Colorimetric determination of aluminium(III) with chrome azurol S and the reactivity of hydrolysed aluminium species

Abstract The metallochromic reagent chrome azurol S, when used in hexamine buffer at pH 4.9, reacts rapidly with monomeric and small polymeric forms of aluminium(III) in aged hydrolysed solutions. It is unreactive toward the polymer Al 13 (OH) 7+ 32 and colloidal Al(OH) 3 and the hydroxyaluminosilicates, imogolite and allophane. The reagent is appropriate for rapid semi-quantitative analysis of labile aluminium in acid lake waters or acid soils.