| Abstract: | Eighteen ultrafiltration membranes ranging in molecular weight cutoff ratings from 500 to 300,000 were tested with water, 0.5M NaCl solution, and, in some cases, with macromolecules and urea in a 3-in. stirred filter cell. Approximately half of the membranes showed a significant decrease in filtration rate during the first 24-hr period. The steady-state rates were less than the manufacturers' rating for about two thirds of the membranes, the discrepancy being greater for the membranes with high molecular weight cutoffs. The filtration rates were linearly dependent on applied pressure over the range at least as great as 15 to 55 psig. The rate decreased as the concentration of macromolecules such as transfer ribonucleic acid (tRNA) increased; the rate for a concentration of 3 mg tRNA/per ml was one-fourth of that observed when no tRNA was present. Some increase in rate (～33 to 50%) was obtained by increasing the stirring speed from 100 rpm to 1000 rpm. The membranes were effective for desalting and concentration of macromolecules but not for separation of large molecules from each other, such as tRNA from bovine serum albumin. Easily denatured molecules such as catalase were not deactivated by filtration at 4°C. |
