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有部分分析资料介绍,在pH5.5～6溶液中,用EDTA络合滴定铅,以二甲酚橙作指示剂,加抗坏血酸掩蔽微量铁,这是错误的。由于Fe~(2+)在此条件下也被滴定,将使结果偏高。实验方法吸取铁(Ⅲ)标准溶液(0.5mg Fe)于250毫升烧杯中,加水30毫升,缓冲溶液(pH6,每升溶液中含无水乙酸钠280克,冰乙酸10毫升)20毫升。相同条件制备两份。其中一份加抗坏血酸约0.3克,摇匀使溶解。加二甲酚橙指示剂2滴,试液显紫红色。滴加EDTA溶液,试液由紫红色逐渐变成黄褐色。
Some analysis of information, in pH5.5 ~ 6 solution, with EDTA complex titration of lead, xylenol orange as an indicator, plus ascorbic acid to mask trace amounts of iron, which is wrong. Since Fe ~ (2+) is also titrated in this condition, the result will be high. Experimental Methods Iron (III) standard solution (0.5 mg Fe) was pipetted into a 250 ml beaker and added with 30 ml of water and 20 ml of buffer solution (pH6, containing 280 g of anhydrous sodium acetate and 10 ml of glacial acetic acid per liter of solution). Prepare two copies under the same conditions. One of them is added with about 0.3 g of ascorbic acid and shaken to dissolve. Add two drops of xylenol orange indicator, the test solution was purple. Dropping EDTA solution, the test solution gradually turned from purple to brown.