The color reaction of chromium(Ⅲ)with chrome azurol S(CAS)and cetyl pyridinium bromide(CPB)is studied in the presence of benzoate.It has been found that benzoate notably accelerates the reaction and also causes a increase in the absorbance of the complex.Based on this reaction

a new determination method for chromium(Ⅲ)is establishd.In the benzoate buffer (pH5.0-5.7).the heating time for the formation of the complex can be reduced to 2 minutes. The intensely blue complex exhibits maximum absorbance at 642nm and has a molar absorptivity of 1.5×105l·mol-1·cm-1.The metal to ligand ratio is 1:2.The method is the most rapid and sensitive one for the spectrophotometric determination of chromium( Ⅲ). The method has been applied to the determination of the chromium content of steel with satisfactory results.