Complexation and molecular speciation in the silica sol-gel process characterized by electrospray ionization fourier transform ion-cyclotron resonance mass spectrometry

The sol-gel reactions of tetraethyl orthosilicate have previously been char acterized by various instrumental methods, each revealing different aspects of the reactions that eventually form glass, SiO2. In this paper, we use e lectrospray ionization Fourier transform ion-cyclotron resonance mass spect rometry (ESI FT-ICR MS) to characterize the hydrolysis and condensation int ermediates based on alkali and transition metal ion attachment to ionize th e intermediates. Sodium trifluoromethanesulfonate and nickel(II) nitrate he xahydrate were added to solutions containing tetraethyl orthosilicate, elec trosprayed, and the resulting species observed. Sodium ion binds nonspecifi cally to silicates, whereas nickel produces a tris-tetraethyl orthosilicate nickel(II) complex. Sodium-bound dimers were also observed; they could be dissociated without damage to the silicate backbone by infrared multiphoton dissociation. It is thus possible to observe all of the hydrolysis product s (OH exchanged for OCH2CH3) for a given silicate oligomer as well as diffe rent silicate oligomers.