Ultrafiltration behavior of selected pharmaceuticals on natural and synthetic membranes in the presence of humic-rich hydrocolloids.

The separation behavior of the frequently administered pharmaceuticals sulfamethoxazol (Sulfa), carbamazepine (Carba), diclofenac (Diclo), and ibuprofen (Ibu) on different natural and synthetic ultrafiltration membranes was studied. Commercially available cattle intestine natural membranes (NM), polyethersulfone (PES), and regenerated cellulose-based (RC) flat membranes (nominal cut-off 1 kDa) have been investigated as ultrafiltration membranes in a small tangential-flow ultrafiltration unit (TF-UF). First, the nominal cut-off of the NM membranes under study was assessed at approximately 5 kDa, by using polystyrenesulfonate standards for pore-size classification at low TF-UF pressure (0.25 x 10(5) Pa). Working pressures of >1.5 x 10(5) Pa strongly increased the cut-off of NM, in contrast with that of PES and RC membranes. Sulfa, Carba, Diclo and Ibu (1 mg L(-1) each) in colloid-free aqueous solutions (400 mg L(-1) NaCl) completely permeated through NM membranes, but less through PES and RC, which had particular sorption capability towards Diclo. The drugs were routinely determined by using high-performance liquid chromatography (HPLC). Detailed TF-UF investigation of drug retention on NM in the presence of humic hydrocolloids revealed strong interactions between aquatic humic substances (HS) and Diclo and Ibu (but not with Sulfa and Carba) causing retention of up to 80% of Diclo and Ibu, probably because of their binding to macromolecular HS. The standard deviation (SD) of both drug and HS permeation through a single NM was between 2.5 (Sulfa) and 4.0% (Diclo), in contrast with the SD of permeation through separate membranes taken from different lots [SD up to 14.0% (Diclo)], presumably caused by natural variation of the studied NM. Accordingly, membrane filtration of drug-containing water samples on cattle intestines enables both analyte/matrix separations for Carba and Sulfa in the presence of humic colloids and analytical discrimination between free and colloid-bound Diclo and Ibu fractions.