配位滴定中铬黑T蓝绿色现象探究  

Exploration of the Blue Green Phenomenon of Eriochrome Black T in Coordination Titration

作　　者：胡亚兰 刘素梅 陈怀侠[1] HU Ya-Lan;LIU Su-Mei;CHEN Huai-Xia(College of Chemistry and Chemical Engineering,Hubei University,Wuhan 430062,China)

机构地区：[1]湖北大学化学化工学院,湖北武汉430062

出　　处：《化学教育（中英文）》2024年第12期112-116,共5页Chinese Journal of Chemical Education

基　　金：分析化学国家一流课程建设项目;湖北省名师工作室建设项目;湖北大学研究生教育教学改革研究项目(JGYJS202305)。

摘　　要：研究了铬黑T(EBT)为指示剂的配位滴定法中,滴定终点后出现的蓝绿色现象的原因。溶液pH测定表明,氨性缓冲溶液保持了滴定过程中溶液酸度的稳定性,pH的微小变化,并不能导致溶液出现蓝绿色。吸收光谱分析表明,过量的乙二胺四乙酸二钠盐(EDTA)使EBT在黄光575 nm处吸收减弱,而在红光622 nm和664 nm处吸收增强,从而出现红光互补的蓝绿色。反相高效液相色谱分析显示,过量EDTA使EBT保留时间延长,说明EDTA降低了EBT极性。甲醇不会改变EBT的不同颜色,十六烷基三甲基氯化铵使不同颜色EBT均呈现蓝绿色。据此推测,氨性缓冲溶液中EDTA分子正电荷基团≡NH^(+)与EBT分子的负电荷基团—SO_(3)^(-)或—O^(-)发生静电作用,同时,EBT酚羟基可能与EDTA的—N—或—COO^(-)形成氢键,导致EBT吸收光谱和液相色谱保留时间改变。因此推测,EDTA与EBT之间的静电及氢键作用使EBT出现蓝绿色。The blue-green phenomenon in the coordination titration using eriochrome black T(EBT)as the indicator was investigated.The pH measurement results indicated that the ammonia buffer solution maintained the stability of the solution acidity during the titration process.The slight change of pH did not cause the solution to appear blue-green.The absorption spectrum analysis showed that excessive ethylene diamine tetraacetic acid disodium salt(EDTA)affected the absorption spectrum of EBT,reduced the absorption of EBT at yellow light 575 nm and enhanced the absorption at red light 622 nm and 664 nm.Thus,blue-green with complementary red light appeared.Reversed phase high performance liquid chromatography analysis demonstrated that excessive EDTA prolonged the retention time of EBT,which shown that EDTA reduced the polarity of EBT.Methanol did not alter the different colors of EBT.Hexadecyltrimethylammonium chloride causes different colors of EBT to appear blue-green.It can be inferred that in ammonia buffer solution,static electricity occurred between the positively charged group≡NH^(+)in EDTA and the negatively charged group—SO_(3)^(-)or—O^(-)in EBT,and EBT phenolic hydroxyl group may form hydrogen bonds with —N— or —COO^(-)of EDTA,resulting to the changes of absorption spectrum and HPLC retention of EBT.As a result,the electrostatic and hydrogen bonds between EDTA and EBT may be the nature of blue-gren phenomenon.

关 键 词：配位滴定法 铬黑T 蓝绿色 吸收曲线 高效液相色谱 

分 类 号：O655.2[理学—分析化学]