Characterization of Thin Film Poly (vinyl alcohol) Hydrogels with Different Immobilized Ligand Groups

Fourier Transform Infrared Spectroscopy (FTIR) and Atomic Absorption Spectroscopy (AAS) were used to characterize immobilized metal affinity (IMA) hydrogel membranes functionalized with different immobilized chelating ligand groups. In this study, poly (vinyl alcohol) (PVA) membranes were prepared and functionalized with a spacing element, butane diol (diglycidyl ether) (BDE), grafted to a chelating ligand group such as N-(2-hydroxyethyl) ethylenediamine N-N’-N’- triacetic acid (HEDT), nitrilotriacetic acid (NTA), and iminodiacetic acid (IDA) and a divalent metal ion (Cu2+ or Ni 2+). The transport properties of the IMA membranes functionalized with different chelating ligands were determined at different operating conditions.   Additionally, FTIR showed the different characteristic adsorption frequency between the bond vibrations of the functional groups after membrane synthesis. The resulting spectra showed different band frequencies in certain regions between the ranges of 1100-1150, 1550-1650, and 2900-3000 cm­^-1 from the specific group behavior such as hydroxyl, acetate, amine, and carboxyl groups associated with PVA cross-linked with glutaraldehyde. These results showed that cross-linking had occurred with the change in chemical structure of the hydrogel. The data also implied that few differences occur in the hydrogels’ structure when the chelators are attached. Elemental analysis using the AAS indicated that all synthesized hydrogels bound at least 4mg of metal (Cu or Ni) per gram of membrane which is sufficient for protein separation. The equilibrium swelling of hydrogels in water and different buffers with varying pH values (5, 6.5, 8) were similar, which suggests that that the solution environment for each IMA membrane characterized was similar. Additionally, sorption isotherms for the IMA membranes functionalized with different chelators were generated for a model protein, chicken egg white lysozyme (CEWL) at varying pHs in control and affinity membranes.