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络合滴定钙镁,通常控制pH=12～13,让溶液中共存的钙离子生成氢氧化镁沉淀,但当镁离子含量高时,大量的氢氧化镁沉淀对钙离子的吸附与共沉淀,影响钙测定结果的偏低。为了消除镁盐氢氧化物影响,早期文献有加入蔗糖,甘油,聚乙烯醇或糊精等做分散剂以减少沉淀吸附,其中糊精效果最好,但糊精空白高且易发霉。文献加入适量酒石酸盐使部分镁离子生成络合物,减少镁盐沉淀,但过量酒石酸盐对钙络合滴定指示剂变色有一定影响。以上方法并不能完全消除镁盐沉淀的吸附,有的文献分二份溶液;一份先滴定
Complexometric titration of calcium and magnesium, usually controlled pH = 12 ~ 13, so that the solution of calcium ions coexist to generate magnesium hydroxide precipitation, but when the magnesium ion content is high, a large number of magnesium hydroxide precipitation of calcium ions adsorption and coprecipitation, affecting Low calcium measurement results. In order to eliminate the influence of magnesium hydroxide salt, early literatures add dispersant such as sucrose, glycerin, polyvinyl alcohol or dextrin to reduce sediment adsorption, of which dextrin has the best effect, but the dextrin is blank and easy to mold. In the literature, some tartaric acid salts are added to make some of the magnesium ions to form complexes, which can reduce the precipitation of magnesium salts. However, excess tartrate has certain influence on the color change of calcium complexation titration indicator. The above method does not completely eliminate the adsorption of magnesium salt precipitation, some literature points in two solutions; a first titration