EDTA容量法连续测定钙和镁的改进

Improvement of Volumetric Method for Continuous Determination of Calcium and Magnesium Using EDTA

改进了用EDTA连续快速测定矿石中钙和镁的方法。在用EDTA滴定钙之后的溶液中加入NH4Cl,使溶液中的碱度降低至pH10左右,以Mg(OH)2沉淀溶解为标志。加入pH10的缓冲溶液,补加K-B指示剂,用同一EDTA标准溶液继续滴定镁。此法克服了用HCl调节pH值法滴定镁结果系统偏高的缺点。经大量生产考察,结果准确、稳定,与分别滴定后从钙镁合量差减法和外检结果十分一致。对w(MgO)为21.10%的样品进行精密度试验,其RSD(n=10)为0.6%。

A method for continuous titration of calcium and magnesium using EDTA is proposed in this paper. The NH4Cl is added to the sample solution after titration of Ca2+ by EDTA to keep the sample solution in pH=10. After adding NH4OHNH4Cl buffer solution (pH=10), titration of Mg2+ with same EDTA standard solution is performed. The new method solves the problem that the results of magnesium are systematically high in traditional titration procedure. The method has been applied to the determination of Ca and Mg in geological samples in routine analysis. The results are in good agreement with those provided by other methods. The precision for the sample with w(MgO)=21.10% is 0.6% RSD (n=10).