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Mini-TOF-MS with Electron Impact Ioniser


This instrument is based on the existing Mini-TOF-MS instrument, and has an additional electron impact (EI) ioniser. This allows a client to sample and analyse gas molecules without the use of a laser ionisation source. The EI source puts out a continuous sheet of 70eV electrons (variable energy capability). Ions created in the source region are extracted the first element of the ion extraction optics, which pulses at up to 50kHz to create the TOF mass spectrum. When using this pulsed extraction scheme, the instrument is configured with a digital pre-amplifier, a TDC and an acquisition computer.


This instrument may also be used with a pulsed laser. In this case, the EI ioniser is turned off, and the laser is oriented so that it passes between the extraction lens and the ground plane 10mm away. When the laser is pulsed, it is the laser that initiates the TOF 'start', and the extraction lens voltage can be constant. For this scheme the pre-amplifier is switched over to the analogue board (because there are normally copious ions produced per laser pulse). The data acquisition then needs to be analogue, by using a digital 'scope or an analogue counting card.


This instrument was designed to permit the client to begin work using the EI ioniser, with the intention of adding the pulsed laser at a later stage.

To see an outline schematic of the instrument, please see the PDF sketch. The instrument adds on to a client vacuum system, and the client can specify the re-entrant distance of the ionising region to match the experiment. In the event that the pressure is high within the client chamber, a port exists on the side of the TOF spectrometer to permit differential pumping of the detector region.

Here is an example of the mass spectrum produced from a UHV system during testing


09 February 2009 19:41

© Kore Technology Limited 2009