Cellmax artifical capillary cell culture system.

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Next Subject		 Membramedsu2001-04-18Click here to register.
i want serine molecules to go through the dialysis Membrane Spectra/Por 12000-14000(MWCO), since the MW of serine is 109.5 which is much less than the specification12000-14000, why i can't find any difference of conductivity after 5 hours dialysis.

Thanks for your answer!


Best Regards

Dong SU
 
Re: Membrame
jpartee2001-04-19Click here to register.
There are several problems that might be occurring with your experiment.

Dialysis bags separate by molecular weight, and if the lone molecule that exists in the solution is of a lower molecular weight than the pores, it will pass.

There are several possibilities that can cause your dialysis procedure not to work.

The main problem is when a molecule binds or aggregates to other molecules making a larger structure.  This frequently happens with certain dyes and some proteins. 

Another problem is that serine might be binding to the Regenerated Cellulose itself.  This rarely happens because RC is usually non-reactive.  It normally occurs (rarely) with highly charged particles that repel themselves from the minor charge that exists in the membrane.

The third and somewhat unusual problem is a when the "osmotic" pressure from the outside of the bag is higher than the inside.  This will result in the buffer flowing into the bag and expanding it to a rather large and rigid state. Of course, your test solution will not flow out since the pressure is causing the solution to move in the opposite direction. In order for dialysis to occur, the buffer and test solution should contain the same base solvents.  Ideally, the only difference in the test solution and the buffer is that the buffer will lack the molecule you want to get rid of, I.E. salt.

In cases of buffer exchange, you will want to use buffers of similar density.  I.E. water and ETOH are close.  Make sure that you leave plenty of airspace in the bag when doing a buffer exchange, the solution will want to equilibrate and this means that the dialysis bag will swell somewhat. 

For note, if you dialyzing and the bag swells to the hardness of a sausage, you need to leave more airspace so the solution can equalize with the buffer.  The bag can break if it swells to much.

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