Electron Ionization LC-MS with Supersonic Molecular Beams The New System and Design

Svetlana Tsizin, Chemistry, Tel Aviv University, Tel Aviv, Israel
Boaz Seemann, Chemistry, Tel Aviv University, Tel Aviv, Israel
Tal Alon, Chemistry, Tel Aviv University, Tel Aviv, Israel
Alexander B. Fialkov, Chemistry, Tel Aviv University, Tel Aviv, Israel
Aviv Amirav, Chemistry, Tel Aviv University, Tel Aviv, Israel

Electron Ionization LC-MS with Supersonic Molecular Beams (EI-LC-MS-SMB) system was recently combined with an Agilent 5977 MSD. The new system features user friendly design and implements several advanced design features based on over a decade research.

EI-LC-MS-SMB is based on a unique LC-MS interface with novel soft thermal vaporization inlet, vibrational cooling of molecules in supersonic molecular beams and their electron ionization. An effective pneumatic spray is generated from the liquid eluted from the LC column followed by fast thermal vaporization at ~1.5 Atm. The supersonic expansion is retained at about 0.15 Bar to suppress cluster formation with the solvent vapor, and the molecular beams are skimmed and afterwards ionized. The electron ionization takes place in a unique fly-through ion source and results in Cold EI spectrum – spectrum of vibrationally cold molecules that has enhanced molecular ion and provides improved library based identification.

Basing the system on Agilent 5977 MSD instead of previously used Varian 1200L MS-MS system makes it a relatively low cost yet robust EI-LC-MS apparatus plus it can be easily exchanged with GC-MS with Cold EI. This 5977-EI-LC-MS with SMB relies on several principles that were discovered in the previous system generations: the vaporization chamber and SMB nozzle are separated by a flow restriction capillary and an axial temperature gradient is maintained in the vaporization chamber to prevent onset thermospray instabilities.

Applications with cannabis flower extracts, a series of antioxidants and leachables and fast LC-MS of octafluoronaphthalene, pyrene, cholesterol and Agidol-40 mixture were performed with the new EI-LC-MS-SMB system. The results provide a glance to its numerous advantages as it is the only LC-MS method that can identify sample compounds at the isomer level, without any matrix ion suppression effects and non-polar compounds, whose analysis is practically impossible by Electrospray, can be identified through automated library search.