To determine effective diffusivity of a solute in a gel by the thin disk method, what configuration does the apparatus use?

Introduction:
Effective diffusivity in gels is a key parameter for predicting mass transfer within immobilized enzyme matrices and cell-laden hydrogels. The thin disk method provides a straightforward way to estimate diffusivity by monitoring solute transport across a defined gel thickness.

Given Data / Assumptions:

• The gel acts as a stationary diffusion barrier.
• Two well-mixed liquid compartments are separated by the gel disk.
• Concentration gradient across the gel drives diffusion.

Concept / Approach:
By mounting a thin gel disk between two compartments of a diffusion cell, one can follow the time course of solute appearance in the receiving side. Using mass balance and Fick's law for one-dimensional diffusion through a slab, effective diffusivity is back-calculated from the measured flux and known gel thickness and area.

Step-by-Step Solution:

Verification / Alternative check:
Repeat measurements at different gel thicknesses; calculated diffusivities should be consistent if assumptions hold (no gel swelling, isothermal conditions, negligible partition resistance).

Why Other Options Are Wrong:

• Options b–d omit or garble the essential feature: the compartments are divided by a thin gel slab that controls diffusion.

Common Pitfalls:
Edge leakage around the gel disk leads to overestimation of diffusivity. Ensure tight sealing and verify uniform gel thickness.

Final Answer:
a diffusion cell with two compartments divided by a thin gel