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Categories of exhibits

EI/CI & ion trap assembly

Exhibit no. 872

Coupling of EI/CI with a 3D ion trap can be realized in two ways. In the internal ionization mode, the sample is introduced into the interior of the ion trap and subjected to EI/CI by a pulsed electron beam. The ion trap plays the role of source and analyzer. Since the primary ions can interact with the neutral sample molecules for an extended time (up to 200 ms), undesirable ion-molecule reactions are often observed. The process is known as self-chemical ionization. In the external ionization mode, the ions are extracted from the source and pulsed into the ion trap using an ion gate. The traps with external sources appeared on the market a few years after the internal ionization traps. External ionization provides spectra that are more similar to those seen on quadrupole mass spectrometers. Such spectra provide better library search results.

The exhibit is an ion source/mass analyzer assembly from GCQ, an instrument for GC/MS applications, manufactured by ThermoQuest in the 1990s. The ion source for external ionization consisted of an ion volume and the source lenses, which transmitted ions to the analyzer. The ion volume required regular cleaning. I/R tool consisting of a shaft, handle, and guide ball was used to insert or remove the ion volume without a need to vent the instrument. The analyzer consisted of two endcap electrodes and a ring electrode separated by two silicon nitride spacer rings. The ring electrode was supplied with a 1.03 MHz RF voltage. Ions produced in the EI/CI source entered the analyzer through a hole in the entrance endcap electrode. The instrument provided unit mass resolution in the m/z 10 – 1000 range. An automatic gain control ensured that the ion trap was filled with the optimum number of ions.

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