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在湘Q/HG68—80企业标准(简称企标)中规定:一水硫酸锌含量的测定是在PH10的氨性缓冲溶液中,以铬黑T为指示剂,用EDTA标准溶液直接滴定锌,最后算出一水硫酸锌的含量。从文献资料得知:这种滴定方法受到多种元素的干扰,铬黑T指示剂也被许多元素封闭,如Cu~(2+)、Co~(2+)、Ni~(2+)、Al~(3+)、Fe~(3+)、Ti~(4+)等。Ca~(2+)Mg~(2+)、Cd~(2+)Mn~(2+)、Pb~(2+)、Hg~(2+)等元素亦会部分或全部被络合滴定。对上述提到的锰、铁、重金属(镉、铅、汞等)在企标中作了单项测定,规定了很底的极限度,其干扰程度可忽略。剩下的铜、钴、镍、铝、钛、钙、镁共存时的干扰测定问题需要解决。这些元素中,有的也属于重金属。但没有测定,多年来我们化验了很多样品,结果如下表;
In Hunan Q / HG68-80 enterprise standard (referred to as the enterprise standard) provides: Determination of zinc sulfate monohydrate content in the ammonia buffer solution of PH10, chrome black T as an indicator, with EDTA standard solution titration of zinc directly, Finally calculate the content of zinc sulfate monohydrate. It is known from the literature that this titration method is disturbed by a variety of elements. The chrome black T indicator is also blocked by many elements such as Cu 2+, Co 2+, Ni 2+, Al ~ (3 +), Fe ~ (3 +), Ti ~ (4 +) and so on. Ca 2+, Mg 2+, Cd 2+, Pb 2+, Hg 2+ will also be partially or fully complexed by complexometric titration . On the above-mentioned manganese, iron, heavy metals (cadmium, lead, mercury, etc.) in the enterprise standard made a single determination, provides a very bottom limit, the degree of neglect can be neglected. The remaining copper, cobalt, nickel, aluminum, titanium, calcium and magnesium coexist when interference problems need to be solved. Some of these elements also belong to heavy metals. But not measured, we tested a lot of samples over the years, the results in the table below;