Ultrafiltration in an Unstirred Batch Cell
The ultrafiltration of bovine serum albumin (BSA) in .15 M NaCl (pH = 7.40) and .10 M sodium acetate (pH = 4.70) was investigated in an unstirred batch cell. Data were analyzed to minimize the effects of inter-membrane variations and other experimental errors. BSA systems were studied over a wide range of concentration (1–10 g/100cc) and at higher pressures than previously reported (150 psig). Results confirm that BSA does reach a pressure-independent flux region. A constant property integral method solution, which has the simplicity of the popular film theory model, compared quite well with the exact solution. Agreement between acquired BSA data and theoretical predictions is excellent, with the maximum error less than 3%. Not only is the assumption of constant diffusion coefficient shown to be reasonable for the unstirred batch cell, but also that the difference in the calculated value of the diffusion coefficient for BSA at pH = 4.70 and pH = 7.40 is small. This finding is further confirmed by separate diffusion coefficient determinations by ultracentrifuge technique. The values of Cgel as determined from ultrafiltration data are 37.0 g/100cc at pH 4.7 and 57.5 g/100cc at pH 7.4. These values correspond reasonably well to literature values.