高氯酸处理-硫酸亚铁铵滴定法测定铜合金中铬

使用硝酸溶解样品,冒高氯酸烟至150 mL锥形瓶瓶口0～5 s,在硫酸-磷酸介质中,以苯代邻氨基苯甲酸作指示剂,硫酸亚铁铵标准溶液滴定溶液中铬,建立了一种高氯酸处理、硫酸亚铁铵滴定铜合金中铬的分析方法。试验探讨了铜合金以及指示剂的溶解方法,结果表明,硝酸与高氯酸联用,能够完全溶解铜合金基体、铬及铬的化合物,冒HClO₄·2H₂O烟氧化铬到铬;而苯代邻氨基苯甲酸和碳酸钠研匀后加水溶解,可以作为指示剂,由于试液中铜离子的背景蓝色与指示剂的颜色复合,构成滴定终点前后的紫色-绿色互补色,指示剂变色敏锐。铈、锰等不干扰铬的测定。按照实验方法测定标准样品中铬,结果的相对标准偏差(RSD,n=8)为0.46%,测定值和认定值基本一致。方法用于铜合金样品中铬的测定,结果与过硫酸铵氧化、硫酸亚铁铵滴定法测定结果相吻合。

Determination of chromium in copper alloy by ferrous ammonium sulfate titration after perchloric acid treatment

The sample was dissolved with nitric acid. When the perchloric acid fume was generated to bottleneck of 150 mL conical flask for 0-5 s, the content of chromium  in solution was titrated with ferrous ammonium sulfate standard titration solution in sulfuric acid-phosphoric acid medium using N-phenylanthranilic acid as indicator. The analysis method of chromium in copper alloy by ferrous ammonium sulfate titration after perchloric acid treatment was established. The dissolution method of copper alloy and indicator was tested and discussed. The results showed that the copper alloy matrix, chromium and chromium compounds could be fully dissolved by nitric acid and perchloric acid. The chromium was oxidized to chromium by HClO₄·2H₂O fume. The N-phenylanthranilic acid was grinded and mixed with sodium carbonate. It was dissolved with water and used as indicator. Since the blue background of copper ions in sample solution was combined with the color of indicator, the complementary purple-green around the titration endpoint was formed. The color change of indicator was sensitive. The determination of chromium was not interfered by cerium and manganese. The content of chromium in standard sample was determined according to the experimental method. The relative standard deviation (RSD, n=8) was 0.46%. The found results were consistent with the certified values. The proposed method was also applied to the determination of chromium in copper alloy sample, and the found results were consistent with those obtained by ferrous ammonium sulfate titration after ammonium persulfate oxidation.