不经分离、高敏、连续光度滴定混合物中钕和铁

Highly Sensitive,Sequential Photometric Titration of Iron and Neodymium without Separation

提出以Ｆｅ（３＋）（Ｎｄ（３＋）－ＣＡＳ－ＣＰＢ－Ｃ２Ｈ５ＯＨ作为不经分离、高敏、连续光度配合滴定混合物中Ｆｅ（３＋）和Ｎｄ（３＋）的多元胶束配合指示体系。滴定Ｆｅ（３＋）和Ｎｄ（３＋）的适宜ｐＨ分别为２．３～３．２和６．０～８．６。用ＥＤＴＡ目视滴定Ｆｅ（３＋）时，终点处由蓝紫变粉红色，对比度大（Δλ＝１３０ｎｍ）、灵敏度高（配合物摩尔吸光系数ε（６３０）＝１．１４×１０５Ｌ·ｃｍ（－１）·ｍｏｌ（－１），至少可检测０．４μｇ／ｍＬ，滴定线性范围为０～２．８μｇ／ｍＬ。线性相关系数为０．９９９４；目视滴定Ｎｄ（３＋）时，终点处由绿色变橙黄，Δλ＞１８０ｎｍ，ε（６３０）＝７．６×１０４，至少可检测１μｇ／ｍＬ，滴定线性范围０～３．７μｇ／ｍＬ，线性相关系数０．９９９４。对于铁钕硼混合物样品则不经分离在６３０ｎｍ处连续光度滴定，可更精密、高敏、准确地确定终点，变异系数１．７６％～２．８６％，标准加入回收率９６％～１０４％，且简便、快速。

A sequential photometric titration method for the determination of iron(Ⅲ) and neodymium(Ⅲ) is described with EDTA as the titrant and with Chrome Azuol S(CAS) and cetyl pyridium bromide(CPB)-ethanol as a micellar coordination indicator system,i.e.,a multi-component metallochromic indicator.The suitable PH ranges for iron and neodymium are 2.3～3.2 and 6.0～8.6,respectively.For the visual titration of iron(Ⅲ),the end-point color change is from blue-violet to pink.Its contrastΔλequals to 130 nm.Its molar absorptivity ε(630) is 1.14×105L·mol-1·cm-1,while the linear range is 0～2.4 μg/mL with a correlation coefficient of 0.9994.On the other hand,the color change for neodymium titration is from green to orange-yellow.Its contrast Δλis greater than 180 nm. Its molar absorptivity ε(630)is 7.6×104L·mol-1·cm-1,while the linear range is 0～3.7μg/mL with a correlation coefficient of 0.9994.The method has been successfully applied to the analysis of synthetic samples of iron,neodymium and boron without separation. The relative standard deviations for Fe(Ⅲ) and Nd(Ⅲ) are 1.76% and 2.86%, respectively.The recoveries are 96%～104%.