Invited Paper VT-WeA3
Double Deflection and Enhanced Detection - The Use of a Novel Ion Optics for Metastable Rejection and Improved Detection in the Low ppb Range

Wednesday, October 21, 2015, 3:00 pm, Room 230B

During electron ionisation in a Quadrupole Mass Spectrometer (QMS), metastable neutrals are produced in addition to positive ions. The ion source in current QMS Residual Gas Analysers (RGA) is coupled with “line of sight” into the mass analyser and detector. Conversion of the metastable neutral into an ion and electron can cause increased noise, especially at lower masses. The higher noise level can determine the limit of detection in the RGA. The baseline signal can vary with changes of bulk gas and/or pressure.

The use of ion optics with novel cylindrical geometries between the ion source and mass analyser, enables a focused beam of ions to be displaced onto a second parallel axis, then back to the original axis. The cylindrical geometry provides good focusing resulting in no loss of signal, combined with a simple and robust mechanical design. The tuning is robust with a single low voltage lens setting.

The theory and performance of this elegant and innovative deflection system will be discussed, highlighting applications in which it offers a competitive advantage over current RGA designs.