Column Chromatography

M

martin

Hi All, Advice needed.
My head of department is introducing a new demo to us. She wants to demo column chromatography, so has any one done this in a school before and if so could you supply details. She has given me 2 weeks notice, and I will need to source a small column and then find out what will work. Need to decide what stationary phase, then what solute/sample and then what mobile phase will move the sample down the column. I have not run a column in well over a decade and then it took me a month to sort out the wright combination of solvents for the mobile phase to run on a silica column, with my sample. that was in my University lab tech days.
 
J

JFKtech

Haven't done it yet, but somebody (I wonder if she's on here !) posted a photo of one on a knitting forum I'm on, and I got the instructions off her.

We made green from Sugarflair brand food colouring in primrose (E104 quinoline yellow) and ice blue (E133 blue fcf). It’s got sand in the bottom then Al2O2 powder.

She didn't say what mobile phase, but I'd guess probably water ?
 
Luis Em

Luis Em

if you have the time and inclination and it is essential as part of the curriculum yes, otherwise if it is to show another separating technique it is not worth the time and effort. We did this as the latter and it we tried three times before there was even a semblance of a result. Have a chat with your HoD
 
M

martin

Luis Em said:
if you have the time and inclination and it is essential as part of the curriculum yes, otherwise if it is to show another separating technique it is not worth the time and effort. We did this as the latter and it we tried three times before there was even a semblance of a result. Have a chat with your HoD
Click to expand...
It is my Head of Departments idea, she is introducing more demo`s and practical's for all the years. At the moment it is year 12 and 13 involved. i am now having to prepare two different back titrations for year 12 for this week and next, we have never bothered before to do this in my 10 years here. they have just completed titration of Sodium carbonate.
The RSC demo nice, just concerned about how much organic solvent it uses and which type. I found one demo on the web that uses water then acetone to wash of the second product, I try not carry a lot of acetone as we only use small quantities for the testing for a ketone.
Any help and advice is appreciated.
 
Emil Tac

Emil Tac

Ahhh column chromatography. I had a lot of experience with it many years ago. It's a bit tricky/daunting at first but it's one of those techniques that you get better at it with practice. The video makes it look easier than it is.
Pure food colouring powders + water as the solvent should work well. You do thin layer chromatography first to try and get 2 colours which have high separation.

In fact, you always do thin layer first to identify a good solvent system for separation and then you use flash column to separate the bulk.
 
M

martin

Hi Thanks for reply, no I have not sourced the chemical's, I have raised the issue of what she would use. i asked her did she have a demo in mind, of course not. pointed out that the last time I did a column I used litres of organic solvents to run it, not the type of thing you could do in a school. Then said I have seen on you tube a column separation using ion exchange resin. this used water, then a dilute acid to remove first a copper salt then a chrome salt. The problem was even the cheapest ion exchange resin was over £50 for 100g and might not be the correct type as the you tube demo did not mention what type or grade.
She is thinking about it now.
 
Luis Em

Luis Em

sometimes that's one of our jobs - whilst its all well and good to think of amazing practical activities that we think will benefit the students, we are the ones that have to deliver the wake up call and bring things down to earth. The closest to a decent getting a decent chromatograph is TLC, perhaps your HoD can accept that is the next best option.
 
M

Medchemist

The first issues I can see with this is the volume of solvent needed (and needing disposal) and use and disposal of silica which is basically asbestos dust from your lung's point of view.

You could try a miniaturised column in a pasteur pipette (look up microscale column chromatography) using something a tad safer like talcum powder (I've seen this mentioned in old-school textbooks for separating certain compounds) or cellulose powder which basically makes it paper chromatography in a tube.

The main issue is the skill needed to run a successful column, it really is an art and unless the teacher or yourself has done them routinely in the past the experiment will likely go wrong. e.g. I only started getting the hang of normal columns in my 3rd year of uni, mini-columns are harder.
 
M

Medchemist

SO, I decided to give the mini column a go for the first time in ages...
I tried talc but thats too fine and clogged the whole thing up -

cotton wool (cellulose) jammed in and packed in with a capillary tube works well for separating food colouring using acetone/ethanol (roughly 10% ethanol), I managed to collect blue and yellow dye from green food colouring. It's fiddly and you'll have to try a few different solvent mixture to get one that works for you but it is nice and visual with the colours.
 
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