Miniature polymer-based rectilinear ion trap and coil-less mass spectrometer

Meng Yu, Purdue University

Abstract

Ion trap based mass spectrometers are widely used in chemical analysis. A typical mass spectrometer is a stationary laboratory instrumentation that is inconvenient for on-site chemical detection tasks. In recent years, more and more efforts have been put to develop the portable mass spectrometry system. Ion trap, the mass analyzer, is a key component of the mass spectrometer. A miniature ion trap not only has a reduced size by itself, it also leads the miniaturization of other components, including vacuum manifold, vacuum pump and RF generator. The operating RF voltage is proportional to the square of the ion trap size. The lowered operating RF voltage on the miniature ion trap enables the low-power battery operation as well. With these advantages, miniature ion trap could be a promising candidate that will play a major role in portable mass spectrometer. In this dissertation, a fabrication methodology of creating polymer-based miniature rectilinear ion trap (RIT) is reported. An advanced manufacturing technique (Stereolithography) is used to fabricate the polymer-based rectilinear ion trap with simulation-guided design method. Simulations of electric field, capacitance associated with the ion trap, ion trajectories and mass spectra are performed for evaluation and optimization purposes. Challenges such as achieving uniform post metallization and high thermal stability are analyzed and solved systematically with the aid of the simulation results. The miniature rectilinear ion trap with dimensions of 1.67 mm x 1.33 mm x 16.7 mm (1/3 of the full-sized ion trap) demonstrates a much lower RF operating voltage of 100 V (1 MHz) with a mass range of 300 Th in boundary ejection mode, while a full-sized trap requires 1000 V to achieve the same mass range. By taking the advantage of the lower RF operating voltage, a coil-less RF generator is designed and implemented to provide the RF supply for the miniature ion traps with a much smaller size compared with the LC tank configuration. To prove the functionality of the coil-less RF generator, the RF system on Griffin 600 miniature mass spectrometer is directly replaced with the coil-less generator. Low power, instantaneous multi-frequency mass detection is demonstrated to produce broad mass range coarse scan and high resolution single peak analysis. Mass resolution of 0.66 Th (FWHM) is obtained at m/z of 69. With the complete elimination of the large size LC tank, coil-less RF generator exhibits an ideal low-power, simple circuit configuration for miniature mass spectrometer. Optimal multi-resolution operation is introduced and it can be realized with the miniature polymer-based RIT and the coil-less RF generator. The combination of the miniature polymer-based rectilinear ion trap and the coil-less RF generator is a unique platform and it makes a big step closer to the handheld mass spectrometer.

Degree

Ph.D.

Advisors

Chappell, Purdue University.

Subject Area

Electrical engineering

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