By T. Hassell on Thursday, May 13, 1999 - 06:36 am:
What ion-pairing reagent would be recommended for retaining very polar compounds on a RP-C18 columns?
By JD on Thursday, May 13, 1999 - 11:12 am:
It depends on the charge of the compound. For bases (positive charge), use a negatively charged ion pair, such as hexane, heptane, or octane sulfonate. For acid (negative charge), use tetrabutyl ammonium. For a good discussion of ion pairing, see the Snyder, Glajch, and Kirkland "Practical HPLC Method Development" book, 2nd edn (Wiley).
By jclark on Friday, May 28, 1999 - 05:54 am:
Does anyone remember the proper or usual range of concentrations for ion-pair agents in general? I think it is 25-150 mM but I'd like confirmation of this.
By Tom Jupille on Tuesday, June 8, 1999 - 02:35 pm:
Depends on the chain length of the IP reagent and on the organic solvent concentration of the mobile phase. The concentration should be below the critical micelle concentration. Aside from that, the critical issue is selectivity (i.e, you want a concentration that puts the peaks where you want them). There are useful nomograms for selecting the ion-pair reagent concentration (and chain length) in a paper that appeared in Journal of Chromatography a few years back:
Bartha, Vigh, and Varga-Puchony, J. Chromatog., 499 (1990) 424-434
Also, you might want to check out the more extensive discussion in the second edition of "Practical HPLC Method Development" by Snyder, Glajch, and Kirkland (Wiley, 1997).
Tom Jupille / LC Resources Inc.
By Anonymous on Monday, September 22, 2003 - 11:00 am:
I have had good results for analytes such as organic acids through c9 using a formic acid:dicyclohexylamine ion-pair reagent. column was c18 ODS. Start initial method development with say ~30:70% AcCN:H2O. Detection is by n-->pi* transition at ~210nm. Good luck.