Sciencemadness Discussion Board

thin layer coating apparatus for preparative thin layer chromatography

Chromatogram - 12-5-2012 at 23:25

I've been conjuring up ways of making my own thin layer plate coater for some preparative TLC. The cheapest I've found of the retail versions is about $500 and I'm on a tight budget. I believe that stanley levels...
http://www.stanleytools.com/showPic.asp?PID=42-240&PIC=c...
could be utilized as a track for a hand-operated hopper/doctor blade. I can even think of ways to motorize this using a roller/motor I cannibalized from an old printer. Spacers could set the proper gaps for the doctor blade/adsorbent interface. An example of a hand-operated version of what I'm aiming for...
http://www.fpl.fs.fed.us/documnts/fplrn/fplrn119.pdf

Tell me what you folks think. Suggestions for a DIY thin layer apparatus/kit.

GreenD - 13-5-2012 at 04:50

yeah I think just buying two metal rails, welding / spacing them apart would be the best. The actual applicator, I would just think a piece of hard plastic would work, that sits on the rails, has the appropriate weight, and you simply push it along.

But personally I'd rather just buy the stuff.

watson.fawkes - 13-5-2012 at 09:45

Quote: Originally posted by Chromatogram  
Suggestions for a DIY thin layer apparatus/kit.
How thin is thin? The answer matters, because the thicker it can be, the lower tolerances you need and the easier it is to source or repurpose adequate materials.

Hexavalent - 13-5-2012 at 10:09

I've always made my own TLC plates per 'The Home Scientist''s guide on YouTube (can't provide a link because I'm on my phone) and made my best efforts to use a simple pasteur pipette to pick up a precise volume of the liquid reagent, which then solidifies, and to release it onto a glass microscope slide where I use a glass rod to spread it fairly evenly. The Rf values aren't the best, but they suffice for most of my purposes in my lab work.

S.C. Wack - 13-5-2012 at 10:24

Quote: Originally posted by watson.fawkes  
The answer matters, because the thicker it can be, the lower tolerances you need and the easier it is to source or repurpose adequate materials.


Not to mention how much material can be separated...maybe TLC (Thick Layer Chromatography) is suitable, who knows.

We are unaware of your real needs (what would actually work), how much use it would get, are you talking window panes or what, etc. Maybe you could just use masking tape and glass tubing.

[Edited on 13-5-2012 by S.C. Wack]

Chromatogram - 13-5-2012 at 15:18

Finally a forum with like-minded people. I've tried the other sites but they seem to be inundated with punk kids who don't know what I'm talking about.
Quote: Originally posted by GreenD  
yeah I think just buying two metal rails, welding / spacing them apart would be the best. The actual applicator, I would just think a piece of hard plastic would work, that sits on the rails, has the appropriate weight, and you simply push it along.

But personally I'd rather just buy the stuff.


Yeah, I may end up doing that if I can't get the reproducibility I'm looking for but I think it's very doable. A simple plastic trough/blade is worth the effort. I think the plastic doctor blades for printers might work here.
Quote: Originally posted by watson.fawkes  
Quote: Originally posted by Chromatogram  
Suggestions for a DIY thin layer apparatus/kit.
How thin is thin? The answer matters, because the thicker it can be, the lower tolerances you need and the easier it is to source or repurpose adequate materials.


2mm planar depth for preparative TLC on 20cm x 20cm plates. This will give me the recoveries I'm looking for. I realize that the larger the depth the poorer the resolution will be. Now if I can taper out the bottom of the plates then I can get that extra umph of resolution.
Quote: Originally posted by Hexavalent  
I've always made my own TLC plates per 'The Home Scientist''s guide on YouTube (can't provide a link because I'm on my phone) and made my best efforts to use a simple pasteur pipette to pick up a precise volume of the liquid reagent, which then solidifies, and to release it onto a glass microscope slide where I use a glass rod to spread it fairly evenly. The Rf values aren't the best, but they suffice for most of my purposes in my lab work.


I tried that and I wasn't very happy/impressed with my results so I'm taking it to the next level.

I've never casted/coated my own plates so this is new territory for me. I've used pre-made plates and had very good results with some resolutions I was doing. Most of the hand operated coaters on the market require you to slide the plate under the hopper/doctor blade instead of sliding the hopper/doctor blade over the plates. This might be a better option for a more homogenous coating? I don't know. I think I'll try a setup, first, that involves sliding the hopper/blade over the plates and see how that works out.

Thanks for the replies. I hope to sharpen my botany/biotech skills while I'm here.

watson.fawkes - 13-5-2012 at 18:08

Quote: Originally posted by Chromatogram  
2mm planar depth for preparative TLC on 20cm x 20cm plates.
Get yourself some 2mm diameter drill rod. Drill rod is the cylindrical stock that custom drill bits are made from. It's readily available and cheap; only a couple of dollars from McMaster-Carr for a one foot length if you don't have a good hardware store locally. Drill rod also has good tolerance on its diameter, unlike some things that look similar at first glance.

Make yourself a coating jig and just epoxy the lengths of rod directly onto your base surface. A sheet of glass would make an easy base.

For a knife, use a metal knife with enough thickness so that it doesn't bow when you draw it across the jig. You can get replacement blades for wood planers that are 10" or 12" across. The advantage of these is some of them come pre-drilled so that you can mount a handle (just a strip of wood) on the knife.

The other approach is to make a spin coater. This device relies upon good process control of the slurry for consistency viscosity and cohesion, but when these are taken care of, spin coating is very consistent.

