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碘量法测定铜的应用迄今已有百余年历史。对其测定条件及干扰的消除方法不断有所改进。在条件掌握合适的情况下可获得较准确的结果。该方法的基本反应为Cu(Ⅱ)与碘离子定量反应生成碘化亚铜和游离碘。随即用硫代硫酸钠标准溶液滴定所释的碘,从而间接计算试样中铜的含量。分析操作中的关键是: 1 酸度的控制 要求控制溶液的酸度在pH 3.4～4.0之间。如pH〈3,则砷、锑将参与反应,而且空气的氧化作用使终点反复。如pH〉4,则可能产生铜的氢氧化物沉淀,导致结果偏低。通常用乙酸-乙酸盐缓冲体系控制酸度。也可用NH_4HF_2作为缓冲剂。氟化氢铵还可掩蔽Fe(Ⅲ)而避免其干扰。为避免大量氟化物对环境的污染,也可采用其它铁的掩蔽剂,如三聚磷酸钠等。
Iodometric determination of copper has been used for more than a hundred years. Its measurement conditions and interference elimination methods continue to improve. In the conditions of the right circumstances can get more accurate results. The basic reaction of this method is the quantitative reaction of Cu (II) with iodide to generate cuprous iodide and free iodine. Then with sodium thiosulfate standard solution titration of the release of iodine, which indirectly calculate the copper content of the sample. The key to the analysis is: 1. The control of acidity requires that the acidity of the control solution be between pH 3.4 and pH 4.0. If pH <3, then arsenic, antimony will participate in the reaction, and the oxidation of air so that the end of the iteration. If pH> 4, a hydroxide precipitate of copper may be produced, resulting in a low result. Acidity is usually controlled with an acetate-acetate buffer system. NH_4HF_2 can also be used as a buffer. Ammonium bifluoride can also mask Fe (III) to avoid its interference. In order to avoid a large number of fluoride pollution of the environment, you can also use other iron masking agents, such as sodium tripolyphosphate and so on.