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已知磷酸盐存在对鈣鎂的絡合滴定有干扰。根据柯里尔(R.E.Collier)报告,开始干扰时磷与阳离子的比值不一定,只能求得近似值。他用0.125M EDTA滴定70毫升溶液中含有0.1毫克鈣3毫克磷(卽P/Ca=30)时无干扰。他还报告,虽然磷酸鈣可沉淀,但滴定仍可进行,因为在加入EDTA时沉淀徐徐溶解。若有磷酸鎂存在,則能使終点提早出現。但在70毫升溶液中含有1毫克鎂和1毫克磷(卽P/Mg=1)时,仍可在加入氨-銨緩冲溶液后立即进行滴定。威尔孙(A.E.Willson)在絡合滴定叶片組織中鈣时发現正磷酸盐有干扰,P/Ca≥0.1;絡合滴定牛乳中鈣时磷酸盐也有干扰,P/Ca≥0.8。开奈(A.D.Kenney)与杜凡
Phosphate is known to interfere with the complexometric titration of calcium and magnesium. According to R.E.Collier’s report, the ratio of phosphorus to cation is not constant at the beginning of the disturbance and can only be approximated. He titrated with 0.125M EDTA 70 ml solution containing 0.1 mg of calcium 3 mg of phosphorus (卽 P / Ca = 30) without interference. He also reported that although calcium phosphate precipitates, the titration can still be performed because the precipitate slowly dissolves when EDTA is added. If there is magnesium phosphate, can make the end of early appearance. However, when 1 mg of magnesium and 1 mg of phosphorus (卽 P / Mg = 1) are contained in a 70 ml solution, the titration can still be performed immediately after the addition of the ammonia-ammonium buffer solution. A.E. Willson in the complexation titration of calcium in the leaf tissue found orthophosphate interference, P / Ca ≥ 0.1; complexation titration of calcium in milk phosphate also interfere with, P / Ca ≥ 0.8. A.D. Kenney and Du Fan