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当试样中含有铀时,用氯化亚锡还原,以重铬酸钾滴定法定铁,所得结果偏高。为了快速而准确地测定样品的全铁量,我们试验了铁的EDTA滴定法。关于EDTA滴定三价铁,不少文献有了记述。根据Ringbom曲线,在pH 1—3的酸度下,金属-EDTA络合物的稳定常数小于10~(20)的金属离子,一般不起干扰作用。已有人确定,大量的Pb~(++),Zn~(++),Cd~(++),As,Ca~(++),Mg~(++),Ba~(++),Al~(3+),Ti~(4+),Mo,Hg~(++),Co~(++),Ni~(++),K~+,Na~+,NH_4~+不起干扰作用,Cr小于3毫克、Cu~(++)小于0.5毫克时也无影响。我们补充试验了UO_2~(++),Ce~(4+),Zr~(4+),Th~(4+)的干扰情况,证明了在pH 1—3的酸度下,除钍定量干扰外,其余三个离子没有影响。而且EDTA滴定法比重铬酸钾滴定法,操作手续简单、准确度和精密度也较高。
When the sample contains uranium, with stannous chloride reduction to titrimetric determination of potassium dichromate, the results obtained high. In order to quickly and accurately determine the total iron content of the sample, we tested the iron EDTA titration method. About EDTA titration ferric iron, a lot of literature has been described. According to the Ringbom curve, the metal-EDTA complex has a stability constant of less than 10 to (20) metal ions at an acidity of pH 1 to pH 3 and is generally not disturbing. It has been determined that a large number of Pb ~ (++), Zn ~ (++), Cd ~ (++), As, Ca ~ (++), Mg ~ (++), Ba ~ Al ~ (3 +), Ti ~ (4 +), Mo, Hg ~ (++), Co ~ (++), Ni ~ (++), K ~ +, Na ~ +, NH_4 ~ + Interference, Cr less than 3 mg, Cu ~ (++) less than 0.5 mg also had no effect. We have additionally tested the interferences of UO_2 ~ (++), Ce ~ (4 +), Zr ~ (4 +) and Th ~ (4 +) and proved that the quantitative interference of thorium In addition, the remaining three ions have no effect. And EDTA titration than potassium dichromate titration method, simple procedures, accuracy and precision are also higher.