The purity of recrystallized disodium dihydrogen ethylenediaminetetraacetate dihydrate was determined accurately by titration with zinc ion coulometrically generated from an amalgamated zinc anode. The reagents used were of 99.446% ±0.002% homogeneity when the sample was dehydrated and stored in a hygrostat (relative humidity, ca. 58% at 20 °C) over 1 year. Aluminium of high purity (99.99%) was coulometrically titrated with the purified reagent. Aluminium was allowed to react with a certain amount of the reagent, excess of the reagent being titrated with zinc ion anodically generated. The end point was determined potentiometrically using a mercury electrode. The purity was found to be 99.976% with a standard deviation of 0.010% for 6 degree of freedom. Cause of the lower result (0.01%) is discussed.
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