Chromatography Forum

Hi,
I am new to ion-pair chromatography, and I would like to know how to determine the volume of mobile phase containing 1 mM sodium octanesulfonic acid as ion-pairing reagent needed to equilibrate a column (C18 column, 4.6x150 mm, 5 microm). Could you guide me through the process? Reading various reports, I got some idea, and it appears that about 1L of 1 mM sodium octanesulfonic acid is needed for equilibration. I am near?

Thanks.

Much less than 1 L (<100 mL) is enough. The higher the fraction of the organic solvent in the eluent, the lower the equilibration time. Start pumping the mobile phase, then start a sequence of injections of a standard solution. When the analyte retention time becomes stable, the equilibration is complete.

Another suggestion is to monitor the baseline at 200-240 nm. The end of equilibration is usually manifested by a small sharp asymmetrical peak after a period of drifting baseline.

...and once you have an approximate time to equilibrate, you can skip the injections and put your waste line from the detector back into your MP bottle and recycle, so long as your conditioning is isocratic (no need to waste more than a few column volumes of the MP for equilibration if you don't want to).

Remember to put that waste line back into waste before you start your run!

I will try it that way. Thanks a lot!