褪色分光光度法测定高浓度硝酸体系中微量草酸

Fading spectrophotometric determination of oxalic acid in high concentration nitric acid system

建立了测定电解破坏高浓度HNO_3体系中微量草酸根的分光光度法。在pH 5.6的六次甲基四胺-HCl缓冲溶液中,草酸根与Fe(Ⅲ)络合,使Fe(Ⅲ)与磺基水杨酸根离子络合形成的橙红色络合物浓度减小,其最大褪色波长在443 nm。考察了溶液酸度、试剂浓度、反应温度和时间、NO_3^-浓度等对吸光度的影响。结果表明:草酸根浓度在5×10^(-5)~1×10^(-3)mol/L范围内遵循比尔定律,线性回归方程为:△A=0.2628ρ+0.0098,相关系数R2=0.999。方法应用于实际样品的测定,加标回收率在95%~103%之间,检出限为1.4μmol/L,相对标准偏差为(n=6)为0.03%~0.06%,满足草酸根分析的需求。

A new spectrophotometric method has been developed for determination of trace amounts of oxalic acid in high concentration nitric acid system. In p H 5. 6 hexamethylene tetramine and hydrochloric acid buffer solution,the orange red of sulfosalicylic acid-ferric ion complex fadea after adding oxalic acid for binding with Fe（ Ⅲ）. The maximum fading wavelength located at 443 nm. Several factors effected on the absorption,including solution acidity,reaction temperature and time,reagent concentration and nitrate concentration,were studied and optimized. The results showed that the concentration of oxalic acid obeyed the Beer＇s law in the range of 5 × 10^（-5）^ 1 × 10^（-3）mol / L and the regression equation was △A = 0. 2628ρ ＋ 0. 0098 with the correlation coefficient R2 of 0. 999. The recoveries of the studied compound were in the range of 95% ^ 103% with the detection limit of 1. 4 × 10^（-6）mol / L and the maximum relative standard deviation（ n = 6） were 0. 03%～0. 06%. The method could be used for a rapid and cost-effective alternative for the quality control of oxalic acid in mother liquor generated from plutonium oxalate precipitation process.