Would someone please comment on the "effectiveness" that ion-pairing reagents have when using polar-embedded stationary phases? Specifically, I am working with an application that is a mixture of amines and a neutral compound. Above pH 10.5, the amines are neutral but the hydroxyl group of the neutral compound is deprotonated (pKa 9.4). Unfortunately, this compound is not retained and Working at low-pH results in long run times. Do ion-pairing reagents like quaternary amines have a similar affect towards weakly acidic compounds as they do with carboxylates?

I have never seen anybody doing ion-pair chromatography with something like your compound (maybe a phenol?) at pH 10. However, there is nothing that I can see that would prevent this from happening. I would give it a try - if it works, you got some material for a publication in J. Chromatogr.

I have done some work with tetrabutylammoniumhydroxide and buffer pH 8.0.

It works pretty well.

Good luck

Our company, Allsep Technologies, has several columns with embedded ion pairing reagent. If you visit our website at www.primesep.com you can find methods for separation of amine mixtures with neutral compounds and acidic compounds in one isocratic run (for example benzylamine, bezoic acid, benzonitrile, mixture of aminoacids). There is also an example of phenol in the mixture. The beauty of our columns that they can work in a single mode (ion-exchange, normal phase mode, ion exclusion and reverse-phase modes) and combination of two or more modes. Check our website or call us (see website for details). We can help you with method development and column selection. Mobile phases are LC/MS compatible (ACN-water-ammonium acetate or TFA or any other acid formic, acetic etc.) You can email us at mail@allsep.com