主题：【已应助】USP滴定液

原文由 深海的海豚(lqqer) 发表:
遇到了一个USP方法，测定含量，原文和译文如下：请大家帮忙看一下翻译是否准确，另外红色字体是否指0.05mol/L硫酸铁铵滴定液，USP药典我不会查，网上搜了一下也没有找到相关内容，不知道相关滴定液在哪里能找到，如何配制和标定呢？谢谢！

原文如下：

Assay— Transfer about 200 mg of Pentetic Acid, accurately weighed, to a 125-mL conical flask, add 50 mL of water and 1.5 mL of 1 N sodium hydroxide, and swirl to dissolve the specimen. Add 10 mL of 0.1 N ammonium thiocyanate, and mix. Add about 40 mL of methyl ethyl ketone, mix, and allow the layers to separate. Titrate with 0.05 N ferric ammonium sulfate VS, stirring continuously. As the titration proceeds, the aqueous phase turns from colorless to yellow, and the organic phase remains colorless. As the endpoint is approached, stop the titration, mix, and allow the layers to separate. Add 0.1-mL increments of 0.05 N ferric ammonium sulfate VS, mixing and allowing the layers to separate after each addition, until the organic layer turns from colorless to pink. Each mL of 0.05 N ferric ammonium sulfate consumed is equivalent to 19.668 mg of C₁₄H₂₃N₃O₁₀.

译文：

含量—精密称定200mg喷替酸至125ml锥形瓶中，加入50ml水和1.5ml 1mol/L的氢氧化钠溶液，搅拌溶解样品。加入10ml 0.1mol/L硫氰酸铵溶液，混匀。加入40ml甲基乙基酮，摇匀，并且分层。用0.05mol/L硫酸铁铵滴定液进行滴定，并持续搅拌。随着滴定的进行，水相从无色到黄色，有机相保持无色。接近滴定终点时，停止滴定，摇匀，静置分层。持续加入0.05mol/L硫酸铁铵滴定液，每次加入0.1ml，摇匀，每次滴加后静置分层，直至有机相从无色到粉红色。每毫升0.05mol/L硫酸铁铵的用量相当于19.668mg 的C₁₄H₂₃N₃O_{10 。}

原文由 happyjyl(happyjyl) 发表:

ferric ammonium sulfate是硫酸铁铵，VS是指滴定液（volumetric solutions）。

N在USP里指normal solutions，你说的mol/L在USP里指molar solutions。二者的定义见下：
http://www.pharmacopeia.cn/v29240/usp29nf24s0_volumetric-solutions-1345-1360.html
对有些溶液来说1N即1mol/L，对硫酸铁铵溶液来说是否如此我就不知道了。我化学不好，你问问别人吧。

USP里有专门的章节介绍如何配制滴定液，详见VOLUME 1的Reagents, Indicators, and Solutions里Volumetric Solutions。我手头没有USP，哪位网友有的话上传一下吧。

原文由 影子(hyheying) 发表:
药典上只有0.1N的，0.05N的在这个基础上称样量减半配制再标定就可以了：
Ferric Ammonium Sulfate, Tenth-Normal (0.1 N)

FeNH4(SO4)2·12H2O, 482.19

48.22 g in 1000 mL

Dissolve 50 g of ferric ammonium sulfate in a mixture of 300 mL of water and 6 mL of sulfuric acid, dilute with water to 1000 mL, and mix. Standardize the solution as follows.

Accurately measure about 40 mL of the solution into a glass-stoppered flask, add 5 mL of hydrochloric acid, mix, and add a solution of 3 g of potassium iodide in 10 mL of water. Ins-ert the stopper, allow to stand for 10 minutes, then titrate the liberated iodine with 0.1 N sodium thiosulfate VS, adding 3 mL of starch TS as the endpoint is approached. Correct for a blank run on the same quantities of the same reagents.

Store in tight containers, pro-tected from light.