Laser ablation coupled to Fourier Transform-Ion Cyclotron Resonance-Mass Spectrometry [FT-ICR-MS] was used for analysing allophane alummosilicates and mixtures of Al2O3/SiO2. We show that both positive and negative ionization modes in FT-ICR-MS allows direct analysis of the various Al/Si ratios in allophanes and mixed alumina/silica samples. FT-ICR-MS technique provides a routine analytical methodology providing insight into the Al/Si molar composition and the origin of any aluminosilicate materials. (c) 2007 Elsevier B.V All rights reserved.