Dialysis
Science often uses dialysis for the purpose of filtration by exploiting the principals of diffusion and an object's (or objects') particular size. In this exercise we extracted salt from a sample using MWCO 6,000-8,000 dialysis tubing.
Purpose: Demonstrate effectiveness of dialysis for filtration.
Materials:
Gloves
Dialysis Clamps
Dialysis Tubing (Spectral Por (16mM diameter 12-14000 MWCO, Fisher Lot 08-667B)
Conductivity Meter
Stir Plate/Stir Bar
10X PBS (by: CM 9/11/12)
50mL Conical Tube
1000 mL Beaker
5mL Pipette
diH2O
Timer (SN 11178883 WWR)
Procedure:
- Gathered materials and soaked tubing in beaker of diH2O for approximately 5 minutes.
- Used 5mL pipette and pipette aid to open tubing and separate to make sure soaking was effective.
- Folded over the end and then clamped the end of the tubing shut and tested to make sure it wasn't sliding. Then used new 5mL pipette to add 5mL of 10xPBS to dialysis tube. Then folded over and clamped the other end shut.
- Replaced the dialysis tubing with the sample in the beaker of 1000mL diH2O. (To have been exceptionally accurate, we should have measured the diH2O with a graduated cylinder before adding to beaker and dropping sample in the beaker.
- Added stir bar to beaker, placed beaker on stir plate and set stir plate at level 1.
- Set timer for 45 minutes.
- Set up a 2nd beaker with diH2O and switched the beakers out after 45 minutes of dialysis. Saved 1st beaker for conductivity measurement. Measured: 1654 microSeamans
- Pour transferred the sample from the tubing into a 15mL conical tube.
- Measured 2nd beaker's conductivity: 188.2 microSeamans. Measured conductivity of sample: 2.98mS.
Observations and Results:
The salt concentration in the 10xPBS was supposed to be so high that you could see it (through water distortion) coming out of the tubing into the water, but I didn't see that happen.
The size of the class is probably the reason why we didn't do this, but it would have been nice to measure the beaker water before, twice during, and then after the dialysis at 10 minute increments so we could see how the dialysis slows down when the concentration gradient levels off, then speeds up again as the new beaker is put in place because the concentration gradient is steepened.
Conclusion:
The rate of extraction is directly proportional to the difference in concentration gradient. The bigger the difference between the sample and the solution the faster the dialysis will go to make the two environments isotonic.