食品中のEDTAの分析 (I)

コバルトイオンおよび過酸化水素による呈色反応の検討

抄録

It was previously reported by Vogel et al. that EDTA reacted with cobalt ion and hydrogen peroxide with development of reddish purple color, and the reaction was applied to the analysis of EDTA in edibles, e. g. wine or fruit juice.
The present experiment was undertaken to see in detail about some conditions necessary for the color reaction, and results obtained were as follows.
1) Amount of cobaltous nitrate solution to be added was found to be equivalent by mole ratio to amount of EDTA.
2) The color intensity was maximum when the concentration of hydrogen peroxide in sample solution was over 1.25M.
3) The color intensity was maximum when sample solution was at pH 3 to 4, whereas at pH 1 to 2 or at pH 5 it was lower than in the former case and at pH 6 the color was decomposed while heating.
4) There was no significant difference of absorbance between the procedure involving heating twice and the one involving heating once, respectively after adding the two reagents. In the latter procedure, the absorbance was stabilized by heating for 10 to 15 minutes at pH 1 to 4, but at pH 5 it reached to the maximum by heating for 5 minutes and declined by following heating.
5) The color produced within the pH range 1 to 4 was stable for 24 hours at room temperature.