CHARACTERIZATION OF HEMODIALYSIS MEMBRANES BY INVERSE SIZE-EXCLUSION CHROMATOGRAPHY

Inverse size exclusion chromatography (i-SEC) was used to characterize three different cellulosic hollow fiber hemodialysis membranes, i.e. low-flux cuprophan and hemophan and high-flux RC-HP400A. With the i-SE C technique the pore size distribution and porosity of a membrane can be determined and adsorption phenomena can be studied. The membranes s howed clear differences in pore size and porosity, the high-flux RC-HP 400A membrane has a larger pore size as well as a higher porosity. For all the membranes it was found that the elution curves were best desc ribed by a homoporous pore volume distribution. It appeared that the b ound or non-freezing water in the membranes was at least partly access ible to solutes. The test molecules creatinine and vitamin B12 both ad sorbed to the cellulosic membranes. The adsorption behavior of creatin ine was strongly dependent on the NaCl concentration present. The obse rvations could be explained by assuming that cuprophan and RC-HP400A a re negatively charged whereas hemophan is positively charged due to th e modification with N,N-diethylaminoethyl ether. The net charge of the hemophan is smaller.