聚乙烯亚胺-金属络合物的稳定常数及配位数的测定

Measurement of Complexation Stability Constant and Coordinating Number of Poly (ethylenimine) with Metals

将聚合物络合超滤(PC-UF)技术与电感耦合等离子体质谱(ICP-MS)结合,利用化学理论计算模型,建立了测定聚乙烯亚胺(PEI)与金属离子络合稳定常数及平均配位数的方法.将该方法用于PEI与Cd2+的络合过程.配制不同浓度比的PEI和Cd2+的混合溶液,待络合反应平衡后,用超滤离心管离心分离高分子PEI-Cd络合物,自由离子Cd2+及其小分子络合物渗滤至滤液中;用10 mL体积分数为3%稀硝酸将滤膜上截留的PEI-Cd络合物解离,离心得到Cd2+的稀硝酸溶液;用ICP-MS分别测定2次超滤后滤液中Cd2+的浓度,利用化学理论模型进行计算,得到PEI-Cd络合物的稳定常数和平均配位数.pH=4.0～5.9时,PEI-Cd络合平衡的研究结果表明,稳定常数和平均配位数均随pH值的增大而增大,较低程度的质子化可使PEI与Cd2+的络合能力增强,络合稳定常数增大.

A rapid and accurate method using polymer inductively coupled plasma mass spectrometry（ICP-MS） complexation ultra-filtration （PC-UF） technique and for the measurement of the complexation stability con- stant and the average coordination number of poly （ethylenimine） （PEI） groups participating in the complex formation of PEI with metal ions was proposed. The method was applied to determine the stability constant and the average coordination number of PEI and Cd2＋ complex. Firstly the mixture of various initial concentration ratios of PEI and Cd2＋ solution were prepared, respectively, then the mixture reacted until the complexation equilibrium reached, and at last Cd2＋ and small components were permeated into the solution and PEI-Cd complex was hold back with centrifugal ultra-filtration kit. Then ultra-filtration followed was completed so as to decompose PEI-Cd complex and obtain Cd2＋ species using 10 mL 3% （volume fraction） HNO3. With the help of chemical model inferred in the study, the complexation stability constant and the average coordinating number of PEI-Cd could be calculated. Effect of pH value （ pH = 4. 0-5.9） on the equilibrium was investigated. The results showed that the complexation stability constant and the average coordinating number of PEI-Cd became larger as pH value increases. This may due to the protonation of PEI reduces as pH values increase, then the binding ability of PEI with metals become stronger.