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E D T A二钠滴定液的标定,中国药典1990年版采用氧化锌作为基准。用前需于800℃灼烧至恒重,且需加酸使溶解并中和过量的酸,方法繁琐费时,而且由于加入甲基红指示剂,致使络合滴定终点溶液由紫色变为纯蓝的敏锐度下降。作者根据铅离子在弱酸性环境中与E D T A能迅速、定量生成稳定络合物(1:1)的特性,选用硝酸铅作基准,在醋酸—醋酸钠缓冲液(pH6.0)及六次甲基四胺的存在下,以二甲酚橙为指示剂,直接进行E D T A滴定。
E D T A disodium titration solution calibration, Chinese Pharmacopoeia 1990 edition using zinc oxide as a benchmark. Before use at 800 ℃ burning to constant weight, and the need to add acid to dissolve and neutralize excess acid, cumbersome and time-consuming, and because of the addition of methyl red indicator, resulting in complex titration end solution from purple to pure blue Decreased sharpness. According to the characteristics of Pb (superscript 2 +) and EDTA (EDTA), the stable complex (1: 1) can be generated rapidly and quantitatively by using lead nitrate as the standard. In the presence of tetramine, xylenol orange is used as an indicator for direct EDTA titration.