Application of the critical precipitation assay to complex samples: Aluminium binding capacity of human gastrointestinal fluids

Aluminium is a toxic ion that is partly absorbed from the mammalian gastrointestinal tract. Previous work has noted that the gastrointestinal fluids have their own intrinsic metal binding properties, especially for copper (2+) and iron (3+) ions. To date, however, there have been no investigations with gastrointestinal fluids and the aluminium (3+) ion. Recently we described a critical precipitation assay to examine the binding capacity of single ligands in solution. However, this assay should be applicable to complex solutions of natural systems (i.e., environmental and biological fluids). Using this technique we now show that human small bowel contents avidly binds aluminium (4.5 mmol L-1) compared to bile (≥0.58 mmol L-1) or gastric juice (≥0.17 mmol L-1), while pancreatic juice showed no significant binding (