マグネシウム共存試料中のカルシウムの分光光度滴定

概要

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The chelatometric titration of Ca2+ in the presence of Mg2+ is mostly accompanied with a negative error. The authors observed that such error was avoidable by the addition of a proper amount of Al3+, though the reason is still remained uncleared. An optimum amount of Al3+ to be added was found to be about 2.5 mg for each 10 mg of Mg2+. Aluminum ion must be added and mixed well with the sample solution prior to the pH adjustment. After the pH being adjusted to 13, the titration was carried out in the presence of Dotite NN, as an indicator, and of both KCN and trimethanolamine as masking reagents. It is desirable to detect the end point spectrophotometrically measured at 650 mμ, because the visible change of the color at the end point is not observed so clear. The addition of more than 10 mg of Al3+ to 100 ml each of the titrated solution makes the end point obscur.
社団法人日本分析化学会の論文