Supersonic gas chromatography/mass spectrometry

Abstract

A new gas chromatography/mass spectrometry (GC/MS) system was designed and evaluated which we have named 'Supersonic GC/MS'. It is based on a modification of a commercially available GC/MS system to include a supersonic molecular beam (SMB) MS interface. In this system the standard electron ionization (EI) ion source was replaced with a fly-through EI ion source mounted in the path of the SMB. A hyperthermal surface ionization (HSI) ion source combined with a 90 degrees ion mirror (for the EI-produced ions) was also added, and placed inside the quadrupole mass analyzer in place of its original EI ion source. The 'Supersonic GC/MS' system requires 18 cm added bench space plus the addition of an air-cooled 60 L/s diffusion pump and a 537 L/min rotary pump. The system is user friendly since all the gas flow rates, heated zones, sampling and data analysis are performed the same way as the original system and are computer-controlled via the original software. Similar EI sensitivity was obtained as with the original system for hexachlorobenzene and octafluoronaphthalene, while improved EI detection limits were demonstrated for methyl stearate and eicosane due to the significant enhancement of their molecular ion abundances. A GC/MS detection limit of 500 ag for pyrene was demonstrated using HSI. Good supersonic expansion cooling was achieved with large alkanes, despite the use of a rotary pump at the nozzle chamber instead of a diffusion pump. High temperature GC/MS analysis was demonstrated for large polycyclic aromatic hydrocarbons (PAHs) including ovalene and decacyclene (ten rings). Library searches with EI mass spectra are demonstrated, and it is explained why the enhancement of the molecular ion actually improves the library search in most cases. The analysis of large phthalate esters is also described, and the improvement obtained is shown to originate from their enhanced molecular and high mass fragment ions.

Behaviour of carbamate pesticides in gas chromatography and their determination with solid‐phase extraction and solid‐phase microextraction as preconcentration steps

“…Several special devices have been designed to minimise the decomposition of thermally labile compounds in GC (short columns [4,5]; programmed temperature vaporizer devices [4,6]; low pressure GC [7], and supersonic GC [8]). Several reports have studied the photodegradation of such pesticides [9,10].…”

Direct addition of fluorine to arylacetylenes

“…The main feature of this method is to provide electron ionization while the sample is vibrationally cooled in a supersonic molecular beam. This considerably enhances the relative abundance of molecular ions [25,26]. Silica gel 60H (Merck) and petroleum ether/ethyl acetate were used for flash chromatography.…”

LC–MS with electron ionization of cold molecules in supersonic molecular beams

“…The SMB was collimated by a skimmer with 0.8 mm diameter. This pumping capability and skimmer diameter are identical to what we have in our supersonic GC-MS system [31]. After skimming, the collimated SMB entered a second vacuum chamber pumped by two Balzers 63 mm diffusion pumps with 135 l/s pumping speed each and total net pumping speed of 210 l/s (after considering the gate valve's gas conductivity).…”

“…(c) No nitrogen generator is required as the system gas requirement is relatively very low or none. (d) The same MS and vacuum system can also serve as a supersonic GC-MS [21,31] with the replacement of only one flange.…”