retention time

[jazberella]

Hi,

I am trying to develop method for organic acid determination (tartaric, malic, lactic, citric,...). I am working on Agilent 1100 HPLC and using ZORBAX Eclipse XDB-C18 column.
I have problem with column stabilization. I can t get the same retention time between days, even after 1 hour of equilibration with mobile phase.I m using phosphate buffer/ACN=99/1 at pH=2.1

What can be the problem?

Thanks,
Mary

[Peter Apps]

Hello Mary

There are probably two problems. There is too little acetonitrile in the mobile phase to keep the stationary phase wetted (check the thread launched by Ghie Malig on June 29), and the pH is dangerously low for the stationary phase, which is probably being stripped off the column.

There must be standard methods for this analysis, save yourself a heap of trouble and just do a literature search.

Good luck Peter

[Bryan Evans]

The trick is to use a column that has these 3 characteristics:

1. The ability to retain more polar compounds
2. Does not collapse under highly aqueous mobile phase conditions
3. Durable under highly acid conditions (i.e. polyfunctionally bonded
ligand phase as opposed to monomerically bonded ligand phase)

Our Unison columns work very well under these conditions:

http://www.imtakt.com/TecInfo/TI109E.pdf
http://www.imtakt.com/TecInfo/TI130E.pdf