High performance photolysis TOFMS
Kore has developed a second-generation higher performance system for gas phase kinetics studies. One instrument has been delivered to the University of Bordeaux and a second to University of Leeds, who already own an older Kore system. Typically the reactions take place in a flow tube and are started with a pulsed laser. The transient that follows may be studied by examining ions already present, or by ionising using a second laser or an electron impact source. Using a time-of-flight mass spectrometer allows all species to be followed at once. Both analogue and digital outputs are available, the appropriate choice depending on the repetition rate available from the laser(s). For example, ion counting in raw list mode, over many nominally identical transients to build up good statistics, allows great flexibility in the subsequent retrospective data processing.
Novel ion-collection optics, placed in line with the gas entry, allow a differential pumping aperture to be sited within the spectrometer itself, close to the pulsed extraction region. This allows the spectrometer to tolerate a relatively high pressure in the source region without heroic pumping measures. The pumping system used in this example, consists of 2 240l/s turbomolecular pumps backed by a scroll pump.
There can be up to 4 pressure regions:
|The flow tube where the chemical reactions take place||typically 1 bar|
|A roughing chamber, pumped by the scroll pump||typically 0.1 to 1 mbar|
|The ion extraction chamber, pumped by the first turbo||typically around 10-4 mbar|
|The spectrometer, or at any rate the bulk of it, including the detector and pumped by the second turbo||typically around 10-6 mbar|
- Positive and negative ions.
- Mass filtering of matrix peak (Bradbury Nielson gate).
- Variable energy electron impact ioniser sited as close to the inlet as possible for high sensitivity.
- In-line geometry to avoid energy spread issues from supersonic expansion.
- Choice of detectors - discrete dynode with post-acceleration or dual microchannelplate.
- Analogue and digital (counting) ion detection.
- Interchangeable inlet orifice plates for maximum flexibility.
- Provision for cooling inlet apertures
- Transient acquisition mode for very high time resolution measurements.
- Ports for laser ionisation in both pulsed ion extraction region and roughing chamber.
- Simple to operate, dry vacuum system.
- Flexible triggering modes to accommodate various laser schemes.
© Kore Technology Limited 2013