A new type of ICP-TOF mass spectrometer is currently under development at the Institute for Analytical Sciences, Berlin. The project is supported by Gesellschaft für Optik und Spektroskopie, Berlin, and by Analytik Jena. The TOF allows a real simultaneous analysis of the entire mass domain. First two prototypes have been completed at the end of last year.
The ICP-TOF shows an orthogonal configuration at horizontal plane. This setup has several advantages, for instance a principally reduced background noise. In addition, some critical mechanical and electrical switching processes are limited. Just before detection, the ion beam is reflected and rotated by 90 degrees into a vertical plane.
At the prototypes, ions are provided by a 2000 W crystal controlled semiconductor rf-generator coupled with an automated matching network. The plasma runs at 27 MHz using a water-cooled induction coil.
Ion extraction and beam focusing are performed to ensure a compact initial spatial distribution of the ion packages. This allows to obtain mass spectra with a resolution of Δm/m ≥ 500.
The asymmetrical ion drift tube comprises usual devices like beam steering, electron absorber grids, and a reflectron. For detection a multichannel plate is placed at the focus of the reflectron accompanied by sophisticated hardware electronics for read-out. The unique "stopwatch" of the TOF, based on an application-specific integrated circuit (ASIC), permits the counting of 1 ns pulses. The entire detection process for a complete mass spectrum cycles at 30 kHz.
Up to 16 time windows can be defined to blank out or dilute selected ion groups if desired. This can be necessary to protect the detector from high load, for instance from carrier gas ions.
The new ICP-TOF is, among others, well suited for small sample volumes, transient signal detection, and isotope ratio measurements. Preliminary detection limits are settled in the lower ppt range.
One of the prototypes has been used by scientists from the Chair of Analytical Chemistry at Hamburg University since the beginning of October, and it is hoped that independent data gained under field conditions will be available soon.
Related Studies:
Nicolas H. Bings,
Plasma time-of-flight mass spectrometry as a detector for short transient signals in elemental analysis, Anal. Bioanal. Chem., 382/4 (2005) 887-890.
DOI: 10.1007/s00216-005-3198-0
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