Sterically protected ODS

[Alex Buske]

Hi,

I am just trying to reanimate an old method. The protocol demands a "Sterically protected ODS silica gel" column. So far I found Zorbax Stable Bond and Waters Symmetry Shield.
Any other suggestions?

Alex

[tom jupille]

In general, the best bet is to use the *exact* column from the original protocol. A different column, even if meeting the same general description, will probably have somewhat different selectivity.

How old is the method you are trying to duplicate? If memory serves, the Zorbax Stablebond came on the market before the Waters Symmetry Shield (Uwe will correct me if I'm wrong! ), so it's a more likely candidate for an older method.

[Victor]

I am not sure why your method specifies a Sterically protected ODS silica.

However, the Zorbax Stablebond is the classic example of this phase (not sure if there are any others?). The advantage of this column is very good stability at low pH and elevated temperature.

Waters Symmetryshield is an embedded polar group phase. This is a not a sterically protected phase if I remember correctly, but it has good inertness. However, it has slightly different selectivity to conventional ODS phases (and the Zorbax phase). I would follow Tom's advice and select the Zorbax phase in the first instance, if you are trying to obtain the exact selectivity of the original method. But the Waters phase might well work too.....

[mohan_2008]

Zorbax RX came prior to Zorbax SB. Agilent says "both columns are same" yet recommend RX for basic compounds.

[Bruce Hamilton]

According to my copy of Agilent Zorbax Column Selection Guide of 15 Jan 2004 ( 5989- 0433EN) the Rx and SB C18 are significantly different. The C8 columns are identical.

For example, the Rx using dimethyl sidechain groups and is not end-capped. The result is good peak shape of compounds over pH range 2-9, and good general purpose use.

The StableBond columns use bulky diisobutyl ( For C18 ) or Diisopropyl ( for C8, C3, CN etc ) sidechain groups that sterically protect the key siloxane bond from hydrolytic attack at low pH. They also are not endcapped - to enhance low pH durability. They are compatible with low pH ( claimed down to 1 ) and highly-aqueous mobile phases.

Most of the column selection data is freely available from the Agilent WWW site. I highly recommend users obtain copies relevant to the columns they are using.

Bruce Hamilton

[Alex Buske]

Thanks for all the comments.
After having tried several rather modern columns with little success I suspect the old type of silica gel being responsible for the separation. Maybe some more silanol activity can help.

Alex