harmonized Kingdon traps as mass analyzers for FT based mass spectrometers

Kingdon trap [1] is the simplest ion trap consisting of wire and cylindrical electrode surrounding with different potential.  Well-known Orbitrap [2], has emerged as development of R. D. Knight’s idea [3], who modified the cylinder electrodes geometry to make the field inside Kingdon trap quadratic (harmonic) and proposed measuring the frequencies of ions oscillating in such field by resonant excitation of their motion along trap axis, to determine their masses [3]. Later the generalization of the idea made by Yury Golikov [4] and Claus Koester [5], who has offered the options for harmonized traps with multiple internal electrodes, having some advantages over Orbitrap, was described recently by us in [6].

Electrode geometries in these traps could be obtained by composing electric potential distribution from quadrupolar potentials and sum of logarithmic potentials and choosing equipotential surfaces for the trap electrodes on the bases of practical reasons (trap dimensions, ion frequencies and maximum allowed voltages on the internal electrodes. Two and four internal electrodes Kingdon traps with fused electrodes in the last case were made by high precision machine work and by different 3D printing methods.  Different type of ion sources was tested with these new traps: thermoemission ion source, laser desorption ionization, MALDI, for the case of ion production inside trap vacuum chamber and ESI in case of external ion introduction (in progress). The maximum resolving power (around 300K) has been obtained in case of thermoemission. Among four electrode Kingdon trap geometries providing trapping fields with quadratic dependences of electric potentials on one of the coordinates and satisfying Laplace equation the geometry with fused electrode pares was chosen. The trap with such geometry electrodes was found to be less sensitive to surface imperfections and truncation of the electrodes. Many variants of the trap were manufactured. The new type of the traps with internal electrodes as conventional wires of around 100 µm in diameter have been also made and tested. It was shown that substituting the internal electrodes of very complicated geometry by metal wires significantly simplify trap production and tuning. Low weight, low dimensions and power consumption make the analyzer suitable for portable and transportable mass spectrometer devices. Potential applications for space research and biomedical analyses will be discussed.

Reference

1. Kingdon KH (1923) Physical Review. 21(4):408–418

2. Knight R (1981) Applied Physics Letters. 38 (4): 221–223

3. Makarov A (2000) Analytical Chemistry. 72 (6): 1156–62

4. Nikitina DV (2006) Ion traps in dynamic mass spectrometry Ph.D. Thesis, St. Petersburg, Russia.

5. Köster C (2009) IJMS, 287, 114-118.

6. Nikolaev E, et.al. (2018) JASMS  DOI:10.1007/s13361-018-2032-9