The aluminium oxide crystal structure comprises octahedrally and tetrahedrally coordinated aluminium coupled by oxygen atoms. The aluminium oxide surface is covered by free hydroxyl groups. There are different acidic and basic centers (Broenstedt acid, Lewis acid and Lewis basic centers) that result in anion and cation exchange properties. Aluminium oxide exhibits a higher pH-stability than silica gel, especially in the alkaline range. Aluminium oxide occurs in various crystal modifications resulting in different pore diameters.

Standardised aluminium oxide 90, for adsorption analysis according to Brockmann, is a sorbent of medium polarity. It is frequently used when the cation exchange properties of basic alumina are required. Furthermore, aluminium oxide may be used as an alternative to activated carbon, when the organic character of activated carbon can be problematic.