EDTA络合滴定法联合测定硅钙钡镁合金中钙钡镁

建立了一种快速测定硅钙钡镁合金中钙、钡和镁含量的分析方法。以盐酸、硝酸和氢氟酸分解试样,高氯酸冒烟除去残余的盐酸、硝酸和氢氟酸,经过氨水沉淀分离铁、铝等干扰元素后,在pH 10的NH₃·H₂O-NH₄Cl缓冲体系中,以邻甲酚酞指示滴定终点, EDTA络合滴定法测定钙镁合量;在pH≥12的氢氧化钾缓冲体系中,分别以钙指示剂和钙黄绿素-茜素混合指示剂指示滴定终点, EDTA滴定法分别测定钙及钙钡合量。根据钙钡合量与钙含量的差值和钙镁合量与钙含量的差值,可分别得到钡和镁含量。经氨水沉淀后试液中残余的铁、铝和其他干扰离子用三乙醇胺掩蔽,钡对滴定钙和钙镁合量以及镁对滴定钙和钙钡合量的干扰分别通过生成硫酸钡和氢氧化镁沉淀的方法消除。建立的方法用于实际硅钙钡镁合金中钙、钡和镁测定,测定值与对照方法测定值相符,钙、钡和镁的相对标准偏差分别为0.38%、1.9%和1.9%。

Combined determination of calcium,barium, magnesium in silicon-calcium-barium-magnesium alloy byEDTA complexometric titration

A rapid method for the determination of calcium, barium and magnesium in Si-Ca-Ba-Mg alloy was established. After the sample was dissolved in HCl-HNO₃-HF, the residual of which was removed by smoking of HClO₄, and the interference elements such as Fe, Al were separated by aqueous ammonia, the aggregate content of Ca and Mg was titrated by EDTA complexometric titration in the buffer system of NH₃·H₂O-NH₄Cl at pH 10 with o-cresolphthalein as indicator; the content of Ca and the aggregate content of Ca and Ba were titrated by EDTA titration in the buffer system of potassium hydroxide at pH≥12 with calconcarboxylic acid and calcein-alizarin as indicator. The content of Ba and Mg was obtained based on the difference between the content of Ca and the aggregate content of Ca and Ba as well as the difference between the content of Ca and the aggregate content of Ca and Mg. Fe, Al and other interference ions left in the sample solution after aqueous ammonia precipitation were masked by triethanolamine. The interference of Ba in the titration of Ca and the titration of Ca and Mg ,and the interference of Mg in titration of Ca and the titration of Ca and Ba were eliminated through generating barium sulfate and magnesium hydroxide precipitates. This method has been applied to the determination of Ca, Ba and Mg in practical Si-Ca-Ba-Mg alloy, whose results were in good agreement with those of the reference method. The relative standard deviations (RSDs) of Ca, Ba and Mg were 0.38%, 1.9% and 1.9%,respectively.