What solute won't leak through dialysis tubing

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In summary, when using dialysis tubing with a molecular weight cutoff of 12,000 to 14,000 MW and a sugar solution to demonstrate osmosis, it was observed that the sugar began to leak through the membrane after a few hours. To avoid this, a solute with a larger molecular weight, such as a high MW polymer like PEG 20k, may be used instead. The leakage may be caused by a siphoning effect from gravity and the solution clinging to the membrane, but there is no significant loss of solution. The use of table sugar, with a molecular weight of 342 Da, may not be effective as it is much smaller than the MWCO of the membrane. Moving the membrane and observing changes
  • #1
I purchased dialysis tubing from carolina medical supplies with a molecular weight cutoff of 12,000 to 14,000 MW. I've been using a sugar solution to demonstrate osmosis but I've noticed that if I leave it alone for an hour or two the sugar begins to leak through the membrane. Is there anything else I could use instead of sugar that wouldn't leach out while still being a good solute to demonstrate osmosis and osmotic pressure?
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  • #2
Is the solution more so clinging to the membrane than leaking/pouring out? I think there is a slight siphoning effect seen which is caused by gravity; the clinging or gathering of solution can sometimes plug pores and flow back into the membrane after a while. There is no real loss of solution if it is still clinging to the membrane. Have you measured the real loss, or are you going by appearance?
  • #3
12,000 to 14,000 MW cut off means that molecules smaller than 12,000-14,000 Da will be able to pass through the membrane. Most sugars are well below this cutoff (e.g. table sugar [sucrose] is 342 Da). You would need to use some type of molecule (likely some type of polymer) with a molecular weight much greater than 14 kDa (the general guideline if you don't want your molecule to escape is to use a MWCO that is one third of the size of your macromolecule). For your purposes, something like a solution of PEG 20k or some other high MW polymer might work.
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I know it's leaking out because if I move the membrane I can see the sugar in the water (it distorts the light since it makes some of the water denser) and using a lot of table sugar changes the color of the water and when I wait longer I can see the fresh water starts to change color too. And yeah, it's strange because it does take a while to flow through (much less than the water) so I'm assuming it might be the water molecules clinging too it that makes the sugar in affect bigger when they're dissolved but still small enough to slowly make it through the membrane
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Related to What solute won't leak through dialysis tubing

1. What is dialysis tubing?

Dialysis tubing is a semi-permeable membrane made from regenerated cellulose that is used in processes like dialysis and osmosis to separate molecules based on their size and charge.

2. Why is it important to use dialysis tubing in experiments?

Using dialysis tubing allows us to control the movement of certain molecules in a solution, allowing for separation and analysis. This is especially useful in experiments where we want to isolate a specific molecule or measure the rate of diffusion.

3. What types of molecules can pass through dialysis tubing?

Small molecules such as water, ions, and small proteins can pass through dialysis tubing. The exact size of the molecule that can pass through will depend on the pore size of the tubing being used.

4. Can all solutes pass through dialysis tubing?

No, not all solutes can pass through dialysis tubing. The membrane is selectively permeable, meaning it only allows certain molecules to pass through based on their size and charge. Larger molecules such as proteins and nucleic acids will not be able to pass through.

5. What solute won't leak through dialysis tubing?

Most solutes with a molecular weight greater than 10,000 Daltons will not be able to pass through dialysis tubing. This includes large proteins, nucleic acids, and other macromolecules. Smaller molecules such as ions and small proteins may still be able to pass through depending on the pore size of the tubing.

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