Chromatography Forum

I assume most are familiar with the Octanesulfonic and Sodium Lauryl Sulfate Ion pairing reagents for basic compounds.

I am looking for an Ion pairing Reagent that satisfies one of the two species below:

1. The Ion Pairing reagent is more highly retentive / better uptake.

2. The Ion pairing reagent has a higher (charge density?). More Specifically, it has a higher affinity for the anionic species I am testing.

I have not had much luck finding an IPR that satisfies these conditions.

Is there an IPR that has akyl chains in the magnitude of say......14 or greater?

Thanks in Advance

Signed,
-Impatient Chemist....who is tired of spending time on the internet looking for answers....hahahaha

Are you trying to ion-pair an anionic analyte with an anionic reagent? That won't work at all. Try tetrabutylammonium or hexadecyltrimethylammonium to ion-pair with your anionic analyte.

Maybe you should think in terms of an ion exchange or mixed-mode column. Ion-pair chromatography is "interesting" enough using standard reagents.

Actually, at the moment I am using Sodium dodecyl Sulfate for my separations.

I started with hexanesulfonic and increased to heptane, then octane, then Decyl then Dodecyl Sulfate.

The more Methanol I had in the chromatography the better resolution I achieved between my analyte and the corresponding impurity. Keep in mind, I held the retention time of my analyte constant to see what composition of Methanol gives the best resolution. I also adjusted the concentrations of my IPR to get better retention but I had limited success due to longer equilibration times with increasing IPR concentration in the buffer. Gradient changes tend to make my reproducibility poor so that is out of the question.

Thanks
-Rick

I am taking the bet that, the more methanol I add the better my resolution gets. In order to achieve the same retention time, I need a longer akyl chain in the IPR. So, I was looking for that, hence the question above.

P.S. Aren't tetrabutylammonium or hexadecyltrimethylammonium used for testing acidic compounds and not basic compounds? I am testing basic compounds.

Assuming that it is just a typo and you wanted to write cationic at the place of anionic and that you are familiar with adequate equilibration times and the effect of organic modifier on the analyte retention during ion pairing chromatography, you could try long perfluorinated carboxylic acids for your separation.

In particular you could try
Tridecaflurheptanoic acid (TDFHA)
Pentadecafluoroctanoic acid (PDFOA)

As alternative you can try Primesep columns, which have ion-pairing reagent, attached to the surface of silica. Compounds are retained by at least two mechanisms reverse phase and ion-exchange. We have 5 different columns for retention of basic analytes and three columns to retain anionic compounds. We also have column Primesep AB which has both cation and anion ion-pairing reagent on the surface.
all columns show different selectivity for ionizable compounds as well as hydrophobic:

//allsep.com/Technology_NovelStationaryPhases.php

In literature section you can find a few brochure about alternative to IP chromatography:
http://allsep.com/Brochures_Home.php

If you have tough separation we are offering FREE screening service. If you provide us with the sample (or if we have it in the lab) we will screen our columns with your compound.

We introduced this technology almost two years ago and some people think that it is worth to try:

http://www.sepsci.com/chromforum/viewto ... 8e0df4ad40

Contact us if you need more information

regards,

Vlad

Skipjack,

Another option worth considering is simply using longer chain sulfonic acids. Certainly SDS should provide more attention than octanesulfonic acid but you will find considerably enhanced retention using octadecanesulfonic acid or one of the shorter chain intermediates between octanesulfonic acid and octadecanesulfonic acid. The whole family of these ion pair reagents are available from Sigma-Aldrich. You have to watch, though, if you're working above the critical micelle concentration in your mobile phase (the critical micelle concentration is highly dependent upon the amount of solvent present so you can't go by published data on this value in water) as working above the critical micelle concentration will result in reduced retention with increased mobile phase concentration of the ion pair reagent.

Question for SIELC

If the ion pairing reagent is attached to the surface of the silica how then can it function properly. Isn't the idea that you form an ion pair, and the pair then travels down the column.

Of course the process involves the pair partitioning into and out of the stationary phase, and also some equilibrium between the pair and the dissociated ions. But still it seems to me the basic ion-pairing process won't work if the ion pair reagent is "tethered" to the column.

adam, "ion-pair" chromatography can also be visualized as a variant on ion-exchange, with analyte ions interacting with surfactant ions stuck to the stationary phase. For a really good discussion of the subject, see the thread on ion-pair from a couple of months ago:
http://www.sepsci.com/chromforum/viewto ... highlight=