1. MAO speciation by electrospray ionization mass spectrometry
J. Scott McIndoe Department of Chemistry, University of Victoria, PO Box 3065, Victoria, BC V8W3V6, Canada
ESI-MS analysis of methylaluminoxane (MAO, an activator for olefin polymerization catalysts) under anaerobic conditions in non-polar solvents permits the characterization of a host of charged oligomers:
Why we think that ESI is a good match to studying these types of systems. But there are issues that have made it less desirable for others to use it for organometallic/catalysis type systems. Some or all of these things need to be overcome in order to run the types of spectra we want to run and they have all been addressed by our group. The main ones that I have focused on are the sensitive materials and the observation of neutral compounds. Why this is an issue will be apparent in the next few slides.
Compare to traditional methods of investigation
Have the top points appear simultaneously
Take more time to explain points in red (make two slides? YES! Traditional vs us)
Real condition, in situ, real catalytic systems, doping of small amounts of material
One peak/species but there is further investigation possible (MSMS) more information than just the m/z
Reaction chamber, solution analysis etc etc
Compositional information is obtained from a combination of m/z ratio, isotope pattern and chemical reasonableness. Each component of the complex mixture can be analyzed by MS/MS, which provides the number of structural building blocks in each oligomer, namely AlMe3, MeAlO and Al2O3. The charge arises when the oligomer acquires an anion (X–), so the mass spectrometrically-observed distribution represents the most strongly Lewis-acidic components of the mixture. Speciation changes upon addition of water, Lewis bases and catalyst precursors have been probed.