Surface modification of porous graphite for ion exchange chromatography

Three distinct types of weak anion exchanger have been prepared by adsorption of polyethyleneimine (PEI) on to porous graphite (PGC): PGC coated dynamically with PEI, PGC coated with. an insoluble monolayer of PEI, and PGC coated with a cross-linked polymeric PEI. Using model solutes iodate, bromide, nitrate and nitrite, dissolved in aqueous buffers, the modified PGC's show typical ion exchange behaviour, and give chromatographic performance similar to that of bonded ion-exchange silica gels. Retention is reduced by increasing the ionic strength of the buffer, and by increasing the pH. A mechanism to explain the observed trends is presented.