电位滴定法测定乙醛肟的含量

Determination of Acetaldoxime by Potentiometric Titration

用比色法测定乙醛肟中 Ｆｅ３ ＋ 的干扰问题，提出了测定乙醛肟的电位滴定新方法。乙醛肟水解产物羟胺先将过量 Ｆｅ３ ＋ 部分地还原为 Ｆｅ２ ＋ ，然后用 Ｋ２ Ｃｒ２ Ｏ７ 标准溶液对 Ｆｅ２ ＋ 进行滴定，可间接地测得乙醛肟的含量。在电位滴定法测定乙醛肟时，不存在 Ｆｅ３ ＋ 的干扰问题，其平均回收 率为９９ ．６２ ％ （ ｎ ＝ ９ ， Ｒ Ｓ Ｄ＝ ０ ．１ ％ ） 。取适量乙醛肟标准溶液或样 品溶液（ 约 含１ ｇ 乙醛肟） 于 ２５０ ｍ Ｌ 烧杯中，分 别加入０ ．２ｍ ｏｌ／ Ｌ Ｈ Ｃｌ 溶液２０ ｍ Ｌ，０ ．０１ ｍ ｏｌ／ Ｌ Ｆｅ３ ＋ 溶液２０ ｍ Ｌ，在沸水浴中加热１０ ｍｉｎ ，冷却至室温后，再加入０ ．６ｍ ｏｌ／ Ｌ Ｈ３ Ｐ Ｏ４ 溶液２ ｍ Ｌ，最后用 Ｋ２ Ｃｒ２ Ｏ７ 标准溶液进行电位滴定。该方法具有准确度 和重现性都较好，操作又特别简便的优点。

Several spectrophotometric determination methods have been used for determination of acetaldoxime. In those methods, the interference from Fe 3+ is a common problem. In this paper, acetaldoxime is determined by potentiometric titration. Hydroxylamine(the hydrolysate of acetaldoxime) reduces Fe 3+ into Fe 2+ partly, then Fe 2+ is titrated with K 2Cr 2O 7 standard solution. Finally, the content of acetaldoxime is computed indirectly. There is no any interference from Fe 3+ in the new method. The recovery of acetaldoxime in the proposed method is 99.62%( n =9, RSD=0.1%). Pipette standard solution or sample solution containing about 1 g of acetaldoxime into 250 mL beaker. Add 20 mL of HCl stock solution(0.2 mol/L) and 20 mL of Fe 3+ stock solution(0.01 mol/L), and heat in boiling water bath for 10 min. Remove the beaker from water bath, let the solution cool to ambient temperature. Add 2 mL of H 3PO 4 stock solution(0.6 mol/L), and titrate with K 2Cr 2O 7 standard solution as the titrant. The results are satisfied.