Spectrophotometric Determination of Rare Earths with DBC-Arsenazo

The optimum experimental conditions of color reaction between DBC-arsenazo and rare earths were studied.In pH 2.2 HCl-KCl buffer solution,the rare earths react with DBC-arsenazo to form 1∶3 blue-purple complexes.The maximum peaks of the rare earths lanthanum(Ⅲ),cerium(Ⅳ),europium(Ⅲ),yttrium(Ⅲ) complexes are 630nm,632nm,632nm,632nm,respectively.The apparent molar absorptivities of the complexes are eLa(630nm)=1.02×105 L· mol-1·cm-1,eCe(632nm) =9.98×104 L·mol-1·cm-1,eEu(632nm)=9.60×104 L·mol-1·cm-1,eY(632nm)=9.40×104L· mol-1· cm-1,respectively.The above mentioned rare earth complexes remain stable within 70 min.Beer's law is obeyed over the concentration ranges 0～1.0μg· mL-1,0～ 1.0μg·mL-1,0～1.0μg·mL-1,0.05～ 0.8μg·mL-1 for lanthanum(Ⅲ),cerium(Ⅳ),europium(Ⅲ),yttrium(Ⅲ),respectively.The corresponding linear regression equations are ALa =0.0735C-0.0006,ACe=0.0624C-0.0237,AEu=0.0642C-0.0017,AY=0.0503C-0.0814,C being the amount of μg of rare earth in 10 mL of solution.The correlation coefficients are γLa = 0.9994,γCe= 0.9937,γEu= 0.9991,γY =0.9913,respectively.The method was applied to the direct determination of total rare earths in rain water and lake water samples with satisfactory results. The relative standard deviations and standard addition recoveries of the method were 2.46% and 2.64%,97.30% and 102.0%,respectively.