EDTA络合滴定法与草酸盐重量法测定锂盐中钙含量的方法对比

对用EDTA络合滴定法和草酸盐重量法测定不同锂钙质量比的锂盐中钙含量的方法进行了对比。EDTA络合滴定法中,用三乙醇胺作为Li+的掩蔽剂,钙指示剂作为指示剂,用EDTA滴定溶液中钙;草酸盐重量法中,用草酸铵作沉淀剂,溶液中钙以草酸钙形式沉淀析出后灼烧成碳酸钙形式测定钙含量。实验结果表明,用EDTA络合滴定法测定锂盐中钙含量,锂钙质量比小于5且用三乙醇胺作掩蔽剂时,虽然可以测定钙含量,但是分析结果很不稳定,相对误差在-1.00%~0.50%范围;当锂钙质量比大于5时,三乙醇胺已无法掩蔽锂离子,无法分析钙含量

Contrast of EDTA complexometric titration and oxalate gravimetric method in determination of calcium in lithium salts

The calcium contents in lithium salts with different mass ratio of Li and Ca2 were determined by EDTA complexometric method and oxalate gravimetric method,and the results were compared.In EDTA complexometric method,triethanolamine was used for the screening agent for Li and calconcarboxylic acid was used for the indicator for calcium,and the calcium in solution was titrated with EDTA.In oxalate gravimetric method,ammonium oxalate was used for a precipitating agent and the calcium in solution was precipitated in the form of calcium oxalate,and then the precipitate was burned to calcium carbonate for the determination of calcium content.The results showed that when the mass ratio of Li and Ca2 was less than 5 and triethanolamine was used as the screening agent,the calcium in lithium salts could be determined by EDTA complexometric method.However,the analysis results were very unstable and the relative error was in the range of-1.00%-0.50%.When the weight ratio of Li and Ca2 was higher than 5,triethanolamine could not mask lithium ions and the calcium content could not be determined.Therefore,this method was not applicable for the accurate determination of calcium in lithium salts.While the calcium in lithium salts was determined by oxalate gravimetric method,the existence of abundant lithium ions had no influence on the determination and it could be applied to the accurate determination of calcium in lithium salts.