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最近,Raoot等曾对测定锡的重量法、氧化还原法和络合滴定法作了简要的评述,并提出用巯基乙酸或巯基丙酸分解Sn-EDTA络合物,然后用硝酸铅滴定释出的EDTA来测定锡,选择性较高。我们曾发现乳酸对锡(Ⅳ)有较强的络合能力,能选择地置换络合锡的EDTA,并应用于测定合金和锡精矿中的锡。Kragten测得Sn(Ⅳ)-EDTA络合物的稳定常数为10~(34.5),可见该络合物相当稳定。用乳酸置换络合锡的EDTA时,要加入过量的铅促使置换反应完全。Sn(Ⅳ)-DCTA络合物的稳定常
Recently, Raoot et al. Gave a brief review of the gravimetric, redox and complexometric titration methods for the determination of tin and proposed that the Sn-EDTA complex be resolved with thioglycolic acid or mercaptopropionic acid followed by titration with lead nitrate EDTA for the determination of tin, the selectivity is higher. We have found that lactic acid has a strong ability to complex tin (IV), selectively displaces complexed tin EDTA and is used to determine tin in alloys and tin concentrates. The stability constant of Sn (Ⅳ) -EDTA complex measured by Kragten is 10 ~ (34.5), showing that the complex is quite stable. With lactic acid exchange complex tin EDTA, the excess lead to promote replacement reaction completely. Stability of Sn (Ⅳ) -DCTA Complex