Peak tailing due to silanol interaction?

[DJ]

I have recently run uracil, benzylamine, and phenol on a silica-C18 and compared it to a polystyrene-divinylbenzene column. Under isocratic conditions (40% MeCN containing 25 mM phosphate, pH 7.5),

The peaks for phenol and uracil were symmetrical on either column, while benzylamine tailed on both. Most puzzling is that tailing was much more pronounced on the PS-DVB. Would this seem to indicate that tailing effects for this solute are due to more than silanol interaction?

[chromatographer1]

The separation mechanism for the second column: are you aware of HOW it separates the analytes?

Do you know the pore size distribution? The uniformity of the pore flow paths?

Changing the temperature of the mobile phase will affect the peak shape as well as the flow rate and the amount of sample placed onto the column.

best wishes,

Rod

[tom jupille]

Would this seem to indicate that tailing effects for this solute are due to more than silanol interaction?

It certainly would. The fact that only the one compound tails rules out physical problems (e.g., a poorly packed column). In general, you can expect to see tailing when the distribution isotherm becomes non-linear and flattens out at higher concentration. The key question then is the one Rod mentioned: what's the mechanism? One (simplistic) speculation is that the benzylamine overloads more easily on the PS-DVB column. You could check that easily by seeing if the peak shape gets better at lower concentration, but that really doesn't address the fundamental question of "why?".

[chromatographer1]

The most likely explanation is there is trapped acidic functional groups in the pore structure of the polymer.

This can be a catalyst residue from the polymerization of manufacture.

Or due to some pore size issues, the benzylamine is getting trapped in the pores marginally. That is the sizes of the pores just barely permits the slow transfer in and out of the amine. An example of this on another level is the 60A versus 300A pore silica based RF columns when separating peptides. The smaller pores do not work as effectively. This COULD be a factor in your situation. Thus my query about the pore sizes.

Good luck

Rod

ps Of course the pH could also be a factor if the amine is in an equilibrium situation.