A novel planar ion funnel design for miniature ion optics

Simulation study of three new quadrupole ion funnels to improve low-mass ion transmission

RATIONALE

By applying radio frequency (RF) and direct current (DC) voltages to corresponding ring electrodes, ion funnel (IF) can efficiently focus and transmit ions. However, IF has an inherent mass discrimination problem that will greatly limit low mass-to-charge (m/z) ion focusing and transmission. To improve the transmission efficiency (TE) of the IF, this paper explores three new profile quadrupole ion funnels (QIF).

METHODS

Computer simulations of the potential field distributions of QIFs and conventional IFs were performed to assess their focusing characteristics. To compare the TE, ion optics simulation programs SIMION and AXSIM were used to perform a series of simulations. Three QIF types (toroidal, cylindrical, and hyperbolic configurations) were used to improve ion TE, and their transmission and focus performance were also compared with conventional IF.

RESULTS

By simulating the trajectories of ions in the IF, the optimum electrical parameters for three new QIFs were obtained and compared with conventional IFs, with TE improvements recorded for m/z < 100 of 16%, 20%, and 13%.

CONCLUSIONS

The results indicate that studying these three new IF configurations has great research significance for improving sensitivity to low m/z ions in mass spectrometer instruments.

Multiplexing Quadrupole and Ion Trap Operation Modes on a "Brick" Miniature Mass Spectrometer

Although a quadruple mass analyzer and an ion trap mass analyzer have complementary analytical features, they usually have different geometries, operational modes, and electronic control systems. As a continuous effort to extend its coverage, both quadrupole and ion trap operation modes were realized on a "brick" miniature mass spectrometer with a single mass analyzer. In the quadrupole operation mode, low-mass ions ranging from 31 to 502 Th can be analyzed. On the other hand, the ion trap mode can be utilized to cover ions with higher mass to charge ratios (up to 922 Th), as well as performing tandem mass spectrometry. To realize the multiplexing of both operation modes, a printed circuit board (PCB)-based multi-electrode quadrupole-ion trap mass analyzer was designed and integrated in the system. To cover both volatile and non-volatile molecules, two ionization sources were also implemented, including a nano electrospray ionization source and an in-vacuum plasma ionization source. Performances of the instrument operated in these two modes were characterized, such as mass resolution, sensitivity, and mass range. Results demonstrate that the combination of the quadrupole and ion trap operation modes can provide new capabilities when solving analytical problems.

Evaluation of a New DC-Ion Funnel Drift Tube for Use in Proton Transfer Reaction Mass Spectrometry

We have developed and characterized a novel drift tube called the direct current-ion funnel (DC-ion funnel) drift tube, consisting of 20 traditional ring electrodes and 5 new DC-focusing electrodes (DC-FEs) for use in proton transfer reaction mass spectrometry (PTR-MS). Ion trajectory simulations demonstrate the ion focusing effect of the DC-FE and DC-ion funnel drift tube. Further comparative experiments show that the PTR-MS with the novel DC-ion funnel drift tube has a higher sensitivity (3.8-7.3 times for the volatile organic compounds considered in this work) than the PTR-MS with a traditional drift tube. Different from conventional radiofrequency (rf) focusing methods, the DC-ion funnel drift tube can realize ion focusing with only a DC electric field and no additional rf power supply, which makes it especially suitable for instruments requiring miniaturization and low power consumption to improve detection sensitivity. In addition, the DC-ion funnel drift tube can easily be coupled to other types of mass spectrometers to increase their detection sensitivity.