erythromycin estolate

[michaelcarolus]

Hi All

We are analysing Erythromycin Estolate as per EP. During the analysis of the assay we can not get suitable chromatography with the reccommended column i.e "stationary phase: styrene-divinylbenzene copolymer R (8 µm) with a pore size of 100 nm" We are using a Phenomenex Polymerx column which is equivalent to the recommended column in the EP. After trying another type of column we found that a Waters Xterra C18 gave us much better chromatography. Are we allowed to use the Waters Xterra C18 column for the analysis of erythromycin?

Thanking you in advance
Michael Carolus

[AdrianF]

I notice the EP requires a colum temperature of 70C and the injection volume is 200ul. It may help to preheat the mobile phase.

There is a similar column from Polymer laboratories which may be better.

I doubt you could change column as the column is used for related substances. You would have to do work to show the equivalence of the 2 methods. ie you have to get the EP method to work before you can change it!

[Bruce Hamilton]

Are you sure your column is equivalent?.

The 2007 Phenomenex Catalogue shows PolymerX as being a 100A, not 100 nm?. That would be a very significant difference.

I don't yet have EP 6.0, but the EP knowledgebase notes that the column used for related substances was a PLRP-S, which I presume is the Polymer Labs range, and they offer both 1000A ( 100 nm ) and 100A ( 10nm ) products.

Polymer Labs are now owned by Varian, so the local agent should be able to confirm the correct column referenced by the EP.

Bruce Hamilton

[michaelcarolus]

Thanks for the advice. I will try to source the correct column.
Mike