Cellmax artifical capillary cell culture system.

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Next Subject		 dialysis ratesrthrift2001-02-07Click here to register.
Can you show me how to estimate the flow of a solute across a dialysis membrane? (or can you just tell me the answer for a real case like the one I will describe?) I am calculating based on Ficke's law, F (flow) = -D(dC/dx) The solute is sparingly soluble, so the water inside the membrane is always saturated (only about 80 nanograms/mL for one compound of MW 500 daltons) as long as there is some of the compound still there undissolved. (The low solubility is the source of the problem.) Assume a sink outside the membrane, so the concentration is zero outside. Assuming the membrane is 10 microns thick (?), completely porous, dC/dX ~ 8000000 ng/cm^4. I figure the diffusion constant must be ~ 30 cm^2/sec, so F~ 2 mg/cm^2/day. Is this reasonable assuming good stirring, I mean how close is this to reflecting reality? Are there corrections for how much of the membrane is solid, not porous?

Thanks very much
Richard
 
RE: dialysis rates
rthrift2001-02-07Click here to register.
(Actually I meant the diffusion constant D ~30 x 10^-7 cm^2/sec) (since that of sucrose, MW 342, is 46x10^-7cm^2/sec)
 
RE: dialysis rates
lil stevie2001-02-08Click here to register.
Generally diffusion in dialysis membranes is significanly slower than in solution by a factor of at least 2 to 10. This depends on the batch the membrane is from as well as the membrane's MWCO and how close the size of the solute is to the size of the membranes pores.

Since you'll have a very dilute solution of a marginally soluble material you may also lose some material to the membrane surface (depending upon whether it's more soluble in water or in wet cellulose).

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