Simulation of unidirectional ion ejection in linear ion traps with asymmetric radiofrequency voltage.

Rationale: Linear ion traps with simplified structure have been widely used in miniaturized mass spectrometers. However, linear ion traps usually have low ion detection efficiency when used in a miniaturized mass spectrometer, in which only one ion detector can be installed. To solve this problem, an asymmetric radiofrequency (RF) voltage was applied to introduce asymmetric electric fields in the trapping volume of linear ion traps, which would lead to unidirectional ion ejection.

Portable linear ion trap mass spectrometer with compact multistage vacuum system and continuous atmospheric pressure interface.

A portable linear ion trap mass spectrometer featuring a compact three-stage vacuum system, a continuous atmospheric pressure interface (CAPI), and a miniature ion funnel was developed and characterized. The dimensions and weight of the instrument were 38 × 26 × 23 cm3 and ∼20 kg, respectively. The combination of a three-stage vacuum system and CAPI reduced the pressure smoothly from atmospheric to ∼5 × 10-4 Torr, ensuring that the miniature ion funnel, quadrupole ion guide, and linear ion trap operated in a suitable and stable vacuum environment.

Simulation of Unidirectional Ion Ejection in an Asymmetric Half-Round Rod Electrode Linear Ion Trap Mass Analyzer.

An asymmetric trapping field was generated from an asymmetric half-round rod electrode linear ion trap (A-HreLIT), and its performance of unidirectional ion ejection was studied. Two different asymmetric structures of A-HreLITs were constructed, one rotating y electrode pairs toward an x electrode with an angle θ, and the other stretching one x electrode with a distance α. The center of trapping field was displaced away from the geometrical center of the ion trap, defined to be the midpoint along the axis of y between x electrodes, which leads to unidirectional ion ejection through one x electrode.