Chromatography Forum

I have a mixture of PAH in an alkane solution that I am having trouble separating with ordinary methods. Most of the PAH in this solution have a high degree of alkylation making them extremely difficult to resolve (there are a very large number of PAH, and they tend to coelute).

My understanding is that a normal phase column will separate PAH by ring number with little sensitivity towards the alkyl groups. So my plan is to use a normal phase column to fractionate the sample by ring number, then use a reverse phase column to analyze each fraction.

I plan to buy a cyanopropyl column for this purpose, but I am wondering if there is a stationary phase better suited for this purpose. Is there a column that is more sensitive to ring number and less to alkyl groups?

Thanks in advance.

It is not normal phase per se that tends to separate the PAH according to ring number. You need an amino column to do that.

It is not normal phase per se that tends to separate the PAH according to ring number. You need an amino column to do that.

Thanks for the clarification. I was aware that I needed a specific stationary phase, but I didn't make it clear in the post. I believe my choices are either a cyano or amino column.

I had heard that an amino column would be ideal, but I am also told that compounds with carbonyl groups (which are present in my sample) will bind permanantly to the stationary phase. Is this true?

I am not aware that cyano columns do this group separation as well. I have some doubts though. Nitro-phases do this though via clear pi-pi interactions.

You are right that amino phases are prone to react with aldehydes and ketones. Since you have such things in your sample, the amino column is not a good idea.

I would go for the nitro-phase, but you may have to dig until you find a supplier. Check with Macherey-Nagel in Germany!

How do phenyl phases or Hypercarb behave with PAH?

Phenyl columns give more retention for pi acceptors, but I don't think that this will help here.