Formation of ternary complexes of aluminium with some triphenylmethane reagents and cationic surfactants

The conditions for the formation of ternary complexes of aluminium with Eriochrome Cyanine R (ECR), Chrome Azurol S (CAS) or Pyrocatechol Violet (PV), in the presence of zephiramine, cetyltrimethylammonium (CTA) or cetylpyridinium (CP) ions have been examined. In the systems aluminium-ECR/CAS-zephiramine/CTA/CP, the complexes formed (at pH 5–7) have molar absorptivities of 1.1–1.2 × 105 l mol–1 cm–1, which can form the basis of sensitive spectrophotometric methods. The systems involving PV and cationic surfactants are unsuitable for spectrophotometric methods. The molar ratio of ECR/CAS to aluminium in the ternary complexes is slightly higher than 2 : 1. The recommended method based on the aluminium-ECR-zephiramine system has been applied to the determination of aluminium in river water.