Chromatography Forum

I want to separate 2 large ring-molecule compounds with only a hydrogen bond that differs from one another. I used TFA in water and ACN as my Mob Phase. My separation as of now is not great (only 0.4 min). Any suggestions of the column and mobile phase to use would be greatly appreciated?

Thanks a lot.

Would you like to disclose the column and condistions you've found worked best, and what didn't work?. Can you increase resolution by changing the column length or particle size?.

Thanks,

Bruce Hamilton

Packings with an embedded polar group have been demonstrated to give more retention for hydrogen-bonding analytes. (U. D. Neue, J. E. O’Gara, A. Méndez, “Selectivity in Reversed-Phase Separations: Influence of the Stationary Phaseâ€

Would you like to disclose the column and condistions you've found worked best, and what didn't work?. Can you increase resolution by changing the column length or particle size?.

Thanks,

Bruce Hamilton

I was using C18, 3.5um, 150 x 4.6, the other was a cyano.

If your C18 column did not contain an embedded polar group, as suggested by Uwe, you should try those columns first.

You may also find some of the chiral columns provide different separation mechanisms that may improve resolution.

Bruce Hamilton

A polar-embedded RP column that Uwe suggested is worth trying first. There are several types of such phases including amide-embedded (e.g. Ascentis Amide - Supelco), carbamate-embedded (e.g. Symmetry Shield -Waters), and sulfonamide-embedded (e.g. Acclaim PolarAdvantage).
It is not quite clear to me what you mean by "compound with only a hydrogen bond." What functional group do you mean here? Is this a carboxylic grop or an amide group, or something else?

A polar-embedded RP column that Uwe suggested is worth trying first. There are several types of such phases including amide-embedded (e.g. Ascentis Amide - Supelco), carbamate-embedded (e.g. Symmetry Shield -Waters), and sulfonamide-embedded (e.g. Acclaim PolarAdvantage).
It is not quite clear to me what you mean by "compound with only a hydrogen bond." What functional group do you mean here? Is this a carboxylic grop or an amide group, or something else?

Thanks for suggestions. It has 4 aromatic rings but acidic in nature. The H2-bond diference stems from the group that connects 2 rings.

If your C18 column did not contain an embedded polar group, as suggested by Uwe, you should try those columns first.

You may also find some of the chiral columns provide different separation mechanisms that may improve resolution.

Bruce Hamilton

I'm hesistant about chiral due to the difficulty in changing systems from Normal to RP or vice versa. We have limited resources. But i'll try the columns suggested by Uwe and the group. Thanks!

Alpert, are you talking about a hydrogen bond (a C-H bond, etc.) or about hydrogen bonding (a -H....O-, etc., bond)?

Alpert, are you talking about a hydrogen bond (a C-H bond, etc.) or about hydrogen bonding (a -H....O-, etc., bond)?

The bond was from an alkyl group bridging 2 aromatics. A C-H bond technically speaking.

What is in place of the H? It is difficult to see what the real difference is.

Hello Albert.

Embended polar group could work very well; both compunds have similar pKa?
these two aromatics rings are polycliclics?
I ask because phenyl columns vary selectivity for polyciclic compounds.

Cheers.

Oscar