Ion optical element and mass spectrometer

An ion optical element used in a mass spectrometer,

• the ion optical element comprising:
• a plurality of rod electrodes, each having a convex portion formed at one end thereof;
• a plurality of electrode members, each connected to each of the plurality of rod electrodes, respectively;
• and
• a non-conductive base member having a window portion through which ions pass, and fixing the plurality of electrode members and the plurality of rod electrodes at positions surrounding the window portion,
• wherein each of the plurality of electrode members has a first through hole formed therein,
• the base member has a first concave portion formed therein corresponding to the convex portion, and
• the convex portion is engaged with the first concave portion through the first through hole, thereby the plurality of electrode members and the plurality of rod electrodes are positioned with respect to the base member.