Electron impact, hyperthermal surface ionization and fast GC-MS in supersonic molecular beams
- Tel-Aviv Univ., Tel Aviv (Israel)
Supersonic Molecular Beams (SMB) are characterized by undirectional motion with controlled hyperthermal kinetic energy (0.1-30 eV), intramolecular vibrational super-cooling, mass focusing as in an ideal high load jet separator, very high flow rate (on the gas chromatography flow rate scale) up to 240 ml/min and sample inlet at atmospheric pressure. These features make SMB an ideal sample introduction method, enable a unique fast GC inlet and result in important implications to molecular ionization processes including electron impact (EI) and hyperthermal. surface ionization (HSI). The authors` research is aimed at exploring and exposing the benefits of SMB for analytical organic mass spectrometry. The experimental apparatus is shown and is described. A 50 cm long megabore capillary column connects the atmospheric pressure open inlet to a supersonic nozzle, and serves as an ultra fast GC short column. The authors demonstrate ultrafast GC-MS achieved with this 50 cm transfer line capillary. One of the main features of this unique GC is the carrier gas relatively high flow rate of up to 240 ml/min which is possible due to the flow rates involved with the supersonic beam interface. This ultrafast GC is extensively described. Alternatively, a conventional GC with a short (4 meter) column serves as a fast GC inlet with intermediate GC resolution and unlimited choice of column length, ID and flow rate. Electron impact ionization in supersonic molecular beams is achieved using a Brink type open ion source operated with {approximately} 10-20 mA emission current. A background ion filtration method is applied, based on differences in the ion energy emerging from the hyperthermal molecular kinetic energy in the seeded SMB. Background ion filtration is achieved in the authors` VG-SXP-600 quadrupole through biasing of its exit lens and the cancellation of its internal ion energy ramping with mass.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- OSTI ID:
- 110830
- Report Number(s):
- NREL/CP-433-7748; CONF-9410343-; ON: DE95004052; TRN: 95:005145-0005
- Resource Relation:
- Conference: Applications of free-jet, molecular beam, mass spectrometric sampling conference, Estes Park, CO (United States), 11-14 Oct 1994; Other Information: PBD: Mar 1995; Related Information: Is Part Of Applications of free-jet, molecular beam, mass spectrometric sampling: Proceedings; Milne, T. [ed.]; PB: 305 p.
- Country of Publication:
- United States
- Language:
- English
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