Aluminum - pyrocatechol violet reactivity with various complexing agents

A spectrophotometric method for determining the speciation of aluminum using pyrocatechol violet (PCV) is tested on a series of known ligands over a range of concentrations and at two fixed pH values. The procedure assumes that the colorimetric signal is defined by the competition of the Al-ligand complex with Al-PCV. The stability constants determined are in agreement with literature values. Time to steady state is more than 10 min. A procedure for determining the conditional stability constant, the total ligand concentration and the reactive A1 at a fixed pH is proposed.