Abstract
Gas chromatography mass spectrometry (GC-MS) is a widely used central analytical technology. Commercially available GC-MS systems use different types of mass analyzers such as Quadrupole, Ion Trap and/or Time of Flight, but practically all systems utilize the same Nier type electron ionization (EI) ion source and the same standard GC-MS transferline interface. Consequently, the various GC-MS vendors characterize their systems by a short list of specifications that relate to improvements in the technology of GC or of MS and not of the interfacing technology and ion source. This article presents a list of 62 ways in which the performance of GC-MS as a whole can be improved by an innovative interface and ion source. Such an interface can possibly lead to a GC-MS revolution in a way that is similar to that whichis brought to Liquid Chromatography Mass Spectrometry (LC-MS) by the Electrospray ionization interface and ion source and not by improvements to the technology of LC or MS. These 62 possible GC-MS improvements (grouped into eight main categories) are not merely theoretical as they are provided by the Cold-EI GC-MS interface, which is based on the ionization of vibrationally cold sample molecules in a Supersonic Molecular Beam (SMB) within a fly-through ion source. An explanation and discussion is provided for each of these possible improvements.
Highlights
Gas chromatography mass spectrometry (GC-MS) vendors typically describe and characterize their systems using a small set of specifications that include octafluoronaphthalene (OFN) signal to noise ratio (SNR), mass range and scan speed
Such an interface can possibly lead to a GC-MS revolution in a way that is similar to that which is brought to Liquid Chromatography Mass Spectrometry (LC-MS) by the Electrospray ionization interface and ion source and not by improvements to the technology of LC or MS
These 62 possible GC-MS improvements are not merely theoretical as they are provided by the Cold-electron ionization (EI) GC-MS interface, which is based on the ionization of vibrationally cold sample molecules in a Supersonic Molecular Beam (SMB) within a flythrough ion source
Summary
GC-MS vendors typically describe and characterize their systems using a small set of specifications that include octafluoronaphthalene (OFN) signal to noise ratio (SNR), mass range and scan speed. Cold EI with its supersonic molecular beams interface and fly-through ion source brings multiple benefits and improvements into GCMS which can initiate a new GC-MS revolution. This manuscript lists 62 GC-MS improvements brought forth by the Cold EI interface and ion source, encompassing any and every important aspect of GC-MS, and explains how the unique features of GC-MS with Cold EI enable these benefits. The Electron Ionization (EI) of cold molecules in SMB was termed as “Cold EI” Within this interface a supersonic molecular beam is formed by the expansion of a gas through a ~0.1 mm pinhole into a vacuum chamber. The basic standard GC-MS instrument modifications for its conversion into GC-MS with Cold EI include: a) The analytical column of a conventional GC with unrestricted column type (ID), length and flow rate is connected to a supersonic nozzle via a heated transfer line and mixed with added helium make up gas (typically 60 ml/min). b) Sampling to the MS vacuum system is in the form of skimmed supersonic molecular beam, as the organic sample compounds expand with the added make up helium gas from the supersonic nozzle into a separately (differentially) pumped nozzle vacuum chamber; c) The electron ionization ion source is modified to allow for unperturbed axial passage of the molecular beam (fly-through) with a high (typically 8 mA) ionizing electron emission current; d) A suitable 90 degrees ion mirror is added to suppress mass spectral noise, keep the mass analyzer clean and for minimizing the added bench space
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