Posted 1 March 2011 - 10:19 PM
Posted 1 March 2011 - 10:34 PM
Those are the basic rules, but normally you have to play around with varying system until you find one that works. I normally start at 50% ethyl acetate in hexane as a baseline and then change in from there. It does massively depend on the compound that you are using though.
O, and the stationary phase is also important. Normally, silica gel is acid, and so amines do not move as they get protonated. There are several ways around this problem; either add a second base (normally triethyl amine) that neutralises the acid silica so your amine doesnt stick. Alternatively you could use alumina (aluminium oxide) as the stationary phase, which is basic in nature.
Edited by Horza2002, 1 March 2011 - 10:45 PM.
Posted 2 March 2011 - 01:20 PM
In the second part we dissolved and l-aspartic acid the sucrose in water and used 15 mls of ethanol and 10 mls as the mobile phase and the tlc plate with silica as the stationary phase, but that didnt work either!
What went wrong?
Edited by liambob1, 2 March 2011 - 04:40 PM.
Posted 2 March 2011 - 05:48 PM
It could be that you didn;t put enough sample onto the TLC for you to be able to see any spots forming...it also be that the solvent systems were too polar and you compound just raced off the top of the plate. However, if you didn't see any spots at all anywhere in the plate, I would say that you either didn't put enough sample on or you used the wrong visulising method to detect them.
If you used straight ethanol on the second one, then you would have serious problems of the silica dissolving and therefore giving you heterogenious stationary phase to flow through.
Posted 2 March 2011 - 07:03 PM
Posted 2 March 2011 - 10:28 PM
You shouldn't use water as a cosolvent no...the water will be able to pick up protons from the silica gel and so you will have localised differences in the pH which will therefore alter your retention time. Some solvent systems naturally just run slower than others...
While yes, you can use the same solvent for the mobile phase that you used to dissolve the sample in; however I wouldn't recommend it. Typically you should use a solvent that dissolve your sample extremely well and so if you use it as your mobile phase, it will move very fast as far up the plate. So it yes indeed possible, but not advisable.
Posted 3 March 2011 - 07:39 AM
Posted 3 March 2011 - 08:53 AM
Posted 3 March 2011 - 10:05 PM
Posted 8 March 2011 - 08:49 AM
solvent are like methanol ,ethanol,
Edited by icepeaks635, 8 March 2011 - 08:50 AM.
Posted 9 March 2011 - 07:32 PM
A good way to find a good "mobile phase" (with the desired retention factor) for your compound is just to make 5 different solvent mixtures at once, prepare 5 different tlc plates at once, put them in there, run them and stain them (spares time). Take the best solvent mixture or change polarity again after that.
The sugars themselves should not be visible in the UV (if you use the nomal tlcs, that is), but KMnO4 should definitely stain your sugars in high enough concentrations. Otherwise, have a look at Horza2002's list of stains...
Edited by Dan_iel, 9 March 2011 - 07:36 PM.
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