Arsenazo III disodium salt is a diazo dye reagent used in the spectrophotometric determination of aluminum, gallium and indium. Further, it is used in the complexometric determination of lanthanides, thallium, scandium thorium, uranium and yttrium. In addition to this, it acts as a metal indicator and form specifically colored metal ion complexes in aqueous media.
Purification Methods
Contaminants include monoazo derivatives, starting materials for synthesis and by-products. It is partially purified by precipitation of the dye from aqueous alkali on addition of HCl. More thorough purification is achieved by taking a 2g sample in 15-25mL of 5% aqueous NH3 and filter. Add 10mL HCl (1:1) to the filtrate to precipitate the dye. Repeat the procedure and dissolve the solid dye (0.5g) in 7mL of a 1:1:1 mixture of n-propanol/conc NH3/water at 50o. After cooling, filter the solution and chromatograph the filtrate through a cellulose column using a 3:1:1 mixture of n-propanol/conc NH3/water as eluent. Collect the blue band and evaporate it to 10-15mL below 80o, then add 10mL of conc HCl to precipitate pure Arsenazo III. Wash it with EtOH and dry it in air [Borak et al. Talanta 17 215 1970]. The sodium salt is then obtained by dissolving it in the equivalent amount of dilute NaOH and freeze-drying. The purity of the dye can be checked by paper chromatography using M HCl as eluent. It is used for the estimation of Th, U, Zr, Cd and Zn [Michaylova & Yuroukova Anal Chim Acta 68 73 1974.]
