The ability of a variety of nanofiltration and reverse osmosis membranes to retain the naturaludhormone estrone are examined here as a function of solution conditions. While size exclusionuddominates retention with the tighter membranes, both size exclusion and adsorptive effects appearudto be instrumental in maintaining high retention on nanofiltration membranes that otherwise exhibitudrelatively low ion retentions. These adsorptive effects may be driven by hydrogen bonding betweenudestrone and the membrane. Electrostatic attraction appears to aid retention with an apparent slightuddecrease in retention at high NaCl concentrations. Deprotonation of estrone leads to a significantuddecrease in retention, most likely as a result of the effect of strong electrostatic repulsive forcesuddecreasing the proximity of the negatively charged estrone to the negatively charged membraneudsurface and thus lowering the potential for adsorptive retention. This deprotonation effect is absentudfor tight RO membranes. The results reported here indicate that while open nanofiltrationudmembranes may be effective in retaining estrone under some conditions, the extent of retention mayudbe very susceptible to maintenance of adsorptive capacity at the membrane surface and depend onudsolution chemistry.
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