在0.20 mol·L-1盐酸介质中,锆(Ⅳ)与三溴偶氮胂形成1∶1蓝紫色络合物,加入草酸可置换络合物中的三溴偶氮胂,使显色溶液的吸光度升高,草酸的浓度与吸光度升高值成正比.在506 nm波长处,草酸浓度在1.0×10-4~6.5×10-4mol·L-1范围内遵守比耳定律.方法的表观摩尔吸光率ε506 nm=1.23×103L·mol-1·cm-1,检出限为0.074 mg· L-1.方法已直接用于地下水以及西红柿样品中草酸含量的测定,所得结果与文献<参考文献原文>的方法结果相符.测定值的相对标准偏差(n=13)均小于2%,所测得的回收率在95.7%~103.9%之间.

It was found that the absorbance of the blue-purple complex formed by tribromoarsenazo (AsA-TB) and zirconium(Ⅳ) in 0.20 mol·L-1 HCl medium was increased upon the addition of definite amount of oxalic acid as measured at 506 nm.An equivalent amount of AsA-TB was displaced from the Zr(Ⅳ)-AsA-TB complex by oxalic acid in forming a more stable and colorless complex between Zr(Ⅳ) and oxalic acid,and the absorbance of the test solution was increased due to the increase in concentration of free AsA-TB,which was liberated in the displacement reaction.Beer′s law was kept in the range of 1.0×10-4 to 6.5×10-4mol·L-1.Molar absorptivity of this method was found as 1.23×103L·mol-1·cm-1.Detection limit found was 0.074 mg·L-1.The proposed method has been applied to the determination of oxalic acid in tomato and ground water,giving results in conformity with the results obtained by the method given in literature.Values of RSD′s (n=13) obtained were less than 2%,and values of recovery were in the range of 95.7% to 103.9%.