I describe the miniaturization of a linear-type ion trap mass spectrometer for possible applications in portable chemical analysis, and demonstrate the advantages of using lithographically patterned electrode plates in realizing an ion trap with dimension r0 less than 1 mm. The focus of the work was to demonstrate the viability and feasibility of the patterned electrode approach to trap miniaturization, and also to discover potential obstacles to its use. Planar ceramic substrates were patterned with metal electrodes using photolithography. Plates that were originally used in a linear trap with a half-spacing (r0) of 2.19 mm were positioned much closer together such that r0 = 0.95 mm. A capacitive voltage divider provided different radiofrequency (RF) amplitudes to each electrode, and the capacitor values were adjusted to provide the correct electric field at this closer spacing. Electron ionization mass spectra of toluene and dichloromethane demonstrate instrument performance with better than unit mass resolution. Compared with the larger plate spacing, the signal intensity is reduced, corresponding to the reduced trapping capacity of the smaller device, but the mass resolution of the larger device is retained. A further miniaturized linear ion trap with a half-spacing of 362 µm was designed and tested. A series of obstacles and troubleshooting on ion source, analytical method, and electronics were present. These experiments show promise for further miniaturization using patterned ceramic plates and provide a guide for the ion trap miniaturization. The feasibility of a wire linear ion trap was also demonstrated. Unit mass resolution was obtained, indicating a promise for further optimization and miniaturization of the wire linear ion trap. In addition to the practical experiments on the miniaturized linear ion traps, I theoretically studied ion motion in the toroidal ion trap using SIMION simulations, which show classical chaotic behavior of single ions. The chaotic motion is a result of the non-linear components of the electric fields as established by the trap electrodes, and not by Coulombic interaction from other ions. The chaotic behavior was observed specifically in the ejection direction of ions located in non-linear resonance bands within and adjacent to the region of stable trapping. The non-linear bands crossing through the stability regions correspond to hexapole resonance conditions, while the chaotic ejection observed immediately adjacent to the stable trapping region corresponds to a "fuzzy" ejection boundary. Fractal-like patterns were obtained in a series of zoomed-in regions of the stability diagram.



College and Department

Physical and Mathematical Sciences; Chemistry and Biochemistry



Date Submitted


Document Type





linear ion trap, miniaturization, toroidal ion trap, non-linear field, chaotic motion, ion trajectory simulation

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Chemistry Commons