|  | Alternative Medicine | Apothecary

Iodine Diffusion Through Dialysis Tubing: Molecular Weight Cutoff and Permeability Explained

Dialysis Tubing Permeability

Dialysis tubing (e.g., regenerated cellulose) has a molecular weight cutoff (MWCO), typically 12,000-14,000 Da. Molecules smaller than the MWCO diffuse through; larger molecules are retained.

Iodine (I2) Molecular Weight

Iodine gas (I2) has a molecular weight of 253.8 g/mol (Da). This is far below the 12-14 kDa MWCO of standard dialysis tubing.

Conclusion: Iodine CAN Pass Through

Iodine molecules readily diffuse through dialysis tubing. The statement that dialysis tubing is "not permeable to iodine" is incorrect for standard tubing.

Common Confusion: Starch-Iodine Complex

In classic biology experiments (e.g., dialysis tubing with starch solution inside, iodine outside), iodine enters the tubing and reacts with starch to form a blue-black starch-iodine complex. The complex is too large to exit, so color change occurs inside the tubing. This demonstrates selective permeability: small molecules (iodine, water) pass; macromolecules (starch) are retained.

Practical Implications

  • For iodine removal/purification, use activated charcoal or ion exchange, not dialysis.
  • For separating iodine from macromolecules, dialysis works well.
  • Always check MWCO specifications for your specific tubing.

Apothecary - Related Articles