Liquid chromatography mass spectrometry with supersonic molecular beams

Abstract

A new approach for liquid chromatography mass spectrometry (LC-MS) is described, based on achieving soft thermal vaporization followed by supersonic expansion and direct sample compound ionization, while in a supersonic molecular beam (SMB). The soft molecular vaporization step utilizes spray formation that is continued by fast thermal vaporization inside a channel supersonic nozzle, followed by ultrafast supercooling in a supersonic expansion. The short time (several microseconds) spent by the vaporized compound in the heated nozzle prior to its expansion cooling may result in incomplete vibrational equilibrium and thus reduced degree of dissociation. In addition, even if vibrational equilibrium at the nozzle temperature is obtained, the sample compounds have significantly reduced time for their dissociation, which is thus further minimized (kinetic consideration). As soon as the molecules expand and form a SMB, they are supercooled and any further dissociation is avoided. While in the SMB, the sample molecules can be ionized either by electron ionization as described in this paper or by hyperthermal surface ionization. The major goal of this method is to obtain high quality library searchable electron ionization mass spectra, for a broad range of thermally labile compounds, with higher sensitivity than that achievable by particle beam LC-MS. The soft thermal vaporization nozzle is described and mass spectral results with corticosterone are demonstrated. The potential advantageous features of this new method are discussed.

Condensed Phase Membrane Introduction Mass Spectrometry with Direct Electron Ionization: On-line Measurement of PAHs in Complex Aqueous Samples

“…Typically, relatively simple mass spectra are obtained, with intense molecular ion signals [25]. Several researchers have been developing approaches to ionize trace level analytes directly from liquids using EI, including molecular beam based interfaces by the Amirav group [26,27] and direct EI (DEI) by the Cappiello group [28][29][30]. With DEI, a low flow of liquid carrier is admitted directly to a heated EI source under high vacuum.…”

Isotope abundance analysis for improved sample identification with tandem mass spectrometry

“…18 We note that IAA is also highly compatible with electron ionization LC/MS with SMB. 19,20 Regardless of its high compatibility with GC/SMB-MS and LC/SMB-MS, IAA can also be used to improve sample identification with standard GC/MS and electrospray LC/ MS and indeed IAA was successfully applied with files generated on a standard Agilent model 5975 MSD GC/MS system (Agilent Technologies, Santa Clara, CA, USA). IAA and accurate mass analysis have a similar algorithm for the generation of relevant elemental formulae, and, when the analysis ends, both provide a list of possible elemental formulae with declining order of fit to the experimental data.…”

An Interpretation of Alternative Plugs Flow Liquid Chromatography in a Slightly Modified GC/MS System

“…In the initial studies of LC/MS measurements, a moving-belt system was applied to an LC/EI-MS interface and a particle-beam (PB) system was also developed. 25,26 A modified LC/EI-MS system with both PB-like molecular ionization mechanisms comprising a nebulizer was developed by Amirav 27 and a re-ionization source using EI ionization was developed by Ikuta. 28 These MS detection systems provide library-searchable EI mass spectra and have the same sensitivity as LC/APCI-MS systems.…”