Chromatography Forum

Mobile phase is Ammonium Sulfate, ph about 3.3, intersil amino column. As brand new dedicated amino column gets older main peak comes faster and faster (RT shift from 12 mis. to 5 mins.). Is this common with NH2 column and how to stabilize RT of main peak ?

Silica-based amino columns are notorious for this problem. The amine group creates a high pH in the microenvironment of the surface, leading to hydrolysis of Si-O-Si links. The first to be hydrolyzed are the links that hold the silane to the surface. Result: Steady loss of functional groups in the coating and shorter retention times, as you have noted. Solutions are as follows:
1) Use an amino column that is designed to be more durable. Some of these are made from silane oligomers, which are harder to hydrolyze off. The Shiseido CAPCell PAK NH2 column is supposed to be particularly good this way.
2) Use a polymeric amino column. Make sure it's based on a reasonably polar polymer. not polystyrene-DVD, or you may have pronounced hydrophobic interactions. There are now several on the market that are satisfactory, although the selectivity may be different from a silica-based material.
3) Use a silica-based anion-exchange material where the amine groups are not attached via a silane link. Perhaps the only example of this is our PolyWAX LP material, in which linear polyethyleneimine is adsorbed to silica and then crosslinked to itself to form a macromolecular coating that envelops the silica particle.

Andy thanks for the information. Is there any other Ammino column manufacturer (such as phenomenxe, waters or thermofisher etc.) equivalent to Shiseido CAPCell PAK NH2 column?
I want to buy a column from another manufacturer to solve this problem.
Thanks

Vijay, as far as silica-based amino columns are concerned, the Shiseido column seems to be exceptional, if not in a class of its own. If you really feel that it's important to order a durable amino column from some other company, then I suggest that you contact their sales department and ask if they make a column that fits that description.

VJ, what are you trying to separate?
maybe you could use the newer type of tertinary or quaternary amines columns used with HILIC these days instead of NH2 column
also is it a one peak application? an assay?
then you can anyway cut the retetion time to a lot less using a shorter column and go under 10 minutes. as long as it stays stable of course