Inexpensive Dialysis Method

Dialysis- Inexpensive Method

Dialysis is a technique that uses a porous membrane to move small enough solutes (micro or nano size) from an area of high concentration to an area of low concentration.  I used this technique in lab to remove ammonium hydroxide, acetic acid, or excess and unwanted dye from a sample.  There are many dialysis techniques, and the one I used is shown in the picture on the right. A mixture was placed in a small micro-centrifuge tube with a small hole on the lid, then a small square of dialysis membrane was cut and placed on the micro-centrifuge tube in between the lid, and was held tight after the lid was closed.  The hole on the lid will allow small solutes like ammonium hydroxide to pass through the porous membrane while keeping the sample in the tube.  The micro-centrifuge tube was then placed in a beaker containing solution of choice.  In my case, I wanted my sample of interest to stay in 95% ethanol, therefore I had a beaker full of 95% ethanol.  The tubes were then left to stir overnight, and within this time frame, solutes would move through the membrane out into the solution in the beaker (95% ethanol).  I found this specific dialysis technique to be less expensive compared to using a dialysis membrane bag,  this is because it uses less membrane, and the membrane itself is very expensive.  I also like this technique because after dialysis, I am able to safely remove all of my sample, compared to when using only a membrane bag where the sample usually gets trapped in the corners of the bag. Loosing sample can be an issue when your sample is pure, expensive or if present in a small amount.

The purpose of using dialysis, was to completely remove ammonium hydroxide.  To test the presence of ammonium hydroxide, I added copper nitrate to a tiny amount of my sample.  If after adding copper nitrate, my dialyzed solution turned purple, then ammonium hydroxide is still present. Dialyzing the same sample for a few more hours should remove the left over ammonium hydroxide.  But if after adding copper nitrate, the dialyzed sample turned cyan blue, then all the ammonium hydroxide was removed successfully.

Citations:
Zeelen, Johan. Dialysis of small volumes. Photograph. 01/22/04. http://www.xtal-protocols.de/prot/protein.html. Access: 09/09/13