[Honclbrif]

For TLC standards, I would dissolve them in whatever gives the best solubility. I find that it does not matter what your TLC standard is dissolved in, so long as it is suitably volatile the solvent will evaporate before you ever run the plate.

For columns, to avoid potential funny business, I prefer to dissolve my sample in the mobile phase with which I will be running the column. Obviously to get the tightest bands you want to keep the volume of solution you are loading to a minimum (i.e: high concentration). The number I've been quoted and which has worked well for me is "less than 2% of the bed volume".

To load: pack your column as usual (slurry pack please, dry packing is for delinquents), then drain the solvent down until it is level with the top of the bed (or sand if you are using a sand layer on top), then use a pipet to gently dribble your solution down the sides of the column. Start as close to the bed as you can get and be as gentle as possible, the last thing you want to do is to disturb the top of the bed (another reason why a sand layer is usually a good idea). Drain until the solvent is again even with the top of the bed, then dribble a few mL of mobile phase in and drain as before. Repeat with solvent 3 or 4 times to get it good and loaded, then gently pipet solvent in until you have about 5 cm of solvent above the bed, then pour more solvent in until the column is full. Now elute as you normally would.

[Honclbrif]

I don't think you want to dissolve the compound for column chromatography.  If you did the sample would end up all over the place and you wouldn't get any separation.  I usually put the pure/crude sample at the top of the column, drain the column down to the level of the silica, then fill it up with the eluent and go.

Good advice if your material is an oil, but if it is a solid you've got to dissolve it in something first. Just throwing the solid in there and waiting for it to dissolve as the mobile phase runs would probably be a disaster if the material does not dissolve rapidly.

The only exception to this I know of is if the material is not particularly soluble in the mobile phase. In this case dissolve it in something which it is very soluble in, add a few grams of silica gel, and vac off the solvent. Pack the column, then add the pre-loaded gel to the top and elute as normal.

[voidSetup]

Oh yes I forgot about that lol.  I'm in undergrad and have only been working with oils lately.

[nox]

Re: Columns

I think it really depends on what you're working with and what you're trying to separate really. For me I've found the most important factor in getting a good separation is to run your column really, really, really slow. Most of my reactions end up giving me a spot that runs partially into my product spot (Rf difference less than 0.05). I've found though that if you run the column in a solvent system where your stuff runs at an Rf of 0.05 (basically barely nudging off the baseline), you can still get fairly good separation. Before you ask yes I tried different solvent systems, the resolution is just as bad.