Preparing your own thin layer chromatography plates (and then using them)

tlc-buatan

Image Notes

1.These were made with lab grade silica gel, on glass slides, with plaster of paris as the binder

2.  These were made with silica gel from dessicator packets, prepared in the same way as above but with less suspension to work with (hence the gaps near the edge)

step 1: Gather the materials

First off you need some basic supplies:

  1. an oven, generally comes with houses
  2. a weigh scale, nothing too fancy should be accurate to one tenth of a gram, e.g This digital scale from Amazon an old plastic bottle you don’t care about, not too large (I used a 150mL one)
  3. a pan, for resting the plates on and for putting in the oven.
  4. a mortar and pestle, larger ones are easier to work with than smaller ones
  5. a syringe, 10cc minimum, plastic works fine, I got mine from Home Depot
  6. glass slides, you can also use sheets of tin or plastic, basically anything stiff that won’t interact with water

Then you need your “chemicals” for preparing the slides:

  1.  Anhydrous Calcium Sulfate, a.k.a. Plaster of Paris, I liberated mine from an artsy friend
  2. Water, from the tap, or distilled if impurities are an issue
  3. Silica Gel – This is the desiccant in those little packets you find in medicine bottles and assorted what-nots.

 Note: Silica Gel is hygroscopic, and its fine particles can be harmful if inhaled. It is not a bad idea to wear gloves and a mask while grinding this stuff.

step 2: Weigh out and mix the silica gel and plaster of paris

The plaster of paris is the binder and is present only to keep the silica from sloughing off the glass slides. I have found 10-20% (by weight) plaster of paris in the final mix works well.

For this project, weigh out:

  •  1.0g plaster of paris
  • 4.0g silica gel (ground)

Combine these in the mortar and pestle and grind together very well. The mixture should be very homogeneous and the finer the particles the better the separation.

step 3: Suspend the powder in water

Transfer the powder into an old plastic bottle that you will never want to use for anything else again (especially if you let the plaster set before cleaning it out and are as lazy as I).

Add 10mL water (or a water to powder ratio of 2:1), the syringe is handy for this.

Cap the bottle and shake violently for one minute, the bottle that is. The goal is to form a slurry of all the solid in water

tlc-buatan-2

step 4: Coat glass slides with suspension

Draw up the newly formed suspension into the syringe.

With the slides cleaned and dried (and free of fingerprints or oils), move the tip of the syringe back and forth width-wise across the slide while applying gentle pressure to the plunger. The motion is sort of like tiling a field. You don’t want to pour or dispense it all at once as the layer will form a hill instead, and will be too thick. By going back and forth slowly you can dispense a reasonably even, thin, layer of suspension across the plate.

The thickness of the layer is important, less than 1mm when dry is preferable so be careful not to overdo it.

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step 5: Air dry followed by activation

You want to air dry the slides to allow the plaster to set. Just leave the slides in a calm place for about an hour, or until they are white and smooth.

Prior to using, the tlc plates need to be activated. This entails driving off any remaining water that would still be held by the silica gel. This, apparently, frees-up the -OH groups of the silica gel to do your bidding as a stationary phase does.

Activation is done by heating the plates in an oven at 120C for 30-45 minutes. At this stage there really is no harmful chemical residues to worry about and this can be done in a regular household oven (unless the oven caretaker objects of course).

 After they have cooled the plates are ready for use so that you may elute to your heart’s content.

 The advantage of using glass slides is that when you’re done with the plate you can always scrape off the stationary phase, clean it, and re-layer it.

step 6: Some final notes on preparing the plates

These plates can be used like any other, though generally home-made plates have a more brittle stationary phase so be gentle. Tweezers are a good investment, and wield the “science tongs” carefully for with great power comes great responsibility.

I’ve heard that some silica gel desiccant packets contain fungicides and other chemical dopants, they may interfere with the operation of your plates. I have absolutely no advice on how to deal with this besides, perhaps, cleaning the silica powder before hand with a non-polar solvent. I did not have this problem and the plates I made from the desiccant packets worked the same as ones I made from lab grade silica gel (for chromatography, oooh).

Other stationary phases can be used as well, alumina for example. In this case slightly less water can be used, about 1.5:1 ratio instead of 2:1 as alumina does not absorb as much water as silica (and you want to maintain the consistency of the suspension). Cellulose can also be used, though I haven’t experimented with it, I hear that you don’t need to use a binder as cellulose is sticky enough on its own. You can, of course, experiment with your own stationary phases. There is a lot of literature out there, ripe for the googling.

Sources:http://www.instructables.com/id/Preparing-your-own-thin-layer-chromatography-plate/

you can also download homemade-tlc-plates

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