Mechanism of creatinine adsorption from physiological solutions onto mordenite

Mordenite framework type zeolites with different Si/Al ratios and H+ as charge compensating cation were found to be specific adsorbents for creatinine. Adsorption isotherms were determined varying the composition of the solvent systematically from pure water to physiological buffered saline solutions containing albumin. The adsorption mechanism is studied using different experiments: by following pH, ionic exchange and adsorption enthalpies during the adsorption process and by analyzing ex situ the chemical form of the adsorbate by 13C MAS-NMR. It is shown that creatinine adsorption, which is the highest when adsorbed from pure water, is reduced when adsorbed from sodium chloride solution or from physiological buffered saline solutions.Once adsorbed, creatinine is present in protonated form within the zeolite, in equilibrium with other cations of the medium. The level of this chemisorption is higher than the one determined in case of carbon type samples. When albumin is added to the physiological buffered saline solutions, adsorption level is only slightly modified, indicating that the weak albumin adsorption observed on the external surface of zeolite particles does not prevent creatinine access to the micropores. Adsorption by zeolites could, thus, be a complementary method for uremic toxins elimination during haemodialysis.