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以钙黄绿素为指示剂,络合滴定法测定钙是一个很好的方法;但由于市售钙黄绿素指示剂往往不纯,残留一定的萤光,致使滴定终点变化不敏锐,影响了指示剂的应用和推广。我们在多年使用钙黄绿素中,发现只要将市售的指示剂进行一般的提纯,就可以减少残留的萤光,使钙黄绿素在络合滴定中终点变化敏锐、清晰。其提纯方法如下: 称取3.90克钙黄绿素,溶于50—60毫升水中,加入10毫升15％氯化钙溶液(用纯碳酸钙或氧化钙配成盐酸溶液),摇匀,用0.5mol/L氢氧化钾溶液将试液中和到pH8.5左右,稍放置一些时间,使沉淀下沉,用中速滤纸过滤,以水洗涤沉淀5—6次,弃去试液,
Calcein as an indicator, complexometric titration of calcium is a good method; but due to commercial calcein indicators are often impure, leaving some fluorescence, resulting in changes in the titration endpoint is not sensitive, affecting the indicator Application and promotion. We have been using calcein for many years and found that by simply purifying the commercially available indicator, we can reduce the residual fluorescence and make the calcein sharp and clear at the end of the complexometric titration. The purification method is as follows: Weigh 3.90 g calcein, dissolved in 50-60 ml of water, add 10 ml of 15% calcium chloride solution (with pure calcium carbonate or calcium oxide dubbed hydrochloric acid solution), shake, with 0.5mol / L potassium hydroxide solution and the test solution was neutralized to pH8.5 or so, a little time to allow the precipitate sinking, with medium-speed filter paper to wash the precipitate 5-6 times with water, the test solution was discarded,