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Paddywhacker
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What part of the world are you? Overseas shipment is probably not worth the hassle.
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Chordate
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In the states.
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HexJam
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Does anyone know what the UV reactive material is that they mix in? Or some suitably available substitute?
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chemrox
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Really good set of posts.. outstanding. I look for bargains on the commercially made ones but for slide sized I might try again. I didn't add enough
binder to the last .. also filter paper has a virtue or two.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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peach
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I'm not sure what precisely is used on the commercial plates to make them glow, only that it's usually a 254nm fluorophor.
There are a number of alternatives to UV glows, alternatives which can be beneficial in that they will show specific functional groups, as opposed to
anything that quenches the UV dye.
Have a look at these for some examples.
Here's curly arrow talking about vanillin stain.
And Hanessian's stain.
Very pretty!
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HexJam
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Hey, great links, thanks! I have some of those chemicals so I think I might have a go at doing some staining after I've made my plates.
I take it that a plate isn't reusable once you've used a stain on it though? (I've never done TLC before, excuse my noobness).
I was going to have a go trying to TLC an aspirin / paracetamol (acetaminophen) tablet to see if I could separate the two, a KMnO4 stain aught to do
the trick on those right?
One last thing... I notice lots of TLC experiments use hexane as the solvent, which is proving difficult to get a hold of. Is there some common
use/source of hexane I'm overlooking? If I use a different set of solvents is there some way/formula to convert the Rf values I'd calculate to the
same kind of scale as the reference ones that use hexane/other solvents?
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HexJam
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Ah ha! Apparently the chemical they add to make it UV active is "... usually manganese-activated zinc silicate". This doesn't really help me much,
but I thought I'd included it for completeness ;-)
(source: http://en.wikipedia.org/wiki/Thin_layer_chromatography#Analy... )
[Edited on 7-7-2011 by HexJam]
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peach
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Funnily enough, manganese activated zinc SULPHIDE is what I've been trying to make for a while. It illuminates when exposed to electric fields. I
think UV may make it glow as well, but haven't tried it myself.
Plates aren't really reusable, particularly once they've been stained.
Really, you don't even want your finger prints on the surface. So you should handle them by their sides and most definitely wear some gloves, or
you'll end up ruining your kick ass results with contaminants.
If you look at this page on wiki, scroll down to the table of solvents and look in the none polar section for possible alternatives.
Hexane is used as an ideal none polar as it is incredibly simple in terms of functional groups (it has none) and has zero polarity to it. Cyclohexane
is even better, since it doesn't even have ends to the molecule. Benzene used to be used, but has double bonds and is of coarse carcinogenic.
In answer to the calculating part, if you were planning to do preparative chromatography, to prepare a sizeable mass, I would recommend you instead
give it a test yourself with your solvent mix and plates of choice.
[Edited on 7-7-2011 by peach]
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not_important
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Quote: Originally posted by HexJam  | Ah ha! Apparently the chemical they add to make it UV active is "... usually manganese-activated zinc silicate". This doesn't really help me much,
but I thought I'd included it for completeness ;-)
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AKA Willemite
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smaerd
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sorry to bump an old thread but I had a go at this and it works like a charm.
My only complaint is drawing on the plates must be done VERY gently. It is too easy to go through the solid-phase. Perhaps one of those chalk line
markers(for marking wood) would be more ideal depending on the eluent of course.
edit - the silica I used was Sigma brand for column chromatography(too lazy to read off the size). The CaSO4 I used was from a brew-store(gypsum).
Which was dehydrated in an oven for 1 hour at I believe 350*F to form the proper hydrate("plaster of paris").
Here are the results:
A harmine/harmaline extraction, eluted with HEET(methanol) no other additives. My spotting was done very poorly and it was not fully developed, but
this was my very first plate. A 5 and 3/4 inch pasteur pipet has a very small mouth that can be used instead of a thin capillary if one is VERY
careful(which I obviously was not).
[Edited on 16-8-2011 by smaerd]
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smaerd
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So I've been trying to read up on making better TLC plates. Trying to think of better ways to get the silica onto microscope slides and I ran into
this article saying some people use silicic acid rather then gypsum?
I don't know much about silicic acid or how to use it in this context I was wondering if anyone had any experience?
It also gives some pretty nice tips such as using methanol instead of water so the slurry can be stored rather then having to use it all and use it
quick.
