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锡的EDTA螯合滴定主要矛盾是Sn(Ⅳ)有强烈的水解倾向,尤其对含锡量较高的铅基合金影响更大.解决Sn(Ⅳ)的水解,提高螯合物的条件稳定常数,许多分析工作者做过大量的试验,如降低pH值,用HEDTA作滴定剂,铋盐作回滴剂等,使分析结果稳定、准确.然而不少中小企业的理化室因试剂供应有困难,至今仍采用古典的碘量法测定锡.作者就现有条件,对抑制Sn(Ⅳ)的水解做了条件试验,证明Sn(Ⅳ)是能够抑制的.在单独测定锡时,只要在溶样时加一定量固体氯化钾;在锡铅顺序滴定时,采用酒石酸—硝酸溶样,都能够抑制Sn(Ⅳ)的水解.条件试验还表明,铜含量在1.50%以下时,不干扰测定.而大于1.5%铜量时可加少量流脲,即可消除铜的干扰.对锡干扰较大的是Al(Ⅲ),但一般铅基合金中几乎无铝,故可以不予考虑.本方法在滴定时溶液的pH在5～6之间为宜.
The main contradiction of EDTA chelation titration of Sn is that it has a strong tendency to hydrolyze Sn (Ⅳ), especially to lead-based alloys with higher tin content. Solve the hydrolysis of Sn (Ⅳ) and improve the stability constants of chelates , Many analysts have done a lot of tests, such as reducing the pH value, using HEDTA as titrant, bismuth salt as dropping agent, etc., to make the analysis result stable and accurate.However, many SMEs’ , The classical method of iodometry is still used to determine the tin. Under the current conditions, the authors tested the inhibition of the hydrolysis of Sn (Ⅳ) and proved that Sn (Ⅳ) can be inhibited. When the sample is added with a certain amount of solid potassium chloride, the dissolution of Sn (Ⅳ) can be inhibited by the tartaric acid-nitric acid solution when the tin-lead order titration is carried out.The condition tests also show that when the content of copper is below 1.50%, the determination does not disturb While more than 1.5% of the amount of copper can be added a small amount of urea, you can eliminate the interference of copper.Induces more on the tin is Al (Ⅲ), but the general lead-based alloy almost no aluminum, it can not be considered. Method titration solution pH of 5 to 6 is appropriate.