Supersonic molecular beam interface

L.G. Randall and A.L. Wahrhaftig, Direct coupling of a dense (supercritical) gas chromatograph to a mass spectrometer using a supersonic molecular beam interface, Rev. Sci. Instrum., 52 (1981) 1283-1295. 

Supersonic gas chromatograph-mass spectrometry (GC-MS) apparently has several advantages over standard GS-MS methods for the detection of thermally unstable molecules <2004JCH233>. A GC and MS are interfaced with a supersonic molecular beam (SMB), and activation of cold compounds in the SMB occurs by electron ionization or cluster chemical ionization. The gas flow rate is very high, permitting the elution of compounds that would normally be degraded. Ethylene sulfone was one of the analytes for which the technique was demonstrated. 

With the thermospray interface (Figure 4.38(a)), the mobile phase, usually containing an ammonium ethanoate buffer, is passed through a heated probe (350-400°C) into an evacuated source chamber where it forms a supersonically expanding mist of electrically charged droplets. The liquid evaporates to leave charged solid particles which then release molecular ions such as MH+ and, VI by an ammonia chemical ionization (Cl) process. The analyte ions are skimmed off into the mass spectrometer whilst the vaporized solvent is pumped away. An electron beam is also employed to enhance the production of ions by Cl. 

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