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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 spectrophotometric method was established for the determination of trace oxalate in high concentration HNO3 system under electrolytic destruction. The oxalate complexed with Fe (Ⅲ) in hexamethylenetetramine-HCl buffer at pH5.6 reduced the concentration of orange-red complexes formed by the complexation of Fe (Ⅲ) with sulfosalicylate ions , The maximum fading wavelength at 443 nm. The effects of solution acidity, reagent concentration, reaction temperature and time, NO_3 ~ - concentration on absorbance were investigated. Beer ’s law was obeyed in the range of 5 × 10 -5 ~ 1 × 10 -3 mol / L. The linear regression equation was: △ A = 0.2628 ρ + 0.0098, correlation coefficient R2 = 0.999. The method was applied to the determination of real samples with recoveries of 95% ~ 103%. The detection limit was 1.4μmol / L and the relative standard deviation (n = 6) was 0.03% ~ 0.06% The demand.