ジチゾンを指示薬とする亜鉛,鉛の定量とβ-メルカプトプロピオン酸による鉛の隠ぺい

概要

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Determinations of zinc and lead in 40% alcoholic solution at pH4.5 were made by titration with 0.025M EDTA solution using 2cc of 0.025% dithizone as an indicator. For determination of zinc in the presence of lead, 2cc of β-mercaptopropionic acid was added, boiled for several min. for the masking of lead, and the zinc was determined as above by titration with 0.025M EDTA. By use of these methods, determinations of zinc and lead in silicates were carried out for the solution after removal of silicic acid as follows : (1) A definite volume of the solution was measured out, 8cc of 20%NH4·HF2 added for masking of iron, aluminum, titanium, etc., adjusted to pH4.5, 2cc β-mercaptopropionic acid added, boiled for several min., and the zinc was determined as above. (2) Another definite volume of the solution was treated with 8cc of 20%NH4·HF2, adjusted to pH4.5, a known excess of EDTA added and the excess was back-titrated with zinc acetate with the same condition as above for seeking of the total sum of zinc and lead. The amount of lead was calculated from the difference in (1) and (2). Satisfactory results were obtained.