HCl-HNO3消解法测定聚环氧琥珀酸螯合物中的钙含量

针对聚环氧琥珀酸（PESA）螯合物中钙含量的测定难题，研究了多种分析方法，发现PESA螯合物中的钙离子不能使铬黑T等金属指示剂正常显色，因而难以用EDTA直接滴定法和返滴定法测定。沉淀分离法、离子交换分离法、溶剂萃取分离法等分离方法均不能将PESA与钙离子有效分离。PESA对普通氧化剂很稳定，但HCl-HNO₃的氧化效果非常好，因而PESA螯合物中的钙离子含量可用HCl-HNO₃消解EDTA滴定法测定。该分析方法的测定结果具有良好的精密度和准确性，相对标准偏差范围为0.52%～1.56%，加标回收率范围为97.5%～102.0%，Cl^-，CO3^2-，SO4^2-对测定结果无干扰。

Determination of calcium chelating with polyepoxysuccinate by complexometric titration and HCl-HNO3 pretreatment

Calcium chelating with PESA was determined and the reasonable analytical conditions were selected. Calcium could not be separated from PESA efficiently by traditional methods such as deposition, ion exchange and solvent extraction, etc. Direct complexometric titration can not be adapted to this system because common metallic indicators are not able to link to the calcium in the presence of PESA. In this article, the samples were digested in HCl-HNO₃ system before compleximetric titration. By this method, the effect of epoxysuccinate on the determination is eliminated successfully. The recovery range of the three types of samples is 98.2%～101.7%. The relative standard deviations are from 0.52% to 1.56%. This method is rapid, simple and accurate.