Influence of ionic strength on membrane selectivity during the ultrafiltration of sulfated pentasaccharides

Due to their numerous biological properties, natural sulfated polysaccharides have attracted the interest of the food and pharmaceutical industries. Membrane processes were thought to be especially suitable for their production at industrial scale. The aim of this study was to evaluate the effect of sodium chloride, often used as a preservative and a precipitation adjuvant, on the ultrafiltration of sulfated pentasaccharides. In pure water, results showed a complete retention of the polymers on membranes with molecular weight cut-off up to eight times the molecular weight of the studied pentasaccharides. When NaCl was added to a concentration of 0.5 mol L(-1), retention rates decreased significantly (≈-50%). As no relevant modification of the molecules size was observed through hydrodynamic radius measurements, these variations of selectivity were fully attributed to the screening of membrane surface charges by the electrolyte. Therefore, optimising the ultrafiltration of charged molecules need absolutely exammining electrostatic interactions.