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在碱性介质中,硫化钠还原次甲基蓝而使其褪色,硒对此反应有催化作用.West等根据此原理拟定了硒的动力学分析法,但方法中常见共存离子允许量较小,致使难于在实际中应用.本文在6N盐酸酸度下,经巯基棉吸附分离后,再用West法测定硒.硒的吸附率为98—100%,在4—80ppb范围内,硒含量与催化反应的速度成正比.巯基棉在不同的酸度条件下可吸附10多种离子,在6N盐酸介质中被吸附的元素有Pt(Ⅳ)、Pd(Ⅱ)、Au(Ⅲ)、Te(Ⅳ)、As(Ⅲ)和Se(Ⅳ).在常见的试样中,前4种元素几乎不存在,故可以不考虑;经王水溶样后,砷已转为高价,不被吸附;仅硒(Ⅳ)能被定量吸附.另外,锡和锑在溶矿时生成锑酸和锡酸的胶性沉淀,引起硒的吸附损失,其存在量不能超过硒量的25倍.测定40微克硒时,下列量的杂质不干扰测定:100mg的Hg(Ⅱ);50mg的As(Ⅲ)、Zn(Ⅱ)和Bi(Ⅲ);5mg的Ag(Ⅰ)、Cu(Ⅱ)、Pb(Ⅱ)、In(Ⅲ)和Cd(Ⅱ); 1mg的Sn(Ⅱ)和Sb(Ⅲ);以及大量的Cl~-、NO_3~-和SO_4~=.
In alkaline medium, sodium sulfide to reduce the methine blue and make it fade, selenium has a catalytic effect on this reaction.West et al developed a kinetic analysis of selenium according to this principle, but the method of common coexistence of ion allows a small amount , Which make it hard to be applied in practice.In this paper, the adsorption of selenium and selenium was measured by West method under the condition of 6N hydrochloric acid acidity and adsorption by thiol cotton.The adsorption rate of selenium was 98-100% (4), Pd (Ⅱ), Au (Ⅲ) and Te (Ⅳ) in the 6N hydrochloric acid medium, and the adsorption rate of Pt (Ⅳ), Pd , As (Ⅲ) and Se (Ⅳ). In the common sample, the first four elements are almost nonexistent, so they can not be considered; Ⅳ) can be quantitatively adsorbed.In addition, tin and antimony in the dissolution of the formation of antimony acid and stannic acid gel precipitation, causing the loss of selenium adsorption, its presence can not exceed 25 times the amount of selenium.Determination of 40 micrograms of selenium, The following amounts of impurities do not interfere with the assay: 100 mg of Hg (II); 50 mg of As (III), Zn (II) and Bi (Ⅲ) and Cd (Ⅱ); 1mg Of Sn (Ⅱ) and Sb (Ⅲ); and a large number of Cl ~ -, NO_3 ~ - and SO_4 ~ =.