Characterization of silicate monomer with sodium, calcium and strontium but not with lithium and magnesium ions by fast atom bombardment mass spectrometry

Fast atom bombardment mass spectrometry (FABMS) was applied to the direct detection of silica species dissolved in LiCl, NaCl, MgCl 2 , CaCl 2 and SrCl 2 solutions in order to investigate its dissolution process in solution. Several species of dissolved silicate complexes in the solution were directly detected by FABMS. The peak intensities of [SiO 2 (OH) 2 Na] − , [SiO 3 (OH)Ca] − and [SiO 3 (OH)Sr] − increased with increasing concentrations of NaCl, CaCl 2 and SrCl 2 , whereas the peak intensities of [SiO 2 (OH) 2 Li] − and [SiO 3 (OH)Mg] − did not increase with increasing concentrations of LiCl and MgCl 2 . These results indicte that silicate and cation bind in the solution not after but before ionization. The isotope pattern of Sr 2+ confirmed the existence of the silicate–Sr complex not only with increase of the concentration of silica but also the mass numbers of Sr. The silicate complexes formed with Na + , Ca 2+ and Sr 2+ showed high stability in chloride solution. This is in good accordance with the fact that Na + , Ca 2+ and Sr 2+ accelerate the dissolution of silica to form complexes during solution equilibrium. Considering that the stability constant was examined and reported in other papers, this new findings that Mg 2+ does not form a complex with silicic acid (Si(OH) 4 ) is very important. Copyright © 2002 John Wiley & Sons, Ltd.