Sciencemadness Discussion Board

Size of chromatography column

thors.lab - 12-10-2020 at 01:38

I've been doing a little bit of analysis and small scale purification these days. Mostly recrystallization, LLE, and TLC.

I want to get into column chromatography. I'm looking for columns but I'm unsure of what size I'm going to want. I'm looking to purify in the 500mg — 5g range.

I like these StonyLab guys, their glassware has been quality and fairly affordable for me. They have options for 250, 100, and 50mL.

The 100mL one for example is 60mm od and 200mm length. How much product would this size be ideal for? 1g? 5g? 500mg?

Additionally, how much pressure do I apply, and how? If I'm adding eluent in the top with something like a sep funnel, how would I go about pressurizing? I've thought of using something like an aquarium air pump with a flow rate adapter. Though that adapter is kind of unnecessarily expensive and doesn't leave a nice way for me to add eluent, besides just removing the adapter. Also what the heck is that second sidearm for?

Also, is that what that reservoir on top is for? I've only seen straight chromatography columns. Is the extra reservoir so I can just add a ton of eluent in one go and not have to worry about removing the flow rate adapter? But then I wouldn't be able to do gradients very well.

Also what are your thoughts on dry vacuum column chromatography? I watched a video on it and it seems like a *very* appealing technique. Easier to scale, uses less solvent, and uses a vacuum which is a bit nicer than pressure.

[Edited on 12-10-2020 by thors.lab]

Sigmatropic - 12-10-2020 at 10:03

Column chromatography ranges everywhere from 1/10 to 1/100 g of crude product to g of silica. Typically 1/20-1/40.
The column once poured has a volume in mL ~1.6 times the weight of silica in grams.
5 g purification in the worst case scenario is 500 g of silica but best case only 50g. Though normally in the 100-200 g range. Your 0.5 g example, 50 g worst case, 5 g best case, normally 10-20 g.
Considering the 100 ml column fits the full range for the 0.5 g sample get one of those. Depending on how badly you want to run preparative column chromatography, say anything in excess of 1 g, get some larger sizes as well. Bear in mind that column chromatography is quite wasteful, think stationary phase, eluent and time spent doing the column, concentrating the fractions... Are you sure your goal is worth the time and money?

Applying pressure is optional, gravity columns are much simpler and don't fall dry when left unattended. Applying pressure can be done in so many ways everyone has their own preferences, reducing valves, leaky adapter at low flow, leaky adapter at high flow, balloons on adapters, whatever.

Yes that is what the reservoir is for, you end up doing block gradients.

Dry vacuum column chromatography, to me is just another form of chromatography... Haven't heard of it much really, there are automated column chromatography machines...
It physically doesn't matter if you apply pressure on the top or vacuum on the bottom, so go with a vacuum if you have no compressed air. Apparently it doesn't matter that much if your column falls dry if dvcc works, but I wouldn't do it since that is not how I learnt it.

Also don't let anybody trick you into skipping lunch because of you're running a column, they can easily be left for n hour.

Edit: now that I think of it this 1.6 may refer to the volume of solvent in the column, not the actual volume in the column. I'll try and find a reference

[Edited on 12-10-2020 by Sigmatropic]

thors.lab - 12-10-2020 at 11:36

Thank you friend! Great replies! That's basically all the information I needed haha.

You're right it does seem very wasteful and getting nonpolar solvents here in California is a bitch and a half. DCVC apparently reduces waste by a lot and allows you to separate several grams of material with just a small column.

How much eluent would you say is spent for a column in your 15g of silica column separating 500mg of material?

DavidJR - 13-10-2020 at 06:17

Hmm, I've tried the dry column vacuum chromatography technique a few times and never had great results with it. But clearly, some people do.

Mathias94 - 13-10-2020 at 09:59

Quote: Originally posted by DavidJR  
Hmm, I've tried the dry column vacuum chromatography technique a few times and never had great results with it. But clearly, some people do.

May I ask what kind of compound you tried it on?

Fyndium - 13-10-2020 at 10:37

Can you do multiple runs on single column or is it single use only? Aka, can the packing be reused?