Rapid non-equilibrium aluminium-ligand interactions: studies on the precipitation of aluminium by laser light scattering, ultrafiltration and centrifugation

The study aimed to develop simple assays to study aluminium-ligand interact ions in natural/biological systems where equilibrium is rarely reached and thus where the initial seconds or hours of interactions are important. The immediate and non-equilibrium precipitation of aluminium hydroxide, in aque ous solution at neutral pH, was therefore studied by laser light scattering (diffraction), ultrafiltration and centrifugation. The interaction of weak ligands, present in the gastrointestinal lumen, on the precipitation of al uminium. hydroxide was also investigated. The initial kinetics and particle sizes of precipitated aluminium hydroxide were sensitive to a number of ex ternal factors, including the presence of weak ligand (bicarbonate), sheer force (stirring), electrolyte concentration and initial (i.e. added) alumin ium concentration. However, after a few seconds (no weak ligand), or severa l hundred seconds (with weak ligand), the subsequent observed changes to th e solid phase were of small magnitude and occurred slowly. Thus, a 25-min w indow, within 5 and 30 min of pH adjustment, can be used to study the inter actions of aluminium-ligand. This may approximate better to most natural sy stems where unperturbed aluminium-ligand equilibrium must rarely exist. (C) 2001 Elsevier Science B.V. All rights reserved.