Chromatography Forum

Kostas,

Sorry for the confusing statement.
May be this is not applicable for all compounds. I think that a lot of RP columns with a polar group might be called "switch mode" in terms of hydrophobicity at very high organic. How much hydrophobicity you have on the column when you mobile phase contains 70%-80% ACN, you have strong polar group on the surface and you analyte is polar ionizable compound with moderate hydrophobicity? If you can say that at 0% organic you have hydrophobic interaction of 10 (just the number) then at 70-80% of ACN you can assume that is much less (below 1?). You probably have some hydrophobic interaction when analyzing a highly hydrophobic compound (naphthalenes, steroids, vitamins, etc.) but most of the pharmaceutical compounds. So for this purpose Primesep columns are "switchable", because you can enhance or suppress two modes of interaction and make them relatively small based on the choice of the mobile phase.

regards

Well, Steve, the reason that I asked about the "highly polar surface derivatization" of your column is that some of these types of columns do not contain any endcapping or related things at all, but are just plainly unendcapped columns, and the "polar surface derivatization" is just marketing speak. May I interpret your reaction such that this is the case for your column also?

According to some reviews from PITTCON (see below) it seems that the Pyramid column has somekind of polar end-capping. However, it is not specified.

http://www.lcgceurope.com/lcgceurope/ar ... p?id=92336
http://www.iscpubs.com/articles/aln/n0405ste2.pdf

New technology is always attrative, maybe I'll try a mixed-mode column, thanks, SIELC_Tech. But I still have a question, is 70% the highest organic content used in mixed-mode column? usually I flush columns with 100% ACN to elute nonpolar compounds, 70% isn't enough.

Blackdrum,

We do not have C18 ligand, the molecule on the surface is less hydrophobic than C18 - it is equivalent of C13-C14. You can operate Primesep columns from 0% organic to 100% organic, but my bet that with double gradient (organic and buffer) you can use less than 100% of ACN and elute all compounds (ionic and non-ionic) it is the metter of choosing right Primesep column

Blackdrum-
I had little luck developing a method for cysteine/cystine with commonly available columns. These compounds just had trouble 'hangin on' to the column. I tried the SIELC column, and was very happy. Method was developed and validated in short order. Very subtle changes in acid content really allowed me to move the analytes around.

Good luck.
s