Restroing C18 after Ion reagent

[bgiles]

I have been told that once you use an ion pairing reagent (specificaly heptane sulfonic acid) on C18 the column should be dedicated to ion pair chrom from that point foward. Any experience with regenerating/removing ion pair reagent successfully/unsuccessfully?

thanks

The Dude

[Mark Tracy]

Sulfonic acid type ion pair reagents can be safely removed from the column. 90% methanol, 10% pH2 phosphate for 10 column volumes, followed by 100% methanol will do it. Quaternary amine reagents are much harder to remove.

If you have the luxury of devoting a column to ion-pair, it still is a good idea.

[DR]

Agreed - Triethylamine, nonylamine... much harder to remove.

[syx]

Sulfonic acid type ion pair reagents can be safely removed from the column. 90% methanol, 10% pH2 phosphate for 10 column volumes, followed by 100% methanol will do it.

Do we need certain concentration of phosphate buffer for this purpose? Is 0.025M enough?
Is it safe to run 100% methanol after buffer as your guidance? We should rinse the buffer out from column with non-buffered mobile phase before pure organic solvent, shouldn't we?
Thank you.

[Mark Tracy]

I'm sorry for the confusion. I meant to say 10% aqueous phosphate buffer. The exact phosphate concentration is not important, and should be as low as possible. Actually, any acidic solution will do; the idea is to protonate any active silanols and remove the cations.

[syx]

Could it be like this sequence:
- methanol - 0.01M phosphate buffer, pH 2.0 (90:10) - 10 column volumes, to remove ion-pair reagent from system
- methanol - water (90:10) - 10 column volumes, to remove buffer from system
- methanol 100% - 20 column volumes