Chip-scale quadrupole mass filters for a Micro-Gas Analyzer

Abstract

Mass spectrometers are powerful analytical instruments that serve as the gold standard for chemical analysis. This tool has numerous applications ranging from national security, industrial processing, environmental monitoring, space exploration, and healthcare to name a few. These systems are typically large, heavy, power-hungry, and expensive, constraining its usage to a laboratory setting. In recent years, there has been a growing interest in utilizing mass spectrometers outside the lab. Microelectromechanical systems (MEMS) technology holds the promise of making devices smaller, faster, better, and cheaper. The Micro-Gas Analyzer (MGA) project attempts to leverage MEMS capabilities to create a low-cost, high-performance, portable mass spectrometer. Batch-fabrication of various components for the MGA has been demonstrated to date, but the mass filter component still has room for exploration. Chip-scale quadrupole mass filters achieved entirely through wafer-scale processing have been designed, fabricated, and characterized. The device integrates the quadrupole electrodes, ion optics, and housing into a single monolithic block, eliminating the electrode-to-housing misalignments inherent in other quadrupoles. To achieve this integration, unconventional square electrode geometry was utilized. This concept formed the basis of the micro-square electrode quadrupole mass filter (MuSE-QMF). The MuSE-QMF demonstrated mass filtering with a maximum mass range of 650 amu and a minimum peak-width of 0.5 amu at mass 40, corresponding to a resolution of 80.

(cont.) More importantly, the design concept can be extended to complex architectures that were previously unachievable. Batch-fabricated quadrupoles in arrays, in tandem, or with integrated pre-filters can have significant impact on the future of portable mass spectrometry. Additionally, the MuSE-QMF makes a case for operation in the second stability region, and motivates new studies on quadrupole ion dynamics.