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中药白矾(明矾)具有祛痰、燥湿、防腐消毒等疗效,主含12水合硫酸铝钾KAl(SO_4)_2·12H_2O。药典规定,本品含KAl(SO_4)_2·12H_2O不得少于99.0%。铝的络合滴定方法很多,文献已有评述。滴定剂多用乙二胺四乙酸二钠,滴定方式以返滴定为主,其中尤以双硫腙,或二甲酚橙作指示剂、以锌盐或铅盐作返滴定剂的方法终点色变最敏锐、测定准确度最高,但应采用实际滴定度。1977年版药典应用双硫腙法测定白矾中的铝,即在含50%乙醇的醋酸盐缓冲溶液(PH4.5)中,以双硫腙为指示剂用锌盐返滴定乙二胺四乙酸二钠。本文指出,由于药典方法未采用实际滴定度或空白试验校正,测定结果偏高约0.9%。为了提高测定准确度,应作空白试验校正。考虑到双硫腙法所用指示剂稳定性差,需临用新制,
The traditional Chinese medicine Alum (alum) has a curative effect such as sputum, dampness, antiseptic and disinfectant. It contains 12 aluminum sulfate potassium sulfate KAl(SO_4)_2·12H_2O. According to the Pharmacopoeia, this product contains KAl(SO_4)_2·12H_2O not less than 99.0%. There are many methods for complexometric titration of aluminum, and the literature has been reviewed. The titrant is mostly disodium edetate, and the titration method is mainly used for back titration, especially dithizone, or xylenol orange as indicator, zinc salt or lead salt as the back titrant method. The sharpest and most accurate measurement, but the actual titers should be used. The 1977 Pharmacopoeia used the dithizone method to determine aluminum in white peony, ie, in the acetate buffer solution (pH 4.5) containing 50% ethanol, back titration of EDTA with zinc salt using dithizone as indicator Disodium. This article points out that since the pharmacopoeia method is not calibrated with actual titer or blank test, the assay result is about 0.9% higher. In order to improve the accuracy of the measurement, blank test corrections should be made. Considering the poor stability of the dithizone method used in the indicator, it is necessary to use a new system.