Nitrite co-elution and moving towards smaller particle sizes

[H2Oh]

I've been running a 5 micron C18 column - Zorbax ODS for a few years but I'd like to move towards a 3 micron to speed up the separation and not sacrifice much resolution.

I've always had a problem with having nitrite elute with a broad low intensity peak on either side of one of my azole analyte peaks. The 3 micron column has sharpened the nitrite a little and I wonder if I can modify my separation to recompletely resolve the peaks.

I only have isocratic pumps though.

Any idea how to get my nitrite out before everything else?


I have PDFs of my chromatograms but nothing to link to online. Can I still attach images?

[Bryan Evans]

Below is a separation for econazole nitrate and micronazole nitrate.
We'd recommend Unison UK-C18 for this separation:

http://www.imtakt.com/TecInfo/TI182E.pdf

What is your mobile phase composition?

[H2Oh]

~51%DI/49%methanol with 0.25% acetic acid detecting at 254 nm.

[Bryan Evans]

Yes, if you have chromatograms, that would be helpful. If you can't
post them - please email them to me.

Thanks

[DR]

In going to a 3µ packing, you will have to lower your flow rate a little bit to get the same resolution (or better, if flow for the 5µ column was not optimal).

Look into Tinypics, Imageshack or other free picture hosting sites to get photos added to the thread (I think Tom has a tutorial on this process around here somewhere - consult the FAQ).

[H2Oh]

http://img205.imageshack.us/img205/2719 ... umstd4.pdf

Here's a link to imageshack for the chromatogram. My 5 micron column had the nitrite co-elution problem too. It's a little more pronounced with the 3 micron though with a sharper nitrite peak.

I'm going to try cutting my methanol concentration down on the advice of the column maker.

Thanks for all the help so far.