Exposition

Ion trap - internal ionization

Exhibit no. 927

The quadrupole ion trap is a mass analyzer, which consists of a central ring electrode and two end-cap electrodes with hyperbolic surfaces. It uses dynamic electric fields to capture and mass‐selectively eject gaseous ions into a detector. The device is also referred to as the Paul trap.

In the internal ionization mode, a gaseous sample is introduced directly into the interior of the ion trap and subjected to electron ionization by a pulsed electron beam. The ion trap acts as both an ion source and a mass analyzer, and these functions are fulfilled sequentially in time. Internal ionization is used for GC/MS and GC/MS/MS applications.

The exhibit is an ion trap with internal ionization from Saturn 2000R GC/MS manufactured by Varian Inc. in 2000. The filament endcap, exit endcap, and RF-ring electrodes have hyperbolic inner surfaces. The electrodes separated by quartz spacers were accommodated in a heated aluminum block. The GC capillary column passed through a transfer line directly into the ion trap assembly. Rhenium filament served as a source of electrons and a cylindrical electrode (“electron gate”) controlled the entry of electrons into the ion trap cavity. When the trap required electrons, the gate potential changed from negative to positive for a variable length of time (10 μsec to 65 ms). The ions produced in the ion trap were ejected through seven holes in the center of the exit endcap electrode into an electron multiplier. The electrode surfaces were coated with a thin layer of non-conductive silica (less than 0.1 microns) to reduce surface adsorption and thus serious chromatographic peak tailing. The coating known as “SilChrom” was deposited onto the electrode surfaces by a chemical vapor deposition (CVD) process. The instrument could work in both EI and CI mode with a mass range of 10 to 650 u.

Wikipedia: Quadrupole ion trap

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