Flowing-afterglow mass spectrometry
Flowing-afterglow mass spectrometry (FA-MS), is an analytical chemistry technique for the sensitive detection of trace gases. Trace gas molecules are ionized by the production and flow of thermalised hydrated hydronium cluster ions in a plasma afterglow of helium or argon carrier gas along a flow tube following the introduction of a humid air sample. These ions react in multiple collisions with water molecules, their isotopic compositions reach equilibrium and the relative magnitudes of their isotopomers are measured by mass spectrometry.
Trace gas analysis
One of the first papers reporting the use of the flowing afterglow studied ion-molecule reactions pertinent to the Martian atmosphere. This flowing afterglow technique replaced the then standard stationary afterglow. The flowing afterglow has many attractive aspects: well-understood laminar behavior, viscous gas flow, a large density of carrier gas which allows the study of thermalized reactions, and the capability to make new reactant ions in situ. The ambipolar plasma is sampled using a nosecone and detected using conventional quadrupole or tandem mass spectrometry, depending on the application. One of the drawbacks of the flowing afterglow technique is the possibility of generating multiple reactant ions. This problem is circumvented by implementing the selected ion flow tube (SIFT).
The flowing afterglow technique can be used to identify and quantify the volatile organic compounds (VOCs) of a sample as long as the fundamental ion chemistry is known. The commonly used ions are H3O+, O2+*, and NO+. All ions have drawbacks and advantages. Strategies that have been employed to identify the VOCs include using gas chromatography coupled with flowing afterglow and using a complement of reagent ions. Detection limits are typically in the parts per billion range if there is limited sample or parts per trillion if there is an unlimited sample size.
- Handbook of Stable Isotope Analytical Techniques. Elsevier. 2004. ISBN 0-444-51114-8.
- Norton, RB et al. (1966). "Ion-neutral reactions in the Martian ionosphere". Planetary and Space Science 14 (10): 969–978. Bibcode:1966P&SS...14..969N. doi:10.1016/0032-0633(66)90133-4.
- Adams, NG, Smith (1976). "The Selected Ion Flow Tube (SIFT); A Technique for Studying Ion-Neutral Reactions". International Journal of Mass Spectrometry and Ion Physics 21: 349–359. doi:10.1016/0020-7381(76)80133-7.
- Newman K, Mason RS (2006). "Organic mass spectrometry and control of fragmentation using a fast flow glow discharge ion source". Rapid Communications in Mass Spectrometry 20 (14): 2067–2073. doi:10.1002/rcm.2560. PMID 16767685.