It also says that the freshly made plates should be tapped against a table gently to remove air-bubbles, which I didn't know was good practice. As
well as air-drying prior to oven heating another mistake I've made in the past.
Another nice hint I've read about was wrapping two ends of a stir bar(kind of like a dumbell the width of a microscope slide) with masking tape or
similar to the desired height(above a microscope slide) and rolling over the silica slurry to give an even uniform coating.
It's definitely a bit of an art, I'd like to hear more discussion and or experiences about.
Attachment: 061009_Making_TLC_Plates_from_Bulk_TLC_Silica_Gels.pdf (93kB)
This file has been downloaded 4485 times
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Paddywhacker
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Here is an interesting technique that I came across today, involving depositing the thin layer on the outside of a glass rod or test tube.
The only problem is that powder for making TLC media is pretty well unobtainable.
Attachment: test tube TLC.pdf (128kB)
This file has been downloaded 1445 times
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watson.fawkes
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Unobtainable? Why do you
think that?
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smaerd
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I bought a Kg of silica media for column chromatography for I think 40 USD on an auction site. Worked pretty good for TLC plate making and for column
chromatography  .
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Paddywhacker
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Silica gel G?
The stuff for plates contains binder and a fluorophor, which shouldn't be in the stuff for columns, and different mesh sizes too.
Sure, silica flour can be had from the pottery suppliers, but it make muster.
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watson.fawkes
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| Quote: Originally posted by Paddywhacker | Silica gel G?
The stuff for plates contains binder and a fluorophor, which shouldn't be in the stuff for columns, and different mesh sizes too.
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Silica gel (if you don't want to make it) is readily available as a desiccant. All it needs is crushing. The
G is for gypsum (CaSO4), that is, plaster of paris. The F in silica gel GF is the fluorophore. Water tracing dyes are all fluorescent; they're used
with portable black light lamps. Fluorescein, originally trade named Uranine (and still sold under that name), remains one of the most common such
dyes.
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Paddywhacker
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I believe the best fluorophors are inorganic, but that isn't the problem. The problem is making a mixture that actually works for TLC, with
reasonable adherence to the glass. I have tried but was never happy with the result. It was always a pathetic imitation of the real thing.
Column material is also another difficulty. In order to get uniform grain sizes of the right mesh size for reasonable flow rates it is necessary to
mix the silica gel with water and a binder, let it set, then grind and sieve it. My formulations, using gypsum as the binder were always too fragile
and crumbled to sub 200 mesh ... useless.
Grinding up up kitty litter is a better proposition than grinding up desiccant silica gel. Sure, there is plenty of that available, but I recon it to
be too hard.
If anybody has actually cracked the formulation of these products then please post a photo essay in the prepublications forum.
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watson.fawkes
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| Quote: Originally posted by Paddywhacker | The problem is making a mixture that actually works for TLC, with reasonable adherence to the glass. I have tried but was never happy with the
result. It was always a pathetic imitation of the real thing.
[...]
Grinding up up kitty litter is a better proposition than grinding up desiccant silica gel. Sure, there is plenty of that available, but I recon it to
be too hard.
If anybody has actually cracked the formulation of these products then please post a photo essay in the prepublications forum. |
At least we're out of the realm of "unobtainable" into "I didn't make it work".
The photo essay you're looking for is in the very first post of this thread. The author uses desiccant silica gel, although he did grind it with a
ball mill.
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Mailinmypocket
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| Quote: Originally posted by watson.fawkes | | Quote: Originally posted by Paddywhacker | The problem is making a mixture that actually works for TLC, with reasonable adherence to the glass. I have tried but was never happy with the
result. It was always a pathetic imitation of the real thing.
[...]
Grinding up up kitty litter is a better proposition than grinding up desiccant silica gel. Sure, there is plenty of that available, but I recon it to
be too hard.
If anybody has actually cracked the formulation of these products then please post a photo essay in the prepublications forum. |
At least we're out of the realm of "unobtainable" into "I didn't make it work".
The photo essay you're looking for is in the very first post of this thread. The author uses desiccant silica gel, although he did grind it with a
ball mill. |
I tried making plates today following the original process in the first post of this thread. It was a failure. I used silica gel desiccant beads,
crushed to a very fine powder along with the plaster of paris in a 4:1 ratio. The plates were easy enough to coat, dried nicely and then oven dried.
They looked great (for a first try anyways) but the layer wiped off with the touch of a finger, almost like a compact layer of talc- shit.
