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自发现钙、镁的 EGTA 络合物 logK 值相差5.8单位(logK_(Ca-EGTA)=11.0,logK_(Mg-EGTA)=5.2)以后,开辟了滴定钙的新途径,提高了滴定钙的选择性.但由于还没有发现对钙专一指示剂,所以大量镁存在时于不产生 Mg(OH)_2沉淀的 pH 条件下,用直接指示剂目视法确定终点的络合滴定钙的方法,尚未见报导。我们在用铍试剂Ⅰ比色测定镁的实验中观察到乙酰丙酮能阻止镁的显色,又参考乙酰丙酮有萃取镁而不萃取钙的性能,利用乙酰丙酮同钙镁作用的差别性,以乙酰丙酮为掩蔽剂,采用偶氮氯膦Ⅲ为指示剂,在 pH10以 EGTA 滴定钙,成功地解决了大量镁存在下钙的测定问题。
Since the log K value of CaTAg and Ca (Ⅱ) in magnesium was found to be 5.8 units (logK_ (Ca-EGTA) = 11.0, logK_ (Mg-EGTA) = 5.2), a new method of titrating calcium was developed and the titration of calcium was improved However, since no specific indicator of calcium has been found, the method of visualization of the end point of complexed titration of calcium with direct indicator visualization in the presence of a large amount of magnesium in the absence of Mg (OH) 2 precipitation, Not yet reported. We use the beryllium reagent Ⅰ colorimetric determination of magnesium in the experiment was observed that acetylacetone can prevent the color of magnesium, and reference to acetylacetone magnesium extraction without the performance of calcium extraction, the use of acetylacetone with the difference between the role of calcium and magnesium to Acetylacetone as a masking agent, the use of chlorophosphonazo Ⅲ as an indicator, titration of calcium with EGTA at pH 10, successfully solved the problem of determination of calcium in the presence of a large amount of magnesium.