Composition distortion in MBMS sampling
- Univ. of California, Los Angeles, CA (United States)
The focus in this review is on molecular-beam mass-spectrometer (MBMS) sampling systems, as opposed to microprobes. A typical MBMS sampling system consists of a sampling probe (usually conical), a skimmer (also usually conical), and a detection system (usually some form of mass spectrometer with signal averaging). Important advantages of MBMS sampling include (a) the characteristic time for the expansion in the free jet can be made very small in comparison with many chemical relaxation times and (b) the sample monitored by the detector comes essentially from near the centerline of the sampling probe, thereby minimizing interactions of the sample with the probe surface. Notwithstanding these advantages, experience has shown that care is required to either minimize or correct for composition distortions arising from the presence and operation of a MBMS sampling system. Most of the known origins of such composition distortions were discussed already in the review of MBMS sampling prepared by the author in 1972. The present review is an update of that prior review. Hence, as appropriate, the present review will sometimes simply reference the earlier review, sometimes modify that review, and sometimes supplement it with results obtained during the past two decades. Hence the relevant literature appearing since 1972 is emphasized. The origins of distortions are reviewed in approximately the order in which they are encountered by a sample as it is captured and processed. Hence, the main body of the review begins with the possibility of radical recombination at the external probe surface and ends with the possibility of species fragmentation during detection; a later section on miscellaneous origins begins with the possibility of condensation in the free jet and ends with the possibility of contaminating the time-averaged signal for a given sampling location by the stored time-averaged signal for the prior sampling location.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- OSTI ID:
- 110828
- Report Number(s):
- NREL/CP-433-7748; CONF-9410343-; ON: DE95004052; TRN: 95:005145-0003
- Resource Relation:
- Journal Volume: 103; Journal Issue: 3; 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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