ESI-MS Study of Speciation in Hydrolyzed Aluminum Chloride Solutions
Solutions of AlCl3 were analyzed at concentrations from 0.03 to 5.0 mmol dm-3 and pH from 3.5 to 6.0 using an electrospray ionization quadrupole mass spectrometer (ESI-Q-MS). Mass spectral data were compared with those obtained by 27Al nuclear magnetic resonance (NMR) spectroscopy and potentiometry. Hydrolytic aluminum species were present in solution mainly as +1 positively charged complexes with n coordinated water molecules (n = 1-3). Analysis revealed that polymeric complexes of +2 and +3 charges (at higher Al concentrations and pH > 4) contained coordinated chloride ions. The general appearance of the mass spectra is dependent on instrumental parameters such as solvent flow rate, ionization source temperature and cone and capillary voltages. Thus, fine tuning of the instrument with respect to these parameters was performed. Sample cone voltages not exceeding 50 V led to the best agreement between potentiometric, 27Al NMR and mass spectral data.