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大量磷存在时,用EDTA络合滴定钙是困难的。由于Ga~(2+)-EGTA络合物的稳定常数较大(logKc~+-EGTA=11.0),作者叙述了一种不需添加任何掩蔽剂,以钙电极为指示电极,在pH≥11时,用EGTA电位法测定磷矿中钙的方法。方法简便、快速,相对标准偏差为2％,加入回收率为97—103％。 EGTA滴定Ca~(2+)的滴定曲线:用Ca~(2+)电极为指示电极,饱和甘汞电极为参比电极,EGTA电位滴定Ca~(2+)的试验表明,pH>8,EGTA就能完全络合Ca~(2+);pH<10,到达终点所需的EGTA量
Titration of calcium with EDTA complex is difficult when large amounts of phosphorus are present. Since the stability constant of Ga ~ (2 +) - EGTA complex is relatively large (logKc ~ + -EGTA = 11.0), the authors described a method that does not require any addition of any masking agent and uses a calcium electrode as the indicator electrode. When using EGTA potentiometric method for determination of calcium in phosphate rock. The method is simple and rapid, the relative standard deviation is 2% and the recovery rate is 97-103%. Titration curve of Ca 2+ with EGTA titration: Ca 2+ electrode was used as indicator electrode and saturated calomel electrode as reference electrode. EGTA titration of Ca 2+ showed that pH> 8, EGTA can completely complex Ca ~ (2 +); pH <10, EGTA amount required to reach the end point