Sensitive Spectrophotometric Determination of Chromium with 2-(5-Chloro-2-pyridylazo)-5-dimethylaminophenol

Abstract

The optimal conditions for the development of complexation reactions between Cr(III) and 2-(5-chloro-2-pyridylazo)-5-dimethylaminophenol (5.CIDMPAP) were studied. When a mixture of a hydroethanolic solution of the reagent and an aqueous solution of Cr(III) were heated, three different complex species were formed, depending on the composition and pH of the medium (ε=1.7×10⁵l mol-1 cm^-1). All of them were hardly soluble when the proportion of organic solvent was low. The stoichiometry of the different complexes was determined, the formation mechanisms were elucidated and the respective constants were calculated. A useful absorptiometric method is proposed for Cr(III) in concentrations ranging from 15 to 400ppb. The proper ways to reduce interferences produced by Fe(III), Nb(V), Ta(V), Ti(IV), V(V), Co(II), Zr(IV), Sn(II), Al(III), Mn(II) and Cu(II) are described. The methods were applied to chromium determination in water samples with very satisfactory results.