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在弱酸性介质中,在有羟胺存在并煮沸的情况下,钼能与羟胺和2-[(5-溴-2-吡啶)偶氮]-5-(二乙氨基)苯酚(简称5-Br-PADAP)作用形成蓝色的不溶于水的三元络合物,但在聚乙二醇辛基苯基醚(简称OP)存在下可不析出沉淀。此三元络合物的组成为Mo(Ⅳ):NH_2OH:5-Br-PADAP=1:1:1,其最大吸收在600—605毫微米,摩尔吸光系数为4.8×10~4,在10毫升显色液中含0.1％5-Br-PADAP溶液0.6毫升,钼量在30微克以下遵守比耳定律。 我们采用在显色后加入混合掩蔽剂并煮沸的办法来消除共存离子的干扰,方法具有很高的选择性,尤其可在大量钨存在下直接测定钼。
In weakly acidic media, molybdenum can react with hydroxylamine and 2- [(5-bromo-2-pyridyl) azo] -5- (diethylamino) phenol -PADAP) forms a blue, water-insoluble ternary complex but does not precipitate in the presence of polyethylene glycol octylphenyl ether (OP). The composition of the ternary complex is Mo (Ⅳ): NH 2 OH: 5-Br-PADAP = 1: 1: 1, the maximum absorption is between 600 and 605 nm, the molar absorption coefficient is 4.8 × 10 4, 0.6 ml of 0.1% 5-Br-PADAP solution in ml of color developing solution and Beer’s Law is obeyed below 30 μg of molybdenum. We eliminate the interference of coexisting ions by adding a mixture of masking agents and boiling after color development. The method is highly selective and allows the direct determination of molybdenum in the presence of large amounts of tungsten.