抄録
Chelatometry of aluminum for the determination of zeolite in detergents has been investigated. Aluminum ion liberated from zeolite dissolved in dil. nitric acid forms a complex with EDTA at pH 33.5, and can be determined by titrating the excess amount of EDTA with zinc (II) acetate at pH 56 using xylenol orange as an indicator. It is well known that Al-EDTA complex is selectively dissociated into each species by boiling in the presence of fluoride ion. This fact suggests that aluminum ion can be determined without interferences from other contaminated heavy metals. Therefore, aforementioned test solution under the end point is treated with fluoride ion, and then liberated EDTA equivalent to aluminum is determined by titrating in the same manner. Sodium citrate, sodium malate, and sodium tartrate give no interferences to the determination of zeolite, however the presence of STPP, NTA and EDTA affords low recovery of zeolite. Interference by STPP can be completely eliminated by its hydrolysis in nitric acid. In order to exclude the interference from EDTA, the present method is modified for the simultaneous determination of zeolite and EDTA. The results of determination of EDTA in the presence of zeolite are in good agreement with those obtained from total nitrogen measurements. Consequently, the present method becomes applicable to the determination of zeolite in commercial detergents with satisfactory accuracy.
