Design of 3-D Printed Quadrupole Mass Spectrometer

Abstract

Previous attempts at miniaturizing Quadrupole mass spectrometers (QMS) have focused on micromachined devices. The resolution of a QMS varies with the square of its length (for a fixed frequency). Thus, MEMS scale QMS have limited resolution due to their small lengths. Also, macroscale QMS requires higher vacuum levels as the scattering tends to degrade the resolution. The length scales in 3-D printed devices promise a better balance between resolution and higher-pressure operation than previous miniaturization efforts. This paper reports a design and fabrication of portable QMS using 3-D printing technology. 3-D printing provides a more optimum scale for miniaturizing QMS as the devices can be a few cm's in length with the various components being correctly aligned. The simulation of QMS is performed using COMSOL Multiphysics. Mathieu's first stability region is plotted for the base peaks of chemicals in the range 20-200 amu. The 3-D printed prototype of QMS is illustrated with hollow cathode as an ionizer, quadrupole mass filter as a mass analyzer, and Faraday cup as a detector. N2+ ions are passed through the QMS for preliminary testing of the device. A 2 MHz AC signal is applied to the mass filter. Preliminary testing gave a current of $22\ \mu\mathrm{A}$ when the device was tuned to N2+ and $0\ \mu\mathrm{A}$ when the mass filter voltage is not applied.