Cold EI Interface for LC-MS

Boaz Seemann, Chemistry, Tel Aviv University, Tel Aviv, Israel
Svetlana Tsizin, 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

Cold Electron Ionization LC-MS by Supersonic Molecular Beams (SMB) and a fly-through ion source (EI-LC-MS-SMB) is based on a unique LC and MS interface with SMB and a novel soft thermal vaporization inlet.  The unique fly-through electron ionization ion source, enabling ionization of vibrationally cold compounds in the SMB (hence the name Cold EI) with enhanced molecular ions and improved library based identification.

Effective pneumatic spray of LC eluting compounds is followed by thermal vaporization and supersonic expansion without cluster formation of the solvent vapor. The vaporization chamber and the supersonic nozzle are separated by a flow restriction capillary which is highly beneficial to achieve effective spray vaporization at above ambient pressure combined with good vibrational cooling without cluster.

The new interface technology enables new capabilities for LC detection. The automated library identification is a powerful tool unavailable for the LC-MS users. Furthermore, the provision of extensive fragment information is the key to identify sample compounds at the isomer level regardless of the retention time.

Contrary to Electrospray Ionization (ESI), Electron Ionization is not compound dependent and the determination of molecular ions in Cold EI is much simpler, as there are no quasi molecular ions, no clusters and no adduct-ions and/or unexpected fragments. Moreover, no ion suppression or enhancement effects are exhibited in Cold EI, unlike in ESI and/or APCI for improved quantitation and the ability to have faster LC separation.

The range of compounds amendable for analysis is broad, and includes also highly non-polars. The uniform semi-quantitative ionization yields can improve impurities analysis and chemical reaction yields using the coherence between peak integration and relative concentration in a mixture.