Molecules of a drug move through a polymer membrane and into blood that flows ne

Question

Molecules of a drug move through a polymer membrane and into blood that flows next to the membrane.

a. What kind of mass transfer (molecular diffusion, or convection) occurs in the polymer, and which occurs in the blood phase?

b. If the mass transfer inside th epolymer represents the limiting resistance, how would each of the following affect the overall rate of mass transfer? In each case, explain your answer. i. increase the flow rate of blood. ii. modify the drug to decrease its molecular size.

Explanation / Answer

a. Since the mass transfer occurs accross a polymer membrane it takes place through molecular diffusion while in case of the blood phase mass transfer occurs through convection.

b. (i) As the rate limiting step is the limiting resistance of the epolymer so an increase in the blood flow rate would have no effect of the overall rate of mass transfer i.e. the flow of blood contributes in no way to an increased or decrased mass transfer.

(ii) If the drug molecular size is decreased then the diffusion of the drug throught the polymer membrane would be easier and less hindered thus resulting in faster and larger number of drug molecule to pass throught the membrane to the blood phase helping in the increasing the overall mass transfer rate.

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