Stationary phase options for ion-pairing agents

[KalB]

My separation utilizes an ion-pairing agent to allow sufficient retention of my analyte and related species. I would like to redevelop the method and eliminate the ion-pairing agent. Would my best choice be a polar embedded stationary phase or a highly aqueous stationary phase (e.g. Atlantis dC18) to allow sufficient retention (k' > 2.5)? I am certain everyone can appreciate some of the challenges with using ion-pairing agents. Any recommendations for stationary phases (and rationale for choosing a given phase) would be appreciated.

Thanks!

[lmh]

what's your analyte?

[KalB]

Thiol with an acidic group

[praveenpaliwal]

You can try Purosphere STAR also.
Waters Atlantis D-C18 is also a very good choice.
You can also try HILIC column of Merck

Best regards

Praveen

[Vlad Orlovsky]

Alternatively you can try anion-exchange reversed-phase columns (mixed-mode), where ion-pairing reagent is attached to the surface of silica gel.
Here are few applications for acidic compounds:
http://www.sielc.com/application_163.html
http://www.sielc.com/application_139.html
http://www.sielc.com/application_164.html
http://www.sielc.com/application_138.html

You can use almost any mobile phase which is compatible with your detection technique and with column pH ranges.

Contact me if you have specific questions about our approach.

[Uwe Neue]

You will get more retention for very polar compounds on the Atlantis dC18 or even better on the newer Atlantis T3 column.

[KalB]

Uwe,

Can you provide me with a comparison of the Atlantis dC18 and Atlantis T3 from a stationary phase perspective?

Thank you!

[Uwe Neue]

Both the Atlantis dC18 and the Atlantis T3 have about the same surface coverage, which maximizes retention in mobile phases with a purely aqueous composition (without the need for organic modifiers). The Atlantis T3 is the newer version. It uses a much improved endcapping process which provides additional stability under acidic mobile phase conditions. Otherwise, the properties of both packings are very similar. For a new application, I would recommend to use the Atlantis T3.

[Vlad Orlovsky]

here is comparison of Obelisc R, Zorbax SB-AQ, Synergy C18 and Atlantis T3 for retention of various polar analytes. As you can see mixed-mode can provide much higher retention for polar ionizable analyte due to the presence of two mechanisms - reversed-phase and ion exchange:
http://www.sielc.com/pdf/SIELC_August_2008.pdf

if you compounds are not ionizable, Atlantis T3 in RP (very low organic) or HILIC (with high organic) should work for you.

Contact me if you have questions.

[Bryan Evans]

Is there any more information about the solute?
Seems like Normal Phase would be a good option

Below are organic acids on Unison UK-Amino:
http://www.imtaktusa.com/site_media/fil ... TI542E.pdf