[synthon]

Anyone see any reason why this might not work?

I've got a polar primary amine in an aqueous mixture that I'm planning to purify on strong cation exchange resin (DOWEX 50X8).  I've washed the column with acid, then water until the eluent is pH 6.  I acidified the amine to pH 2.  I'm planning to elute with water until ninhydrin+ fractions appear. 

It seems straightforward, but I've had difficulty with ion exchange before, so...can anyone see potential problems I've overlooked?

Thanks -- 

[Dan]

I don't think your amine will move much (if at all) if you elute with water on a strongly acidic resin, but I may be wrong.

I used to do these Dowex columns regularly and, after loading the crude and washing the column with water until pH 6-7, always used 1-2 M NH₃(aq) to liberate the resin-bound amine.

[synthon]

Thanks, I was planning to use NH3 to elute if it didn't come off, but I've generally had difficulty getting my amines to stick to the resin and they usually just wash right through in the first fractions.

[Babcock_Hall]

How much excess capacity of resin do you have?  I have often used about 20-fold excess.

[synthon]

Going by what they say at aldrich (~1 meq(?)/mL), I've got an excess of right at 20x (not including the salts from adjusting pH).  I just eluted the amine with 1M NH3, and it looks like it came off with other impurities, so it looks like I'll be running again using 0.5M.

But glad to see it stick!  Just a matter of fine tuning now.

[synthon]

Worked perfectly using 0,5M NH3.  Nice and pure amine for BOP coupling.  Thanks for the help !   

Off topic, anyone know why typing 'help' + '!' prints *delete me*?

[OC pro]

Have done this alot for purification of amino acids. If ammonia is not basic enough, trimethylamine will elute almost every amine. After evaporation of solvents I regularly used to freeze-dry my compounds to make them dry enough for further reactions.

[Babcock_Hall]

OC pro, We synthesize amino acids also (and purify them by ion exchange), but I have not heard of using trimethylamine before.  Do you have a reference handy, by any chance?

[OC pro]

I have to correct myself. Aqueous trimethylamine of course! Don´t have any reference.

[amg123]

Thanks, I was planning to use NH3 to elute if it didn't come off, but I've generally had difficulty getting my amines to stick to the resin and they usually just wash right through in the first fractions.

I am having the same problem in getting the amine to stick. How did you eventually fix this problem?