鉄(III)の共存する鉛の(Cu-PAN)-EDTA滴定

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EDTA titration of lead in solution of pH 5 containing small amount of iron(III) has usually been thought as not being affected by iron(III) provided that Cu-PAN is used as an indicator. From the results of similar titration using XO indicator, however, the present authors doubted of this concept, and assumed that positive errors would be caused by the presence of iron(III) for percentages of lead obtained in EDTA titration of such solutions even with Cu-PAN indicator. This assumption came from their general observation that iron(III) had so slower chelate formation rate against its so larger chelate formation constants, and was verified, in this paper, by small but definite positive errors found for the first time in this titration system. These positive errors were supposed to have the same origin as in the titration of solutions containing iron(III) only, as both showed similar dependance on the quantities of iron (III) present. On the other hand, errors were larger than, and thought to have somewhat different mechanism from, the case of XO-EDTA titration.<BR>Masking of iron (III) for the determination of lead without further separation process was successful by a successive titration method based on the one developed by the authors for the case of XO-EDTA system. After the solution containing lead and small amount of iron (III) was titrated at pH 2.5 for iron (III) using sulfosalicylic acid indicator, the solution was then adjusted to pH 5 and titrated for lead using Cu-PAN indicator.<BR>This method was applied successfully to the determination of lead in lead slag, showing quite a practical but excellent nature, as the separation process of lead sulfate precipitate was able to be minimized yet it rather maximized precision and accuracy of the titration.
社団法人日本分析化学会の論文

鉄(III)の共存する鉛の(Cu-PAN)-EDTA滴定

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