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经典的硫酸钡重量法测定钡,方法准确度高且不需要特殊的设备和试剂,但与大量铅共存时,需预先分离铅后才能沉淀硫酸钡。本文采用络合掩蔽的方法,消除了硫酸钡沉淀中夹杂Fe(Ⅲ)、Bi(Ⅲ)等,在大量铅共存下直接沉淀硫酸钡,大大简化了分析手续,改善了操作条件。本法适用于X～50％钡的测定。 经试验表明:30ml15％NaAc或50ml5％EDTA均能抑制100mgPb(Ⅱ)使之不产生PbSO_4沉淀。而Pb(Ⅱ)(100mg)、Ba(Ⅱ)(100mg)共存时,只有EDTA可以抑制PbSO_4沉淀。20ml10％柠檬酸足够络合掩蔽1.5mgFe(Ⅲ)和2mgBi(Ⅲ)而不污染硫酸钡沉淀。这些络合掩蔽剂的加入,对Ba(Ⅱ)沉淀为BaSO_4均无影响。EDTA的加入量,根据试样中含铅量而确定,必须满足于全部络合Pb(Ⅱ),并稍有过量。为了使混合络合掩蔽剂发挥其络合效能,选用了微酸性(pH5～6)的乙酸钠介质中沉淀硫酸钡。
Barium gravimetric method for the determination of barium, high accuracy and does not require special equipment and reagents, but with a large number of lead coexist, the need to pre-separation of lead in order to precipitate barium sulfate. In this paper, complex masking method is adopted to eliminate the inclusions of Fe (Ⅲ), Bi (Ⅲ) and so on in barium sulphate precipitation. The direct precipitation of barium sulphate in the presence of a large amount of lead greatly simplifies the analysis procedure and improves the operating conditions. This method is applicable to the determination of X ~ 50% barium. Experiments show that: 30ml15% NaAc or 50ml5% EDTA can inhibit 100mgPb (II) so that does not produce PbSO_4 precipitation. When Pb (Ⅱ) (100mg) and Ba (Ⅱ) (100mg) coexist, only EDTA can inhibit PbSO_4 precipitation. 20 ml of 10% citric acid complexed enough to mask 1.5 mg Fe (III) and 2 mg Bi (III) without contaminating the barium sulphate precipitate. The addition of these complex masking agents has no effect on the Ba (Ⅱ) precipitation as BaSO_4. The amount of EDTA added, determined by the amount of lead contained in the sample, must be sufficient to completely complex Pb (II) with a slight excess. In order to make the mixed complexing masking agent exert its complexation efficiency, a slightly acidic (pH5 ~ 6) sodium acetate medium was used to precipitate barium sulfate.