Supersonic gas chromatography/mass spectrometry

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 modifica tion of a commercially available GC/MS system to include a supersonic molec ular beam (SMB) MS interface. In this system the standard electron ionizati on (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 co mbined with a 90 degrees ion mirror (for the EI-produced ions) was also add ed, 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 sp ace plus the addition of an air-cooled 60 L/s diffusion pump and a 537 L/mi n rotary pump. The system is user friendly since all the gas flow rates, he ated zones, sampling and data analysis are performed the same way as the or iginal system and are computer-controlled via the original software. Simila r EI sensitivity was obtained as with the original system for hexachloroben zene and octafluoronaphthalene, while improved EI detection limits were dem onstrated for methyl stearate and eicosane due to the significant enhanceme nt of their molecular ion abundances. A GC/MS detection limit of 500 ag for pyrene was demonstrated using HSI. Good supersonic expansion cooling was a chieved 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 de monstrated for large polycyclic aromatic hydrocarbons (PAHs) including oval ene 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 p hthalate esters is also described, and the improvement obtained is shown to originate from their enhanced molecular and high mass fragment ions. Copyr ight (C) 2001 John Wiley & Sons, Ltd.