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一般测定样品中高含量铅时,多采用硫酸铅沉淀分离-EDTA滴定法测定,而将此法应用于测定粗锡中铅含量时,锡和铋的干扰不可忽略.实验选择在聚四氟乙烯烧杯中以盐酸-硝酸-高氯酸、盐酸-高氯酸-氢溴酸溶样,在此条件下样品中锡可与氢溴酸反应生成溴化锡而被挥发除去,将溶液经硫酸铅沉淀分离后,于滴定前加入巯基乙酸以掩蔽铋,在乙酸-乙酸钠缓冲体系中,以二甲酚橙为指示剂建立了EDTA滴定法测定粗锡中铅含量的方法.试验进一步对沉淀陈化时间、乙酸-乙酸钠缓冲溶液加入量、微沸时间等条件进行了优化,确定最佳条件如下:陈化时间为2 h、pH值为 5.5~6.0的乙酸-乙酸钠缓冲溶液加入量为30 mL、微沸时间为10 min.将实验方法应用于测定粗锡中铅,测得结果与电感耦合等离子体原子发射光谱法(ICP-AES)基本一致,相对标准偏差(RSD,n=11)为0.68%和0.38%,加标回收率为98%~102%.

The high content lead in sample is usually determined by EDTA titration after lead sulfate precipitate separation.However, the interference of tin and bismuth cannot be ignored when the method is applied for the determination of lead content in crude tin.The sample was dissolved in PTFE beaker with hydrochloric acid-nitric acid-perchloric acid and hydrochloric acid-nitric acid-hydrobromic acid.Under the experimental conditions, the tin in sample could react with hydrobromic acid to form stannic bromide, which would be removed through volatilization.After treatment by lead sulfate precipitate separation, the mercaptoacetic acid was added into solution before titration to mask bismuth.The determination method of lead in crude tin by EDTA titration was established in HAc-NaAc buffer solution using xylenol orange as the indicator.The experimental conditions were further optimized, including the ageing time of precipitate, the dosage of HAc-NaAc buffer solution and the slight boiling time.The optimum conditions were finally obtained as follows: the ageing time was 2 h, the dosage of HAc-NaAc buffer solution at pH 5.5-6.0 was 30 mL, and the slight boiling time was 10 min.The proposed method was applied for the determination of lead in crude tin, and the found results were consistent with those obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES).The relative standard deviation (RSD, n=11) was 0.68% and 0.38%, respectively.The recoveries of standard addition were between 98% and 102%.