EDTA titration of zinc using 2-(2-benzoxazolylazo)-1-naphthol as an indicator in the presence of a surface-active agent.

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  • 界面活性剤を用いる２‐（２‐ベンゾオキサゾリルアゾ）‐１‐ナフトール指示薬による亜鉛のＥＤＴＡ滴定
  • カイメン カッセイザイ オ モチイル 2 2 ベンゾオキサゾリルアゾ 1 ナフ
  • 界面活性剤を用いる2-(2-ベンゾオキサゾリルアゾ)-1-ナフトール指示薬による亜鉛のEDTA滴定

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Abstract

2-(2-Benzoxazolylazo)-1-naphthol (α-BOAN) reacts with zinc in an aqueous solution containing non-ionic surfactants such as Brij 35 [polyoxyethylene(23)lauryl ether], and forms a soluble complex. The combining ratio of α-BOAN-zinc complex at pH 5.5 and 8.4 was shown to be 1 : 2 by molar ratio method and continuous variation method. The α-BOAN-zinc complex has two absorption maxima at 562 and 594 nm, whereas the reagent blank at 490 nm. The apparent formation constants of the α-BOAN-zinc complex and the acid dissociation consants of α-BOAN were determinded as logKRZnR= 6.92, logK2RZNR<SUB>2</SUB>= 15.4 and pKa<SUB>2</SUB>=6.93 ± 0.03, pKa<SUB>1</SUB><1, respectively, in the surface-active agent [0.8 % (w/v)] at 0.1 mol dm-3 (NaClO4) ionic strength and at 30 °C. On the basis of the results, the optimum conditions for EDTA titration of zinc using α-BOAN as an indicator were examined. The titration curves simulated for the zinc/EDTA/α-BOAN system as showed that in pH 4.55.5, the sharp color change from blue to orange was observed by the visual titration at the equivalence point. The proposed procedure is as follows: To a sample solution containing zinc (ca. 400 μg), add 10 ml of acetic acid/sodium acetate buffer solution (pH 5.5), 2 ml of Brij 35 solution (0.1 g ml-1) and 0.2 ml of α-BOAN(10 mol dm-3). The solution was made up to 50 ml in a 32 mm-cell with water, and then titrated with EDTA standard solution (10-2 mol dm-3).

Journal

  • BUNSEKI KAGAKU

    BUNSEKI KAGAKU 34 (7), 404-408, 1985

    The Japan Society for Analytical Chemistry

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