S.C. Wack - 13-5-2012 at 19:16

Now, admittedly I use homemade SiO2, but I can't see how any fancy mechanism can improve on a glass rod and layers of tape for uniformity, and if you want a nice taper, well, obviously...

IMHO the key is the exact amount of water, just a little more than is needed to form a slurry, and working it around with surface tension on the rod, but not longer than a minute or so. At first it barely wets the glass then suddenly it spreads nicely.

I've heard 2 ml/g for genuine product but I need just about 4 ml. Every 5 layers of duct tape on the sides on a 13"x15" plate (giving a 13x13 surface) takes 20 g. of ghetto sgG, IME, BTW, FWIW.

I'm not sure that air bubbles are any less troublesome with slick-looking equipment; obviously there are less convenient methods such as organic solvent slurries then water spraying, dusting, etc. that avoids this completely.

[Edited on 14-5-2012 by S.C. Wack]

Dr.Bob - 13-5-2012 at 19:34

I have made a few plates years ago, but had a terrible time doing it. It is very hard to make plates, but prep might be easier, sin e the layer is thicker. Chromatotron plates are a lot of fun as well, being circular. The biggest problem that I have had is keep the layer on the plate after it dries, I think some companies use some sort of polymer additive or coating on the plate to help adhesion. Best of luck.

I like classic rock...

Chromatogram - 13-5-2012 at 23:04

Here's a really good gem I found, a classic...
Thin Layer Chromatography - James M. Bobbit
Reinhold Publishing Corporation 1963

Mentions the "poor man's layers," as it calls them. Using tape on the sides of the plates to measure out a depth to the layers, pouring the slurry in and smoothing it out with a glass rod or spatula. I'm afraid my reproducibility would be poor with this method and the book mentions that "The method is not very satisfactory for preparing thick layers." It does mention that if each side had a straight edge to it (i.e. instead of tape use a metal straight edge) for gliding the glass rod/spatula/doctor blade/whatever across the excess works superior.

I'm looking more at making a Kirchner or Stahl type apparatus. I like the Kirchner and now that I have this book as a reference I'm on my way. Thanks folks. ;) I'll have to lurk around here for awhile.




[Edited on 14-5-2012 by Chromatogram]

S.C. Wack - 14-5-2012 at 02:53

Quote: Originally posted by Chromatogram  
"The method is not very satisfactory for preparing thick layers."


The only visible imperfections when done correctly are from less than perfect mixing of the water and slurry before it was poured out. If nothing else, removing a layer or two of tape after drying and running the tube over again smoothes this out as well.

There is no give to the tape or the rod, nor is either wetted by silica.

Assembling some items...

Chromatogram - 16-5-2012 at 23:11

So, I've pulled a couple of items together...

A push plate made of 16 gauge steel and a steel wedge for a guide-on/straight-edge...


I need to finish some kind of block/assembly that allows me to adjust the depth of the layers. If you can refer to my reference, the Kirchner-type apparatus is what I'm after. I'm thinking some kind of metal block that is threaded for me to be able to adjust the depth of the layers on either end of the doctor blade. Or I could have it fixed and use spacers on the bottom of the push plate to create the desired depth to the layer?

I wish I had an optics table to work with... :(

I've also grabbed some steel drill rods/wedges that could work for the less expensive method (Poor Man's Layers) of just removing the excess with a straight edge.

Now, I will do a comparison of the "Poor Man's Layer" versus my DIY to get a feel if I just wasted my time and money to potentially save you time and money.

Truth be told, I just may end up putting this on the shoulders of a machinist friend of mine, that is to say if I can learn to bond/weld metal. A first time for everything.

Chromatogram - 17-5-2012 at 15:42

For reasons of rust, I'll bond some aluminum sheets to this setup. I'm gonna try my hand at cutting some metal with a metal blade/grinder.


Chromatogram - 17-5-2012 at 21:19

Silica Gel G with sodium fluorescein

"Mangold has stated that a reasonable approximation of the commercial product can be prepared by thoroughly mixing silicic acid, 200 mesh, with 10 to 15 per cent newly calcinated calcium sulfate (prepared by heating reagent grade calcium sulfate dihydrate at 180 degrees for 24 to 48 hours) of the same grain size. A 200-mesh screen [sieve] produces particles smaller than 0.12 mm." Thin Layer Chromatography - James Bobbitt, pg. 19.

"Several reagents are commonly incorporated into thin layers so that the resulting spots on the developed chromatogram can be seen without using a spray reagent. This is particularly helpful in preparative work. The fluorescing agents, with one exception, are usually blended with the dry adsorbent before the layers are prepared. The exception is sodium fluorescein which is normally dissolved in the liquid used to make the slurry. When the developed plates are placed in short wave UV, compounds containing conjugated double bonds show up as dark spots."
Table 2.2. - 6. "Sodium fluorescein" 0.04% sol. in water phase. Thin Layer Chromatography - James Bobbitt, pg. 20-21.

The Morgan apparatus for preparative TLC on page 56. Pretty simple set-up. Could use micro-pipette tip/capillary tubing system for spot application of samples or if you had a very deft hand you could do it with a small gauge needle and syringe.

Sorry about the large images. Feel free to prune...

Chromatogram - 19-5-2012 at 17:37

Sorry about the large images. I need to work on my computer literacy. Mods feel free to remove them, as I don't think I can edit them any longer. Here's a schematic of the push plate. I'm gonna write one up on the doctor blade/hopper apparatus to go with this. This is where I'm at presently, working with a pilot version. A final finished product pic soon to come.

[Edited on 20-5-2012 by Chromatogram] - Some irrelevant dimensions.

[Edited on 20-5-2012 by Chromatogram]

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