铅铜的选择性螯合滴定

曾应用SO_4~(2-)释放Ba-EDTA中的EDTA,当有Pb~(2 )存在下,Pb~(2 )同BaSO_4共同沉淀。当Ba~(2 )量超过Pb~(2 )的10倍以上,Pb~(2 )全部掺入到BaSO_4晶格中,形成混晶沉淀。这种沉淀比PbSO_4更稳定。利用这一性质,曾掩蔽Pb~(2 )直接螯合滴定Zn~(2 2-5])。进一步研究发现,在微酸性介质中加入SO_4~(2-)Ba~(2 )可以定量释放Pb-EDTA中的EDTA,生成更稳定的硫酸铅钡:

Selective Chelatometric Titration of Lead and Copper

EDTA is added to the sample solution and the excess is removed by ti-tration at pH 5-7 with Zn(NO3)2(XO-CTMAB indicator). H2SO4 and 20% BaCl2 are added to decompose Pb-EDTA chelate and Pb is indirectly determined by titration with Zn(NO3)2, then thioglycollic acid is added to displace Cu-EDTA chelate and Cu determined with the same titrant. The method is selective and has been used for the analysis of alloys and ores.