EDTA滴定法测定粗锡中铅

Determination of lead in crude tin by EDTA titration method

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2h、pH值为5.5~6.0的乙酸-乙酸钠缓冲溶液加入量为30mL、微沸时间为10min。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(ICPAES)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 precip-itate separation. However, the interference of tin and bismuth cannot be ignored when the method is ap-plied for the determination of lead content in crude tin. The sample was dissolved in PTFE beaker with hy-drochloric acid-nitric acid-perchloric acid and hydrochloric acid-nitric acid-hydrobromic acid. Under the ex-perimental 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 mer- captoacetic 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 precipi-tate ,the dosage of HAc-NaAc buffer solution and the slight boiling time. The optimum conditions were fi-nally obtained as follows： the ageing time was 2 h, the dosage of HAc-NaAc buf fer solut ion at pH 5. 5-6. 0 was 30 mL, and the slight boiling time was 10 min. The proposed method was applied for the determina-tion 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%, respect ively. The recoveries of standard addi t ion were between 98% and 102%.