Chromatography Forum

Dear Chromatographar:

Could you tell me which would be the following column:

End-caped polar-embedded Octadecylsilyl amorphous organosilica polymer R. This column is required for Analysis of Azythromycin according to EP-5.0.

Thanks

The EP further describes this column as follows:

"Synthetic, spherical hybrid particles containing both inorganic (silica) and organic (organosiloxanes) components, chemically modified at the surface by the bonding of polar embedded octadecylsilyl groups.

To minimise any interaction with basic compounds, it is carefully end-capped to cover most of the remaining silanol groups. The particle size is indicated after the name of the reagent in the tests where it is used."

Sounds to me like simply a C18 column, based on the use of the word "octadecylsilyl". But if you want to be certain, the easiest thing to do (assuming you don't get a better answer here, of course), is to call one of your favorite HPLC column manufacturers (be it Waters, Phenomenex, Varian, etc) and ask what column they sell that is used to satisfy the EP assay for Azithromycin.

No. This clearly specifies an embedded polar group. Thus it is an octadecyl packing with an embedded polar group. In addition, it specifies a hybrid particle. The only hybrid particle is XTerra, and the packing with the embedded polar group is the RP18. Thus this method specifies XTerra RP18 as the packing. Unequivocally.

Oh. I forgot: the only manufacturer that makes XTerra RP18 is Waters.

lol at the EP. If the XTerra packing was the only hybrid on the market at when 5.0 was published surely they could of saved these problems by simply stating it

Or is the information there incase the end-user is developing his own phase to use..?

Uwe, does the XTerra have a C18 chain off the polar group? I can't tell from the literature.

Thanks for the correction Uwe.

No. This clearly specifies an embedded polar group. Thus it is an octadecyl packing with an embedded polar group. In addition, it specifies a hybrid particle. The only hybrid particle is XTerra, and the packing with the embedded polar group is the RP18. Thus this method specifies XTerra RP18 as the packing. Unequivocally.

Thanks Mr. Uwe. I think Xttera is only one hybrid perticle and this column is patent to Waters. But Waters never claim XTerra as a "Polar Embedded" column. No where I get that XTerra have any "polar Embedded" group or this is a "Polar Embedded." Waters claim their Atlantis dC18 as a "Polar Embedded" column but not XTerra. So, How can we be sure that XTerra is that column.

Thanks again.

So, Why can we be sure that XTerra is that column.

1. If Uwe tells you than an embedded polar group Xterra column is available, trust him (he developed them!)

2. Xterra columns are available in several functionalities. Specifically, the Xterra RP8 and RP18 columns have an embedded polar group.

Thanks Mr. jupille, For my curiosity I want to know how Xterra act as a polar Embedded column? Which part of RP18 act as Polar Embedded group?

I will admit that Waters product nomenclature leaves a lot to be desired. The "Xterra MS" is a C18, the "Xterra RP18" is an EPG column. It must make sense to someone at Waters

However, go to Waters web site and download the Xterra brochure:

http://www.waters.com/WatersDivision/pdfs/Lxterra.pdf

It has all the details.

XTerra is the name of the pH stable hybrid packings with a methyl group in the matrix of the packing. As Tom has pointed out, there are several different packings with a different surface chemistry available.

In most of our packings, the ones with the embedded polar group have "Shield" added to the name, and the packing itself is called RP18 or RP8. The standard stuff without embedded polar groups is called C18 or C8. For XTerra, we did not do this wise thing, and thus there can be some confusion.

The XTerra RP8 and XTerra RP18 have a carbamate group embedded in them. Let me try the chemical formula here to make it clear:

Surface-Si(CH3)2-(CH2)3-O-CO-NH-R

where Surface is the packing and R is the hydrophobic ligand.

This information is also available at the Waters web site or I can send publications to those that are interested. It was first published in Anal. Chem. 67 (1995), 3809-3913.

Thanks Mr. Uwe Neue for your explanation. As there are Carbamate group in RP18, XTerra is Polar Embidded. Now I am clear.

From the EP official site:

the column is : l = 0.25 m, diam. = 4.6 mm, 5 µm, pore size : 12.5 nm, carbon loading : 15%, XTerra RP 18

Thanks Maris!

I am not familiar with the EP. How do you get at the information of what column is used in a particular assay? For the USP, you need to subscribe to their service, which gives you access to the website where you can find this information. Or, they used to sell a reagent book. But I do not know what the EP is offering on this subject.

http://extranet.pheur.org/publications/ ... s_sw.shtml

than type the compoound of interest and press "search". For most of them, where the official onograph is available the column is listed.

Regards