Raise your hand if you know what Thin Layer Chromatography (TLC for short) is. No? If you raised your hand, please bear with me through a brief introduction.
Chromatography is a means of separating mixtures of compounds into individual components. It takes many shapes and sizes. Today we are going to talk about silica gel based chromatography. Think about a filter for your tap water. Some of these filters are simply very fine mesh that filter out particulate junk you don’t want in your drinking water. Others are essentially pads of activated charcoal (read: charcoal of uniformly small particle size that has been treated with a weak acid) that the water filters through achieving the same goal. These filters hold on to some tiny particulate matter while allowing water to pass through.
Chromatography in the laboratory is very similar to this. We use silica gel (basically tiny uniform sand grains that have been chemically treated to have alcohol groups hanging off them) as a filter. Certain compounds will stick to the silica gel and other compounds or materials will simply go right through it. As chemists, we make use of this to purify crude mixtures of materials that we synthesize in the laboratory. We control the amount of silica gel, and the solvent that we use in order to optimize what will come through the filter and what is left behind. We try to figure out how to make the stuff we don’t want stick to the silica gel (like the particulate junk in the water filter) while allowing our desired material to pass through (like the water through the filter). Since silica gel is not exactly dirt cheap (HA! That’s funny, cause you could argue it is basically fancy dirt…) we use small plates of aluminum foil that have been surface coated with silica gel (TLC plates) to optimize our conditions before we attempt to ‘filter’ our bulk material.
Have you ever used a tiki torch? You know how the wick of the torch sits in the flammable liquid in the canister, drawing it up to the top of the torch where it actually burns? The fancy term for this ability to draw the fuel up the wick is capillary action. TLC plates also perform capillary action. If you place them in a small reservoir of solvent, they will draw that solvent up to the top of the plate. If we place a spot of our crude mixture on the bottom of the plate, it will also be drawn up with the solvent. Depending on how each of the compounds in the crude mixture interacts with both plate and the solvent – we might be able to separate our mixture into it’s components.
All of this sounds technical and is actually quite simple. So! To demonstrate the ideas behind TLC and silica gel chromatography (and to have fun looking at all the pretty colors), Harry and I spent an incredibly nerdy Sunday afternoon performing TLC on our slightly ridiculous collection of fountain pen inks.
Did I mention that I am head over heels for this man? He’s sexy, smart, nerdy, and comes up with fun ideas like this? I was doomed from the start.
Fountain pen inks, fountain pens, and dilution samples of the inks.
This is what an TLC plate looks like after it has sat in its solvent reservoir for about five minutes. Capillary action has drawn the solvent of choice (water and acetonitrile) up the plate. The dot of each ink placed a the bottom of the place (along the pencil drawn line with cross hashes at the bottom of the plate) was pulled up the plate with the solvent. You can see that each ink separated into it’s components revealing which colors the manufacturers (Diamine and Lamy) use to generate the gorgeous colors we see when we write.
The pictures which follow are more examples of this with various inks from various manufacturers.
Waterman and Thornton’s basic green/red/black inks.
Various Diamine inks, none of which contain shimmer.
All of our greens. All in a row.
The black inks are particularly interesting to me. It’s neat to see what combination of colors each manufacturer uses to provide the deepest black. The onyx black is, in my opinion, the truest black on paper so it is neat to see that it also contains the most distinct pigments.
This one is fun because you can see that Diamine uses the same basic pink to affect the color profile of both their amazing purple pazzazz and their deep magenta (which is hands down one of the prettiest pinks I have ever used).
Whoever said chemists don’t know how to have fun?
If you have any questions about various fountain pen inks, chromatogrpahy, or TLC – please feel free to comment!
See also – http://imgur.com/a/Eds0S (Harry’s post about this!)