Our ESI-FTICR MS, an Ionspec QFT-7 from Varian Inc, was installed in Oct. 2006. Equipped with a Micromass/Waters Z-Spray electrospray ion source, a Micromass/Waters Z-Spray APCI source, and a MS Horizons NSI Source, it offers high resolution measurements and is a stunning choice for ion manipulation as well as MSn.
Both electrospray ionization (ESI) and nanospray ionization (NSI or nano-ESI) allow a very gentle ionization of polar and ionic analytes with low to very high m/z. The analytes need to be dissolved completely in methanol, 2-propanol or acetonitrile. Acetone and/or THF and up to 50% of water or 20% dichloromethane or chloroform are tolerable for ESI as well, while up to 95% water can be used in NSI. The analytes should be stable against oxygen and moisture. Easily oxidized analytes may undergo oxidation during the ionization process. In positive ion mode a voltage of approx. 4 kV is applied at the spray capillary in case of ESI, and approx. 800 V in case of NSI). As a result, usually multiply charged, cationized ions of the kind [M+nH]n+ or [M+n(Cat1+)]n+ are detected. For APCI, the sample has to be volatile enough. Typically the [M+H]+ ions are generated.
Samples should be as pure as possible. Surface-active substances like SDS or inorganic salts suppress the ionization of the analytes as well as damage the instrument due to discharges. Surfactants sometimes cannot be detected due to interference with the ionization mechanism.
The quadrupole section of the mass spectrometer provides mass selection and ion storage as well as the possibility of collisional activation (CID) before the ions are transferred into the 7 Tesla superconducting magnet.
The quadrupoles also limit the mass range to a maximum of about m/z 6,500, but even higher m/z ions may be detected in the ICR cell when highly charged parent ions are submitted to tandem MS. The ICR cell (ion cyclotron resonance cell) provides a number of fragmentation methods like IRMPD, SORI-CID, ECD and the extremely time consuming BIRD. Additional leaking and pulsing valves facilitate gas phase reactions with gases and volatile liquids as well as stable-isotope exchange experiments, e.g., H/D exchange. Thus, this instrument provides us with many methods for structure elucidation, investigation of reaction mechanisms and physicochemical properties of the studied analytes.
A limited number of specially trained users can use the instrument themselves. Two PCs are located in room 13.06 for data evaluation.