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Author: Subject: things to remember while making column?
medchem
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[*] posted on 15-8-2010 at 17:10
things to remember while making column?


hello guys,
Plz check out the information on column chromatography and things to remember while making column. You can leave some of your point missing in the post so that newbies can understand more...;)
<a href="http://medchemblog.blogspot.com/2010/08/column-chromatography.html">link here</a>




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chemrox
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[*] posted on 18-8-2010 at 07:11


Two things jumped out at me: most forums have rules about language usage. I would ask that you pay more attention to written communication. If you're not a native English speaker then its understandable that your usage would not be perfect but please try. Now to the column peparation- you've said nothing about applications and scale. I have long columns and short ones, skinny and fat ones. For most separations I like slightly polar solvents or non-polar/polar mixes where the bp's are close. You said "lower polar." I've no idea what that means. I thought it could mean lower boiling polar but also considered slightly polar. I don't like using cotton wool; too hard to clean. I prefer glass wool. I like any clean well sorted fine sand. I like to have columns setup for multiple uses as silica gel is expensive. Therefore my samples go in in solution on top of the upper sand layer. I like columns with reservoirs for most uses, I try not to use the technique for routine cleanup when distillation and/or recrystallization will do as good or better job. For cleaning up compounds that are too high boiling for hard vacuum distillation or for which a solvent combination for effective separations can't be found I've come to prefer flash chromatography. For compounds with similar boiling points and structures columns come into their own imho. For those I like long columns and sample collectors and if available (I don't have one) pid detectors. Numbering and spotting a hundred samples takes a lot of motivation. I really like your reaction of the month entries-good job!



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Globey
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[*] posted on 18-8-2010 at 16:38


In a pinch, I've had good luck taking the cheapest toilet paper you can find, and making a water emulsion out of it with the aid of an Osterizer blender. You want a wet, fluffy, whipped up pulp. Of course there is white sand as well. Old fluorescent tubes.

Feel free to PM me if I can be of any help to you. I'd rather have the info posted on forum so more people have access to the info., but it seems lately any post is just an invitation to have negative, anti-social posts made in retort. That's is typically the sign of an unhappy person. Don't worry, be happy!
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medchem
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[*] posted on 18-8-2010 at 18:30


@chemrox, thanks for your feedback

As you know, mostly solvent combinations is used for eluting compounds.
While making column, it's better to make column in less polar solvent (for e.g if you are using solvent mixture of EtOAc and Hexane for elution, it's better to use less polar solvent-hexane). But it's not applicable all the time. Sometime we have to make the column in the solvent mixture (starting eluting solvent), depending upon compound's solubility.




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Ozone
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[*] posted on 18-8-2010 at 19:06


If you are going to use resin, pre-swell it before packing the column. Swelling dry resin in a column frequently results in catastrophic failure (e.g. you will be cleaning up tiny glass bits for a long time.

Also, pre-wash *any* packing that you use; it is frequently dirty, even when new. This is especially true of resins and granulated carbons.

Cheers,

O3




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Paddywhacker
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[*] posted on 19-8-2010 at 12:33


Globey, are you using the cellulose pulp as the column packing, or as the plug at the bottom?

As mentioned by Chemrox, silica gel for columns is expensive. It is also difficult to acquire. Alternative packings and sources of packings are a very useful resource.
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peach
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[*] posted on 30-8-2010 at 12:44


There's videos in the MIT digital lab manuals on TLCs, advanced TLCs and columns. You may wish to include a link to them. Google "MIT digital lab manuals" and follow the links.



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[*] posted on 26-9-2010 at 20:47


<a href="http://ocw.mit.edu/resources/res-5-0001-digital-lab-techniques-manual-spring-2007/videos/">Link </a>to MIT video library of various experiments



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