Chromatography Forum

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!

what's your analyte?

Thiol with an acidic group

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

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.

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

Uwe,

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

Thank you!

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.

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.

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