Study on the analogy of gel permeation chromatography and cuprophan dialysis for the isolation of uremic 'middle molecules' using model compounds

Selectives of substituted nitrobenzens in gel permeation chromatography and cuprophan membrane dialysis were compared. Glucuronide-, glucoside-, acetic acid- and lactoside-substituted p-nitrobenzens were chosen as model compounds so-called ‘middle molecules’ in uremia. It was found that there was not a single linear relationship between the substituent effects in both processes. This was because of the anomalous behaviour of the model compounds in gel permeation. A combination of adsorption and ionic rejection in the latter technique, for the various solutes, was not encountered in cuprophan membrane dialysis, which appeared to be governed only by the molecular mass or volume of the solute. Therefore, gel permeation seems to be inappropriate for the analysis or isolation of so-called middle molecules in sera of uremic patients. Dialysis or filtration on relatively inert membranes is less susceptible to anomalies.