Before scrapping it all, a small dog of methylene blue was applied and the plate placed into some solvent. The solvent started to climb the plate
quickly, but stopped because the phase immersed in solvent fell off. I'm thinking the only fix to this would be to try adding more calcium sulfate
next time, any ideas? Has anyone tried the above prep with reasonable luck?
Attached photos...
 
[Edited on 13-2-2013 by Mailinmypocket]
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watson.fawkes
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| Quote: Originally posted by Mailinmypocket | | I tried making plates today following the original process in the first post of this thread. It was a failure. I used silica gel desiccant beads,
crushed to a very fine powder along with the plaster of paris in a 4:1 ratio. The plates were easy enough to coat, dried nicely and then oven dried.
They looked great (for a first try anyways) but the layer wiped off with the touch of a finger |
What drying
schedule did you use? Plaster of Paris starts to calcine at 100 °C, which is easy to exceed in an oven.
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Mailinmypocket
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| Quote: Originally posted by watson.fawkes | | Quote: Originally posted by Mailinmypocket | | I tried making plates today following the original process in the first post of this thread. It was a failure. I used silica gel desiccant beads,
crushed to a very fine powder along with the plaster of paris in a 4:1 ratio. The plates were easy enough to coat, dried nicely and then oven dried.
They looked great (for a first try anyways) but the layer wiped off with the touch of a finger |
What drying
schedule did you use? Plaster of Paris starts to calcine at 100 °C, which is easy to exceed in an oven. |
Ah... I think that might be the problem then. Calcining never occurred to me - I let the plates air-dry for an hour, and then oven dried as per the
article, at 120c for 45 minutes.
The lowest my makeshift lab oven (toaster oven) goes is 90c, I have to try again and use a digital thermometer to monitor the T as I doubt the
thermostat on a 19$ toaster oven is "lab grade", and if I'm going to crush more of those damned stubborn silica beads I want it to work.
[Edited on 13-2-2013 by Mailinmypocket]
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Mailinmypocket
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Has anyone had some reasonable luck in making TLC plates? Again I followed the OP's attached procedure without luck. I think it would be nice to make
a visual guide on how to make them so that TLC can be available to more amateurs (Rf values might be hard to determine with the variable grain sizes
but that's another issue).
I ground up more silica desiccant beads in a large mortar and pestle, this creates a lot of airborne dust that is dangerous to inhale, use a mask or
do it outside. After about 10 minutes it was the consistency of talcum powder. Then the plaster was mixed in and ingredients were ground together for
an additional 10 minutes. Then I followed the procedure but once the plates dried I baked them for an hour at only 90c to avoid calcining the plaster,
which was a suspected problem in my last attempt.
Again, they came out fragile as hell. Not as much so as last time but the layer can easily be wiped off instead of blown off- I guess that's a small
success. A dab of sharpie marker was placed on the plate, which removed some of the coating... Surprise surprise there! An attempt was made to elute
with ethyl acetate and it did manage to carry some ink up with it but then the immersed portion of the plate started to disintegrate. Any ideas on how
to improve this?
Looks like this...(the top of the plate is bare because I wiped it with a finger :S)
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watson.fawkes
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| Quote: Originally posted by Mailinmypocket | Then I followed the procedure but once the plates dried I baked them for an hour at only 90c to avoid calcining the plaster, which was a suspected
problem in my last attempt.
[...] Any ideas on how to improve this? |
Given that you've got some adhesion now (rather than none), I'd
guess you've still got a problem with the temperature of the TLC plate.
Since you're using a toaster oven, if there's a direct optical path to the heating elements, it's likely that the TLC plates surface is sitting at a
temperature above 90 °C because of radiative heat transfer. Think of the oven as a steady-state heat flow device, rather than a constant
temperature device. The latter is what you want ideally, but the former is what you actually get. The easiest intervention is to make your actual oven
more like an ideal oven.
Just putting a couple of layers of metal separated by an air gap will do a lot to even out the radiative inhomogeneities in your rig. (Incidentally,
this is the insulation technique that the Webb space telescope uses to reject radiative heat load.) Put these layers between the heating element and
your plates.
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sonogashira
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Maybe scratch the glass with sand paper?
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smaerd
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I'll do some experiments this weekend and report back. I did have some success but it wasn't anything too impressive. I could write on the plates if I
was very gentle. I have a few ideas now that I've matured in my knowledge base and experimental technique a bit.
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