Trade-offs in miniature quadrupole designs

Abstract

Pressing needs for miniature mass spectrometers became apparent during the last decade in process monitoring and control, space exploration, and environmental screening. Besides the small footprint, common requirements include low cost, low power consumption, field portability, reliability, autonomy, and ease-of-use. Design concepts and construction technologies of miniaturized quadrupole sensors were guided by cost reduction requirements without sacrifice of performance. The first miniature and complete quadrupole mass spectrometer system was introduced as the Micropole sensor. The concept featured a novel technique to assemble and operate multiple miniature quadrupoles in parallel. The short analyzer length offers a significant advantage by enabling direct mass filtering at pressures up in the 10(-2) torr range. High voltages at higher frequencies (10-20 MHz) are required for acceptable mass resolving powers. Additional trade-offs were uncovered in miniature sensors leading to designs optimized for each class of applications. Real time ray tracing of ions injected and filtered in the quadrupole field is used early in the design stage to predict the performance and reliability of the device.

Miniature toroidal radio frequency ion trap mass analyzer

“…All of these linear devices provide an increase in ion storage capacity by employing a traditional 2D quadrupole with ion gates on either end of the quadrupole rod assembly. In a few cases, these devices have been miniaturized [18] to sizes smaller than typical commercial linear quadrupoles although, to date, none have been miniaturized for the specific purpose of field portable instrumentation. Arrays of linear quadrupoles [19,20] have also been reported.…”

Comparison of ion coupling strategies for a microengineered quadrupole mass filter

“…Slightly lower resolution was achieved with a filter constructed using ceramic spacers and ideal hyperbolic electrodes [3], which were positioned to give an inscribed radius of 0.33 mm (about 50% bigger than the inscribed radius defined by 0.5 mm diameter rods). An array described by Boumsellek and Ferran [4,14] also yielded slightly lower resolution at 50% peak height, but very similar base line separation. This filter was constructed using 1 mm diameter rods that were bonded to glass supports using an accurate glass-tometal sealing technique.…”

Towards the hand-held mass spectrometer: design considerations, simulation, and fabrication of micrometer-scaled cylindrical ion traps

“…As with other mass analyzers, miniaturization of the ion trap brings losses in performance, in this case an inherent loss of sensitivity due to reduced ion trapping volume. To circumvent this problem arrays of CITs can be constructed to regain the sensitivity lost in the miniaturization process [20,[29][30][31].…”

“…Historical limitations on in situ mass spectrometry, including size, power requirements, cost, and complexity, are gradually being lifted by systematic development of eversmaller instruments. Research on miniaturization of almost every kind of mass analyzer (quadrupole ion trap [1][2][3][4][5][6][7][8][9], ion cyclotron resonance [10,11], time of flight [12][13][14], magnetic sector [15][16][17][18][19], and linear quadrupole [20][21][22] is rapidly becoming an active area of science. Miniaturized mass analyzers reduce vacuum system demands, since the maintenance of a constant collision frequency allows an increase in pressure as the analyzer size is scaled down; consequently, power consumption for vacuum and backing pumps may be reduced [5].…”