Abstract:

A rapid and accurate method using polymer complexation ultra-filtration(PC-UF) technique and inductively coupled plasma mass spectrometry(ICP-MS) for the measurement of the complexation stability constant 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.

Key words: Poly(ethylenimine), Complexation stability constant, Coordinating number, Ultrafiltration technique, Inductively coupled plasma mass spectrometry