Supersonic molecular beam mass spectrometry

There are at least three approaches to fast GC/MS (1) use of microbore columns with time-of-flight mass spectrometry (TOFMS) (2) use of low-pressure (LP)-GC/MS to aid separations at increased flow rate " and (3) use of supersonic molecular beam mass spectrometry (SMBMS) (also known as supersonic GC/MS), which can accept increased flow rates and short analytical columns."... 

Supersonic molecular beam (SMB) mass spectrometry (SMB-MS) measures the mass spectrum of vibra-tionally cold molecules (cold El). Supersonic molecular beams [43] are formed by the co-expansion of an atmospheric pressure helium or hydrogen carrier gas, seeded with heavier sample organic molecules, through a simple pinhole (ca. 100 p,m i.d.) into a 10 5-mbar vacuum with flow-rates of 200 ml. rn in. In SMB, molecular ionisation is obtained either through improved electron impact ionisation, or through hyperthermal surface ionisation... 

Enhanced molecular ion implies reduced matrix interference. An SMB-El mass spectrum usually provides information comparable to field ionisation, but fragmentation can be promoted through increase of the electron energy. For many compounds the sensitivity of HSI can be up to 100 times that of El. Aromatics are ionised with a much greater efficiency than saturated compounds. Supersonic molecular beams are used in mass spectrometry in conjunction with GC-MS [44], LC-MS [45] and laser-induced multiphoton ionisation followed by time-of-flight analysis [46]. 

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. 

Amirav, A., "Electron Impact Mass Spectrometry of Cholesterol in Supersonic Molecular Beams," /. Phys. Chem. 94, 5200-5202,1990. 

The combination of pulsed lasers, pulsed molecular beams, and time-of-flight mass spectrometry represents a powerful technique for studying the selective excitation, ionization, and fragmentation of wanted molecules out of a large variety of different molecules or species in a molecular beam [9.93-9.99]. The technique, developed by Boesl et al. [9.93] is illustrated by Fig. 9.29 rotationally and vibrationally cold neutral parent molecules M in a supersonic molecular beam pass through the ion source of a time-of-flight mass spectrometer. A pulsed laser LI forms molecular ions M by resonant enhanced multiphoton ionization. By selecting special intermediate states of M, the molecular ion can often be preferentially prepared in a selected vibrational level. 

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