SENSITIVE SPECTROPHOTOMETRIC DETERMINATION OF CHROMIUM WITH 2-(5-CHLORO-2-PYRIDYLAZO)-5-DIMETHYLAMINOPHENOL

The optimal conditions for the development of complexation reactions b etween Cr(III) and 2-(5-chloro-2-pyridylazo)-5-dimethylaminophenol (5. ClDMPAP) were studied. When a mixture of a hydroethanolic solution of the reagent and an aqueous solution of Cr(III) were heated, three diff erent complex species were formed, depending on the composition and pH of the medium (epsilon=1.7X10(5) l mol(-1) cm(-1)). All of them were hardly soluble when the proportion of organic solvent was low. The sto ichiometry of the different complexes was determined, the formation me chanisms were elucidated and the respective constants were calculated. A useful absorptiometric method is proposed for Cr(III) in concentrat ions ranging from 15 to 400 ppb. The proper ways to reduce interferenc es 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 appli ed to chromium determination in water samples with very satisfactory r esults.